Royalglen

[royalglen]

2005 Chev HD 2500 Diesel went onto limp mode so i changed fuel filter (Delco) and engine light went out--truck ran normal for 50 miles then limp mode again so i changed fuel filter again---fuel in new filter looked good(clean) --bled it at filter but truck won`t go over 1000 rpm --is there a quick way to see if i have a small amount of gasoline in diesel --we are in cold climate so they are into winter fuel even though it is warm here. I will supply more info if need be --Please advise..

[More Power]

Do you have a way to read trouble codes?

Jim

[royalglen]

I don`t have a scanner that works on Diesels. I put air pressure in the tank (5lbs) & did`nt find any leaks. My suspicion is that it is not drawing from the filter. When i that the filters off they are only half full. It has half tank of fuel.

[More Power]

An out of place fuel filter o-ring is the usual cause of an air leak, followed by a faulty fuel filter base. Finding the source of the air leak is your #1 priority.

Jim

[royalglen]

How would I check filter base----do they warp or what causes them not to seal. The o-ring is not a good set-up. When you prime with plunger should`nt the filter leak fuel from the o-ring.

[DmaxMaverick]

A leak that passes air won't necessarily pass fuel. Often, they will leak a lot of air (or little enough over time), yet no fuel. Unfortunately, there's no way to know for sure without something obvious, or trial and error. If it's limping after a period of normal running, the issue is deeper than just a small air leak. If you haven't replaced the fuel cap, do it. They are inexpensive, and can cause issues if the pressure/vacuum vents fail. A normally insignificant air leak can be greatly exploited if there is too much vacuum in the tank. Another indicator of this could be tank collapse (sides sucked in).

[royalglen]

Should there be vacuum at the schraeder valve & if so what reading should I get??? How do you clear the codes??

[DmaxMaverick]

Should there be vacuum at the schraeder valve & if so what reading should I get??? How do you clear the codes??

Yes, vacuum at the "test port" (it's between the filter and pump). 0-3" at idle and mid RPM (unloaded) is a new/good filter. Over 5" is questionable, over 7" is plugged/plugging filter or other restriction. Kennedy (http://www.kennedydiesel.com) sells a real nice gage for this, that plugs right into the port.

You'll need a capable scanner tool to read/clear codes. Many of them can be cleared if you disconnect both batteries, and ground the Batt+ cable for about 30 minutes. It depends on the code.

[More Power]

As DM suggested, a fuel filler cap with a faulty pressure relief valve can cause the fuel tank to experience excessive vacuum. As a test, you could loosen the cap slightly for a long enough time to see if the air in the fuel filter problem subsides. However, whatever is allowing air into the fuel system will still remain, it just won't be so much of a problem with a slightly loosened fuel tank cap.

Vacuum in the fuel tank is caused by at least two things: 1- Using fuel over the miles. 2- A drop in ambient temperature causes the fuel to contract. This is most apparent when filiing the truck with fuel during the warm part of the day, then letting it sit with a low overnight temperature.

Jim

[royalglen]

Someone has sugested it could be the ECM (engine Control Module) . Is this very common?? The codes it sets will tell the tale I guess.

[DmaxMaverick]

If you are seeing limp mode and DTC's (SES lamp), they should tell a tale. ECM failure can happen (actually, PCM, there are no "ECM"s on late models, each system has their own "CM", like PCM, BCM, TCM). No at all common.1 If yours is bad, it is rare. More likely a component or maintenance item failure. If you haven't pulled the codes, wait for that. No point in guessing (yet) if the computer is complaining.

[Kennedy]

Two tools that you should have:

http://www.kennedydiesel.com/images/Dmax-fuel-filter-rest1.gif



http://www.kennedydiesel.com/images/RDT51.jpg




Not knowing the trouble code or reason for the limp mode has us all guessing here. Knowing the restriction of the fuel system verifies the problem and potentially saves unnecessary changes.

[royalglen]

Gentlemen thanks for you feedback--just an update--I had the truck towed to the Dealer & problem was a SCHAFFED wire to injector covered by deductable warranty so should be back on the road soon. Thanks again.