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Discussion Starter #1
Hi everyone,
I've searched through the forum and tried a lot of stuff before deciding to make a post.
I bought the truck not running and found that the spark plug wires weren't in the right places. After fixing that I was able to start it but it had an extremely rough idle that would surge. I tested a lot of stuff and have replaced the IAC valve and MAP sensor. That helped a lot and it now runs smoothly until warm, when it gets really rough again and will die. I noticed that the previous owner had replaced the EGR valve, distributor cap and rotor, oxygen sensor, and spark plugs and wires.

I tested the engine coolant temp sensor and its fine as well as the wires to the ecm. I tested the tps and it also is fine. I don't think it's ever using the oxygen sensor though because if I try to set the timing (with the correct wire disconnected) the timing mark either isn't visible or I'll see it sliding around. The distributor doesn't have very much slack in it so I didn't think it was an issue. I haven't tested the fuel pressure yet because I don't have the right piece for my pressure gauge and I haven't tested compression. The injectors visually look like they're spraying really well and it actually smells rich once it's warm and starting to run rough.

Once it dies I can't get it to restart unless I severely advance the timing and then quickly set it back where it was. What do you think I should try/test next? I'm starting to loose my mind a bit. Thanks so much!
 

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Discussion Starter #2
Here's an update: the truck sat for 4 days and then would not start at all. I played around with it a bit and got it going but it was very much flooded at first. Does anyone think the injectors might be leaking while its off? I drove it around the block a bit and after that it actually ran much better and stayed running while warm.
 

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Try these-
1-Check for vacuum leak. Replace any old hard,cracked lines. Check if hoses are tight on fittings.
2- Leak on intake gasket of TBI, test by spraying starter fluid around intake while idling
3-Add some Marvel Mystery oil or Lucas to fuel to clean possible FI issue
4- Spray carb cleaner into TBI while running (if possible)
5- Test electronic module on side of distributor, assuming you have repair manual.Easy to remove.
6- Double Check all electrical connections on ignition system for tightness and corrosion. Use di-electric grease
7- Check coil resistance
8- Pull off catalytic converter and look thru it. May be clogged. Mine was and caused rough running.
This is a few points I would cover first before taking components apart. I have a 4.3 with 228,000 +/- on it and it is still running great. Not to say a few parts have replaced.

Lake
 

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Discussion Starter #6
Try these-
1-Check for vacuum leak. Replace any old hard,cracked lines. Check if hoses are tight on fittings.
2- Leak on intake gasket of TBI, test by spraying starter fluid around intake while idling
3-Add some Marvel Mystery oil or Lucas to fuel to clean possible FI issue
4- Spray carb cleaner into TBI while running (if possible)
5- Test electronic module on side of distributor, assuming you have repair manual.Easy to remove.
6- Double Check all electrical connections on ignition system for tightness and corrosion. Use di-electric grease
7- Check coil resistance
8- Pull off catalytic converter and look thru it. May be clogged. Mine was and caused rough running.
This is a few points I would cover first before taking components apart. I have a 4.3 with 228,000 +/- on it and it is still running great. Not to say a few parts have replaced.

Lake
Thanks for the reply!
1-I've checked already for vacuum leaks. everything is good there.
2-I've done that already too and the motor doesn't change speed or react in any way.
3-That's a great idea, thanks! I'm also going to add a full tank of fresh gas.
4-I also already did this, it didn't really improve anything.
5-I'm going to do this tomorrow. The temp gauge wasn't working so I figured while I had the coolant drained I might as well replace the engine temp sensor even though it tested fine. I got everything back together and now it has no spark so the problem may have revealed itself.
6-I've done this many times and they are clean and tight.
7-One of the first things I did, and it's well within specs.
8-That definitely could be part of it, I'll check it out once I have spark again if there's no improvement.

When I have it running at operating temperature and go to time it (disconnecting the brown with black stripe wire on the ecm harness) it appears to not be running in closed loop mode since the timing mark is either not visible or floats around. Since I now have no spark and the ignition coil is powered and working I'm hoping that the icm was causing a lot of the problems I'm having. Do you think that thinking makes sense?
 
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