Tbi help!

[Erik the Awful]

is there something specific I should be looking for?

Plugged cats / plugged exhaust. Was the truck running previously? I bought mine from an insurance yard and after an engine swap it would barely run. I dropped the right side exhaust and it ran great. The exhaust was full of mud.
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[Dak24]

Plugged cats / plugged exhaust. Was the truck running previously? I bought mine from an insurance yard and after an engine swap it would barely run. I dropped the right side exhaust and it ran great. The exhaust was full of mud.
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Well I looked and I can't split them apart because for some reason the exhausts a welded together before the muffler, I don't know if that's original or not, however it does seem to flow really well out of the muffler ( like it will blow floor dry completely across my shop floor) so I don't think that is the issue.

 

[Dak24]

I also checked if lowering the fuel pressure would help and it made It didn't, matter fact if I got under 12 psi it would just die, I assume this is because it's a "big block" and needs more fuel.

I also checked if the egr was the problem, I blocked off the ports with a plate and no difference, as it turns out the previous owner had blocked the egr from coming on by sticking a bb in the vacuum line to plug it, I don't know why exactly, the egr valve seems to work fine.

I did some more checking and retested my vac lines all of which were good, checked for cooling system pressure but nothing abnormal looking to me so I don't think head gasget, listened to injectors with a mechanic stethoscope and they pulse really good, I also listened to the heads and I didn't hear any weird ticks or anything. I did find some moisture on the egr plate when I took it back off is this normal?

At this point the only thing I can possibly guess would be the intake manifold gasgets, anyone have experience with how these motors run with a bad one?

Oh almost forgot, when I was running it hot and revved it up real fast my brother looked at it and noticed it smokes just a little bit blue when you rev it hard, don't know if that is another sign for something else or points toward the intake.

 

[sntrym]

You would see high idle if the intake had an air leak, but it would run fairly normal otherwise. You should hook up a laptop with TunerPro or similar to see what the PCM is seeing, then compare to normal operations.

Also, sometimes new parts are not good parts. Make sure you test that new coolant temp sensor to make sure it's reading as expected.

 

[94ChevyZ71]

You would see high idle if the intake had an air leak, but it would run fairly normal otherwise. You should hook up a laptop with TunerPro or similar to see what the PCM is seeing, then compare to normal operations.

Also, sometimes new parts are not good parts. Make sure you test that new coolant temp sensor to make sure it's reading as expected.

I was looking into trying TunerPro to diagnose some of the problems I’ve been having with my 94 k1500. What plug are you using to connect from the OBD1 port to your computer?

 

[PlayingWithTBI]

Here's a link with that info. You'll also need to corresponding .adx definition file for your PCM's service number. You may find it on the TunrePro RT website.

https://www.gmt400.com/threads/tbi-diagnosing-stumped.52667/page-2#post-1158900

 

[sntrym]

I was looking into trying TunerPro to diagnose some of the problems I’ve been having with my 94 k1500. What plug are you using to connect from the OBD1 port to your computer?

An OBD1 to USB cable like this one: https://www.amazon.com/GM-OBD1-Scanner-Cable-Software/dp/B07D6W1D2R

 

[udidwht]

If I'm not mistaken the 94-95 years had 28-32psi fuel pressure earlier years it was 9-13psi.

 

[PlayingWithTBI]

If I'm not mistaken the 94-95 years had 28-32psi fuel pressure earlier years it was 9-13psi.

Yes, for the 7.4L and 94 - 95 injectors (17104288) were smaller too. Another good reason to put a scanner on it and look at your fuel trims.

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[stillwater]

Thanks for posting this chart, haven't seen this in a long time. Very helpful