i cannot figure out the problem my truck has.
at certain rpm's it feels like it is cutting out or has a bad miss and some rpm's it feels fine???
at around 1500 it feels like its cutting out but if i go a little bit over 1500 it feels fine but then once i get at 2000 it starts to cut out again but once i go over 2000 it runs great.i replaced my lift pump and my water/separator is brand new and i also bought a pressure gauge with the tapped banjo bolt and ideling my fuel pressure is about 5psi and whn i rev it up high it still stays where it should be so im not sure.
could bad injectors be causing this? my truck has a little bit over 300,000 on it.
my truck is a 91.5 with a getrag. my smoke screw is bottomed starwheel is bottomed and the full power screw used to be only one turn back from bottomed but once it started doing this i backed it out about 1 1/2 more turns thinking i wasnt getting enough fuel but it didnt help one bit
so i have no clue as to what the problem could be.

 

Some of the IP tuners will chime in shortly, but is there any chance your fuel solenoid wire is making-breaking with certain engine vibrations, ie specific rpms? You could hot-wire it for a test run and see if anything changes.

 

I think that's a very good suggestion.

 

How many miles does your pump have on it?

 

i have that exact same problem, tryed backing the power screw out and it didnt help, thought i had water in the fuel, new fuel filter, and nothing seems to help, no fuel leaks, i couldnt tell you where an air leak was, it seems when i build around 15 lbs of boost or at a certain rpm it just wants to cut out, then if i hit the throttle it advances and runs good. its got a brand new ip on it and it did this before i rebuilt the pump.

 

thanks i will take a look at that and see what it does.

 

Those injectors are well used with 300,000 on them. That could be causing it, they could not be poppin off right.

 

maybe a bad/weak lift pump not supplying enough pressure or volume to build enough case pressure?

 

I had a similar symptom and has not come back since the Ip was rebuilt. The plunger return springs were broken and the rotor a chunk off of it. Hope this is not your problem.

 

i just had my pump rebuilt and i have a high presure piston pump at 15lbs, and brand new lucas pod's

 

sorry for the highjack but could it be an air leak, i mean where would come from???

 

*update*

ok i rigged my fuel pressure gauge into my cab temporarily and it stays 5-6 psi and when i floor it it only goes down to 4 psi.

also i decided to see what happened when i free revved it to the rpm where its the worst which is 2000 and i could here popping from the exhaust(i have a stack and had my back window open) while fuel pressure read 5 psi

 

yeh i hot wired mine and it didnt help,

 

Sounds like internal pump problems to me.

 

i changed out the internal pump presure banjo bolt on the return line and it was plum packed with nasty stuff, probably from when i had it all apart, i replaced it and she runs like a top, loads more fuel and better responce, no more miss, also turned my regulator down to 10 psi and that seemed to help. my valves were a 15 and 30 and i adjusted those to 8 and 18, world of difference,

change out your return line banjo bolt right next to the idle screw and see how that works.