Rough idle troubleshooting.... HELP.

[Jayco36REQS]

Ok, so I went to move the 5-ton the other day, and it was idling rough. Here in Orlando FL the temps are always mild.. so it's not a cold start issue. I let the truck idle to air up the brakes to 120psi, and put it in gear, and it felt like I was running on 4 cylinders.... low power, and rough as an old tractor. I stopped popped the hood, and poked around....
- No leaks
- No smoke in the exhaust
- Fuel pressure is good
- Oil looks good... aka no water/fuel in the oil

So I decided to take the truck for a spin around the neighborhood to see if anything changed with driving and heat. After the engine warmed up good, it smoothed out and started running smoother. By the time I got home the truck was running pretty much normal. So I thought... well maybe it was a burp. WRONG.

I went to start the truck again a couple days later and it was rough again... WTF?!?!

The thing is, this truck has been rock solid from the day I picked it up at the Indy depot yard and drove it back home to Dayton, OH.... It didn't matter if it was freezing cold, or hot, or rain... it always ran smooth. I drove it the 1,000 miles down to Orlando when I moved here, and it was great... ran 68mph all the way (except on hills of course..lol) Never got hot, never burped.. zero troubles... it just ran like a top!

Ok... so... any thoughts? Any ideas where to even start trying to figure this out? ANY ideas or thoughts are greatly appreciated!

Thanks!

 

[MtnSnow]

Sounds like your getting air in the fuel. If you haven't replaced the fuel lines in the last couple of years you might want to do so.

 

[Jayco36REQS]

Sounds like your getting air in the fuel. If you haven't replaced the fuel lines in the last couple of years you might want to do so.

Hmmm.... How do you get air in the fuel lines without having a leak someplace? Could the fuel be contaminated or have water in it from condensation? I guess I could change the fuel filter just in case....

 

[Jayco36REQS]

ohh I replaced a big chunk of the fuel lines when I went to the duel fuel line mod..... I did that mod back in OH before my move to FL, and haven't had a problem until just last week.

 

[74M35A2]

The soft fuel lines on these trucks are of limited life, and all past due for replacement if original. From the tank to the engine (to lift pump, anyway), including any filters on the way, this is the suction side. If it has a leak, it will leak air in, not fluid out. Many have found this by pressurizing their fuel tank slightly and these hoses are suddenly wet. So many cases of it that most now simply don't test, they just replace them. Also pull and check fuel tank dip tube, specifically solder joint at top where the tube is soldered to the fitting. Check tube for cracks/splits/corrosion also.

Also make sure fuel filter housing bolt square washer is sitting down into its home squarely, bolt is tight, Schrader vale on top is not leaking, etc....

 

[Jayco36REQS]

The soft fuel lines on these trucks are of limited life, and all past due for replacement if original. From the tank to the engine (to lift pump, anyway), including any filters on the way, this is the suction side. If it has a leak, it will leak air in, not fluid out. Many have found this by pressurizing their fuel tank slightly and these hoses are suddenly wet. So many cases of it that most now simply don't test, they just replace them. Also pull and check fuel tank dip tube, specifically solder joint at top where the tube is soldered to the fitting. Check tube for cracks/splits/corrosion also.

Also make sure fuel filter housing bolt square washer is sitting down into its home squarely, bolt is tight, Schrader vale on top is not leaking, etc....

Good troubleshooting info.... THANKS!!

I'm not used to not having a pump in (or very close to) the tank.... I'll start at the tank and work my way out.

My truck was a 2011 rebuild at Red River, and everything looked new (2,000 miles since rebuild) when I got it 2 months after it was rebuilt. It's been a rock solid truck so far... I'll check back in once I find the culprit.

Thanks again!!