Engine/Transmission (1998.5 - 2002) Here's a wrinkle that I need help with.

[Amianthus]

As some of you may know, I just replaced my VP-44 to cure a stumbling, misfiring, low-power problem, and lastly a stalling problem. The pump replacement went pretty well. All the instructions I needed were found here on the TDR proving that all you need for your Cummins is motivation and your TDR buddies.

Anyway, here's my problem. The pump replacement has cured all of my problems with one exception. The stalling. I need your insight.

The truck will run fine if I drive it normally. If I flog it a little bit to pull out into traffic (sans FMS fuel enhancement) it will go for a couple of seconds and then BAM! The lift pump will quit (pressure goes to 0) and shortly after, it stalls. If I let it sit for a few seconds, and crank on it for a while, it will restart. It only seems to do it if I floor it for a while. What say you? Any ideas?

For those that want to know, I have a two lift pump system that allows me to switch between pumps at the push of a button should one fail while I'm on the road (although that would never happen). Pressure for the PE4200 is usually 13 psi post filter. Pressure for the stock Carter is usually 12 psi post filter. And never drops below 10 psi while running in this condition. I'm going to take some clear tubing and install it to check for air in the system for now. And take it from there.

Well guys (and ladies), I'm open for any suggestions. What do you think? Thanks for the insight in advance.

 

[Gary - K7GLD]

What you first need determine, if you haven't already, is whether loss of fuel pressure is the direct result of lost power to the LP(s), or simply no fuel pressure, but power still applied. An easy way to check for power, is to wire a small 12 volt light bulb across the LP terminals and bring it into the cab of the truck so it can be monitored while you drive, and when fuel pressure drops, see if the bulb is still lit, indicating power to the pump is still present - then you have a better idea of which path to proceed on...

 

[LSMITH]

I have a spare ECM I can send up tomorrow if you are interested in putting it on and testing, I can send you a 99 auto immediately (will work fine on a 5 speed truck) or the TM later in the week. Lift pump power is provided by the ecm as is the injection pump solenoid power... ... ... .



Just a thought. Holler if you want it.

 

[Amianthus]

Welp, I've got some news.

It's not the ECM or the pump. I bypassed the relay and hooked up a test light to the ECM signal to the PE4200 (lift pump). The pump would run no matter what I did with the key or ECM. Anyway, I took it for a spin. It seems that I am getting air into the fuel lines from somewhere (as evidenced by the clear fuel line I installed last night). Driving somewhat normally, it seems to be okay. If I really hit it (FMS on), then she'll die but the lift pump, and the signal to the lift pump from the ECM, stay running. So at least, I know what is causing it to stall.

My question is this, is there anywhere I should check first for an air leak? Something one of you has bumped into in the past? I will look at the whole system, but I'd just like to get an idea of what could be more likely.

Thanks for the suggestions to date and for the offer of the ECM. I won't be needing it, though.

Let me know what you think on this.

 

[willyslover]

how did you attach the lines to your tank ? did you use a AN compression fitting ? BTDT. . pulled the damn thing off and threw it away after several times of trying to make it work correctly... or recheck the O Rings at the PE pump. . it might not leak fuel but suck air

 

[Greg Boardman-RIP]

You might check the lid of the fuel filter canister.

 

[docdyno]

Hate to mention this, but there is a module in some of the tanks to prevent fuel slosh. It has a ~80 micron mesh on the bottom of it to keep big stuff out of the lift pump. ( I have one if you need it) If it is partially clogged you might get enough fuel while cruising, but not when in the FMS mode. Additionally, whenever fuel is pulled "sucked" past any impingement in the fuel system, it is subject to "shearing" which causes aeration of the fuel. Such a problem would also probably only show up during heavy demand times. An impingement might be caused by a deteriorating fuel line, fitting with a burr, etc. - Maybe even your second pump while not in operation. Here's a real long shot. We once had a similar problem caused by a faulty voltage regulator. The voltage went haywire- 20V and the pump ran so fast it cavitated. I hate it that you have to do so much heavy driving to perform your "tests"!

Good luck finding the solution.

 

[LSMITH]

Aron, rig up that air tank you have to pressurize the fuel system to about 15 psi with air, and listen for leaks, a cigarrette or cigar will not ignite diesel fuel but if you use smoke to find where the air is blowing out blow the smoke in there out of your mouth. There is a chance if air is coming out some fuel is coming with it, and it could be atomized enough to burn.



It can suck enough air to be a problem and not leak enough fuel to see. The problem is going to be between the pump that you are using at the moment and the pickup tube bottom. Everywhere else is positive pressure all the time.

 

[Ncostello]

If you put the air to the tank, you might wanna cap off the overflow valve... the one that DC left capped from the factory on some trucks. Otherwise, air will blow out that and it will make it hard to hear smaller leaks. Plus you'll loose the pressure too fast to do any tests. At least mine lets air by when I have applied pressure to my tank. Just a thought.

 

[Amianthus]

I checked the clamps tonight. They're all tight. I will switch out (get rid of) the compression fitting tomorrow. I'll also try to pressurize the tank and see what I can find. It does it with both pumps though, so I don't know if it's the pump suction or the plumbing. I think the pressure test will show me the way. I'll let you know how I do tomorrow. Thanks for the ideas. Keep them coming.

 

[340Mark]

No way would I pressurize the tank!! just pressurize the lines. The tank is not designed for that

 

[Amianthus]

Status Update.

I pressurized the fuel system to 15 psi with air. It held fine with no leaks anywhere. Struck out there. So the only other place I thought it could be suckin air into the pump was from the return line. Long shot, but I bought a new overflow valve. It seems to have worked for now. The pump won't bind or stall. But, I am still losing a ton of fuel pressure under heavy fuel enhancement. It is 14 psi at idle. But under enhancement it drops out to 6-7 psi. This disturbs me. The PE4200 should be more than capable of keeping up. Any ideas guys?