BobOkie

2002 Dodge 2500 (~150k), Cummins engine, no mods except for lift pump replaced in 2011 (FASS DDRP) and again in 2017.
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Latest update: Still having problems with pressure. Took it to mechanic that understands diesel and has done good work for me. He bypassed the ECU and setup the FASS to run directly off ignition. Problem solved. Most pressure readings are between 18 and 20 unless truck is heavily load uphill or accelerating, still rarely drops below 15.
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It is the electrical stupid.
I'm updating this for anyone else that might have the problems I have been working on.

I found my battery connection from alternator to battery was loose. I replaced it and have a solid connection. Now everything is working well (including pressure gauge and a/c, another problem I was working on). Truck runs like a top.

Pressure readings
- pump running after bump start but engine off: 20 psi
- pump at idle, engine running: 15 psi
- pump on road 1500-2000 rpm: 10-12 psi
- wot, 3000 rpm psi drops to 5-7
would like it higher but truck is running fine with no hesitation. Still might work on tank and see if I could get the pressure up but there is no rush.

Also wondering if I needed to replace the injection pump since real problem was old FASS pump wasn't giving necessary pressure - only about 7 psi at idle.

Also wish I had done some research. I think I would have upgraded to a titanium system instead of the straight replacement of the older FASS pump. Maybe in another 6-7 years.

----------- earlier notes ------------------
So I've been having problems with my truck and fuel. I'm scratching my head some this morning.

Some more details -- After replacing the FASS pump with new I get 20 PSI without engine running(old was 7 to 5). Engine running at idle I get 10-12 psi, not moving in neutral rpm up to 2000 drops to about 5 psi. So I think there must be a restriction between tank and lift pump. So current plan is drive on side streets to work until I get close to empty on tank to drop it (currently about 1/2 tank - going highway pressure drops too low).

I think I might do the 5 gallon bucket test first just to help confirm issue - although problem has never been in idle.

Also, thinking about bean sump pump -- has anyone used that? I think I could go that way and eliminate dropping tank. Any suggestions on fuel hose - I'm thinking about replacing hard line from tank to pump while I am dealing with all of these issues.

Yea, I'm not happy with glow shift gauge. I'll replace it at some point but it seems to be working reasonably well now. No longer pegged at 30 psi (unplugged everything and replugged - now working).
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Original issues:

Truck was surging and bucking (during cold weather ~ 20 deg and later in summer). Problem went away and came back after about 6 months (summer). Low pressure going to injector pump (7 psi). Smooth running when first started but would later surge or buck.

Replaced high pressure injection pump. Found old low pressure warning sensor installed after lift pump in 2011 wasn't working.

Installed fuel pressure gauge - idle about 7 psi, but driving dropped almost to 0 -- surging too.

Replaced FASS lift pump. Idle about 12 psi. Drove around a little and pressure would drop to about 5 psi. Thinking there might be air leak or problem with tank at this point. Considering replacing system from tank to pump.


This morning took a longer drive, started out at about 12 psi. After about 15 minutes of driving with hard acceleration psi reading pegged at 30 psi. Some more starts, stops and acceleration gauge not moving.


Turned truck off gauge goes to 0. Restart gauge jumps to 30 psi.


So now I'm wondering -- is gauge not working? or did I finally purge all the air out of the system? or some blockage finally break free?


Installed without running for long
* pressure gauge with hose extension
* new FASS pump
* pre-filter to FASS pump
* lost a fair amount of diesel on line from tank while installing the pump.
Thus there will be a fair amount of air. I did run pump until fuel at pressure gauge before installing it also ran pump until fuel filter was overflowing.


I was disappointed when the initial psi was only 10-12 but what limited amount I could find pump should be about 15 psi.


Thoughts? Appreciate responses.

cougar

If you have a gloshift fuel pressure gauge, throw it in the garbage and get a real one form like Autometer or ISS.
Been a few years sense I've messed with this and I know there will be a lot of argument, but try to keep the pressure between 15 and 20 psi.
The lift pump has a built in regulator. If in deed the pressure hit over 30, then I would suspect that right off.
The injection pump has a 14psi regulator in the return banjo fitting. If it plugs up you could see a higher than usual pressure reading, but the lift pumps regulator should still limit pressure.
Plugged return lines could also raise pressure, but still be limited by the lift pump regulator.

cougar

If you have an excessive amount of water in your fuel, it will freeze and plug things up. It can also damage your pressure regulators.
My suggestion is drain, remove, and clean the fuel tank. Water also allows things to grow inside your thank that can also clog the plumbing.

Desert5600

As a reference, a good functioning FASS DDRP should output 17-18 psi and no less than 12-13 psi at full turbo boost.

BobOkie

Please read my update at top of message. Do you think I am on right track with some type of restriction or air leak between tank and lift pump? I get good pressure with truck off but it drops to low IMO.

Thank you for your reply

Desert5600

Did you ever replace the fuel filter? If so, water or debris in the bottom of the filter canister?

cougar

You could have a clogged tank vent. Leave the fuel cap loose and check it again.
You could also have a pinched fuel line. If you replaced a fitting on a flexible hose, you could have damaged the inside and it's acting like a plug.

BobOkie

Since I still might get in and replace the sending unit, how do you clean out the fuel tank? I figure you don't want to wash it out with soap and water.

BobOkie

Yes, I did replace the fuel filter before all the other stuff.

BobOkie

Yes, that was one of the first things I did both in winter when problem originally surfaced and then this summer when it started again.