93 C3500 running issues

[Jagerking454]

I have a 1993 GMC C3500 7.4L manual trans with running issues.  When the engine is cold the truck has a rough idle and revs up and down.  When the truck has warmed up it idles fine just a little low around 350 RPM.  When in the driveway it revs to redline fine with no issue.  Once the trans is put into gear, the engine will idle fine but as RPMs approach 1000 the engine starts to stumble, loose power, and begins to pop through the exhaust.

 

Parts I have replaced:

distributor ( came with new cap, rotor, and ICM)

fuel filter

fuel pump strainer

IAC valve

MAP sensor

temperature sender

fuel injectors

spark plugs

ignition coil

ECM

TPS sensor

throttle body rebuilt and new fuel pressure regulator diaphragm installed

fuel pump (the first fuel pump was one for a 1993, the second was one for a 1995)

 

After installing the second fuel pump the engine runs smoother but still stumbles during acceleration.  When the distributor was changed, engine was timed to 4 degrees BTC. I disconnected the timing connector and the engine runs better but still has a little stumble and lacks power when driving.  If anyone can give me some ideas or things to check out it would be greatly appreciated.  Thank you in advance!

 

 

 

I have retired the engine to make sure that it is at 4° BTDC....haven't drove it yet but will give an update once I do.

Edited June 21, 2021 by Jagerking454