Engine/Transmission (1998.5 - 2002) Strange lift pump question.

[Mr. C]

Well I'm on my third lift pump and I am not sure it is the problem. The pressure is all over the place some days it is 13 lbs then for no aparent reason it will drop to 4,5 or even zero- this is a new pump only 2 weeks old. Presure was 14 when first installed and now it is generally 5 to 10 at idle. Funny thing is if I bump the starter to put the pump in the 15 second filter priming mode it will run at 15 lbs every time untill the piming mode ends. As soon as I start the engine it is back to a lower presure but the presure is all over the place some times good sometimes zero. The part that really gets me is that it will build 15 lbs durring the priming mode



I have checked the voltage to the pump and it is full battery voltage, I even checked the running amp load of the pump and it is 4 amps with the engine running or durring the priming mode with the engine not running. At first I thought the ECM was not giving it full power but that doesn't seem to be the case. I guess I'll throw another pump at it but wondered if any one had any ideas, this is very strange.

 

[rweis]

How is the actual electrical connector and connections? Has been a problem in the past on lp's. Dielectric grease helps here a lot.



Bob Weis

 

[Mr. C]

Connectors are clean and dry, I thought of that too.

That 15 lbs with a starter bump has me stumped.

 

[ProspectorTim]

When you bump the starter you are building pressure, but not flowing any fuel. When you start the truck, you need fuel flow. Check or replace your filter.
Look for any other flow restrictions - kinked or crushed fuel line, etc.

 

[Steve Campbell]

I have had the fuel tanks out of three different 99-2000 pickups with a partially plugged/clogged "membrane" in the fuel pickup module.

Might be something to consider



Steve

 

[Mr. C]

The filter is new and the one that came out was a couple years old and flowed without restriction, according to the gauge.



I think my next move will be to locate a oil filled mini gauge that will read vaccume to put on the inlet side of the lift pump using one of the tapped banjo bolts that came with my 64 dollar campaign pump, I knew that little adapter would come in handy some day I would be very surprised if there were any gunk in my strainer but the gauge would rat it out if there was.

 

[phoekema]

Just a thought... ... ..... you might consider installing the kit sold by Geno's that relocates the lift pump just ahead of the fuel tank. Since doing this, I have gained 2 - 3 lbs pressure. Gotta believe the pump wil run lots cooler bolted to the frame instead of the engine too.

 

[Texas Diesel]

I had the same symtomps, exactly as you describe. Drive me nuts.



Did the Vulcan LP relocation, fuel filter, overflow valve (ouch$$), nothing helped till I installed the 4th (yes fourth) LP then it stopped. 3 bad and new LP's? Yep! Make sure you get LP's from different production runs.

 

[CMabrey]

I have the same problem with mine right now. Mine isn't as consistent as yours, it only seems to happen in the morning on the way to work. Cruises fine at 15psi and the next thing i know it's down around 5psi. I just put the vulcan big line l/p relocation kit on. I was talking to one of my buddies he mentioned possible cavitation issues?????? I don't know what to do. I guess i'm on my may to get a new l/p, hopefully that fixes it.

 

[nuv22]

DAMMMM!!! you read my mind with this post !! i relocated mine with the vulcan kit new FF, checked the intank flow no problems, all the connectors were fine voltage and amps to the pump ok new relay up front and after 3 months of the vulcan Relocation kit with the 64 dollar campaign pump this CRAP starts happening #@$%! BUT!!!! when i am on the highway doing 75 it works like a champ 11Psi (tested for over 3 hours straight) then drive around the city and wham go from 12-13 to 6! but if i punch it back to normal so i have no idea what the hell is going on. does de ECM control the pump? if so is there a gradual increase of voltage to the pump from idling low RPM (around town driving) to about 2100 RPM? because it never fails if i punch it it will go back to the normal psi for a few minutes. now the only difference i see between the original post and mine is that mine has never gone below 6psi and when its down there if i shut off the truck and bump the starter it tries to run but nothing. any ideas? (only when at 6psi everyother time bump works fine)

 

[IRNGOAT]

I had the same symtomps, exactly as you describe. Drive me nuts.



Did the Vulcan LP relocation, fuel filter, overflow valve (ouch$$), nothing helped till I installed the 4th (yes fourth) LP then it stopped. 3 bad and new LP's? Yep! Make sure you get LP's from different production runs.

do you have a p/n or a price on the overflow valve? i have suspected mine has been sticking faor a while now.

 

[Texas Diesel]

I got my overflow valve as a freeby from my mechanic. He had an extra one laying around.



Replacing the overflow valve did not fix the problem. And if you look at the way the overflow valve is constructed, it couldnt possibly stick closed.

 

[Joe Mc]

Well I'm on my third lift pump and I am not sure it is the problem.

Call Rich @ Glacier Diesel - see GFS-392 link in my signature. I put it on the frame by the tank w/2 micron spin on filter. 20# idle and 18# @ WOT & Edge @ 5-5. I did the replaced too many stock POS Carter LPs until I finally got sick of it and went with something worth while. MHO

 

[Texas Diesel]

The GFS-392 looks promising, especially the "running at 15% load" part. I wonder if it is a brushless DC motor.

 

[Mr. C]

I coresponded with Glacier Diesel about their setup , I run boidiesel and was concerned about compatability. Since I already had a new spare Carter on hand I will run it and if the problems don't end I will do the GFS-392 .



Joe, do you have a link to the filter you are using in front of the GFS-392 ?

 

[BK]

Does de ECM control the pump?

There are supposed to be two mods of operation for the LP. .

Mode 1, full voltage full pressure, normal running.



Mode 2, during STARTing only, 25-50% duty cycle , to reduce the pressure to 7psi. Early on those that installed new pumps, hard wired to 12v or added relays, some had hard starting problems due to the pressure being to high.



Once started it's suppose to go back to Mode 1.

 

[IRNGOAT]

I got my overflow valve as a freeby from my mechanic. He had an extra one laying around.



Replacing the overflow valve did not fix the problem. And if you look at the way the overflow valve is constructed, it couldnt possibly stick closed.

I'm thinking that possibly it's sticking open.

 

[duaneparks]

FWIW, I've had the same problem with mine that started when I changed a fuel filter. I run an Isspro mechanical fuel pressure gauge from a tapped banjo at the bottom of the fuel filter canister. I notice mine drops from 11-13 or so to 4-5 and stays there until I accelerate hard, then it jumps back up to 11-13 (15 at idle). I attributed it to air in the gauge line because it eventually went away, but comes back for a while when I change my fuel filter, then goes away again.



One of these days I'll go re-seal the pressure gauge connections with better teflon paste as has been recommended by a couple of diesel-minded folks I hang around. It would be nice if that's all your problem is! If anything, it's just something else to check outside of what others have mentioned on this thread.

 

[Joe Mc]

I coresponded with Glacier Diesel about their setup , I run boidiesel and was concerned about compatability. Since I already had a new spare Carter on hand I will run it and if the problems don't end I will do the GFS-392 .



Joe, do you have a link to the filter you are using in front of the GFS-392 ?

I moved the stock filter assy back to the frame when I moved the Carter (before going GSF, so I decided to leave it there for a WIF sensor/drain, the fuel heater is there also and as a prefilter for the 2 micon.



Here's a link for the 2 micron I used, it's for a 3rd gen but, I just flipped the mount and installed it on my frame rail. http://www.glacierdieselpower.com/product.asp?pf_id=MK20306-BLK

I bolted it up - high up on the outside of the frame just aft of the rear driverside doors.



No picture of my actual install.

 

[ike]

This may sound stupid, but what type of gage are you running. I bought an eletrinic Westec from Genos. After running it for about three days I had the same issues youdescribe. After replacing the pump it turned out to be a bad gage sensor! The wiring conections at these sensors are fragel, the tend to loosen up. I hope this helps.



Ike