My nightmare.
07-19-2016, 11:26 PM
#1
Heel & Toe
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My nightmare.
Looking for opinions.
I have been fighting this car for a while. I took the car out of storage, it started and was running fine. While it was warming up it backfired and stalled. When I went to restart it would kick back against the starter. When I finally started it, it ran very rough and would stall randomly. Sometimes it would backfire through the intake when it stalled.
I had an extra ignition module, so I tried that first as a quick check. No real change in how it ran. Connected my scanner, it showed no codes. Looked like it was a little lean, long term fuel trims were about 138.
Next thin I changed were the O2 sensors, mostly because they were a little slow in reacting. Still no change.
So, my next thought was distributor gone bad. So I pulled the front of the engine apart and inspected the distributor. It was full of rust, so I figured that was it. I went to eBay and found a supposed new gm distributor. When I received it, it looked like it had been installed and removed. Did not appear to have been run, or at least not run very long. Didn't feel like waiting, so I installed it. New water pump,seals plugs and wires also. Still no change. I have checked all of the grounds to the pcm. I have added grounds from the engine to the chassis. Ohmed every wire from each sensor to the pcm. Ohmed all the injectors. Replaced the Maf sensor. I pulled the intake looking for vacuum leaks. I did find a leaking egr, I pulled that and just blocked it off for now. Still no change. I am pretty much down to pcm bad or I got a bum distributor. Just looking for some ideas where to look next. Anyone had a bad pcm act like this.
Oh, it's a 1994 with a 6 speed.
Thanks for any ideas you all may have.
I have been fighting this car for a while. I took the car out of storage, it started and was running fine. While it was warming up it backfired and stalled. When I went to restart it would kick back against the starter. When I finally started it, it ran very rough and would stall randomly. Sometimes it would backfire through the intake when it stalled.
I had an extra ignition module, so I tried that first as a quick check. No real change in how it ran. Connected my scanner, it showed no codes. Looked like it was a little lean, long term fuel trims were about 138.
Next thin I changed were the O2 sensors, mostly because they were a little slow in reacting. Still no change.
So, my next thought was distributor gone bad. So I pulled the front of the engine apart and inspected the distributor. It was full of rust, so I figured that was it. I went to eBay and found a supposed new gm distributor. When I received it, it looked like it had been installed and removed. Did not appear to have been run, or at least not run very long. Didn't feel like waiting, so I installed it. New water pump,seals plugs and wires also. Still no change. I have checked all of the grounds to the pcm. I have added grounds from the engine to the chassis. Ohmed every wire from each sensor to the pcm. Ohmed all the injectors. Replaced the Maf sensor. I pulled the intake looking for vacuum leaks. I did find a leaking egr, I pulled that and just blocked it off for now. Still no change. I am pretty much down to pcm bad or I got a bum distributor. Just looking for some ideas where to look next. Anyone had a bad pcm act like this.
Oh, it's a 1994 with a 6 speed.
Thanks for any ideas you all may have.
07-19-2016, 11:30 PM
#2
Team Owner
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St. Jude Donor '05
If it kicks back thats concerning. get a fuel pressure gauge on it (auto parts stores rent them) and see what it does when you turn the key to "on". Note pressure , then any drop. If you got a leaky injector no bueno
If they let you tape it to the windshield, drive it hard and see what its doing under a hard load in high gear
Start with simple stuff
If they let you tape it to the windshield, drive it hard and see what its doing under a hard load in high gear
Start with simple stuff
07-19-2016, 11:50 PM
#4
Burning Brakes
No codes? That sounds like opti trouble. Did you check out the harness to the opti? Coil? ECM could be going AWOL. MAF? Diagnosing an LT1 is a bear when no code lights, and it sounds like you are a very advanced mechanic. I hate to sound stupid but they are engines that depend on air/fuel/spark.
It has to be something wrong with at least one. Please keep us posted and invite free thinking ideas. That's what makes this forum so useful.
It has to be something wrong with at least one. Please keep us posted and invite free thinking ideas. That's what makes this forum so useful.
07-20-2016, 01:03 AM
#5
Melting Slicks
this little low voltage harness, twenty bucks or so can be an often overlooked source of problems. Why? the connector end that plugs into the opti is long, thin and plugs in vertically so any moisture or contamination collects there.
Last edited by mtwoolford; 07-20-2016 at 01:05 AM.
07-20-2016, 01:37 PM
#7
Melting Slicks
you changed the Opti/Distributer But from Where? Don't totally trust the chain store Optisparks, Enough has been said in the forum on that.
My 93 Six speed did much the same as yours and I to pulled my Hair out, I to replaced ICM and ran the Flow Charts for Opti failure but my in case it was the Coil itself that had mine acting up.
My 93 Six speed did much the same as yours and I to pulled my Hair out, I to replaced ICM and ran the Flow Charts for Opti failure but my in case it was the Coil itself that had mine acting up.
07-20-2016, 05:19 PM
#8
Heel & Toe
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The distributor I got off ebay. It was supposed to be a new gm. It looked like it had been mounted to an engine when I got it. I pulled the cap and it didn't look like it had been run. It did have a Mitsubishi optical sensor in it. But I don't really know the whole story on it. The coil is about the only thing I haven't changed. I might call the parts place and have them bring me one, it might as well be new as well.
I haven't ruled out the opti just yet. I am just trying to exhaust all other options before taking it back apart.
I haven't ruled out the opti just yet. I am just trying to exhaust all other options before taking it back apart.
07-23-2016, 12:32 PM
#13
Pro
They can leak internally into your vacuum source is why I ask. This can cause fuel trim issues, and the kickback against the starter you speak of due to possible hydrolock conditions. I'd lean towards the ignition first though.
08-07-2016, 02:51 PM
#14
Heel & Toe
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Ok, found the problem.
I took my pcm and tried it on a friends car. Flashed his vin in and it ran perfect. So not the pcm. Pulled the distributor cap to inspect. Brought engine up to tdc and checked alignment. Rotor looks too far advanced. Removed the distributor and found something interesting. The drive coupler master spline on one end is machined incorrectly. That end of the coupler can be installed one tooth advanced or retarded as well as center. Only one end will go in that way. Put it in correctly and it runs fine.
I took my pcm and tried it on a friends car. Flashed his vin in and it ran perfect. So not the pcm. Pulled the distributor cap to inspect. Brought engine up to tdc and checked alignment. Rotor looks too far advanced. Removed the distributor and found something interesting. The drive coupler master spline on one end is machined incorrectly. That end of the coupler can be installed one tooth advanced or retarded as well as center. Only one end will go in that way. Put it in correctly and it runs fine.