Engine/Transmission (1998.5 - 2002) Fuel pressure ???

[MMilliman]

Changed fuel filter before I took off on my deer hunting trip.

Before change pre-filter gage was running 16 lbs, after filter gage running 14/16 psi. had 35,000 miles on truck.

Was pulling tandem axle trailer approx 6000 lbs. about 70mph.

pre-filter was at 14/16 psi. after-filter gage down to 3 psi, sometimes dropping to 0 psi. I slowed down to 60/65mph after-filter gage went up to 6 psi.

Next morning I took filter out to check it, also checking o-ring, and plastic top of filter canister, All Looks OK. At idle both gages showing 14/16 psi. Changed filter again still the same. The first filter was a Fleetguard, the second a Wix (which I found out is a fleetguard).

Any Ideas.

 

[Sticks]

It is possible that your new filter could be clogged already. All it takes in one bad load of fuel to do it.

 

[MMilliman]

Negative, the filter I pulled out was one week old looked OK. Than I changed it anyway with the Wix, still the same problem. :--)

 

[RankRam]

I would exchange the sending units, put the pre where the post is and post where the pre is, just to see if the sender is acting up under load.



I hope this makes sense.

 

[BillGotthelf]

Rankram is right switch the sending unit first. Also with some contaminants in the fuel you can't tell by looking at the filter if its plugged up. The alge that grows in diesel fuel after its treated and dies looks like fine light grey talcum powder.

 

[MMilliman]

Switched units still the same, have run 5 tanks of fuel between filter changes still the same. Had new pusher pump on bench ready to put on but just didn't have time to do it.

 

[RankRam]

If your truck is running well I would think it's got to be gauge related; the next thing I would do is switch your guages. The same as you did with the senders.



This is my line of thinking, eliminate all possible variables and do it one variable at a time.



Hope this helps.

 

[MMilliman]

High speed 70mph+ it feels like it is definitely starving for fuel.

Put new lift pump on still the same. WOT prefilter fuel pressure drops from 16psi to 10psi some times even 8psi. after filter goes from 14psi down to 4psi and even 2 psi.

 

[daveshoe]

Two things the lift pump puts out are pressure and volume. Ya got the pressure thing ok at pre, so should be within 1 psi post.

If you know anyone with a mechanical gage, I would try that. Both pre and post.

This makes no sense at all unless filter is restricted. Would it be possible with your setup to bump the starter and do a flow test pre and post filter? That way you could see the results instead of relying on gage readings.

 

[CstlEng]

Sounds like the relief valve on the VP44 (the one on the return line) could be misbehaving. It could be worth looking at. Unless you are making LOTS of horsepower, not much else would make the pressures behave as you have explained.



Of course cold temps making fuel gel in the filter would act as you describe. Summer fuel\ cold temps?? Fuel heater connected? (I don't know the exact layout in your year, but it is probably easy enough to knock loose a connector or to leave it off when changing the filter element) ???

 

[R.E. Miller]

FWIW,

There actually could be one other thing causing that, it would be rare, but not something I would discount. If after swapping pumps, the problem is not resolved, and all other problem sources are troubleshot, I would take it to the Dodge dealer if warrenty is involved, who normally scurries the thing over to the local Cummins dealer for service. The ECM could infact cause fuel pressure to wander like that, it is RARE, but not something that I haven't seen.

P. S. I used to work on these all day so this is my humble next option

Just trying to help,

Russell

 

[MMilliman]

Thanksgiving Morning, My son and I Findley put pusher pump on, that night went up to northern Michigan for the last 3 days of deer hunting.

On the trip up I-75 North, It was running 22psi prefilter 20psi after filter. Also WOT prefilter was 20psi. and not lower than 16psi after filter. Took it up to 100mph. And No power loss.