GM's Misfires - Sluggish - Coil Arcing

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GM's Misfires - Sluggish - Coil Arcing (Page 1)

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Author	Topic: GM's Misfires - Sluggish - Coil Arcing
Michelle Junior Member	posted 04-28-2003 07:14 AM I see a lot of posts regarding this issue. Many 1996-1997 (un-confirmed other years as well) GM engines have a problem with false codes and misfires, blown coils, arcing and alike. The problem with the dealer is the data they get or don't get is WRONG because the scanner only shows DTC codes. When when these engines reach 80,000 or so miles the "Knock" sensor retards the timing (thinking it's pinging) due to increased engine noise up to 28 deg thus causing cross firing inside the dist cap and a slew of other issues. In my case, the new expensive coil wire arced to the PCM sensor wires causing may sensors to indicate random readings such as TPS at 80% during idle. There is a GM Tech Bulletin #76-65-04 regarding a software update. READ MY POST DATED 2/26/2004 FOR THE GM SERVICE BULLITEN.. Condition : Read carefully, the MIL light and DTC codes MAY or MAY NOT show, and WITH or WITHOUT real faults. See notes #5 and #7 Michele Software Development [This message has been edited by Michelle (edited 02-26-2004).] IP: Logged
carfixer Member	posted 04-28-2003 01:27 PM Can you provide a TSB number for this? I would like to see what you're referring to. The problem you describe would be better related to the ignition system rather than the engine as the cam offset will effect the HVS ignition system on V8 engines, but not the V6 engines. IP: Logged
Michelle Junior Member	posted 04-28-2003 03:02 PM Hi, I posted the URL of the TSB in my last post. If the ignition timing is too far off on any distributor system, like 28 degrees, the spark will simply jump to the nearest cylinder in the cap, or my case the EGR sensor. M. IP: Logged
carfixer Member	posted 04-28-2003 05:08 PM These articles cover a similar problem. It's all about timing. The reason it does it on the 8 cylinder engines and not on the 6 becomes obvious when you think about the distance between the posts on a 8 cylinder as compared to the 6. On the 8 cylinder cap the posts are closer together and the timing between cylinders is closer. It's also true that GM had to do some software changes (flashing the EEPROM) to correct some of these problems. Here's the articles about cam offset and timing. Here's a brain teaser for those who fancy themselves an accomplished wrench head. http://www.xssupply.com/Misfire%20Mystery/MisfireMystery.htm Here's a simple explanation. http://www.xssupply.com/CMPOffset/CMP-Correction.htm IP: Logged
Michelle Junior Member	posted 04-28-2003 07:48 PM Excellent reference! We pulled the lead off of the Knock Sensor and the timing retarded 42 degrees, and never threw a DTC or MIL? I have a lot of misfires on #6 and found that the old cap had a spark leak within the plastic of the cap between the coil lead and #6. On the 6 cyl these are very close, and the carbon trace was inside the molding of the cap, after smashing it open. As the previous post indicates, (in the link) the rotor can handle advance ok, but if the KS can retard as much as 38 deg, then there is the problem. Tuesday, we will try a new KS and see if it is the lifter noise that is causing a false KS signal. IP: Logged
carfixer Member	posted 04-28-2003 09:42 PM >Tuesday, we will try a new KS and see if it is the lifter noise that is causing a false KS signal. Before you do that read this and the link below. I'm posting these on a website where I'm the webmaster. My friend is a 27 year GM dealer tech and does these case studies on vehicles he runs across in the dealership. I really shouldn't be posting them on the web, but I'll take them down soon. He has a website where you can follow a different "case study" every week. He also has a few small articles called "take 5" that he puts up every month. The references above are a "case study", the long one, and a "take 5". He charges $25 for a 6 month subscription to the website. You can learn a lot about driveability problems in general, and a ton on GM. Just the archieves alone will keep you busy learning for a long time. Here's the link to Knock Knock http://www.xssupply.com/Knock%20Knock/Knock.htm IP: Logged
Michelle Junior Member	posted 04-29-2003 10:09 AM Thanks, Your site is excellent. Explain to me why I'm seeing 38 degrees knock retard with or without the sensor connected. The knock sensor measures > 30,000 ohms, and according to the Hayes Manual it should measure 3,900 ohms (remember they take things appart and measure them just like we do), so I thinking it's bad any way. Virtually any mechanic or dealer stops at the DTC's on the scan tool. Show them a computer readout such as Auto-Tap's and you may as well hand them an EKG! My dealer told me that he didn't give a s#t what the Auto-Tap shows, if the TECH II dosent show a DTC then it ain't broken. As to why it drives like s#t, he asked me what I expected from a Van with 86,000 miles. The actual mechanic is very interested in learning more, however, the shop labor manual is all he is allowed to go by. I called GM Cust Service and got the usual ticket #, and they only proceeded to ream out the dealer(s) (3 at this point) and offered me a voucher for a new Van. Like, we'll toss in the fog lamps if you pay list price? Most dealers really do care, however they must use GM proceedures, GM parts and GM training. No thinking outside the box. M. [This message has been edited by Michelle (edited 04-29-2003).] IP: Logged
carfixer Member	posted 04-29-2003 11:35 AM Can you tell me what year, make, model, engine, and trans your vehicle is? I'll look up some factory info on it. IP: Logged
Michelle Junior Member	posted 04-29-2003 02:38 PM 1997 Astro AWD Automatic 4.3 L35 (W - Engine) Point #5 in the following bulletin describes the problem. http://calid.gm.com/vci/bulletins/766504.htm Scan shows: Idle 678 rpm Spark advance 20 deg Ign timing: 6 Knock Retard 38 deg Why does point #5 in the bulletin refer to the cam retard offset. Where and how is this set and how could the vehicle run flawlessly until 86000 miles? The dealer said that the cam timing must have been wrong since it was built as the chain didn't slip. Even now it can still beat the average Mustang, it just feels like jello around town and misfires at 1500 idle. PS, I connected the NEW Knock Sensor and grounded it with it on the carpet, and the Knock Retard went to 2-6 degrees. M. [This message has been edited by Michelle (edited 04-29-2003).] IP: Logged
carfixer Member	posted 04-29-2003 04:43 PM >Why does point #5 in the bulletin refer to the cam retard offset. Where and how is this set and how could the vehicle run flawlessly until 86000 miles? What is your cam offset reading on the scan tool? If the timing chain didn't jump or the chain isn't stretched bad the distributor MIGHT have moved a little or the prom may have developed a problem. If the cam offset is over -10 degrees, turn the distributor counter clockwise while monitoring the cam offset on the scan tool. Bring it down to less than -10 degrees of cam offset. Preferably about 0 to -5 is good. >PS, I connected the NEW Knock Sensor and grounded it with it on the carpet, and the Knock Retard went to 2-6 degrees. Your KS was open. The VCM will default to retarded timing when the sensor is bad. The thing is I would expect the MIL to lite and a code to set. The VCM should not go to default unless it sees a failure in the sensor or it's circuit or. At that time it should lite the MIL and set a code. IP: Logged
Michelle Junior Member	posted 04-29-2003 06:52 PM As noted on the last line of your page link below, the dist is NOT adjustable on the V6 engine. http://www.xssupply.com/Misfire%20Mystery/MisfireMystery2.htm However!!!! What is the parameter name for the cam offset and I will look for it. I have a CPM retard, is that it? My dealer, "MR Goodwreck" chopped off the end of the dist lock down clip and rotated the non adjustable dist to adjust for the 38 deg offset. Now, no other dealer will touch it citing that I need a new $275 dist in order for them to even connect a scan tool to it. Nobody knows how to set the dist back to where it belongs. The good news is the dealer who chopped off the clip is willing to replace the dist at their cost. But then were back to why is it so far retarded that it cross fires, if nothing jumped? According to my GM source, there is no cam offset spec, because IT's NOT adjustable on the V6. Can you try looking up what the code is (CPK ?) and let me know, and secondly, can you try pulling the knock sensor wire off a running engine and see if it throws a code? Thanks. [This message has been edited by Michelle (edited 04-29-2003).] IP: Logged
hd5416 Junior Member	posted 04-29-2003 10:37 PM quote: Originally posted by carfixer: >Tuesday, we will try a new KS and see if it is the lifter noise that is causing a false KS signal. Before you do that read this and the link below. I'm posting these on a website where I'm the webmaster. My friend is a 27 year GM dealer tech and does these case studies on vehicles he runs across in the dealership. I really shouldn't be posting them on the web, but I'll take them down soon. He has a website where you can follow a different "case study" every week. He also has a few small articles called "take 5" that he puts up every month. The references above are a "case study", the long one, and a "take 5". He charges $25 for a 6 month subscription to the website. You can learn a lot about driveability problems in general, and a ton on GM. Just the archieves alone will keep you busy learning for a long time. Here's the link to Knock Knock http://www.xssupply.com/Knock%20Knock/Knock.htm I am a tech and would like to know how to get on this website. IP: Logged
JeremyB Member	posted 05-01-2003 07:15 AM What you're looking for is cam retard on your scanner and the normal range for the 4.3W is -20 to +20 due to the fixed distributor. I read a post on another site a while ago that said a new distributor gear fixed a slew of problems Here it is: FYI - I have been seeing a lot of posts about vortec misfires. For six months, I myself have been dealing with a misfire but only at very light throttle. Idles great and accelerates great but misfired terribly with very light throttle. This problem came on gradually and has been getting worse. Replaced: cap, rotor, plugs, wires, all 8 injectors with no fix. The fourth mechanic I went to recently found the problem. He hooked up a spark analyzer to the engine and found the timing was off slightly only during the misfire. He pulled the entire distributor out and found the gear to be very worn. The first three techs said nothing is wrong with any sensor but they could not find the problem. I showed him all the misfire posts that I printed out from vmag. My truck has been very well maintained and never missed an oil change. He thinks GM possibly got a bad batch of improperly heat treated distributor gears. If anyone is having misfire problems and can't figure it out, try pulling the distributor and check the gear. As you all know, be careful with this procedure. This may save you from all the headaches and cost that I have gone through. IP: Logged
carfixer Member	posted 05-01-2003 06:15 PM That website is http://www.flatrater.com IP: Logged
Michelle Junior Member	posted 05-02-2003 12:44 AM JeremyB Thanks for that tip, I will have it checked. I have been told by a major fleet shop manager of 4.3L astros, that the reluctor is only press fit onto the dist shaft instead of welded as usual. He said that the reluctors slip thus causing all sorts of timing problems. Has anyone heard of this? M. IP: Logged
hd5416 Junior Member	posted 05-02-2003 08:33 AM quote: Originally posted by carfixer: That website is http://www.flatrater.com Thank you I have join www. flatrater.com IP: Logged
tdlong98 Junior Member	posted 05-02-2003 11:03 AM I have a 98 chevy truck, and I had a PO300. The truck was missing and backfire. I just replaced the dis gear and it fixed the hole problem. I took the truck to many places and no one could help me. But JermmyB told me about the gear. Wow what a great thing. Dean IP: Logged
wtd Member	posted 10-05-2003 08:08 PM Will a bad distributor gear cause arching on the outside of the coil but without any misfire codes being set? I'm still having problems with the coil arching on my 98 chevy truck with the 5.7L. All new ignition components do not fix the arching for long. Performance is very sluggish. What is the correct timing advance and idle speed for this engine? Mine is 22 degrees of advance at idle and the engine RPMs at idle is 578 rpm. RPMs in drive is 514 RPM and seems low to me. Any information on this is greatly appretiated since I've been dealing with this problem for two years and none of the shops or dealers I've taken it too have been able to fix it. Wayne IP: Logged
Michelle Junior Member	posted 10-28-2003 12:07 PM I have replaced the gear with no change in the problem. The coil arcs from the top of the coil tower to the top of the coil, so many times that there is no paint left on it. It threw it's first actual MIL today, yepee! P P0300 Engine speed = 150.4 Calculated load = 6.3% Closed loop intergerator valve = 5 Desired air fuel ratio = 166 Desired EGR = 3% Ignition voltage = 0.8 (yes taht's correct) Engine run time = 995328 IP: Logged
trouble Junior Member	posted 12-04-2003 05:22 PM Hello all, great post, I have p0300, engine misfires, I tried the usual stuff, plugs, wires, fuel injectors, cap n rotor... looks like I'll be replacing the Distributor, hopefully this weekend,... > Question is it time to replace the Timing Chain? I have a 96' truck with 169,500 miles on it, and I do hear a light pinging " noise ", what causes this, is it fixable? IP: Logged
Michelle Junior Member	posted 02-26-2004 08:14 AM Service Information MALFUNCTION INDICATOR LIGHT (MIL) ON, POOR DRIVEABILITY Bull #76-65-04 SUBJECT: MALFUNCTION INDICATOR LIGHT (MIL) ON, POOR DRIVEABILITY CONDITIONS (PERFORM FLASH CALIBRATION) MODELS: 1996-97 CHEVROLET AND GMC LIGHT DUTY TRUCKS 1996-97 CHEVROLET TILTMASTER AND GMC FORWARD W4 MODELS 1996-97 OLDSMOBILE BRAVADA WITH 4.3L, 5.0L, 5.7L ENGINES (VINS X, W, M, R - RPOS LF6, L35, L30, L31)CONDITION: AN OWNER MAY REPORT THAT THE MALFUNCTION INDICATOR LIGHT (MIL) IS ON AND/OR THE VEHICLE HAS ONE OR MORE OF THE FOLLOWING DRIVEABILITY CONDITIONS. 1. 5.7L (L31) ONLY: SURGE OR CHUGGLE AT SPEEDS OF 42 TO 65 MPH WHILE AT STEADY SPEED OR UNDER LIGHT TO MODERATE ACCELERATION WITH THE TCC APPLIED. 2. MIL ON WITH DTC P0172 OR P0175 STORED BUT NO REPORTED DRIVEABILITY SYMPTOMS. 3. MIL ON WITH DTC P1406 STORED AND ROUGH ENGINE OR POOR DRIVEABILITY SYMPTOMS. 4. WHEN OPERATING AT ALTITUDES ABOVE 5,000 FEET, AN AUDIBLE SPARK KNOCK NOISE IS HEARD. 5. HESITATION AND/OR MISFIRE DURING LIGHT CRUISE CONDITIONS DUE TO IGNITION CROSS-FIRE WITH NO DTC STORED. THIS WILL ONLY OCCUR ON V-6 ENGINES WITH CAM RETARD OFFSET IN EXCESS OF 26 DEGREES AND V-8'S WITH CAM RETARD OFFSET IN EXCESS OF 15 DEGREES. 6. THE MIL MAY BE ON AND A DTC STORED FOR AN ENGINE MISFIRE BUT NO MISFIRE OCCURRED. 7. ENGINE EXHIBITS AN IDLE SPEED SURGE OR ROLL. 1996 MODELS ONLY 8. MIL ON WITH DTC P0102 STORED BUT NO REPORTED DRIVEABILITY SYMPTOMS. 9. 5.0L (L30) + 5.7L (L31) ONLY: DIFFICULT STARTING IN EXTREME COLD (BELOW 0 DEGREES F) CONDITIONS. 10. 5.7L (L31) ONLY: POORER THAN EXPECTED FUEL ECONOMY WHEN HEAVILY LOADED. 1997 MODELS ONLY 11. MIL ON WITH DTC P0121 STORED BUT NO REPORTED DRIVEABILITY SYMPTOMS. 12. C/K + S/T MODELS WITH EITHER V-6 ENGINE AND MANUAL TRANSMISSION: AN EXHAUST BACKFIRE MAY OCCUR WHILE SHIFTING WITH MODERATE THROTTLE AT ENGINE SPEEDS ABOVE 3500 RPM. 13. EITHER V-6 ENGINE AND MANUAL TRANSMISSION: AN ENGINE FLARE BETWEEN SHIFTS MAY BE NOTED WHEN THE ENGINE IS COLD. 14. C/K, S/T AND M/L MODELS EQUIPPED WITH L35 V-6 ENGINE, AN IMPROVEMENT TO THE VAPOR CANISTER PURGE DIAGNOSTICS IS INCORPORATED INTO THE NEW CALIBRATIONS SO THAT THE TECH II CAN TURN ON CANISTER PURGE AT IDLE SPEED. CORRECTION: FOLLOW THE STRATEGY BASED DIAGNOSTIC STEPS FOR THE CUSTOMER'S REPORTED SYMPTOMS. IF DIAGNOSIS DOES NOT REVEAL A CAUSE, REFER TO THE TABLES BELOW FOR THE APPLICABLE CALIBRATION CHANGE. PERFORM PROGRAMMING PER THE LATEST TECHLINE INFORMATION FOR PROGRAMMING PROCEDURES. IMPORTANT: THE CALIBRATIONS LISTED ARE FLASH CALIBRATIONS AND ARE NOT AVAILABLE FROM GMSPO. THEY ARE AVAILABLE ON 1997 TECHLINE CD DISC 5 AND LATER. WARRANTY INFORMATION: FOR VEHICLES REPAIRED UNDER WARRANTY, USE: LABOR OPERATION LABOR TIME J-6355 USE PUBLISHED LABOR OPERATION TIME 1996 MODEL YEAR MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE T-UTILITY 4.3L L35 AUTO NF2/NB6 -Z49 16232320 16235814 T-UTILITY 4.3L L35 AUTO NF2/NB6 +Z49 16232321 16235815 T-UTILITY 4.3L L35 AUTO NN8 -NA7/NA3 16232322 16235816 T-UTILITY 4.3L L35 AUTO NN8 + NA7/NA3 16232323 16235817 S/T-ALL 4.3L L35 MANUAL NF2/NB6 -Z49 16232324 16235818 S/T-ALL 4.3L L35 MANUAL NF2/NB6 +Z49 16232325 16235819 S/T-ALL 4.3L L35 MANUAL NN8 16232326 16235820 S/T-PICKUP 4.3L L35 AUTO NF2/NB6 -Z49 16232327 16235821 AND, S-UTILITY S/T-PICKUP 4.3L L35 AUTO NF2/NB6 +Z49 16232328 16235822 AND, S-UTILITY S/T-PICKUP 4.3L L35 AUTO NN8 -NA7/NA3 16232329 16235823 AND, S-UTILITY S-PICKUP 4.3L LF6 AUTO NF2/NB6 -Z49 16232330 16235824 S-PICKUP 4.3L LF6 AUTO NF2/NB6 +Z49 16232331 16235825 T-PICKUP 4.3L LF6 AUTO NF2/NB6 -Z49 16232332 16235826 T-PICKUP 4.3L LF6 AUTO NF2/NB6 +Z49 16232333 16235827 S-PICKUP 4.3L LF6 MANUAL NF2/NB6 -Z49 16232334 16235828 S-PICKUP 4.3L LF6 MANUAL NF2/NB6 +Z49 16232335 16235829 T-PICKUP 4.3L LF6 MANUAL NF2/NB6 -Z49 16232336 16235830 T-PICKUP 4.3L LF6 MANUAL NF2/NB6 +Z49 16232337 16235831 S/T-ALL 4.3L L35 AUTO NM8 16232424 16232426 S/T-ALL 4.3L L35 MANUAL NM8 16232425 16232427 M-VAN 4.3L L35 AUTO NF2/NB6 -Z49 16232385 16235846 M-VAN 4.3L L35 AUTO NF2/NB6 +Z49 16232386 16235847 M-VAN 4.3L L35 AUTO NN8 16232387 16235848 L-VAN 4.3L L35 AUTO NF2/NB6 -Z49 16232388 16235849 L-VAN 4.3L L35 AUTO NF2/NB6 +Z49 16232389 16235850 L-VAN 4.3L L35 AUTO NN8 16232390 16235851 M-VAN 4.3L L35 AUTO NM8 16232391 16232428 L-VAN 4.3L L35 AUTO NM8 16232392 16232429 MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE C/K-10/20 TRUCK 4.3L L35 MANUAL NA5/NB6 -Z49 16232310 16235832 C/K-10/20 TRUCK 4.3L L35 MANUAL NA5/NB6 +Z49 16232311 16235833 C/K-10/20 TRUCK 4.3L L35 MANUAL NN8 16232312 16235834 C/K-10/20 TRUCK 4.3L L35 AUTO NA5/NB6 -Z49 16232313 16235835 EXCEPT EXT. CAB STEP SIDE C/K-10/20 TRUCK 4.3L L35 AUTO NA5/NB6 +Z49 16232314 16235836 EXCEPT EXT. CAB STEP SIDE C/K-10/20 TRUCK 4.3L L35 AUTO NN8 16232315 16235837 EXCEPT EXT. CAB STEP SIDE C/K-10/20 TRUCK 4.3L L35 AUTO NA5/NB6 -Z49 16232342 16235843 WITH EXT. CAB STEP SIDE C/K-10/20 TRUCK 4.3L L35 AUTO NA5/NB6 +Z49 16232343 16235844 WITH EXT. CAB STEP SIDE C/K-10/20 TRUCK 4.3L L35 AUTO NN8 16232344 16235845 WITH EXT. CAB STEP SIDE C/K-10/20 TRUCK 5.0L L30 AUTO NA5 -Z49 16232345 16235853 C/K-10/20 TRUCK 5.0L L30 AUTO NA5 +Z49 16232346 16235854 C/K-10/20 TRUCK 5.0L L30 AUTO NN8 16232347 16235855 C/K-10/20 TRUCK 5.0L L30 AUTO NF2/NB6 -Z49 16232348 16235856 C/K-10/20 TRUCK 5.0L L30 MANUAL NA5 -Z49 16232349 16235857 C/K-10/20 TRUCK 5.0L L30 MANUAL NA5 +Z49 16232350 16235858 C/K-10/20 TRUCK 5.0L L30 MANUAL NN8 16232351 16235859 C/K-20/30 TRUCK 5.7L L31 MANUAL NA4/NA5/NM8 16232422 16256096 C/K-20/30 TRUCK 5.7L L31 MANUAL NA4/NA5 16232355 16235864 -NM8/Z49 MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE C/K-ALL 20/30 5.7L L31 AUTO NA4/NB6 -Z49 16232356 16235865 C/K-ALL 20/30 5.7L L31 AUTO NA4/NA5 16232357 16235866 -NM8/Z49 C/K-ALL 20/30 5.7L L31 AUTO NA4/NA5/NM8 16232423 16256097 C-10 TRUCK 5.7L L31 MANUAL NA1/NA5 16232362 16235872 -NM8/Z49 C-10 TRUCK 5.7L L31 MANUAL NA1/NA5/Z49 16232363 16235873 C-10 TRUCK 5.7L L31 MANUAL NN8 16232364 16235874 C-10 TRUCK 5.7L L31 AUTO NA1/NA5/NB6/NF2 16232365 16235875 -NM8/Z49 C-10 TRUCK 5.7L L31 AUTO NA1/NA5/Z49 16232366 16235876 C-10 TRUCK 5.7L L31 AUTO NN8 16232367 16235877 C-10 TRUCK 5.7L L31 MANUAL NA1/NB6 16232368 16235878 -NM8/Z49 K-10 TRUCK 5.7L L31 AUTO NA1/NA5/NB6/NF2 16232369 16235879 C/K-20 TRUCK -NM8/Z49 K-10 TRUCK 5.7L L31 AUTO NA1/NA5/Z49 16232370 16235880 C/K-20 TRUCK K-10 TRUCK 5.7L L31 AUTO NN8 16232371 16235881 C/K-20 TRUCK C/K-10 UTILITY 5.7L L31 AUTO NA5/NB6/NF2 16232372 16235882 -NM8/Z49 C/K-10 UTILITY 5.7L L31 AUTO NA5/Z49 16232373 16235883 C/K-10 UTILITY 5.7L L31 AUTO NN8 16232374 16235884 K-10 TRUCK 5.7L L31 MANUAL NA1/NA5 16232375 16235885 C/K-20 TRUCK -NM8/Z49 K-10 TRUCK 5.7L L31 MANUAL NA1/NA5/Z49 16232376 16235886 C/K-20 TRUCK MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE K 10/20 TRUCK 5.7L L31 MANUAL NA1/NB6 16232378 16235888 C/K 20 TRUCK -NM8/Z49 K-10 TRUCK 5.7L L31 MANUAL NN8 16232377 16235887 C/K-20 TRUCK C/K 10/20 ALL 5.7L L31 AUTO NM8 16232383 16256102 C/K 10/20 TRUCK 5.7L L31 MANUAL NM8 16232384 16256103 G-VAN 10/20 4.3L L35 AUTO NB6 -Z49 16232316 16235838 G-VAN 10/20 4.3L L35 AUTO NA5 +Z49 16232317 16235839 G-VAN 10 4.3L L35 AUTO CV4/NN8 16232318 16235840 G-VAN 10/20 4.3L L35 AUTO NA5 -Z49-EXP 16232319 16235841 G-VAN 20 4.3L L35 AUTO NA5 16232338 16235842 G-VAN ALL 5.0L L30 AUTO NA5 -Z49 16232352 16235860 G-VAN ALL 5.0L L30 AUTO NA5 +Z49 16232353 16235861 G-VAN ALL 5.0L L30 AUTO NF2/NB6 -Z49 16232354 16235862 G-VAN 10/20 5.7L L31 AUTO NA5 -Z49 16232379 16235889 G-VAN 10/20 5.7L L31 AUTO NA5/Z49 16232380 16235890 G-VAN 10/20 5.7L L31 AUTO NA5/NM8 16232301 16256101 G-VAN 10/20 5.7L L31 AUTO NA5/NN8 16232381 16235891 G-VAN 10/20 5.7L L31 AUTO NB6 -Z49 16232382 16235892 G-VAN 20/30 5.7L L31 AUTO NB6 -Z49 16232358 16235867 G-VAN 20 5.7L L31 AUTO NA5/NM8 16227552 16256098 G-VAN 20 5.7L L31 AUTO NA5 -NM8/Z49 16232359 16235868 G-VAN 30 5.7L L31 AUTO NB6 -Z49 16232360 16235869 G-VAN 30 5.7L L31 AUTO NA5/Z49 16232361 16235870 P-CHASSIS 4.3L L35 AUTO NA5 16227523 16235852 P-CHASSIS 5.7L L31 AUTO NA5/NM8 16235811 16256099 P-CHASSIS 5.7L L31 MANUAL NA5/NM8 16235812 16256100 P-CHASSIS 5.7L L31 AUTO NB6 -Z49 16187756 16235871 P-CHASSIS 5.7L L31 MANUAL NA5 -NM8/Z49 16187887 16235895 P-CHASSIS 5.7L L31 AUTO NA5/NB2-NM8/Z49 16187888 16235896 W4 5.7L L31 AUTO NB6 -Z49 16235809 16235893 W4 5.7L L31 AUTO NA5/Z49 16235808 16235894 1997 MODEL YEAR MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE T-UTILITY FOUR 4.3L L35 AUTO NF2/NA3/NB6 -Z49 16243498 16256222 DOOR T-UTILITY FOUR 4.3L L35 AUTO NF2/NB6/Z49 16243499 16256223 DOOR T-UTILITY FOUR 4.3L L35 AUTO NN8 -NA7 16243532 16256224 DOOR T-UTILITY FOUR 4.3L L35 AUTO NN8/NA7 16243533 16256225 DOOR S-UTILITY FOUR 4.3L L35 AUTO NF2/NB6 -Z49 16243502 16256230 DOOR S-UTILITY FOUR 4.3L L35 AUTO NF2/NB6/Z49 16243503 16256231 DOOR S-UTILITY FOUR 4.3L L35 AUTO NN8 -NA7 16243536 16256232 DOOR S-UTILITY TWO 4.3L L35 AUTO NF2/NB6 -Z49 16243504 16256233 DOOR S-UTILITY TWO 4.3L L35 AUTO NF2/NB6/Z49 16243505 16256234 DOOR S-UTILITY TWO 4.3L L35 AUTO NN8 -NA7 16243537 16256235 DOOR T-UTILITY TWO 4.3L L35 AUTO NF2/NB6 -Z49 16243500 16256226 DOOR T-UTILITY TWO 4.3L L35 AUTO NF2/NB6 +Z49 16243501 16256227 DOOR MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STLYE T-UTILITY TWO 4.3L L35 AUTO NN8 16243534 16256228 DOOR T-UTILITY TWO 4.3L L35 AUTO NN8/NA3/NA7 16243535 16256229 DOOR S/T UTILITY TWO 4.3L L35 MANUAL NF2/NB6 -Z49 16243510 16256243 DOOR S/T UTILITY TWO 4.3L L35 MANUAL NF2/NB6 +Z49 16243511 16256244 DOOR S/T PICKUP 4.3L L35 AUTO NF2/NB6 -Z49 16243506 16256236 S/T PICKUP 4.3L L35 AUTO NF2/NB6 +Z49 16243507 16256237 S/T PICKUP 4.3L L35 AUTO NN8 16243538 16256238 S/T PICKUP 4.3L L35 MANUAL NF2/NB6/NA3 -Z49 16243508 16256239 S/T PICKUP 4.3L L35 MANUAL NF2/NB6 +Z49 16243509 16256240 S/T PICKUP 4.3L L35 MANUAL NN8 -NA7 16243539 16256241 S/T PICKUP 4.3L L35 MANUAL NN8/NA7 16243580 16256242 S/T PICKUP 4.3L LF6 AUTO NF2/NB6 -Z49 16243512 16256245 S/T PICKUP 4.3L LF6 AUTO NF2/NB6 +Z49 16243513 16256246 S/T PICKUP 4.3L LF6 MANUAL NF2/NB6 -Z49 16243514 16256247 S/T PICKUP 4.3L LF6 MANUAL NF2/NB6 +Z49 16243515 16256248 S/T ALL 4.3L L35 AUTO NM8 16251340 16256249 S/T ALL 4.3L L35 MANUAL NM8 16251341 16256250 M-VAN 4.3L L35 AUTO NF2/NA3 16243516 16256251 -Z49/NN8/NM8 M-VAN 4.3L L35 AUTO NB7/NC1 16243517 16256252 M-VAN 4.3L L35 AUTO NF2/Z49 16243518 16256253 M-VAN 4.3L L35 AUTO NN8/NA7 16243581 16256254 M-VAN 4.3L L35 AUTO NM8 16251342 16256259 L-VAN 4.3L L35 AUTO NF2/NA3 16243519 16256255 -Z49/NN8/NM8 L-VAN 4.3L L35 AUTO NB7/NC1 16243520 16256256 L-VAN 4.3L L35 AUTO NF2/Z49 16243521 16256257 MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE L-VAN 4.3L L35 AUTO NN8/NA7 16243582 16256258 L-VAN 4.3L L35 AUTO NM8 16251343 16256260 C/K TRUCK REG 4.3L L35 AUTO -Z49 16243522 16256261 CAB STEP SIDE C/K TRUCK REG 4.3L L35 AUTO Z49 16243523 16256262 CAB STEP SIDE C/K TRUCK REG 4.3L L35 AUTO NN8 16243583 16256263 CAB STEP SIDE C/K TRUCK 10/20 4.3L L35 AUTO -Z49/NN8 16243524 16256264 C/K TRUCK 10/20 4.3L L35 AUTO Z49 16243525 16256265 C/K TRUCK 10/20 4.3L L35 AUTO NN8 16243584 16256266 C/K TRUCK 10/20 4.3L L35 AUTO -Z49/NN8 16243526 16256267 C/K TRUCK 10/20 4.3L L35 AUTO Z49 16243527 16256268 C/K TRUCK 10/20 4.3L L35 AUTO NN8 16243585 16256269 C/K TRUCK 10/20 4.3L L35 MANUAL -Z49/NN8 16243528 16256270 C/K TRUCK 10/20 4.3L L35 MANUAL Z49 16243529 16256271 C/K TRUCK 10/20 4.3L L35 MANUAL NN8 16243586 16256272 C/K TRUCK 10/20 4.3L L35 MANUAL -Z49/NN8 16243530 16256273 C/K TRUCK 10/20 4.3L L35 MANUAL Z49 16243531 16256274 C/K TRUCK 10/20 4.3L L35 MANUAL NN8 16243587 16256275 C-TRUCK 10/20 5.0L L30 AUTO NB6 16243419 16256281 K-TRUCK 10 C-TRUCK 10/20 5.0L L30 AUTO NF2/NN8 16243420 16256282 K-TRUCK 10 C-TRUCK 10/20 K 5.0L L30 AUTO NF2/Z49 16204232 16256283 K-TRUCK 10 C-TRUCK 10/20 K 5.0L L30 MANUAL NF2 -Z49/NN8 16251347 16256284 K-TRUCK 10 C-TRUCK 10/20 K 5.0L L30 MANUAL NF2/Z49 16251348 16256285 K-TRUCK 10 MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE C-TRUCK 10/20 K 5.0L L30 AUTO NF2 -NN8/Z49 16243422 162562866 K-TRUCK 10 C-TRUCK 10/20 K 5.0L L30 MANUAL NF2/NN8 16251349 16256287 K-TRUCK 10 C/K TRUCK 20/30 5.7L L31 MANUAL NA4/NA5/NM8 16204188 16256291 C/K TRUCK 20/30 5.7L L31 MANUAL NA4/NA5 -NM8 16243425 16256292 C/K 20/30 ALL 5.7L L31 AUTO NA4/NB6 -KL6 16243426 16256293 C/K 20/30 ALL 5.7L L31 AUTO NA4/NA5 16243427 16256294 -NM8/KL6 C/K 20/30 ALL 5.7L L31 AUTO NA4/NA5/NM8 -KL6 16204191 16256295 C-TRUCK 20/30 5.7L L31 AUTO ZW9 16232516 16256296 C/K TRUCK 10/20 5.7L L31 MANUAL NA1/NB6/NF2 16243431 16256304 -NM8/NN8 C/K TRUCK 10/20 5.7L L31 MANUAL NA1/NF2/Z49 16204196 16256305 C/K TRUCK 10/20 5.7L L31 MANUAL NA1/NF2/NN8 16232484 16256306 C/K 10/20 ALL 5.7L L31 AUTO NA1 -NM8/Z49 16243432 16256307 C/K 10/20 ALL 5.7L L31 AUTO NA1/Z49 16204197 16256308 C/K 10/20 ALL 5.7L L31 AUTO NA1/NN8 16232487 16256309 C 10/20 ALL 5.7L L31 AUTO NM8 16251344 16256310 K 10 ALL C 10/20 TRUCK 5.7L L31 MANUAL NM8 16251345 16256311 K 20 TRUCK G-VAN 10/20 4.3L L35 AUTO NF2/NB6 16243417 16256276 -Z49/EXP G-VAN 10/20 4.3L L35 AUTO NF2/Z49 16204133 16256277 G-VAN 10 4.3L L35 AUTO CV4/NN8 16204134 16256278 G-VAN 20 4.3L L35 AUTO NA5 16243418 16256279 G-VAN 10/20 5.0L L30 AUTO NB6 -Z49 16243423 16256288 MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE G-VAN 10/20 5.0L L30 AUTO NA5 -Z49 16243424 16256289 G-VAN 10/20 5.0L L30 AUTO NA5/Z49 16204135 16256290 G-VAN 20/30 5.7L L31 AUTO NB6 -NM8/Z49 16243428 16256297 G-VAN 20 5.7L L31 AUTO NA5/NM8 16204143 16256298 G-VAN 20/30 5.7L L31 AUTO NA5/Z49 -NM8 16243429 16256299 G-VAN 30 5.7L L31 AUTO NB6 -Z49 16243430 16256300 G-VAN 10/20 5.7L L31 AUTO NA1/NF2/NB6 16243433 16256312 -NM8/Z49 G-VAN 10/20 5.7L L31 AUTO NA5/Z49 16204136 16256313 G-VAN 10/20 5.7L L31 AUTO NA5/NM8 16204130 16256314 G-VAN 10/20 5.7L L31 AUTO NA5/NN8 16243434 16256315 P-CHASSIS 4.3L L35 AUTO NA5 16226705 16256280 P-CHASSIS 5.7L L31 AUTO NA5/NM8 16204158 16256301 P-CHASSIS 5.7L L31 MANUAL NA5/NM8 16204157 16256302 P-CHASSIS 5.7L L31 AUTO NB6 16243457 16256303 P-CHASSIS 5.7L L31 MANUAL NA5 -NM8/Z49 16204162 16256318 P-CHASSIS 5.7L L31 AUTO NA5/NB2 16204163 16256319 -NM8/Z49 W4 5.7L L31 AUTO NB6/-Z49 16235809 16235893 W4 5.7L L31 AUTO NA5/Z49 16235808 16235894FIGURES: 0 GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION. COPYRIGHT 1997 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED. � Copyright General Motors Corporation. All Rights Reserved. [This message has been edited by Michelle (edited 02-26-2004).] IP: Logged
JeremyB Member	posted 02-28-2004 07:07 PM If condition #5 HESITATION AND/OR MISFIRE DURING LIGHT CRUISE CONDITIONS DUE TO IGNITION CROSS-FIRE WITH NO DTC STORED. THIS WILL ONLY OCCUR ON V-6 ENGINES WITH CAM RETARD OFFSET IN EXCESS OF 26 DEGREES AND V-8'S WITH CAM RETARD OFFSET IN EXCESS OF 15 DEGREES exists on your vehicle, it is the problem and this TSB is not the solution for misfires. My 96 K1500 misfired slightly(not enough to light up the MIL for a misfire, but did set a P0172 and P0175) at -11 degrees but quit once I got it back to 0 degrees IP: Logged
Michelle Junior Member	posted 02-29-2004 08:31 AM Since my first post 4/28/2003 the van is still mis-firing but no blown coils yet. Some days it runs like crap, others good. The MIL light comes on for a day or so and then goes off by itself. I gave up on checking the codes, it's always P0300. The CPK reads -4096 on the Auto Tap and Auto Tap tells me that thats what the engine is sending. Thats why I'm thinking a software issue is hiding the real problem in the PCM. If it were a software problem in the PCM, that caused the misfire, then it would have started at 1000 miles, not 86000. So I'm thinking that some other sensor is the cause, but the PCM codes are in error and therefore I'm not seeing the full picture. Also, this is a V6 and the PCM is sending me data on 8 cylinders. If anyone knows which other sensors can cause this to happen, I can have them changed. Obviously, the PCM is not showing the proper sensor data. M. IP: Logged
JeremyB Member	posted 02-29-2004 06:45 PM Maybe the problem is with the Autotap software, I don't know? I know I read somewhere about someone having a screwed up cam retard value on a GM using Autotap. I would check it with another brand of scanner, if it agrees I would seriously believe the PCM might be scorched a little, other than that, check the engine ground wires IP: Logged
Michelle Junior Member	posted 03-06-2004 09:46 AM We tore open the wiring harness from the PCM about 1/2 way back from the PCM that leads to the dist, fuel inj and rear sensors and found (under a clip that holds the wires to the frame) a worn spot in the wiring. At least 2 maybe more wires have no insulation at the clip (pink is one of them) where they seem to have been rubbing each other. The damage was not visible on the outside of the harness. We found it by wiggling the harness while idleing at 1500 rpm. it sputtered when we shook the wires in this area? I will follow up when its in back together. M. IP: Logged
JeremyB Member	posted 03-07-2004 07:49 AM A problem with a pink wire would definitely cause serious problems, injectors get power from pink wires, CMP, CKP, EGR, ICM, ignition coil, EVAP, MAF, O2's, and I believe even the tranny is powered by a pink wire IP: Logged
Michelle Junior Member	posted 03-09-2004 07:35 PM Ok, I give up. Put everything back after taping up the chaffed wires. And went for a test drive. Mis-firing as usual, P0300. After 1 hour of driving, the engine dropped dead. Would only pop back and sputter, but would not start. On the way back in the tow truck, the driver rambles to me, "you need to put a BOSCH distributor cap on them engines to fix that problem, cause it has brass contacts, but I'm not a mechanic"? So what the heck, Monday, we got and installed the BOSCH cap and rotor. The engine has been running like new for 2 days now? Not one mis-fire. I,ve replaced the cap, rotor, coil and wires at least 3 times in the last year, (aluminum contacts on all previous GM caps). Give me a break, could the mis-firing be caused by a bad cap design, what is going on here??? Michele IP: Logged
wtd Member	posted 03-16-2004 07:08 PM Did the Bosch cap and rotor still fix your problem? I'm curious because I'm thinking about trying a brass insert cap on my 5.7L to try and fix an arcing problem on my wires and coil. IP: Logged
Michelle Junior Member	posted 03-16-2004 11:49 PM Yes, since 3/9/2004 the engine has not misfired AT ALL! Driven over 1000 miles, in all conditions. After 1 year of @#$% around with this problem, I am quite upset that GM nor anyone on this forum knew this. Especially, due to the fact that I even stated that we busted open an old cap and found indications of cross firing inside the moulding of the cap. I have the old cap and rotor here, intact if anyone wishes to study it. So far the dealer and 2 mechanics are telling my that upon inspection, there is nothing wrong with the cap or rotor, however, if we put the old cap on, it will not even start, and the bosch cap, it runs fine. M. IP: Logged
sonny Junior Member	posted 03-17-2004 11:07 AM I have been reading these posts with much interest! What you say about the knock sensor makes sense. It seems to me that a simple "fix" would be to de-sensatize the knock sensor. If I am not mistaken, that sensor is bolted on to the lower engine block next to the cylinder wall. Why not place some sound deadening material between the sensor and the engine block? By proper selection of material, everything else would still react as designed. sonny IP: Logged
Michelle Junior Member	posted 03-17-2004 10:39 PM This engine has 1 knock sensor at the rear of the block just below the dist. We connected a new sensor to the wire and left it on the carpet with a ground wire attached. The engine ran much worse. Here is my idea. Today, we studied the old cap and discovered severe burning on the leading side of the electrodes in the cap. This indicates that the timing is consistantly to far advanced. This engine has a fixed dist and no mechanical advance. This means that when the PCM varies the timing, the spark must jump a larger gap depending on where the rotor is at the firing time. Because of the consistant heavy wear on the leading side of the electrodes, this would indicate that spark is firing BEFORE the rotor reaches the electrode. Now, according to my understanding, the knock sensor RETARDS the timing as much as 30 degrees which would bring the rotor closer to the electrode and thus less cross firing. That may suggest that with the knock sensor insulated from the engine, maximum advance is attained, and the spark might actually be hitting the cylinder electrode that just fired again or even another cylinder. This would produce the engine stubble we are experiancing, and really mess up the o2 sensors if it's on the other bank. Now, if the rotor too far past the intended electrode, we might fire the spark at the next cylinder in the firing order, creating pre-ignition. This seems to be what was happening to me with the bad cap, as the engine tries to fire, but kicks back on the starter. Today, we slotted the dist hold down clamp and rotated it about 15 degrees to advance (counter clockwise) and it purrs like a kitten. It's a little sluggish when cold, even stalled once, however once warmed up, the engine is as smoothe and quiet as our 2004 Astro. What I don't understand is if the cap and rotor are fixed, and never change, why did it run for 85,000 miles before all of this mis-firing? It only makes sense that if the PCM can vary the timing +/- 20 to 30 degrees, the spark must have always jumped large gaps. This (as explained by Carfixer) would only be worse on an 8 cyl as the electrodes are closer. M. IP: Logged
sonny Junior Member	posted 03-17-2004 11:44 PM When you advanced the distributot and improved performance, you proved that the engine was previously running in retarded timing! I'm thinking over all of this! 1. The distance between terminals on an 8 or 6 cylinder are actually about the same because the 8 cap is bigger! The distance in degrees is less on an 8. (360/8 = 45, and 360/6 = 60). 2. When you change the timing 20 degrees, you only change the distributor 10. Because the crank (the measure point) turns twice for every turn of the cam which drives the dist. When you said you advanced the dist. 15 degrees, did you measure the change with a timing light at the crank or was it the dist. that was physically advanced? Since the knock sensor seems to be out of the picture, I now suspect a badly worn timing chain. They can jump time a cog or two and still run. This would answer your question about the sudden problem after 85k miles. Even before electronics ran the engines, a timing chain jump was hard to prove without a teardown and in those days you could change the timing at the dist. and still go, but with less power. (However, in most cases, when the chain jumps, it jumps several cogs and the engine stalls!). sonny IP: Logged
Michelle Junior Member	posted 03-18-2004 09:07 AM We turned just the dist, and did not change the timing. This, and most 1997 Astros (at least ours) have mis-fired occasionally at 55-65 mph in overdrive even at 10,000 miles, generally while on cruise control. Initially, the dealers were replacing the fuel pumps because they were loud, but this never stopped the mis-firing. The only other thing that may be related is that the VERY FIRST time this van failed (blown coil and cap 85,000~ miles) the temperature was 4 degrees F at altitude 200ft, cruising cold at 30 mph with no accerleration, it suddenly acted like water in the fuel, and within 2 miles, it dropped dead. Towed to GM dealer, $1000+, full tune, check timing chain, fuel pump. The second time 300 miles after it left the dealer, it dropped dead without any warning after a 200 mile run at 55+ mph, it was -12 degrees F at altitude 4,200. We climbed a few large hills with no issues at all, and arrived at a ski slope, pulled up to valet parking and it died while idleing. Towed 85 miles, to another dealer, and found nothing wrong but a blown coil (this dealer looked at the previous dealers invoice, and informed us that it was never greased, nor had the gear boxes been checked as billed, but this is another issue). Checked timing, fuel pres. 1000 miles later, more mis-firing, changed the cap, it ran fine for 3000 miles mostly express way and downtown Boston but 1 ski run then last week, 45 degrees F, cruising smooth at 35 mph on a flat road and with no warning, sudden engine failure. Very bad, lost power steering and power brakes, the road curved left and I could not turn the wheel hard enough avoid the shoulder, we ended up in the dirt on right side of the road with almost no brakes, thank god for mud, it took 1 hour to drag it back onto the pavement and onto the flat bed (it's favorite place lately). M. [This message has been edited by Michelle (edited 03-18-2004).] [This message has been edited by Michelle (edited 03-18-2004).] IP: Logged
JeremyB Member	posted 04-12-2004 05:21 PM This post on another site is of interest. http://www.gm-trucks.com/forums/index.php?showtopic=28595 The TSB is not for the Astro. IP: Logged
Michelle Junior Member	posted 04-15-2004 12:23 PM Thanks Jeremy This could be it, there is no vent on the 97. M. IP: Logged
Michelle Junior Member	posted 09-25-2004 11:24 PM Hello, UPDATE - If you follow this post, the Astro-Safari 4.3 1997 is still running better than new. Were at 96500 miles and there are NO misfires. We left the dist where the mechanic chopped the hold-down tab off at about 12 deg advanced. It runs great. After a lot of city (Boston) driving and 5 to 10 hours a week of idleing, I will get a MIL, it's usually a O2 bank 2 sensor, however after a a few full power runs in drive 3 NOT (D), the problems clear themselves. This AWD van spends WAY TOO MUCH time in OVERDRIVE!!! Low RPM- less air flow, less cleaning? Let me know if I can provide any additional help. Michelle IP: Logged
walterjas Junior Member	posted 09-27-2004 03:35 PM Wow I have a 97 ASTRO with the same problem I believe that mine came from the factory Screwed up.I have a distributer cap that the dealer replaced at about 30,000 miles and the arcing from the rotor is on the front side of the pin (advanced)Add a little PCM advance a little wear on the dist gear,and the timing chain wear and the gap get's so big the dreaded crossfire appears at about 80,000 miles on mine .What I did was to line up the timing mark on the crank with the mark on the front cover at TDC the I lined up the timing mark on the rotor with the mark on the distributer and cut the hold down to fit!About 10 deg.shift at the dist.WHY DO THESE ENGINES HAVE A DISTRIBUTER ANY WAY???? I guess that they needed a place to put the cam sensor. IP: Logged
aksnarfle Junior Member	posted 10-31-2004 04:19 PM All very interesting. I have the same problem. 96 c/k1500 4wd, w/4.3L. I found several problems while diagnosing this but have not solved the misfires. Coil did not ohm out, replaced. Spark plug wires were leaking (visible arcing) replaced. New cap, rotor, plugs. Still get the P0300. This is driving me nuts. Am going to check the cap but I think it DOES have brass contacts. IP: Logged
hornerm Junior Member	posted 11-24-2004 02:35 PM Lucky, my 1995 Blazer is not on these post. IP: Logged
akdale Junior Member	posted 12-02-2004 01:25 AM HI everyone, popular issue here. I have a 1996 K1500 w a 4.3l. I have the autotap software w/enhanced and the CMP retard is showing odd numbers. Like 4307.9! The truck MIl is on with P0300. All cylinders are misfiring at light throttle at around 45mph. The A/F ratio, according to Auto Tap is never above 10:1.1. Normal things have been done, cap, rotor, plugs, wires, new coi,l and I even bought the injection unit from Lindertech that replaces the poppets with real injectors. I did not see anything odd in the idle timing spec but a GM tech told me it is -13 retarded. Now that explains the sluggish performance but the misfire issue is new. The bad dist gear is looking like the next item to check. I also am kinda not trusting the readings from AUTO TAP and wonder if anyone else here has similar experience with the product. IP: Logged

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