Engine/Transmission (1998.5 - 2002) Airtex lift pump frustration

[Jdonoghue]

Stock lift pump died, so I replaced it with the airtex unit that mounts in the same location. It was OK, not perfect though as I could pull it down below 10 psi pretty easily.



Then it got worse - it would sometimes drop to 0 for a second all by itself, and I could easily pull it down to 0 when accelerating. I figured maybe I got a dud pump and replaced it with another.



A little better, but it just put me back where I was before: a brief shot to 20 psi before I fire the engine up, then idles at 16. Pretty easy to drop it below 10 psi, and if I really get on it, it will drop just below 5.



Time for the tank to come out - I found the 'screen' at the bottom of the tank module had some tears in it and was coming apart. I removed it, and got a fleetguard in-line strainer. Put the tank back on the truck - same results. I did some reading and discovered there's another screen buried within the module inside the cylindrical thing. Tank came out again to check it. That screen was clean. I'm very good at dropping fuel tanks now.



There are no leaks in the tank module or lines, and no restrictions that I can find, I inspected the entire fuel line. I put clear hose on to check for air, no bubbles present.



I have a new fuel filter, and I have also verified that I get a full 12 volts to the pump while the engine is running. I also put a second gauge on to the inlet side of the fuel filter, and it shows the same results, so I know there's no restrictions in the fuel filter assembly.



I'm out of ideas. I'd expect to pull the fuel pressure down that low if I had some serious mods, but I don't have anything fuel-related in the way of mods on this truck.

 

[Floyd4runner]

I have had my airtex pump for about a 1. 5 yr and now every morning I just have to get it up to speed before I can let off and it gets above 5psi, but I have an airdog on the way. I thought it would be better to make a one time investment on this issue.

 

[Fishin Guide]

The Airtex pumps by and large have been pretty good. I warrantied my first one today.



Dave

 

[JLandry]

I found the 'screen' at the bottom of the tank module had some tears in it and was coming apart.

Is it possible some of the debris from the tank screen are stuck in the fuel line somewhere?



Maybe you could try and disconnecting the fuel line at the Airtex lift pump and at the tank outlet, then blow pressurized air from the engine end back toward the tank end to try and clear the line?



I have an Airtex pump and it's been wonderful... no problems at all.



John L.

 

[RJWEST]

???? fuel filter????

 

[Jdonoghue]

The fuel filter is new.



Here's what I'm going to try this afternoon: I'm going to move the pump to the frame near the fuel tank, and run new fuel line from the tank to the pump, then from there up to the fuel canister on the engine. New lines, new pump, new filter.



Jim

 

[JLandry]

Here's what I'm going to try this afternoon: I'm going to move the pump to the frame near the fuel tank, and run new fuel line from the tank to the pump, then from there up to the fuel canister on the engine. New lines, new pump, new filter.

Sounds like a reasonable plan to me Jim.



While you have everything apart, maybe you could carefully blow some compressed air backwards through the Airtex pump to make sure it didn't suck in some tank screen debris?



Hang in there...



John L.

 

[Jdonoghue]

No difference

I relocated the pump to the frame, just in front of the tank. There's no difference in fuel pressure readings. I could exchange this pump for a new one (again), but I really think something else is going on here. I removed the banjo fitting from the inlet side of the fuel filter assembly to check for debris clogging it, it was completely clean.

 

[Jdonoghue]

Sounds like a reasonable plan to me Jim.



While you have everything apart, maybe you could carefully blow some compressed air backwards through the Airtex pump to make sure it didn't suck in some tank screen debris?



Hang in there...



John L.

This pump was installed with an in-line strainer on the suction side so I doubt anything got sucked into it. I also know that the in-line strainer is not causing a restriction.



Jim

 

[JLandry]

There's no difference in fuel pressure readings. I could exchange this pump for a new one (again), but I really think something else is going on here.

Jim,



Is it possible your fuel pressure gauge is giving you false readings and maybe the fuel pressure is adequate after all?



Do you have a different fuel pressure gauge you can try... preferably a test gauge used under the hood (as opposed to one installed in the cab).



Still thinking...



John L.

 

[Jdonoghue]

Jim,



Is it possible your fuel pressure gauge is giving you false readings and maybe the fuel pressure is adequate after all?



Do you have a different fuel pressure gauge you can try... preferably a test gauge used under the hood (as opposed to one installed in the cab).



Still thinking...



John L.

I don't have a good test gauge right now - I have a 0 - 100 PSI gauge, and a very old 0 - 10 psi/vacuum gauge. Tomorrow I'll have to go into town and see if I can get a test gauge. I had tried the 100 psi one earlier, but I don't think it is accurate below 20 psi.



Jim

 

[JLandry]

Tomorrow I'll have to go into town and see if I can get a test gauge.

Jim,



You should be able to find a fuel pressure test set from any auto parts store. It's a good tool to have in your collection. I carry one in my truck at all times even though I have a fuel pressure gauge in the cab. Always nice to have a "second opinion" handy.



John L.

 

[Jdonoghue]

John,



You indicated this in a post to another thread:

~~~~~~~~~~~~~

Starter bumped, but engine not started = 24 psi

Idle = 17. 5 psi

Cruise (1800 rpm) over level terrain = 12. 5 psi

Wide Open Throttle = 7 psi



After engine shutdown, it takes one full minute for the pressure to bleed down to zero psi.

~~~~~~~~~~~~~

Where are you taking your fuel pressure readings from? Mine is done with a tapped bolt in the VP44 inlet.



Very rarely does mine take any time to bleed down at engine shutdown - it usually drops like a rock to 0.



Jim

 

[JLandry]

Where are you taking your fuel pressure readings from?

Jim,



My readings come from the VP44 fuel inlet (the Schreader valve).

Very rarely does mine take any time to bleed down at engine shutdown - it usually drops like a rock to 0.

Since I originally posted my Airtex fuel pressures, I've had more time to watch the pressures under various conditions and temperatures.



I've noticed that sometimes mine seems to bleed down slowly, but at other times it quickly drops to zero. I haven't been able to pin down under what conditions it's slow or fast. It could possibly have something to do with what position some of the components inside the VP44 happen to stop at. It's something I wouldn't worry about.



As far as the general Airtex pressures go...



Now that the weather is warmer, the idle pressure is a bit higher at 18 or 19 psi and WOT is closer to 10-12 psi.



Interestingly, on a trip back in April pulling a loaded travel trailer from Seattle down to Death Valley, CA and back, I noticed the idle fuel pressures climbed at idle at higher altitudes. Idle was over 20 psi and cruise was about 15 psi. I thought about a lot, but never could quite understand why the fuel pressure would be higher at a higher altitude. I'm wondering if the mechanical gauge (a DiPricol) was affected by the lower barometric pressure in the same way an altimeter is. To the best of my knowledge it shouldn't.



The bottom line is that so far I'm quite happy with the Airtex pump I installed. It's definitely performing better than the original stock Carter pump.



Best regards,



John L.