Engine/Transmission (1994 - 1998) Dying Diesel

[MAiton]

Currently I work at a automatic transmission repair shop and on the side they do other jobs. One of these other jobs is a 94 Dodge Diesel. The guy brought it in saying it was intermittently dying after you drove it for an average of 50 kilometers. The shutoff solenoid is new, both return and supply line to and from the fuel tank have been half asked replaced with copper line, a new fuel filter was installed, the overflow valve was supposedly replaced but they ended up using a helicoil because they wrecked the threads taking it out and the prefilter off of the lift pump has been bypassed. Also we were told the return line was crimped off.



This morning I installed I fuel pressure gauge AFTER the filter housing going to the injection pump and took it for a hard drive. Fuel pressure stayed great and it only died once. From there we took it back to the shop where we let it idle for half and hour. After a period of time it went into inconsistent idling until it apparently ran out of fuel. It'd die, and we'd start it back up(after several rotations of the engine) and the fuel pressure never went below 20 even at the last second. We did a volume test and it filled a 600ml pop bottle in mere seconds. I held up on the shut off solenoid while it idled and that didn't help. I crimped off the return line coming from the overflow and nothing changed except for the increase in fuel pressure. I then cracked an injector line(number 2 I believe) and fuel was fine until it went into the reving down mode and the fuel started to disappear leading it to shut off completely.



Now, I'm out of ideas and leaning towards a possible injection pump failure unless I'm overlooking something. Any ideas and thoughts are welcome.



Mike

 

[Joe G.]

Throw away the fuel heater.

 

[bavrit]

I had the exact same thing happen on my 97. It turned out to be a water fuel separator located on the drivers side on the bottom of the block. It had a bad gasket and would vapor lock the engine. I do not know if a 94 has this filter or not. It looks like a 2. 5 inch castle nut dome and unscrews with a 17m mm wrench. Good luck, brad

 

[Vaughn MacKenzie]

Make sure the idle is set to the appropriate speed too, at least 750 RPM with transmission in drive and AC on.

 

[Joe G.]

I had the exact same thing happen on my 97. It turned out to be a water fuel separator located on the drivers side on the bottom of the block. It had a bad gasket and would vapor lock the engine. I do not know if a 94 has this filter or not. It looks like a 2. 5 inch castle nut dome and unscrews with a 17m mm wrench. Good luck, brad

That's the fuel heater/pre-filter assembly. The black hockey puck looking part of it is the fuel heater. It burns up and causes a leak. The odd part of it is that the fuel heater is worthless.

 

[bavrit]

Here is a good explanation

Fuel Pre-Filter Cleaning on Ram/Cummins

 

[MAiton]

As I said in my first post, the pre-filter assembly has been bypassed. Plus if that was bad I wouldn't have been getting the flow results I did.



Any other suggestions?

 

[MAiton]

Make sure the idle is set to the appropriate speed too, at least 750 RPM with transmission in drive and AC on.

The idle is up but as one would believe, if the idle was too low the truck would hunt and eventually die. Most importantly though, it reacts anywhere under 2000rpm. Reving over that will bring it out of it.

 

[tp0d]

Ok, the truck runs for a while then dies? Try leaving the fuel cap loose to stop any kind of vacuum issues...

I would also say to stretch out the overflow valve spring a bit, could be getting weak as it heats up. .

Copper is usually a bad metal to use with diesel fuel. Steel or rubber diesel rated lines are the best to use. .

Could also be a failure in the lift pump when things heat up, the o-rings in the pump's check valves could fail/leakthru and cause a lack of pressure.

When was the last time the fuel filter was changed? This is the easiest and cheapest check, owner could have picked up dirty or algae-laden fuel... ? If its been more than 5k miles, change it out.

Definetly check all fittings pre-lift pump, as this is all suction, any small leak will not be noticable and will bleed air in quickly...

Only other thing that could be an issue is a perforated suction pickup in the tank, how much fuel is in this truck, try filling up to 3/4 tank or better and see if it still does it. .

good luck. .

-j