i have a 94 cummins with 370hp injectors a very aggressive custom cut cam plate, the engine shudders between idle and about 1250 rpm with idle not as smooth as it was before the injectors. once in gear the truck shakes within that rpm range so bad i can't let it run there. there are no problems like this with stock injectors and the 370's tested out fine on my test stand for pop-off and chatter with no leakage. Timing is advanced from 12.2 stock to 15.2-15.5 but still shudders, the pump both lift and injection check out fine and new fuel filter with no fuel restrictions anywhere. the intake is fine no air intake problems but just a wicked shudder. I've been on the phone with every injection shop around here and even with the service manager at cummins bridgeway in grand rapids michigan with still no luck.
what should i try next?

Thanks, Chris

 

Delivery valves are to small on the earlier p-7100 pumps. You could go 181's out of a 96 to 98 215hp stick truck or larger 191's. Laser cut if you plan on going really hot.

 

the pump in the truck i had to change about 6000 miles back and i installed a used one out of a 96 or 97 stick 4X4 and it almost seems worse with this pump than the first one.

 

If it is a 215 hp pump you should not have a studder with 370's. Maybe the pump is bad?

 

Was it calibrated on the bench before you put it in? It sounds like the fuel delivery is off between each port.

 

yes the pump was bench tested before i put it in to make sure i wasn't wasting my time installing it. i had diesel injection service in grand rapids michigan do the bench testing they said it tested out. however changing delivery valves isn't too bad where would you recommend picking up a bigger set to try and see if that cures the problem?

Thanks, Chris

 

Can you find out for sure what pump you have first? That way you should be able to find out what delivery valves are in it.

If you are going to swap them out I would go with 191's.

 

Mine does that a little w/ stock injectors. If I give it more fuel it smooths out instantly. Are you cruising around in a high gear off idle when this happens? If so, just grab a lower gear.

 

i just installed laser cut 191 delivery valves hopeing to pick up some power but mainly to smooth out my idle and my engine stumble around 1100 rpms. And once delivery valves were installed the idle got much rougher almost like a miss now and engine stumbles worse then ever before. timing is still set at 16 degrees and cam plate is still the same. what should i try next?

 

Just a shot in the dark, but have you considered re-installing your AFC guts? Maybe you're putting out the fire...also, has your overflow valve had a checkup lately?
greg

 

ya the overflow valve was replaced about 4 months ago and didnt seem to make any difference. do you think i should step up on the timing a bit more? i just cant believe that it is too much fuel because there really isnt that much smoke considering the fuel plate and injectors with those delivery valves.

 

Yes i think you should bump it up to about 18 or 19 when you go to adding more fuel you should also advance the timing
fuel + timing = more power and smoother operation
fuel alone adds heat
timing alone is more efficent

IMO
Jake

 

For what its worth, my 24 valve does this same thing, but only when its cold. And I have determined two things about my case. One: its the cold fuel that does it, not cold air or a cold engine, and TWO: more timing makes it much worse, since if I remove my EZ box, it gets better, but its still there. With the EZ on, in the winter, it can be wicked. Just like you, no one at all has been able to figure out why its doing this.. Its smooth as silk though in the warm weather....

KP

 

more timing should help. 15* is nothing on timing. but somting is not right, because look at hazelrazors avatir thats what it should smoke like with lazer cuts and 370's. you should be able to swing that pyro right on around.

 

i thought the timing would help but i havent tried that yet, likley this weekend but im wondering if i should try some different DV's because these came from city diesel and it almost ran better with stock DV's. should i possbily consider Scheid for a very high performance set?