Intermittent low power - Causes??
 

Hi All, New to this site and so far I like it a lot. Hopeful I can get some ideas on a problem I have (had?).

I bought a '97 3500 5-speed about six months ago. It only had 115K on is and was in very nice shape. About three months ago (119K) I was traveling on a secondary road towing my trailer when I noticed a loss of power. I needed to keep downshifting to maintain speed and finally it died. Pushing the primer button on the lift pump then trying to start it showed it wanted to fire, but never really ran. Had it towed back to my place (yeah AAA!) and replaced the fuel filter and pre filter screen. It ran fine until a few weeks ago(122K). I was traveling a few hundred miles from home and went to shift. When I put the clutch in, the engine died. When I completed the shift and let the clutch up the engine started and ran fine. About fifty miles later while going up a hill, I had a severe loss of power and pulled over. Again the engine died when I put the clutch in. Got out and looked at the engine( why I don't know) everything seemed fine. Got back in and started it and it ran fine again. By then I was close to home so I just kept going. A few more times I lost power, but the engine kept running, then picked back up again. This time I installed a new transfer pump, bypass valve and replaced the rubber portion of the fuel lines to the engine. Took it for a fourty mile test ride and it ran like a Swiss watch.

I plan on going thousands of miles away next month and don't want to have a repeat while I'm at the mercy of some st ealer. Have these symptoms occured to anyone else? Is there ANYTHING I have left out that could possibly cause these symptoms to reoccur? My confidence in the truck is shaken and I won't put enough miles on it before I leave to feel comfortable.

Sorry if this is long, but I want to be as accurate as possible regarding the symptoms.

have you change the fuel filter again and cleaned the fuel screen,if so was there anything visible that is plugging filters,you might have a bunch of junk in the tank,what about the air filter.

Take a 4" piece of clear line and insert it at the IP fuel inlet, the banjo bolt. Look for air bubbles. Get a fuel pressure gauge and hook it up, look for fuel pressure drop, especially under load. The line may run free of air under no load, but under load, things change. I have been going through hell with this. I am curious to what your problem turns out to be.

There is a silinoid ( spelling) that needs to kept in the up position to run correctly. It gets week and can cause this low power. Maybe someone will add info about it.
When it drops down it shuts it off.

What J-fox Is Speaking Of Is The Fuel Shut-off Silinoid. This Could Very Well Be The Answer. Sometimes These Will Slowly Fail Or The Relay Is Not Making Good Contact. Does This Start When You Hit A Goog Size Bump ?

I have been under the impression that these fuel solenoids are either off or on, no inbetween. The fact it died when I disengaged the clutch and then started right up when I engaged it doesn't make me think that could be the cause, but I certainly don't know. It acted like it is running out of fuel, not like the fuel is shut off when I turn the key. Loose power until I have to downshift to maintain fourty, then it slowly picks up until I have full power back. That's good for ten or fifteen miles and it repeats. I'm guessing so far, no one has encountered this symptom - leave it to me!! :-)
Thanks for the ideas so far.

THIS solenoid can get in a binde or not FULLY lift the arm reducing your fueling. i have had one '97 here in the shop that had this same problem.

Think ya got it. Mine was similar, not dying, but intermitent power except I had poor mileage too. Sounds as if air was being introduced to the fuel sys. A bad o/f valve and questionable return lines can create problems with pump pressure, primarily the o/f valve. I'd trust it now, have a good trip

Thanks guys for the help. Another 300 miles and it seems fine.

This is getting to be an adventure. I haven't worked on diesels since before I could vote. Sounds like a new clutch in the spring as the throwout bearing is making a noise now! I will get to bomb it someday as soon as I get the mechanicals straightened out and the good weather returns.