Hi Folks,

About 6 weeks ago I posted the following:

“In the last year or so, it will periodically (every month or two) loose power and will not idle. It feels a lot like a gas V8 with 2-3 plug wires removed. You can start it and run it as long as the gas is half throttle or better (real hard on the automatic trans). No smoke. EGT's are significantly down while it is misbehaving. Fuel pressures look good, and no codes being thrown. Seems more likely to happen on the bottom part of the tank after it has been run for a short while, shut down, then restarted (e.g. going to the store). Cures itself when left parked for more than an hour, when the tank is filled, or just whenever it feels like it.

Have had the fuel filters replaced twice, pressure regulator replaced, tank pulled and inspected/cleaned.

Anyone seen this problem before? Suggestions?

Thanks in advance for your help.”

It finally acted up when I had some help (a mechanic buddy) around. We traced it to the injection pump, specifically the line to the no. 6 cylinder. Are the delivery valves prone to failure? If so, are they field replaceable units? If I have to buy a new/rebuilt pump, what’s a reasonable price?

All help appreciated, thanks.

 

not really this is the pump everybody turns to when they want relieable power. what do you mean the line going to the #6. are you sucking air anywhere

 

No air, just no fuel pressure in the line from the injector pump to the injector. With the truck running (poorly), we cracked the lines at each of the injectors and all but number six leaked fuel. We cracked the number six line at the number six delivery injector (on the pump) and still no fuel.

 

You most likely have a fuel delivery problem TO THE IP. You need to hook up a test gauge. My bet is either the lift pump is going out, or you have a hole rubbed in the coiled plastic pickup line of the in-tank module and it's sucking air.

Other common failures include the stock steel supply line rusting or splitting.
Failure of steel supply tube over "bell housing" area of trans.
Clogging of the super-fine screen on the bottom of the in-tank module.
Clogging of the screen in the fuel heater/strainer.
Cracking or collapsing rubber fuel elbow between the heater/strainer and LP.
Sucking air at the heater element plug in the heater/strainer.
Fuel solenoid out of adjustment or getting weak.
Relay for the fuel solenoid contacts going out.
Weak overflow valve.

 

The lift pump was replaced earlier (6 weeks ago) and the lines and screens in the tank were thoroughly gone over. So now you guys have me crawling around under the truck looking for cracks or leaks. Is that line between the lift pump and the injector pump supposed to have positive or negative pressure?

 

Well, what you'll have is a line from the lift pump to the fuel filter, and then another line from the filter to the IP. Both will be "positive" pressure. So if you have a leak, you should know it.

From the tank to the fuel heater/strainer, and from there to the lift pump are the suction lines. As I mentioned, the area of the electrical plug for the heat element in the heater/strainer is a common spot to develop an air leak. Also the rubber elbow from there to the inlet of the LP.

I might mention that the '94 I just bought a couple of weeks ago had the LP replaced recently. Then it developed a "fuel delivery problem". The owner didn't know much about diesels or even his in particular. I talked to the mechanic that worked on it for him. When replacing the LP, he also noticed the rubber fuel elbow was cracked. He couldn't get one at the parts house, and Chrysler wanted some stupid price for it. SO, he had just used a piece of regular rubber injection hose, cutting it a little longer to try to make the bend. WASN'T LONG before that line was sucking closed. There is an aftermarket spring device that has a little strap on one side of it. It's made to slip over the new "elbow" and keep it from collapsing.

 

Thanks VinDiesel, I'll be a'lookin. I'll post the results.