posted 12-03-2004 04:10 PM               

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Guess what you can't fix a mechanical problem with a computer!The distributer is out of time to the crank.The crank sensor fires the ignition.The sensor in the distributer is the cam shaft position sensor.MOVE THE DIST. to match the crank IE cut away the hold down clamp so that at TDC crank The dist. is at the alignment point ...My 97 ASTRO with 100,000 miles runs better than when it was new.but at 80,000 miles before i moved the fixed dist about 10 deg.20deg crank it ran terrible and never set a code.GM screwed the pooch on this one

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posted 12-09-2004 02:17 PM               

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What if you are not getting any spark at all?
Do the cam sensor and the crank sensor have to be perfectly aligned and good to produce a spark? I need to know how to check the Coil, Ignition module, cam and crank sensors to see if they are good.

Ronski

[This message has been edited by Ronski (edited 12-09-2004).]

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posted 12-09-2004 08:35 PM               

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As far as the crank position sensor and cam position sensor needed to be properly aligned I would have to say no.When I was checking out the problem I pulled the dist.and moved the drive gear one tooth and the engine ran but immediately set a cam position code.Did you check for codes .I would suggest that you get A Haynes manual for your vehicle you will find procedures to test the coil and sensors.Also a broken wire or loose connection will also cause no spark.My 97 ASTRO had a broken clip on the plug at the PCM where someone forced the plug on when the seal was keeping the plug from seating.later WALT

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posted 12-11-2004 05:57 PM               

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Thanks Walt, My Haynes manual really doesn't talk too much on how to check these parts. I replaced the ignition mod and the coil today and still no spark. I found out there is an auto parts store in town that can program and check VCM's. I thought only the dealer could do this, but It's worth a try. I can buy a reman VCM for $110.00 and have it programed for another $50.00. Monday I'll call the dealer and see what they want for it. This is really a tough one!!
Ronski

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posted 12-15-2004 09:26 AM               

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Well, as it turned out, The reluctor ring was never installed on the new crankshanft before the timing cover was installed. Therefore the crankshaft position sensor coul not get any signal and the VCM would not allow a spark. This is different than if the Crankshaft position sensor had just gone bad, aperently. I will install the reluctor ring to day and check operation....

Ronski

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posted 10-26-2006 07:21 PM               

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I have a similar story. I have a 97 GMC Safari with the 4.3L Vortec V6 (Vin W) engine, same as the 96 Astro this thread started with. It has 154,600 miles on now. I changed the spark plugs at 100,000 miles with the same type that were originally installed, thinking if the first set was supposed to last 100,000, and with how difficult it is to change spark plugs on this van, I didn't want to change another set until 200,000. When the van had about 120,000 miles, the random misfire code P0300 started to appear. I could feel an occasional misfire when on the highway with the engine lightly loaded (not coasting, and not accelerating rather hard). Could feel the misfire on a flat highway, went away when climbing hills or coasting down. It gradually got worse until this fall, especially when we had a week of wet, cold weather. After dry weather settled in, the problem of a misfire diminished, but was still present soon after the engine warmed up a bit, and went away after about 30 minutes of driving. Reading a bunch of threads on this topic, I took the doghouse off and ran the engine in the dark and saw the coil wire glowing at the end of the boot at the coil end, at the end of a paper strip which wrapped the coil wire and touched the transmission dip stick tube (the paper on the coil wire said to keep the coil wire away from any grounded object). I then took the distributor cap and rotor off. I could see one of the plug wire boots on the distributor tower was partially eroded away from arcing from the boot to ground (in this case, the ground was a stud next to the plug wire boot at the distributor which held the plastic intake manifold). Also, the #6 cylinder wire was burned badly inside the distributor tower. I could see a line under the cap running the length of the coil inlet to the center - it wasn't cracked, but it could not be removed in trying to rub it off - so I suspect there was some burning going on in there. I could also see one of the 6 leads under the cap had a spark wear patch very different than the other 5 leads. Five of the leads had a spark wear patch indicating it was picking up spark from the rotor in an advanced time position. But one had a much smaller spark wear patch in the advanced position, and had a larger one on the retarded side of the lead (indicating that particular spark lead was getting some cross-fire intended for the lead next to it). I also tried turning the distributor shaft while still in the engine and felt there was to much play, especially for a spiral gear drive system. The shaft at the top of the distributor also had some radial play, indicating the bushing at the rotor end of the distributor was worn. In pulling the distributor assembly out of the engine block, it was very evident the spiral bevel gear was badly worn, had grooves worn across the front side of all the teeth (which would indicate the timing of the rotor was retarded more now that it had been when new). For that distributor gear running in an oil bath (and I always used synthetic oil) and for as light of a load it had (just turning a distributor shaft), that gear should not have had any signs of wear - it must not have been heat treated properly and was probably too soft. I have a car with spiral bevel camshaft gears that have a heck of a lot more load on them, and has 250,000 miles on it, and those gears look brand new even now, no signs of wear. Also, in turning the distributor shaft when out of the engine, it made a squeaking noise coming from the top side of the housing, also indicating the bushing at the top was worn (which made sense why it had radial play in it). I checked the distributor vents (has two vents with very narrow slits in them, no screens) and both were clear, no clogs. The remanufactured distributor housing had exactly the same vent construction. So I don't think vents were the problem here, although I do believe wet weather causes a humidity increase inside the cap, which can cause probems. Put a remanufactured distributor housing back in (no radial play at all; there was a little lash in the gear mesh, but not as bad as the original unit), new rotor, new cap, new coil wire, but kept the same spark plug wires (maybe should have changed the set because I know two of them had signs of spark errosion, but stores were closed and I needed the van the next day). Started it up, ran perfectly. On the highway, no problem. Time will tell if it comes back again or not. I'll still probably put a new plug wire set in there in a couple weeks. My theory of why this problem develops after this engine gets 80,000 - 120,000 miles? I think the resistance between the coil and the spark plugs increases a bit with age, primarily due to corrosion over time (the original distributor cap, from Delco-Remy, had aluminum contacts, while my replacement had brass contacts, which should have less corrosion problems). Wetter, more humid weather allows an alternative, lower resistance path for the spark, causing some grounding problems. And, the gear wear caused the rotor to be a little farther behind in it's rotation than it should be, so the gap between the rotor and the distributor leads was a bit too large when the ECM is calling for high advance timing (lightly loaded at higher engine speeds), which either caused some no spark due to too high of a gap conditions, or some cross fire conditions internal to the cap (because the rotor wasn't far enough away from the distributor lead it just previously fired). This became apparent when I saw the glowing coil cable when I first tested all the original wires, cap, etc. - as the engine warmed a bit, the glowing got brighter, and the misfire got worse (meaning the resistance in the system, which is highest in the coil wire, was getting larger as the engine warmed, and when the engine warms up running at high idle, the timing advances more). It all fits together. The new components, when checked by running the engine in the dark the same way I did with the old parts in place, did not generate any glowing anywhere, including in the coil wire. However, I routed the coil wire over the heavily insulated air conditioning hose above the distributor, rather than right next to the metal transmission dip stick tube, where the original coil wire was routed. Anyway, I think GM got a bunch of soft distributor gears that, over time, wear and cause too large a gap between the rotor and distributor contacts when the ECM calls for max advance on timing (when going up a hill, the knock sensor picks up more engine noise and retards the timing a bit, and when decelerating, the engine probably can't pick up on a misfire anymore). I also think on this ignition setup, it's imperative to keep all spark plug and coil wires as far away from any ground as possible. Well, that's my story, and I'm sticking to it. Hope this helps others who might be experiencing the same situation. I'm sure the cost to diagnose and fix this at a GM dealership would be very costly. As it was, this cost me about $150 (maybe $175 by the time I purchase a new ignition wire set).

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