Engine/Transmission (1998.5 - 2002) Have a fuel pressure problem question...

[EKoster]

Had a new lift pump and ip installed in July. Just got my gauges installed. When key is turned to run, fuel pressure might come up to a few pounds. Once engine is running, pressure will rise to 12-13 lbs. After running for 10-15 seconds, fuel pressure will drop quickly to 3-4 lbs and sit there. When driving, it will sometimes come back up. I am using ISSPRO gauges with a fuel pressure isolator. Is it possible that I have a pressure delivery prob within the gauge tubing? I figure that if I'm seeing the 12-13 lbs at first, the gauge setup must be working correctly. Does the lift pump tend to kick on and off? Any input is greatly appreciated...



Eric

 

[Texas Diesel]

I had the exact same problem and it was the FP regulator on the VP itself. Got a new one and that was it.



Could be a LP but you need to verify with another fuel pressure gauge.

 

[KTobin]

Ditto on what T. D. says about varifying with another guage. I also have the ISSPRO guage/w issolator and have not encoutered your propblem. It's not uncommon for a new LP to pack it in in just a couple months. You will always see a couple pounds only, when you first turn the key to "on". Once you start the truck, your pressure should come up (depending on the outside ambiant temp, and whether or not you're running winter blend or not) to optimum pressure of 13 to 15 LB with a new pump. The LP does not cycle on and off. Borrow a mechanical guage and run it off the shraider valve of the VP to double check your readings.

Hope this helps



Kevin

 

[Sixpack]

No flame here, but how does checking with another gauge verify the lift pump or the vp fp reg is bad? Maybe I misunderstood and you are talking about checking the fp gauge and isolator...



BTW my truck was doing the same thing so I bought a new lift pump (have not installed it yet) and presto the problems gone, at least for the last 3 days. Go figure.

 

[EKoster]

No flame here, but how does checking with another gauge verify the lift pump or the vp fp reg is bad? Maybe I misunderstood and you are talking about checking the fp gauge and isolator...



BTW my truck was doing the same thing so I bought a new lift pump (have not installed it yet) and presto the problems gone, at least for the last 3 days. Go figure.

I was thinking about a mechanical gauge for verification just after I posted. It freaks me out to think the pressure might have been this low for some time. Probably killed the vp again. Sixpack, the point of the other gauge would be to bypass my addl fuel line, isolator and gauge. I would accomplish this by removing the addl line from the isolator and hooking it up directly to a mechanical gauge.

 

[Rattlin_Ram]

I had a similar problem when my isolator was low on anti freeze. I've got the same gauge and isolator.

 

[EKoster]

I had a similar problem when my isolator was low on anti freeze. I've got the same gauge and isolator.

i'll have to check that. Did you fill the line from the isolator to the gauge with antifreeze also? Would there be a problem if there was too much antifreeze in the system?



I just took the truck out. It had been sitting for a few hours. I had normal fuel pressure for about 10-15 min. Then I took off from a light and it went down again. I parked it and shut it off. Let it sit a few minutes. When I restarted it, I had normal pressure again for about 15 seconds. I notice that the fp starts to waver a little bit then drops way down to 3-4 lbs. If I shut it off again for a sec and fire it back up, I have normal pressure again, for about 15 seconds. Same thing keeps happening till I shut it off. I guess I'll check the antifreeze level and then hook up a mechanical gauge to the vp if no cure.



Also, where does the ecu pickup when to turn on the grid heater? recently, after short drives, the coolant temp shows warm, but if I shut the truck down for a sec and fire it back up, the grid heater cycles on and off for a minute. Thanks



Eric

 

[Rattlin_Ram]

if you want to take the isolator out of it, just hook your gauge up direct... . it is mechanical.....



I filled up the gauges side of the isolator with antifreeze a couple times and bled out the antifreeze at the gauge to get the air out...

 

[EKoster]

if you want to take the isolator out of it, just hook your gauge up direct... . it is mechanical.....



I filled up the gauges side of the isolator with antifreeze a couple times and bled out the antifreeze at the gauge to get the air out...

so if there is air between the isolator and gauge, will that cause a problem?

 

[Rattlin_Ram]

A little bit of air doesn't matter. I still have some in mine and it works fine. But evidently mine was low enough on antifreeze to cause a problem.

 

[Donniey1]

Where are you getting your pressure readings from? I had the fuel filter cap from genos with my gauge reading from there, I had the same problem. I found that the rubber on the top of the filter was blocking the hole where my gauge was reading from.

 

[EKoster]

Where are you getting your pressure readings from? I had the fuel filter cap from genos with my gauge reading from there, I had the same problem. I found that the rubber on the top of the filter was blocking the hole where my gauge was reading from.

I'm using the fuel pressure kit that most places sell. It comes with a braided line and a fitting to replace the current inlet fitting on the VP

 

[fox]

Someone here has had that issue and found that it went away after putting dielectric grease in the lift pump plug. It was a poor connection. It could be other things. I had a time where my FP would drop to 5 psi ( normal was 15). I choose to start at the tank and look the whole system over. My tank had the silk sceen filter plugged with stuff that could not go thru a filter. Hair, fuss, rocks in the tank etc. Cleaned it out and it has been fine every since.

 

[EKoster]

well, I hooked up a mechanical gauge to the output of the isolator and to the output of the braided line and got the same result every time. Full pressure for 25 seconds, then it would drop to 3-4lbs. I noticed when I'm driving, if the fp drops and I step on it a bit, it will occasasionally come back up for awhile.

 

[Sixpack]

I had a time where my FP would drop to 5 psi ( normal was 15). I choose to start at the tank and look the whole system over. My tank had the silk sceen filter plugged with stuff that could not go thru a filter. Hair, fuss, rocks in the tank etc. Cleaned it out and it has been fine every since.

Fox, did you drop the tank? I suppose that would be the only way to access the filter. What all was involved. If mine does that again maybe I'll start there also. I changed out a lift pump that did that with a new one and the problem went away for about 10k. Now I have a new pump (not yet installed) it hasn't dropped in a week... Maybe I have stuff in my tank that is plugging the pickup tube screen.

 

[EKoster]

Last night when i got home, I shut the truck down, then turned the key back and bumped the starter. I could hear the pump running. Pump sounded normal for a second, showing 13 lbs on the gauge, all of a sudden it drops to 4-5lbs and the pump sounds much different. I don't know if that says much, but it at least tells me that the pump is not shutting off. So now, maybe I have a restriction in the tank or the pump is just bad already.

 

[Texas Diesel]

Others including myself have notice the same thing at times. But no one knows why.

 

[EKoster]

here's another strange occurence for you all...

When I was driving around tonight, fuel pressure was normal while driving (using the engine above idle) Occassionally when I would come to a stop and idle for a second, the fuel pressure would drop and stay down. It would stay there unless I floored it to redline for a gear or two, then the fp would come back up and stay up until I came to a prolonged idle again.

 

[Weidner]

Any new news on your truck EK... I am trying to pinpoint a weird fp problem (goes up and down while at high way speeds) on mine right now that a new lift pump did not correct.

 

[nps]

Two possible theories (well, three if you consider the FP guage as a possible culprit).



One - the bypass valve on the LP is intermittently sticking.



Two (more likely) - the lift pump is cavitating and does not catch back up until a demand is put on fuel flow by way of flooring it.