Engine/Transmission (1998.5 - 2002) Is my VP44 starving for fuel or is it dead?

[TomGolden]

Howdy all,



I am having a fueling problem on my truck, and am not sure what the source(s) of the problem is.



Symptoms: under maximum acceleration, when I get over 2000 RPM in the top gearsb (4th, 5th & 6th), my engine defuels tremendously. This is NOT a normal function of the Comp. I get this defueling as low as 2000 RPM, and it only does this under pedal on the floor max acceleration. The instant I lift my foot, the hard fueling comes back immediately. I have the drag, or hot Comp, which does not defuel until at least 3200 RPM, not 2000.



When I "slowly" accelerate (meaning without putting the pedal on the floor), I can go all the way to 3000+ RPM with no defueling, in all the gears.



I have called Aaron at Edge Products and he was kind enough to send me a brand new Comp. Tried it, same behavior. At Aaron's suggestion, I have also checked the VP44 pump wire connection, and it was solid.



I changed my fuel filter, even though it only had 2000 miles on it. Same behavior.



My original lift pump died about 3 weeks ago, replaced it with a brand new one. The pump died the same day I put my first fuel pressure gauge on the truck, so I have no idea what pressures I was getting with the original pump. The new pump idles at 14 - 16 PSI, normal acceleration and cruising 12 - 15 PSI and under WOT, and when I get this strange defueling, I get around 8 PSI, which I know is marginal. I do not drive really aggressively very often, so this problem could have been there for months, I don't know.



Back in February or March of this year, the last time I drag raced (Comp on 5x5, pedal constantly on the floor) this problem did not exist. That was really the last time I think I had put the pedal to the floor.



My theories at this point are:



1 - VP44 is dying. I don't really buy this one, because as I said, under mild acceleration, the defueling does not occur. Only under WOT conditions, and only in the higher gears (so far... ).



2 - Both my original Comp and the new one Aaron sent me are defective. yeah, right.....



3 - Under WOT conditions, even my new lift pump just can't get enough fuel to the VP44.



I certainly hope it is only Option 3. I am going to get the Enterprise Engine helper Carter pump and put it back by the tank, but it will not be for a month or so.



So... . any ideas or thoughts would be greatly appreciated. I just hope desperately that this isn't my VP44 in it's death throes. I seriously doubt I could convince a Stealer to warranty the thing, with my BOMBs...



Thanks all,

Tom

 

[HVAC]

You could try bridging the MAP sensor to eliminate it all together.



Regarding fuel pressure, you should be able to see that on your new gauge.



It's not your VP44 IMO.

 

[TomGolden]

Nowel, thanks for the vote of confidence. I haven't yet tried running with the Comp turned off, will give that a try tomorrow if I can remember to...

 

[stubs]

TomGolden,

I just had the same problem with my truck and the dealers said the my accuator in my turbo was rusted shut or open ( can't rember which one it was) but the put on a new turbo and the problem was fixed. He said I was showing 40 psi of boots and wide open throttle and the computer was shutting my fuel down. Hope the helps you

STUBS

 

[Bigsaint]

Curious as to what you have found, Tom .



Scott W.

 

[Snow man]

It almost sounds like it is defueling under heavy load,like its getti g to much boost. The comp should be lieing to the puter,telling it its getting 18psi of boost,if the harness jumper is bad,changing the comp only wouldnt help any. Id try what Nowel suggested,bypass the map altogether,this way you can eliminate that possiblity. IMO,your VP44 is fine,the problem is somewhere else.

 

[TomGolden]

So what specifically do you guys mean by bypassing the MAP sensor? Just unplugging the Comp from the MAP sensor altogether, or what??



My next project is to get one of the helper pump kits, either from Piers or Enterprise Engine, and get that installed in the next couple weeks, and see if is in fact my lift pump, even though it is brand new, just can't deliver enough fuel under WOT conditions.



I will keep this thread updated until I get this solved.



I hope it isn't somethinf to do with my turbo... I want to upgrade it, but I still haven't found the replacement I want.



Oh well...

 

[Bigsaint]

Tom, does the truck throw any codes when you get the defueling ? I would think that you would get a MIL light and codes if the comp. box isn't isn't doing it's job of fooling the MAP sensor under high boost. Maybe wrong though ?



I'll leave the MAP bridging to Nowel as I have no idea .



I did have an issue with the MIL light and codes which indicated low voltage to the MAP. I cured this with a liberal dose of dielectric grease on all the MAP plugs ( OEM, TST and EZ). I seriously doubt 8 psi's at WOT would cause the defueling issue, but I've been wrong before. Please keep us posted .



Another thing to consider and I don't know how much this will help you, is that I have the same defueling issue with the TST Comp. box, when it's set anywhere above level 6. At or below level 6, I can just nail it and have instant power. Levels 7-9 are very radical in my truck, I really have to ease into the throttle for no shutter. Mine didn't do this with the step 3 injectors, only after I a replaced them with the 5's. FP post filter is at 10 or better at WOT when I get the shutter, go figure.



This is the main reason I like to use the big injectors and the EZ as a daily driver, it's plenty for me and alot easier on the VP44 as you are not asking the pump to perform outside of it's paramiters IMHO.

Scott W.

 

[TomGolden]

Scott, so far I have seen this defueling with the Comp on levels 5x5, 2x5, 2x3, 2x2 and also I think on 3x3 and 3x5. I still haven't tried it with the Comp completely off. I have never set any codes while getting this defueling, nor have any MIL lights come on.



The reason I am seriously thinking it is just the VP44 not getting enough fuel, as I have said above, if I just ease the throttle until I hit 3000 RPM, in any gear, I never have this defueling happen, and my fuel pressure never goes below 11 PSI. But if I just mash the pedal straight to the floor, it will defuel as low as 2000 RPM, in 4th, 5th & 6th gears, and my fuel pressure goes to or just below 8 PSI.



When I get a helper pump installed, I'll update this thread with whatever I experience then.



Tom

 

[Bigsaint]

Tom, another thought, since you are going to try the pusher pump, would be to loose the hardline that runs from the fuel filter outlet to the inlet of the VP44. It would require a short length of -6AN braided SS line, two -6AN 90 degree hose ends, two weber fittings, that replace both banjo bolts and a pressure port fitting for your gauge sender.



This is a source of a major restriction in the fuel system and I believe the use of the Weber fittings will flow even better than bored out banjo bolts. It wouldn't cost you more than $50. 00 and maybe 1/2 hour of your time. I'm still not convinced your starving for fuel with 8 psi's at WOT, but it's worth a try for sure. If nothing else, you'll have a good fuel system.



Scott W.

 

[TomGolden]

Scott, actually one of the very first mods I ever did was exactly what you are suggesting. In April 2001, I had Brandon install a set of -AN6 braided lines from the hard line from the tank to the fuel filter, and from filter to VP44. It was one of the kits Vaughn MacKenzie used to sell is what Brandon told me back then. Ultimately, I would like to go with either -6AN or maybe even -8AN braided lines right from the fuel tank itself all the way up to the VP44.



Last night I tried a test with the Comp completely off. Same result. If I ease into the throttle, I can go to 3000 RPM with no defueling, if I go WOT, I defuel soon after 2000 RPM.



Pusher pump here I come... ...

 

[TomGolden]

Update



Well, ordered one of the helper pump kits with the low pressure Carter pump, went in smooth, now have plenty-o-pressure. I see 21. 5 PSI at idle, and cruising I haven't seen lower than 17 PSI.



However, this did NOT cure my strange defueling problem My next thought is to check my APPS sensor to see if it is dirty, or whatever. I am going to first try the recallibration of the ECM to see if just by some chance, that could solve the problem.



For those interested, I will post updates for each thing I try until I get this solved!



Tom

 

[TomGolden]

pusher pump pictures

Just in case anyone is curious, here is a picture of the pusher pump install. I also put ball valves on each side of the pump, for very quick and dripless pump changes



Oh, and the extra hose clamps in the middle of the one section of the fuel line are just extras, I just wanted them to be very close at hand if I ever need them.

 

[work2muchplay2little]

Re: pusher pump pictures

Originally posted by TomGolden

Just in case anyone is curious, here is a picture of the pusher pump install. I also put ball valves on each side of the pump, for very quick and dripless pump changes



Oh, and the extra hose clamps in the middle of the one section of the fuel line are just extras, I just wanted them to be very close at hand if I ever need them.

Who did you buy the pusher pump from?

 

[TomGolden]

I got the kit (not including the ball valves) from Fred Swanson of Desert Diesel Parts www.desertdieselparts.com



The lit included the pump, 30A relay, wire, wire loom, 2 feet of rubber fuel line, mounting bracket and hardware for the pump.



Update



I unhooked both batteries and tried the ECM recalibration last night, no luck. That did nothing to solve the defueling problem. Next step is to remove the APPS sensor and see if I can clean it out.