Fuel Supply Problem

[Cooker]

Yesterday I changed the fuel filter on my '96. At the same time I unplugged the electrical connection from the fuel heater/prefilter. Fuel started to come out form the connection so I assume the heater is bad and that may have something to do with my cold morning starts (that is another issue).



I buttoned everything back up and fired up the truck, after priming the heck out of it via the primer on the lift pump. All was good.



Not really. Now I seem to have some sort of loss of prime issue. The truck is very hard to start after is sits for a couple hours. I checked the fuel pressure via the bleed bolt on top of the filter housing and I'm getting 11-14 psi at idle (and the overflow valve was replaced about 8 months ago, pressure at that time was 22-24 at idle).



I was originally thinking I somehow messed up a fuel filter change, but now I am lead to believe the lift pump just took a dump There has been a slight amount of fuel around the primer button for about the last 25k miles, but it never affected anything before. I don't think a faulty fuel heater element could have an affect on the fuel pressure as it is before the lilft pump and it is not leaking unless the plug is removed.



Sorry to be so long winded, I just wanted to include all the details.



What do you think? Would you agree the lift pump is the culprit?



Thanks for the help,

Ryan

 

[illflem]

Ryan, my experience it that mechanical lift pumps either work or they don't, no in-between. Sometimes they leak fuel into the oil or vice versa, if the spring gets weak they tick. Sounds like you're sucking air somewhere, maybe the heater or lift pump primer o-ring (the only replaceable part). Maybe it started leaking worse after you used it to prime after the filter change.

 

[Cooker]

Bill,

I too was originally thinking that I was sucking air. You did remind me of something though reguarding the lift pump.



When I bought the truck, the fuel pressure was 45psi at idle and the pump did tick quite a bit. I do not know how long it was run like that (I'm guessing the first 75k miles of it's life), but I assume this could have had some affect on the life of the lift pump.



I agree after using the primer it could be the o-ring, but would the primer o-ring allow enough air in to cause such low FP numbers? Maybe the primer and fuel heater combined could?



I'm just trying to decide where to start.



Thanks for the help,

Ryan

 

[illflem]

Ryan, if you're going to replace the o-ring you need to remove the pump anyways and can check it out. If it was ticking for very long it may have mushroomed the actuator lever on the pump. This and the tick happen when the cam slaps against the lever because it isn't retracting back all the way. It can mess up the cam also if allowed to go on too long. Even if the lift pump isn't going though it's full stroke you should only lose volume, not pressure. Bad new overflow valve already?

 

[Missouri Mule]

Cooker,

If you disconnected the fuel heater/ pre filter sensor and fuel leaked out wouldn't fuel leak out when engine was running?



Did you notice any other area that fuel could be leaking from above fuel heater/prefilter, primer button ?



As I recall when doing fuel pressure test one can reach up and under to squeeze the rubber return line (with fingers or tool),

if pressure goes up bad overflow valve

if pressure stay the same lift pump.

 

[Dieselnerd]

I beg to differ on the lift pump either working or not. Mine worked fine when running but lost it's prime in several hours of sitting. There are check valves inside the pump that go bad and allow the fuel to drain back. The valves are removable (I removed mine) but you can only buy a new pump. I went crazy checking everything the members suggested and until I replaced the pump I lost prime in 3-4 hours every time. Now it starts instantly again after sitting for several weeks. If the check valves are working properly you won't lose prime through the primer button. I had my old pump in pieces and it's pretty simple.



12 Valve Lift Pump, latest style, Cummins P/N 3936316

 

[Cooker]

Missouri Mule,

I don't think fuel will leak out while it is plugged in becasue it is a weather tight electrical connection. When unplugged the seal is broken and fuel leaks out.



The only fuel leak that I can find is from the primer button, and it is not activly leaking, just moisture around that area.



I guess it could be the overflow valve or even possibly the rubber return line, but I am ruling them out becasue this started right after I changed the fuel filter. It seems like it would have to be the filter itself? WIF sensor connection to the filter? Lift pump/primer? or the fuel heater?



Well the heater is bad and needs replacement so thats not money lost, while I'm in there I'll pull the lift pump and take a look at it (Dieselnerd is it easy to see if the valves are faulty).



If these don't fix the problem then I will look at replaceing the fuel filter, lines, and overflow valve.



I thought I might have been overlooking something, but it appears my suspicions may be correct.



Thanks for the help,

Ryan

 

[Dieselnerd]

Cooker, I couldn't tell from looking at the check valves which one was bad. They are kind of a diaphram type valve. If you have never changed your pump and you have over 70,000 miles on your truck, it's probably bad. I found out later from another member that has a diesel repair shop that the early lift pumps have been upgraded several times for check valve problems. He said these usually show up after 60,000 miles or so, mine was just over 70,000. The number I gave you is for the latest pump, mine was just about $150. It's quite a bit larger than the old pump but bolts right in. My idle speed was also going down slowly and I had planned on setting it higher but after the new pump, idle speed came back to normal. You do not need to remove the pump to replace the primer button "O" ring if you are planning to do that. I changed mine out with the pump on the truck. My primer button was leaking too but the new "O" ring didn't fix my loss of prime. If you look at the "O" ring, it's mainly to keep the wobble out of the primer button, the check valves are supposed to keep most of the fuel from getting to the inside of the button in the first place. One other thing, mine is also a 1996 like yours.

 

[LarryB]

I'm not positive but I don't think you can loose prime without air getting in somewhere. A bad check valve could cause insifficient pressure but not loss of prime. The fuel cannot drain back unless there is air to replace the fuel. The return line is placed in the fuel tank below fuel level to prevent this from happening. I'm not saying the problem isn't the lift pump though. A pressuer gauge here would be a big help in diagnosis.

 

[Dieselnerd]

LarryB, take my word that a bad lift pump will cause loss of prime. When the check valves go bad, the fuel drains back. How do I know? I replaced everything except the lift pump and kept losing prime. As soon as I replaced the pump, the problem was fixed. I don't know how the fuel drains back, or where it gets the air but it does, believe me.

 

[LarryB]

Dieselnerd



Calm down and read my last post slowly and carefully. I don't doubt you.



Larry

 

[illflem]

It is very much like picking up water with your finger on the end of a straw though. Air has to get in somewhere to lose prime. Dieselnerd, I don't doubt that your pump was bad but you must have also fixed a leak, minute, possibly unnoticed, somewhere along the way.

 

[Dieselnerd]

Larry and Bill, I don't disagree with the physics. The fuel is leaking down and somehow air gets in. However it was completely contained within the pump. I always let it sit for at least 24 hours between items I replaced (not a daily driver) and the pump was 100% of the problem. I might add that after I described my fix about 6 weeks ago, the following post was added to my thread which reinforced my opinion that the lift pumps can cause loss of prime on their own. If I were to "guess" where the air enters, it would be through the primer button after the check valve has gone bad. The way that "O" ring sits in there along with normal diesel vibration, it's not much of a seal.



POST:

"I see a lot of loss-of-prime conditions, and most of the time a new lift pump is the fix. Around 60-80K, the check valve in the pump starts to leak, and can cause a hard starting problem. Easy fix. "

__________________

Evan A. Beck

The PowerShop

DieselRam.com

ScottyAirSystems

 

[BHaner]

I had the same problem with loss of prime. The local Dodge dealer replaced:



In tank pump / sending unit

Fuel lines from the tank to the pump

Lift pump

Fuel heater

Overflow valve

Return hose



All under the 100k warrantee.



This was about a year ago and the truck had about 60k at the time. I now have about 92k and it is doing it again. I can hear the lift pump clicking and it got worse after I put in a new overflow valve.

 

[HoleshotHolset]

BHaner: Last I knew... . there isn't a pump in the tank.....

The sending unit is there to tell the fuel gauge how much fuel is in the tank... . and to deliver fuel to the engine via the lines/pumps, etc... it's not there to pump anything.



This is not meant as a flame... just an observation.



Matt

 

[BHaner]

There is no pump?

Huh... shows how much the dealer knows... at least I didn't pay for it.



P. S. this is the same dealer that told me my trans was shot and wanted to replace it... . I replaced with a full BD trans for $200 more than they wanted for a rebuilt at the dealer. Found out later it was nothing more than old oil in the trans and a dirty TPS.

 

[HoleshotHolset]

Yeah the STEALERS will have many Chrysler owners thinking that they replaced their fuel filters too.....



Chrysler has been in the habit of making cars with non-serviceable fuel filters for quite a number of years now. The "filter" is in the tank... . and is actually just a fuel sock that keeps the fuel pump from eating crud in the bottom of the tank.



YES, the "filter" can be replaced... . but the tank has to be dropped and the sending unit removed/replaced.



Matt

 

[illflem]

A dealer actually dropped my tank under warranty to find out there isn't a pump in the tank. Had all the mechanics in the shop baffled, they thought for sure that DC screwed up bad and left the pump out. I could understand it back in '95, most dealers didn't know much about diesels, there's no excuse for it nowadays.

 

[Missouri Mule]

From 96 Dodge service manual.



"Check valves within the pump, control direction of fuel flow and prevent fuel bleedback during engine shut down. "



Looking at diagram it looks like all the check valves would have to be bad to get serious bleed back.



The engineers know if they don't have check valves on the pump it will bleed back during normal conditions( no air leaks in system).



If you take a straw put your finger (check valve) on bottom fill it with water put another finger on top, remove finger from bottom the straw. The water stays in the straw (suction) until finger on top is removed . Apparently nothing above the fuel pump causes suction.



Would gravity pull the fuel back down?



Air introduce into the system somewhere?



I have heard that the quick disconnects can suck air into the supply line from the tank.

The fuel drain maniflod removes any air (small amounts) that get into the system by dumping it back into the fuel filter.



So where does this air go to?