2001 Cummins Idle Sputter Since FASS Install
 

Hey All,
I figure I'd try my luck on these forums, as I've had good info over the years come off the brilliants that occupy the forums at Diesel Bomber:rocking: I've posted over at the Cummins forum however no real luck from people there as of yet.
The Story
I have(had?) a flawless running 01 Cummins with factory carter pump. I decided I wanted to finally "future proof" my truck and pick up a FASS Titanium 95GPH Lift Pump to protect the VP44. Since the install I've been experiencing what I can describe as a intermittent "sputter" or "stutter" that happens mainly when the truck has reached a decent operating temp, and it happens far more frequently when fuel tank is more full(still will do it below 1/2tank). Over the past weekend, my truck had sat for 2 day's before firing it up, and when i did, I was forced to bump the starter a few times to re-prime the system before it finally fired up, though this issue may not even be related to my sputtering issue.
here is a video I did that clearly shows the issue happening. Fuel Pressure is pretty solid even at WOT. The issue only happens when at idle.

Another oddity to this issue is that even at operating temps, the issue may not be occurring, however if I turn the truck off, then fire it right back up, the sputtering will begin almost instantly. I've talked with FASS on multiple accounts, and sadly so far I have come up empty handed. My last reply from them was as follows:

"The fuel pressure looks very stable, doesn’t look like a FASS issue, but we can always test the pump to verify this. Just let me know if you’d like to send it in.

Looks like your FP is steady @ 16psi. Even if it dips to 9psi @ wot, the OE fuel pumps only put out 9-12psi max.

A prepump restriction could cause this, but since the fuel pressure looks so steady I doubt this to be an issue. You’d see a pressure fluctuations. Could be air getting in the system (post-FASS), do you ever see any white smoke?

If you are using any liquid thread sealer or pipe dope on ANY of the FASS fittings, this will result in loss of prime. If your fuel system is losing prime, it’s rarely the FASS system, but usually a fitting/connection or somewhere that air is entering your fuel system or fuel is draining back to your tank.

The stuttering issue can be caused by MANY things, injectors, ecm, injection pump, etc. You may seek further assistance from a qualified diesel technician.

Fortunately it looks as though the FASS system is doing it’s job, looks to be flowing a very steady pressure. Which is it’s only job, the transfer fuel from your tank to your injection pump." END QUOTE FROM FASS

One thing I have yet to try is the bucket test, which hopefully I can get sometime this weekend to try. I've now driven about 700 miles with the issue, and not throwing any codes at all. Hoping someone has a miraculous idea! Thank you all for reading this boringly long story, but any help/ideas is much appreciated, I just can't find anyone with this same issue! The Tech at work who walked me through doing it has installed the same unit on many other Cummins, and hasn't seen this issue.

P.S. Truck is mostly stock, just Hypertech Tuner & AFE drop in filter & exhaust(or none let's say). I've tried returning to stock tune, but didn't help.

It sounds to me like air leaking into the system somewhere. Air will cause a stutter but won't change the fuel psi gauge. Check your filters, lines, and connections. Does the fass system come with a new drawstraw kit? I've never installed a fass system before.

Thanks for the reply Tbirdz!
All the lines leading up to the VP look great. I've checked all the fittings many times over, can't seem to find anything. Both Water separator filer, and fuel filter itself are super tight. No visible fuel leaks either. As far as the draw straw kit I had to purchase that separately, I have not yet put it on though, as it wasn't needed with my kit, as I do not have the in tank lift pump from factory.

You still can he sucking air from where the fass connects to the stock tank. No leak will be seen. As said above its a inward leak of air now a outward leak.

Roger, I think I will drop the tank this week and see what I can find! Will post back with results!

Well dropped the tank to visually inspect everything. The bottom basket on the sending unit was all sorts of nasty, cleaned it up, put everything back up, and now the sputter is far far more dramatic now...what gives?!

Yes but you can still be sucking air where the stock "sending unit" meets the aftermarket fuel lines.

I recently deleted my egr and I have a programmer. As soon as I did that whenever I took it to drive if I hit the gas too hard I'll get 3 -4 good jerks. Never did it before the delete and I don't think it's my transmission because I can drive normal and never jerk or feel a slip.Saw someone post something about a butterfly valve or manifold that might be dirty to cause but idk. Anybody have any idea what could be going on? Appreciate any input!

I think your in the wrong section. The 24v VP Cummins didn't have an EGR.

Did you ever figure out the problem?