I have a 99 24 valve and lately it seems that my truck will at times lose it's prime. It doesn't happen all the time, but every now and again I'll go out to start it and the prime will be gone. So I let the lift pump run for a while and then the truck will start up without any problems. Does anyone have an idea why this may be happening? Is the lift pump letting fuel go back to the tank? Any thoughts on this will be appreciated.

 

I can't say for sure since I don't have a 'newer' truck, but I would suspect the lp is getting ready to die if it hasn't already. Do you have a fuel pressure guage on it? If so what were the numbers? I would look at the prussure before I went nuts with trying to find leaks.
Tom

 

You should really have a Fuel pressure on your truck it is vital on 98.5-02 sounds like lift pump is dead and vp44 is pumping fuel not good

 

you may also have a pinhole in the fuel line. the lines behind the fuel tank are known for leaks.

 

Thanks for the input guys. I don't have a fuel pressure gauge but I do agree that I need one. I'm going to get one installed asap. I put a new lift pump in about 30,000 miles ago and I was hoping it would last a little longer than this. (if it is in fact going south) Does anyone have any input on the FASS pumps? Any good or bad exerpiences? I've been thinking about intalling one but I like to hear some feedback from folks that are using them.

 

Ive got a FASS and i think its great! It was a great and relatively easy installation, and have not had a single problem! I would highly reccomend the fass system, but if the vp44 is goin, it may be too late to try and save...

 

Could be the injection pump has finally bit the dust. You do need to put a fuel pressure guage on it post filter to make sure IT IS ACTUALLY LOOSING PRIME...



Jason

 

The truck seems to run fine and the starting issue in on and off. Most of the time it starts right away but every now and again it appears to lose it's prime and will not start until I let the lift pump run. (this usually happens when it sits for a longer period of time) If I bump the starter, the lift pump runs a long time to bring the fuel back up. Once it's done running, I have absolutely no problems. The truck starts right up and runs perfectly.

It just seems to me that the lift pump, or something is at times letting the fuel run back to the tank. Although I don't have gauages yet, it appears that the LP is pumping as much fuel as when I last put it on just from looking at that amount of fuel it pushes out when I open the seperator. But without gauges, I don't know how it is performing when the truck is running. But my real issue is that the fuel at times seems to someone leak back causing the truck to lose it's prime. Is there some kind of check valve or something of that nature that could be causing this?

I really don't think I'm having any issues with the VP44. I could be wrong, but my truck runs perfectly other than this starting issue. Any thoughts?

 

Definitely check for fuel leaks anywhere. Most of the supply side is under pressure so leaks there are obvious. The return side is not under pressure so you can crimp the return hose to pressurize it. If you do not find any leaks, you should consider changing the lift pump. You should put a guage on it regardless of the problem.

 

I also have a 98.5 24v and I also had the EXACT same problem. On mine, it seemed to only happen in cooler weather (<50 F). The truck needed to sit for a couple of hours after shutdown to reproduce the problem. It also seem to occur much more often after a long trip or a short trip loaded.

Anyway, I had the truck towed in seven times to the dealership, but since there where no codes, they just primed it and called me to pick it up. I got to were I would just prime the d**n thing to move down the road. After a considerable amount of yelling at the service manager, they agreed to replace the IP, but the problem was still there. A couple months after IP was replaced, it was time to replace the fuel filter. After changing the filter, I haven't seen the problem since.

It been over 2 years.

Don't know if it means anything, but the filter I put in was the first time I used one NOT purchased by the dealership.

The filter may all be a coincidence, but who knows...............

 

I love my FASS and would not hesitate to recomend one. One other place that frequently comes up as a leak source is the quick disconect on the fuel tank.
A failing LP can also cause these symptoms. I know its been said but a FPG is a must. Good luck

 

After my last post on this thread, my truck got so it would lose it's prime almost all the time. I ended up replacing the lift pump and that seemed to take care of the problem. But this morning when I went to start the truck, it had lost it's prime again... I don't know what to think. The truck runs perfectly... I don't see leaks of any kind so I'm not sure what to do. I might try changing the fuel filter.

 

you are pulling air in somewhere.

 

The first few times I brought my truck into the shop, they did all the pressure tests, tested the LP and IP and dropped the tank and checked it. They couldn't find anything wrong. They sent it to Cummins who also couldn't find anything. Like you, I also was convinced that it had to be a check valve in the fuel system somewhere that was allowing fuel to run back into the tank.

The diesel mechanic was convinced that the system was sucking in air, but it seemed to me that would affect performance?. Like you, mine ran like a top. I got tired of taking it in and them not replacing ANYTHING. So, thats when they agreed to replace the most logical culprit, the IP, but it was back in the shop two days later.

I strongly believe that this was all caused by a bad fuel filter. I installed the filter in Aug (pretty warm here in TX) and the first time it lost prime was mid Nov when the temps got into the 50s. I fought this all winter until I changed the filter in Feb.

During this process I saw alot diesel mechanics scratchin' their heads.

I hope it's that simple for you partner................