Engine/Transmission (1998.5 - 2002) Fuel pressure mirrors tank level and a hard cold start

[Weidner]

My fuel pressuer goes down as my tank level goes down and I have a hard start condition when the truck is cold. I am thinking about droping the tank and checking the fuel module and lines. I am guessing I have air getting in the system or maybe a dirty fuel module/pick up screen.



Any thoughts before I heat up the garage and start tearing this thing apart?

 

[terrywerm]

I know the problem you are talking about very well as I am in Minne-snow-ta too. At least the part dealing with the colder temps anyway.



I see the same thing but if I take a longer trip so that the returning fuel warms the fuel in the tank, the pressure slowly gets better and better. At temperatures above 20 degrees or so, the pressure is always good. As a rule during warm temps, my fuel pressure is pretty constant regardless of the fuel level in the tank. In colder weather that may change and I simply had not noticed a difference. If my FP is above 5 PSI, life is good and I don't worry about exactly how many PSI it is showing. It will change as the weather condtions change, and may change slightly as the level in the tank changes.



As the temps fall, the fuel viscosity changes, making it thicker and harder to draw from the tank, which results in a somewhat reduced supply to the filter and injector pump and reduced pressure. I have had rather good success with either blended fuel and/or fuel additives, but the pressure will be down somewhat when colder weather hits.



I am planning to move my lift pump to a location on the frame, near the tank, probably with the Vulcan big line/relocation kit. I am hoping this will help. I don't think that you need to drop your fuel tank, the reduced pressures are normal. This morning it was zero *F here and when I first started mine this morning, the fuel pressure was down around 9 or 10 PSI, but had recovered to near normal levels of 12 to 15 PSI by the time I completed my 30 mile drive to work.



On the other hand, there is some neat information in this thread:

https://www.turbodieselregister.com/forums/showthread.php?t=162110

It deals with some gunk building up on the intank screen.

 

[terrywerm]

I almost forgot to ask: When you experience the hard starting problem, what do you see happening (spins over nice, doesn't fire, or starts to fire a tad after several revolutions, runs rough with lots of blue smoke, etc. ) You might have a problem where your grid heaters are not working correctly.



BTW - just where in MN are you??

 

[Weidner]

I am used to the cold weather, this actually started b4 it got below feeezing. By cold start, I just mean after the truck sits for a while and the engine is cold. The grid is working fine... I think it is fuel bleed down after it sits, but I am not sure exactly on how to trouble shoot it. My fuel pressure seams normal while my tank is full, but when I get below 1/2 tank I lose some fuel pressure and if I get below 1/4 tank my pressure goes down to 1-2 pounds. I think they might be two issues I guess. I am going to look at it tonight.



by the way I am in New Market .

 

[terrywerm]

New Market? No kidding!! I've got some family over there - my dad grew up near there too. Not far from where I am now either for that matter.



I believe you are correct when thinking that it might be a two part problem.



I would try this on a cold start and see if it starts better:

1. Turn on the key and wait for the Wait to Start lamp goes out

2. Bump the starter to start the lift pump, see if your FP comes up.

3. Repeat step 2 once the pump shuts off.

4. Once you have pressure again, hit the starter.



If it starts nicely, it indicates that you did have some air in the system and running the pump purged it out of there. Much of the time when this is the problem it will pop right off, then stumble and die, causing you to have to try again. If I recall correctly there is a check ball in the LP that is supposed to keep that from happening. Others have reported problems with that ball check from time to time.



As for the problem with the pressure dropping off so much over the course of a tankful of fuel, I'm thinking that you may have a restriction on the inlet screen down in the tank, or you may have a hose between the tank and the LP with a slight kink in it. I would check the hoses for kinks first, then use compressed air to blow back through the hose that supplies the LP so that it clears junk off of the screen. Put it all back together, and try it out to see if your pressure improves. If it does, then slowly gets worse again, you may indeed have some crud in the tank that is partially blocking the screen on the pickup tube. If it doesn't change, it could still be the screen, but the compressed air did not clear the problem. The problem could be elsewhere in the system too, but you'll have to rule out one item at a time.

 

[DMannon]

Be careful blowing compressed air back into your tank through the fuel lines... too much pressure can dislodge the the pickup in the in tank assembly.



The pickup can also get dislodged from a sharp bump to the bottom of the tank.



Either way, a dislodged pickup means air in the fuel at lower tank levels = fluctuating pressures.