Random Fuel Issue: Loss of power & dies back again?

mattdieselman

mattdieselman

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So sorry for the story, but I have damn near pulled my hair out for on this fuel issue. Originally i was having an issue where truck would randomly start to stumble and lose power while driving through town or on the highway. A few times it would just die. No consistent factor when it would happen, except it was becoming more frequent. I usually could try to catch it and knock the truck in neutral and peg the throttle and it would chug back to life in a hail of white smoke. Checked the shutdown solenoid and that was not the issue, fuel filter has been replaced. So I replaced the OFV this weekend with a Tork-Tek one and installed a fuel pressure gauge on the outlet of the fuel filter. Great idle pressure and load. Put 250+ miles on Saturday & Sunday. City & highway miles and truck started up every time like a champ. Today it was -25 degrees out truck started right up ran and got coffee and hit the highway. Truck was running for 25 minutes and doing about 65 MPH and truck lost power and hail of white smoke. It did this 3 times on the way to work. I'd pull over and it would clear up and do it again a few minutes later. I put in some 911 treatment and ran truck for 1 hour before i left work, with now issues on the way home. Please tell me its gelling!!! Anyone had these kind of sporadic issues? Thanks!
 
Should be. Doesn't make sense why it has been so sporadic. The other thought that has been kicked around is kinked / restricted return line???
 
look at the 90* rubber fuel elbow hose between strainer and pump inlet for a delaminated rubber flapper inside. that hose folds in on itself. $30 brand new from cummins but isnt any better, had one cave in like 30 miles after. most dependable solution is hose barbs and a big loop of 1/2" hose zip tied up under the brake booster so it doesnt rub the steering shaft.

you may as well pull the fuel strainer and delete the heater since it has or will melt the plastic around the plug pins and suck air. also check that the lift pump spring hasnt snapped. just pull the big hex plug and its behind that. can be done on the truck if you trim the wheelwell sheetmetal behind the shock tower for access. i highly recommend that trim.

if none of those, i assume the telescopic tank pickup has jammed and your inlet tube is dangling in air. have to drop tank or raise bed. if the screws have worn divits it wont slide, best to extend fully and pin it. tank will read wrong at full but right at empty. my truck will run out of fuel with 9 gallons left in tank because of this.
 
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Thanks guys. Think I have it nailed down. Pulled into the shop at work for the day to let it warm up since it has been -5 F for about the whole week and determined part of the problem was gelled fuel. Think I got a bad batch of fuel. I had 2 bottles of power service in the tank and figured it shouldn't gel up. Next I noticed that fuel pressure is great at idle, but when I put about 2000 RPM no load to the engine, it picks up to 27 psi or so then starts to drop to about 12-15 psi. So, I am going to change the fuel filter, delete the pre-heater and replace the screen & 90 degree elbow, since I already have them, just haven't put them on yet. If I still have the pressure drop after this, I am guessing bad lift pump?
 
yeah it could be. i did have one that behaved flaky like that. genos was the best deal on a replacement, and make sure you switch from bolts to studs on the block. way easier to do if you trim that inner fender and adjust some brake lines a bit.
 
Can be pulling air into the line in a zillion different places from the tank to the cab. IF you havent already done it Id ditch the metal lines and use good quality hydraulic hose. Also install a boiler sight glass in front of the IP so you can see when its sucking air.
I also opened up the fuel sender and pulled the top bung and installed a draw straw setup there, and plumbed it into the fuel pickup at the bottom of the thing, so I could get rid of all the crappy OEM rusty fittings.
 
Matt, another thing to mention is we put a 1/2" drawstraw in it. The feed line 90* hard line coming out the top of the sender had a pinhole leak, so a 1/2" drawstraw was built using copper tubing and compression fittings going to the bottom of the tank. The end of the tubing was V-ed ~1/8" as well.

So we're not going through the sender, but we are returning the fuel through the sender, but through the vertical aux port, not through the stock 90* hardline. The return line is being pulled more taunt that I'd like, but I'm not sure how much that would make a difference. The fact that at 2000 rpm the fuel pressure looks good and then drops off makes me think that the return line might not be able to return fuel fast enough, but I'm not sure how that would drop pressure in the IP. Is that possible for it to hang the OFV up?

I also don't see it being the lift pump if we're making decent fuel pressure.

The hoses were all heavily manipulated when the truck was going through the frame off resto and they are all original to 95. If you still have this issue let's drop the tank, shorten the drawstaw 1/8", change all the lines, and go from there.
 
Yeah, my concern is the drop in fuel pressure under RPM no load. Should be about 10-15 psi higher. I also had a weird issue yesterday where in 3rd & 4th gear pulling into a load RPM band, I had a loss of power. Almost reminded me of an engine that is in derate mode pulling fuel. It never sputtered, but just lost a lot of power. I just need to take a closer look at the lift pump and test I think.
 
Another test to try is put a vacuum gauge between the lift pump and the fuel tank. This will tell you if the screen on the bottom of the fuel module is plugged. Mine was at 4 ins. of hg. Put a new screen on and it went up to 13-14 ins. of hg. I could tell just by looking at it that it was plugged.
 
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