Engine/Transmission (1998.5 - 2002) Wierd VP44 symptom

[John - K5AWO]

My son has a VP44 with the following symptom:

'98. 5 3500 DRW no mods 92k miles



1. Will run as long as the throttle is tipped in.

2. Will kill the engine on Deceleration.

3. Sometimes it will idle, normally dies.

4. LP pressure is 6 psi

(we added a pusher for 12 psi to test. symptoms didn't change)

(he bought a new LP to put on)



He has told me that for the first few minutes while things are cold "Phoenix AZ here" or about 70 deg F, that it will run fairly good but as soon as it warms up, the above symptoms come into play. He can drive to work at 5:00 a. m. but no go on the return at 3:00 pm and +100 local temps.



Driving it is very nerve wracking because it dies almost every time he lift his foot. Finally decided to just park it before something really bad happened (read vehicle accident).



This is his bread winner and he needs it back on the road again to earns $$$ to feed the family.



My son (PJ) and I are new readers here but have spent hours and hours reviewing the old posts on VP44 pumps. I can't recall seeing anything like this. Most posts report the pump dies a hard death.



Anxiously awaiting reports from all on this.

 

[willyslover]

sounds like a TPS is going out. . do some searching using the search button and sit back for much reading



just one thing ... have you changed the fuel filter ??? if not please do that and retry driving

 

[Turbo Tim 1]

When the lift pump pressure was 6 psi, was that sitting at an idle or close to it? Any idea what the LP fuel pressure going down the road was? Could very well be VP time because if 6 psi was at idle then going down the road I'll bet it was zero, alot of these pumps don't like low input fuel pressure. What willyslover said about the TPS makes sense but when you do your search use the acronym APPS because that's what it's called now. You could try the APPS recalibration, that would be disconnecting the batteries for a while 1/2 hour or so and then hook them back up and slowly push the go pedal to the floor and slowly back up. If you do a search you can find more on that procedure.

 

[fox]

Have it checked for codes.

 

[John - K5AWO]

Originally posted by Turbo Tim 1

When the lift pump pressure was 6 psi, was that sitting at an idle or close to it? Any idea what the LP fuel pressure going down the road was? Could very well be VP time because if 6 psi was at idle then going down the road I'll bet it was zero, alot of these pumps don't like low input fuel pressure. What willyslover said about the TPS makes sense but when you do your search use the acronym APPS because that's what it's called now. You could try the APPS recalibration, that would be disconnecting the batteries for a while 1/2 hour or so and then hook them back up and slowly push the go pedal to the floor and slowly back up. If you do a search you can find more on that procedure.

Thanks for the quick answers...



I failed to mention that we had added a pusher pump and changed the fuel filter. The new road test with the old LP @ 6PSI plus 6 psi pusher for a total of 12 psi didn't change anything as to drivability. He did say the fuel pressure stayed at 12 psi most of the time and dipped to 10 psi. I wasn't on the trip so can't answer about WOT.



John



We just received a new LP and will put that on tonight and try again. Will also do the APPS recalibration procedure at that time.

 

[John - K5AWO]

Originally posted by fox

Have it checked for codes.

No codes showing. He is a diesel mechanic, just no work experience on the 5. 9L ISB Cummins. His daily driver bread earner has been faithful for 18 months since he bought it till now.



Mine is almost the same as his only it's a 4x4. Runs fine, wanna keep it that way. It has 16-17 psi at idle, no full time guages yet, that's gonna change fast.

 

[ToolManTimTaylor]

Two 6 Lb pumps won't = 12 lbs. It sounds silly but where is your pressure guage sending unit? You could have 1 dead pump in a psher system and that will totally kill pressures. However when hot it sounds more like an APPS (Acelerator Pedal Position Sensor) or TPS as stated above.



Another issue has been know on the 98 1/2 trucks is the fuel tank vent cap. When he gets to work shut down the truck and IMMEDIATLY hop out and unscrew the fuel filler cap. Paying close attention to hear and listen for a sucking vacuum noise. If the vent is clogged the tank draws itself into a vaccuum denying fuel but pressure will read on the guage ... . you just will not have volume.

 

[ToolManTimTaylor]

OOps sorry guy here is the link to what I mean.



Vent Cap

 

[John - K5AWO]

Two 6 Lb pumps won't = 12 lbs.

-------------------------------------



Hi Tim and thanks for the comments.



We have the pressure guage tapped into the 1/4 NPT port on the outlet side of the fuel filter. Two ports there, we tried them both, about 1 PSI difference.



The original lift pump was making 6 psi. I gave him an inline universal pump I had on hand to see what would happen. We were under no allusions as to it having enough volume, but it did suffice for the testing. It did raise the pressure at the fuel filter an additional 6 psi for a total of 12 psi. Pressure dropped to 10 psi during his moderate testing to see if the problem went away. It didn't.



Since the truck will run when the APPS is tipped in somewhat, we sort of concluded that the mechanical portion of the VP44 is still working, it will go WOT and accelerate just fine. You just don't have any drivability with the engine shutting down off throttle.



I will have him check the tank pressure next trial run.



We have changed the fuel filter twice since this all started. he is going to put in a new one tonight for the APPS calibration routine along with the new lift pump so pressures should be back up to 16 psi or so.



All of this "excitement" has made him really appreciate TDR members. He is going to sign up in his own right as soon as we get the truck going and new customer comes his way with more money than knowledge.....



John

 

[John - K5AWO]

Ram/ISB Low Power Solution

Tim,



I just called my boy and low and behold, he has the tank down because the fuel level sender wasn't working!!!



He happened to be at a restaurant at the time, but when he gets back, he is pulling up that link and looking to see what you mean.



He told me he remembers a plastic cap being on one of the tubes there.



Will report back on the results...