Engine/Transmission (1998.5 - 2002) Interesting LP failure mode

[Texas Diesel]

My LP was doing fine then two days ago after a fill up the pressure gauge started bouncing. The variation was about 5PSI, then steady at 15, then bouncy bouncy.



I removed it and put on my spare ( a good one ) and for 5 miles all ok then the same exact nonsense.



Is it possible that grit was in the fuel and causing the vanes in the LP to stick causing the pressure variations?



Well to test this I put on a NEW LP with a prefilter between the LP and tank. I dont like the suction side restriction but this will help determine if grit in the fuel is causing the vanes to stick. The prefilter has a clear housing and a sediment bowl on the bottom. Tomorrow I will take a drive and see what happens.



Any thoughts?

 

[RAJohnson]

Seeing that you tried your spare with the same results, I think the fill up was a coincidence and you might have a intermittent electrical problem, short or ground. Have you checked the electrical out.

 

[Texas Diesel]

Yes, the motor is running at a constant speed. The pump head sounds like it is cavitating. That is the closest sound I can compare to.

 

[CSnyder]

I have lost 4 lift pumps in the last 6 monthes with the exact same symptoms except they didn't go after a fuel-up. The pressure guage would go to 5 lbs and if I hammered the skinny pedal it would pull it back up to 15 lbs almost like the internals of the LP were jamming up and by sucking ALOT of fuel thru it would get it going again briefly and then a few more miles the same deal. I finally had the dealer install an in-tank LP last week but I'm not so sure it was a good cure as the new style will pull my FP guage to zero under moderate acceleration with no load in tow and I tow heavy 99. 5% of the time averaging about 500 miles a day or more. My next step I'm working on right now after making several calls to the dealer complaining about my loss of power and truck stumbling is to eventually get them to pay for a pusher pump as well before I lose my VP which was just replaced this April. If they won't agree to paying for a pusher pump I am going to make sure they put something on paper that DC will pay for the VP when it dies again from being starved of fuel. I want a written guarantee saying this no pressure in-tank LP is a definate cure or I will not sit by quietly.



Chris

 

[Texas Diesel]

Scratch the prefilter idea.



Put the prefilter on then new LP. Ran good for a few miles then bouncy bouncy.



So I took the prefilter off. Next I added a snubber to the FP line



Guess it's all fixed

 

[RAJohnson]

Scratch the prefilter idea.



Put the prefilter on then new LP. Ran good for a few miles then bouncy bouncy.



So I took the prefilter off. Next I added a snubber to the FP line



Guess it's all fixed

Texas Diesel what type of fuel pressure gauge do you have? And where is it plumbed in at?



Your mention of a snubber refreshed my memory I had a bouncy fuel pressure gauge (Auto Meter) and had it plumbed in at the shradder valve, after installing my FASS it would bounce wildly but not as low as you might be experiencing. Any way I called Brad at FASS and he told me to add a snubber valve which I did. This eliminated most but not all of the bouncy gauge. So I move my fuel pressure gauge back to the bottom of the OEM FF housing. It has been rock solid since doing this except for the normal driving movement as well as the WOT movement. :-laf Hope this helps. Rob

 

[Bob4x4]

I have lost 4 lift pumps in the last 6 monthes with the exact same symptoms except they didn't go after a fuel-up. The pressure guage would go to 5 lbs and if I hammered the skinny pedal it would pull it back up to 15 lbs almost like the internals of the LP were jamming up and by sucking ALOT of fuel thru it would get it going again briefly and then a few more miles the same deal. I finally had the dealer install an in-tank LP last week but I'm not so sure it was a good cure as the new style will pull my FP guage to zero under moderate acceleration with no load in tow and I tow heavy 99. 5% of the time averaging about 500 miles a day or more. My next step I'm working on right now after making several calls to the dealer complaining about my loss of power and truck stumbling is to eventually get them to pay for a pusher pump as well before I lose my VP which was just replaced this April. If they won't agree to paying for a pusher pump I am going to make sure they put something on paper that DC will pay for the VP when it dies again from being starved of fuel. I want a written guarantee saying this no pressure in-tank LP is a definate cure or I will not sit by quietly.



Chris

You have to be kidding :-laf why would D/c Guaranty your modified truck to be ok with a stock fuel pump? :-laf :-laf :-laf



Bob

 

[Texas Diesel]

Texas Diesel what type of fuel pressure gauge do you have? And where is it plumbed in at?



Your mention of a snubber refreshed my memory I had a bouncy fuel pressure gauge (Auto Meter) and had it plumbed in at the shradder valve, after installing my FASS it would bounce wildly but not as low as you might be experiencing. Any way I called Brad at FASS and he told me to add a snubber valve which I did. This eliminated most but not all of the bouncy gauge. So I move my fuel pressure gauge back to the bottom of the OEM FF housing. It has been rock solid since doing this except for the normal driving movement as well as the WOT movement. :-laf Hope this helps. Rob

It's a mechanical hooked between the VP and filter.



This bouncy bouncy problem just started. The gauge readings were steady for the last 12k miles

 

[RAJohnson]

I contributed my Bouncy Oo. Bouncy to some kind of pressure coming back off the VP, either in a pressure relief valve or a pump going south. I am still on the OEM VP but I know it is going south. :{ Any way you might try moving it further from the VP if it continues. Good luck and let us know how it shakes out.

 

[keimmmo]

Texas Diesel,



Remember the 3/8 fuel line I have zip tied to the brake booster lines with a fitting going into the 1/8 in line going to the cab? The idea of the big line is to put volumn between the VP and the guage. My guage has been steady for 90k and counting!



Steve Keim