Engine/Transmission (1998.5 - 2002) Fuel Problems--at a loss as to what to do

[JBodenhamer]

I have a 2001 24v automatic. It has a FASS DDRP and an Edge Juice with attitude. Currently has 163K miles on it. In the last 30K miles, I have replaced the VP44, put on the DDRP, and changed the injectors to the one level upgrade Bosch from stock. Ran great until now. About 2 weeks ago, fuel pressure under load went down to 8 or 9 on level III(where I normally drive it). I put it on level 5 and it went to 3 PSI and I got the edge alarm. I called FASS thinking it was the DDRP going out. After dropping the tank 4 times to clean the stock pickup(mine does not have a pump in it), installing a bad one from Napa, and then fully cleaning and re-installing my original one(which was not dirty by the way), I have made things worse. I got a new DDRP from fass under warranty as mine is 3 years old. I installed it today and buttoned everthing back up and bled the system. It appears to be pumping fine, but on both gauges(the Edge which is upstream from the filter and a Westach gauge I have on the service port), I am at about 12 PSI at idle but it quickly falls when I start to drive. Goes to single digits under any load at all. I do not want to run the system dry or damage the VP44 so it is parked now. My questions are these:

1. Is there an internal pressure regulator in the VP44 that could have failed?

2. It runs fine at idle and appears OK under light load driving(10-20 mph) for short durations. Is there a reason the supply pump might not be getting power correctly? It goes on briefly at key on, then if you bump the starter will run for 25 seconds as it should.



Thanks for the info on this. Any help would be great as I only have 1 vehicle where I am. Presently in Huntsville, Alabama TDY for Army stuff.



Thanks again!



Jon

 

[VolsFan]

My ddrp does the brief pressure spike you describe at key on, then will run for the normal 25 seconds. Not trying to ask a dumb question, but is there still a screen in the feed side of the ddrp? When mine was new, I ran into symptoms you describe, then took the feed side off and saw a screen in there, removed it, and now my pressure never goes below 10 psi no matter what I do.

 

[JBodenhamer]

Yep, there is a small screen in the input banjo to the pump. I have had it there for the entire 3. 5 years the first DDRP was installed, and I also cleaned it fully and replaced it when I installed the new DDRP FASS sent me earlier today. No real change to the problem it appears. Thanks for the suggestion, though.

 

[JLandry]

Jon,



Have you gotten a "second opinion" (so to speak) on the fuel pressures by connecting a different test gauge?



We've had several cases where guys have endlessly chased fuel pressure problems only to discover it's a gauge (or sender) problem.



John L.

 

[JBodenhamer]

@ John,

No, but it does not seem to run right and I have two gauges on it already in different places with different sending units, so I am thinking it is not likely a double bad pressure reading. At this point I am pondering ordering a Vulcan draw straw, the DDRP re-location kit, and just getting rid of all the stock stuff from tank to factory filter. That will at least rule out problems with this stuff. If there remains a problem after this work, I am not sure what the correct next step is. Problem started with low pressure under heavy throttle with edge set in Drive mode (level III). I have never had low pressure problems before this with the DDRP, edge, and the minor injector upgrade. Stock turbo. Stock type VP44. Removing the tank and cleaning the pump sending unit made the problem MUCH worse so I am afraid there is an air leak of some sort in the system now. Not sure how I would have caused that, though, as I was very careful in what I did.

 

[JLandry]

No, but it does not seem to run right and I have two gauges on it already in different places with different sending units, so I am thinking it is not likely a double bad pressure reading.

Agreed... sorry... I missed where you mentioned you already had two gauges.

At this point I am pondering ordering a Vulcan draw straw, the DDRP re-location kit, and just getting rid of all the stock stuff from tank to factory filter.

I think that's what I'd probably do if I were you. While I'm still using the original in-tank pickup, I've already replaced all the fuel lines on my truck and relocated the lift pump to the frame rail right in front of the tank. I have a both a draw straw kit and a tank sump pickup kit standing by for the day when the in-tank pickup decides to crap out.



At the fuel line return fitting on the VP44, there's a device called the overflow valve which is nothing more than a spring loaded ball. It's purpose is to help limit maximum fuel pressure inside the VP44 by allowing excess fuel to return to the tank. I have a hard time believing this simple device could cause the low supply pressures you're seeing, but since it's easy to remove it couldn't hurt to test it or replace it outright. The factory service manual has the testing procedure.



John L.

 

[JBodenhamer]

@ John, I saw info about the valve in some searching here. I will check into that next. I think I will make the order for all the draw straw stuff this afternoon after work(which I have to get a ride to right now thanks to this problem). I am wondering if there is a possibility of power problems to the pump, but since it behaves as you would expect it to with key on and bumping the starter, I am thinking that is not likely the cause.

Fuel problems are one of my most hated issues with vehicles. Probably the cause of this bad karma!

 

[NIsaacs]

I would say that you have a restriction between the pump and tank. Can you disconnect both ends of the line and blow air through it? Try and catch anything that might blow out so you can confirm if something was plugging the line.

Nick

 

[JLandry]

@ John, I saw info about the valve in some searching here. I will check into that next.

You can buy replacements online and since it'd only take a couple of minutes to replace, it might be worth just swapping out before you do anything else.

I am wondering if there is a possibility of power problems to the pump, but since it behaves as you would expect it to with key on and bumping the starter, I am thinking that is not likely the cause.

That'd be pretty easy to check. Just temporarily run a set of jumper wires (a generous length of old speaker wire would work nicely) from the power connector at the pump to a voltmeter in your truck cab so while driving.



John L.

 

[LNaugle]

have you ran the supply to the vp44 into a bucket and looked for air in the fuel? also 1 volt of difference to the pump will make psi difference... .

 

[JBodenhamer]

@ LNaugle, No, I have not but I am taking a different route this afternoon if the parts arrive. I ordered the Vulcan Draw Straw kit and the DDRP frame re-location bracket and kit for the supply pump. I am going to mount it on the frame and run new line all the way from the tank to the factory filter. If I am still running low pressure after this, I am thinking I will purchase a 40 amp relay from the parts store here and divorce the pump from the ECU by wiring the relay to the battery(with a fuse) and connecting the low current side to a switched 12 volt circiut connected to the key switch. Then I will for sure have 12V available to the pump. I will also inspect the overflow valve/pressure regulator in the VP44. Hoping the relocation kit works, though.

 

[JBodenhamer]

I got the draw straw, inline filter screen, DDRP relocation kit, and all associated plumbing installed today. Pressure is back to 13 at idle and stays at 9 or better under hard acceleration at the inlet to the filter. The service port gauge I have reads a bit lower than that(it is an old westtach that I have installed on that location via a genos adapter hose kit), but I think the sender on it might be getting a little worse for the wear as it sometimes floats higher right in line with the Edge readout and sometimes falls a few PSI. I have bled everything including the Westtach sender hose so I know air in that line is not causing a lower reading.

Gotta drive it for a few days to see how things progress for now. What a pain in the neck this has been.