Engine/Transmission (1994 - 1998) Slight stumbling after new modifications

[RStankevitz]

my diesel shop told me it is common on early 12v with the p pump said there is a rough spot on the rack?

 

[Driftwood Ram]

Is there any possibilities that the stumbling could be coming from missmatched injectors-as in not perfectly matched and having slightly different "pop" pressures?

IMHO there are too many trucks that have this "problem" for mismatched injectors to be the cause. I went from old DR. Performance phase 2 injectors with a 215 plate all the way forward to DDP 75hp injectors and a #10 plate to get the shudder.

It already had a shudder in the 50mph area, but this change added another around 35mph. Low RPM t/c locked. If you do not let the t/c lock there is no shudder. Just like lugging with a manual.

A transmission builder has told me it is gov. spring or gov. spring adjustment and that is what Piers is going to work on next Spring when we go back North. For now I just work with the OD on/off button.

 

[K5IP]

JAMOS,

My 95, 175 pump, also had the stumble from the day it was new. The injectors were pop tested. In my case all the injectors were well matched. However, most, if not all of the stumble went away when I changed to 215 injectors so they are in the equation.

Rog

 

[JAmos]

Has anyone had their pump on a test stand trying to figure out the stumble? What about using the wrong copper wasers?



Jordan

 

[HOT0124valve]

i have had the same prob and i looked to the barrels the top of them have a seat that seals let me back up if you pull the barrel you see the delivery valve and in the barrel is the spring and then you look at the spring and it has shims and next it has a tapered seat poppet that holds the shims and spring on the top of that. it has a sealing surface that seats into a seal at the top. if it is worn on ether surface it will leak or bleed off and cause a miss but more thing get over looked at the delivery valves and barrels any of these surfaces have a tiny pit at 1000 psi they open to early or wont suck back fuel. so look over all of it even with a jewlers loop pits and ridges are bad r. r. and it might just fix you prob it did mine

 

[Vaughn MacKenzie]

I went through a maddening process trying to cure the shudder on my '96 and finally gave up after 4 different sets of injectors, 2 injection pumps, 2 valve jobs, and tweaking with the gov. springs. The thing that helped most in the end was the DDP Stage II injectors but it still has a slight miss.

There are 2 things I suspect to be the cause. . . #1) pulsations by the lift pump could be causing some hydraulic harmonics inside the pump (fuel hysteresis) that leaves one cylinder lacking for fuel at the right RPM. Change the RPM a bit or give it a little more throttle and the condition subsides (engine smooths out). So I wonder if regulating the fuel and evening out the LP pulses would help the problem.

#2) or it could be governor related where at the right RPM the springs "bounce" a little and the governor drops fuel for a few microseconds (the bottom of the spring bounce) in time with one particular cylinder (causing it to seem like a slight miss). I think the problem with the P7100 governor is the springs are too "springy" and bounce too much. . . if these springs had some damping, ie. a "shock absorber" of sorts, I think pump hypersensitivity, shudder, the herky-jerkies, etc. could be improved considerably.

Vaughn

 

[okayred]

I had this problem and it stopped after I installed the governor spring washers 2 weeks ago. I agree with Vaughn's #2 above.

 

[hsmith]

Hey Josh, how did the truck do on the way home?

Smitty