Fuel Problem, Yoyoing between WOT and Idle

Jon Walker

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Cedar City, Utah
My truck has had all of the fuel lines replaced, the tank dropped and cleaned, new filters, new water fuel separator, and a new air vent line.

The problem I am having is that I can run at WOT for a brief interval and then the engine stops reving and idles while the truck downshifts and slows down. After coming to a stop for a few seconds the truck will run at wide open throttle again. No white smoke.

I suspect that the fuel filter is being sucked dry because the fuel pressure relief valve has failed. When the filter fills back up it works again until it is empty. I am having trouble locating the fuel pressure relief valve. Have any of you had this problem? Is the valve behind the governor?

The problem still exists after an hour of driving but it seems less frequent. When first starting to drive I can only go WOT for 3-5 seconds. After an hour or so I can go WOT for 1-5 minutes.

Thanks!
 

Jon Walker

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Cedar City, Utah
it is a 1994 3116. My father is a heavy diesel mechanic and he told me to change the fuel filter again. So I am going to replace the fuel filter and see if there is any improvement. After that I think I will remove the governor and check it out.
 

snowtrac nome

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the biggest problem with the 3116 is the primary fuel filters leaking air in to the system which will eventually wreck your injectors you might replace the whole housing with a cat filter or racore. anything other than that cheap filter s&s put on
 

Jon Walker

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Problem isn't the filter. My truck ran great until the filter was sucked dry. Had to take the filter off and re prime it with diesel to get it to run again. I think the problem is the fuel pressure regulator or the governor/lift pump.
 

Suprman

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Why did you take the filter off to reprime? You can crack a line at the fuel pump and press the primer 100 times. The primer pumps all go bad though. If it wouldnt prime up from the hand primer its probably sucking air there. Replace the whole housing.
 

snowtrac nome

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on the 3116 there is no need to open a bleeder bolt the hand pump will just push fuel and air right through the system and out through the return as my cat guy said air in the system is your enemy. it will cause failures in the rest of the system I would do some testing and ensure there is not air getting in through the primary filter housing. the lift pump isn't bullet proof but is pretty robust it needs to run dry more than once to kill it unless you have been sucking air for a while.
 

Floridianson

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For quick easy start after filter change yes I believe it does help. Why would you push all the air through the system if you could let it out at the bleeder. Yes most of the military trucks that have a common rail or like the Deuce will expel the air but take advantage of bleeders. It's why they are there.
 
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snowtrac nome

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the bleeder you refer to is likely a test port to hook a gauge to in order to run testing. I do agree that at times its nice not to just bleed a component but it isn't necessary
 

Jon Walker

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Cedar City, Utah
Read the fuel system section of the TM and now I know how to hand pump the fuel system to prime it.

The problem I am having is that the engine is draining the fuel filter of fuel faster then the filter can be filled up. I can get the truck up to 40mph and then it has to idle for 5-10 minutes before it will drive faster then 2mph. I took the filter off to confirm that it was indeed not full of fuel.

I am currently trying to find the part number for the fuel pressure regulator valve so that I can order one from my Cat dealer.
 

coachgeo

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You mentioned crushed fuel filter previously right..... bad Fuel regulator as you propose, does that really fit this symptom? Pretty sure an Air leaks as others mentioned does as would have algae but read back and saw you cleaned everything out and replaced fuel lines. Have heard in other vehicles of a fuel pickup tube having an air leak in it thus when the tank drained down just below the point on the pickup...... the problems started.

Keep us posted.

PS- also the air leak areas already hinted at appear to be known problem areas specific to this truck. They've been shown to be issues in other threads too. The regulator not so much so.... just more .02 to ponder
 
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Suprman

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If the filter is not full of fuel then its full of air which has to be getting in somewhere. The fuel pump is taking in fuel or you wouldnt be able to drive for the short period. Its a sealed system after the pickup tube. If air wasnt getting in somewhere and you had an issue where the truck couldnt lift fuel then it would just die but the filter would still be full of fuel not air. Replace the primer housing.
 

Jon Walker

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Location
Cedar City, Utah
Ordered the part from the cat dealer, also going to double check for air leaks. If I can't get it sorted out this weekend I am going to take it to the Cat dealer since they are 5 miles away from me.

I had a really good large diesel mechanic go over the fuel system and they found no leaks. I don't know if I will be able to see anything that they didn't catch.
 

Jon Walker

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Location
Cedar City, Utah
I found one fitting that had been installed backwards, the O-ring side of the fitting was connected to a flare fitting and the flare side was connected where the oring should be. It is running better but still getting air into the system. I have checked every other fitting I could find and they all seem to be fine. O-rings are intact and connections are tight.
 

coachgeo

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I found one fitting that had been installed ....
Good catch. Have heard of ways to find vacuum leaks like squirting Ether or even Propane at possible leak places and waiting for a few to see if the engine rev's from the extra juice. more on that one here..... Below is some other ideas.


https://www.youtube.com/watch?v=4iaGXUw6yxs now this is interesting....
Apparently on the 3116. appears some CATs them have a screen that sounds like you've not checked yet. Not sure is same screen is on 3126 as well. Seem to recall this has been mentioned in another thread before but don't quote me on that.


https://www.youtube.com/watch?v=3qmnx7xEbQ8

https://www.youtube.com/watch?v=XauPvGUb9SI

https://www.youtube.com/watch?v=zMok2y05jNE

https://www.youtube.com/watch?v=PnU-SY6egr4

https://www.youtube.com/watch?v=DTAUXdFGCcQ
 
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Jon Walker

Member
31
1
6
Location
Cedar City, Utah
Problem Solved! The new replacement fuel tank pickup was bad. I filled the tank all the way up and the problem went away. Somewhere on the lower third of the pickup there has to be a leak. Taking it in to the mechanic to get it replace and a few other minor things fixed up. :) Pretty happy that it was something simple; even though it was already replaced once.
 
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