Need Help Badly

[Eveready]

Another off-the-wall possibility could be the distributor itself. If you can lay hands on another one to try it might be worth a shot. Distributor issues can mimic many other things. I like the idea of making the fuel pump access a hinged door in the bed.

 

[DerekTheGreat]

It's "rebuilt". Not all rebuilds are equal so there's no telling what you got with this one. Have you done a leak down test? Compression test? Maybe you've got valves that aren't seating right.. Especially since you say the thing never ran right yet was rebuilt to stock specs.

 

[RichLo]

ok, yea something doesn't seem right with the rebuild if its only .10 over, headers and edelbrock intake and otherwise stock. Those things shouldn't have that big of an effect on drive-ability with a stock computer, at least not for 8k miles. The computer should have 'learned' to run right by now. I assume its not throwing any codes (Check Engine Light)?

compression / leak down check, yea. try a different dissy, yea if you have one to try.

To me it still seems like the computer is getting false feedback once it warms up and goes into open loop, but that would most likely cause a CEL. Maybe double check the main sensor connections and make sure there arent any frayed or stripped wires going to them... O2, TPS, MAP, etc.

Another thing to try is unplug or block off the EGR valve.

EDIT, is there any way to go back and verify with the rebuilder that everything was stock? Compression ratio, cam, head work, stroker, etc can have a huge effect on drive-ability with an untuned computer.

 

[lowdown112]

Nope. Gonna try compression tho. Could there be a possibility that old owner put in a fuel pump for a newer c1500 and the regulator can only regulate it down to 14.5psi? How high is the newer c1500 pumps supposed to pump

 

[df2x4]

How high is the newer c1500 pumps supposed to pump

You mean the one that goes on the 96+ Vortec fuel injection trucks? Because those pump at like 60 PSI...

 

[Jglew82]

Check your ignition module inside your distributor. These are a common issue that can cause these symptoms. My 90 was doing this when I still had the TBI engine in it. Fuel pressure was good, EGR wasn't stuck open, etc. Plugs looked rich as well. Changed the module and it was like a new truck. pop the cap and rotor off and do a quick visual - sometimes they can get moisture in and rust up. Part for reference - https://www.napaonline.com/en/p/ECHTP25

EDIT - sometimes it's just as cost-effective to replace the whole distributor since they are relatively cheap these days.

 

[GMTMark]

All of the above replies are quite viable. If you still have problems try a thorough cleaning of any carbon buildup under the egr. One tiny piece of carbon holding it open will cause your symptoms. GM actually made a replacement EPROM for some engines of the time that would cycle the egr quickly to knock carbon out of the way. I don't know if they did it for your model.

 

[Randyb2004]

Step one, plug in a scan tool. Look at engine and air temp both cold and warm. Are sensors working? Next look at O2 sensor readings, .1 to .9 volts and moving around alot. When it starts to die, put a short shot of carb cleaner or starting fluid into the throttle body, if it dies or gets worse you are rich, if it gets better you are lean.

When engine is cold it is in open loop, when it warms up it goes into closed loop. People keep typing these in backwards.

Open loop, it just uses a preset table for air/fuel ratio, in closed loop it uses the O2 sensors to correct mixture. I would suspect the O2 sensor. What does a scan tool say?

Weak spark could be a problem too. Check the distributor as previously mentioned.

My 1995 K2500 did something similar to this a few years back, I switched the fuel injector plugs right to left and that fixed it, the next day I put them back, added some fuel injector cleaner and it has run OK ever since. If someone can explain that to me, then you are a genius! To this day I still think I should replace both fuel injectors, but
I have not.

 

[Steve A]

Has the fuel filter ever been changed? A stopped up fuel filter can look/act like a bad fuel pump and is a lot cheaper and easier to change.

 

[Scout1069]

I believe your fuel pressure is good at 14.5. An adjustable FPR would be a good add as well as a dedicated port to the fuel line at the TBI. But what exactly are the symptoms? Are you getting any codes and if so, what are they?