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1986 F350/6.9 Diesel speeds up on it's own.

J

J.ReinkeFarms

Member
I am having a problem with my 1986 F350. It has the 6.9 with a dealer installed Banks turbo, 4 speed manual. Not the fastest truck in the world but gets me there in style.

Anyway, lately it's been developing a problem. When you are trying to drive the truck a constant speed, say 1500 rpm it will accelerate on it's own to 2000 rpm, and when I say it accelerates on it's own I mean it really moves. Anyone that has driven a 6.9 IDI knows they aren't the fastest thing in the world but it really fogs the black smoke and gets with the program when it happens. If you let off the throttle, ease back into it the thing drives normal. Don't really know what would cause this, I know the pumps on these trucks had that plastic ring that disintegrates and plugs things off for certain years but not sure all the details and not sure if it would cause this. Any help on this would be appreciated.

I tried sending a message to someone on this site about it, but seems for some reason I can't do that.
 
An air leak in the supply side of the fuel system can make a ROOSA pump do some weird things, but most likely the governor in your IP is on it's way out, and getting it fixed before it looses all control and the engine won't idle or shut down would probably be a GOOD thing!
 
Two things... Initially... it sounds like the govenor is going to pieces.... BUT you also have a banks kit. So... first thing is to pull the intake off the turbo and look for oil in the turbo outlet and intake manifold. Check the impellar on the turbo for play. It could be passing oil by the turbo seal and burning the oil if there is a bad turbo bearing.
That said, the govenor is a more likely culprit.

An air leak will make an engine jump when it's not loaded but you usually don't see them sustain that speed increase... and certainly no black smoke associated with it. I'd say it's getting more fuel from somewhere.

Rod
 
RodinNS, thanks for the information on the turbo/oil. That hadn't really crossed my mind before. Hopefully this weekend I can get a chance to start checking things out. Truck only moves about once a month so I'm not in a hurry. I'll post when I find the problem.

Thanks again.
 
Sounds typical for the plastic ring in the governor weight cage coming apart . . . BUT . . .
your truck shouldn't have it. The plastic ring was discontinued by model year 1985 for Ford-IH and all the GMs. They all got swithed to the EID governor-plate (elastomer insert drive). Also, all pump repaired from older trucks were supposed to be updated to it.

Is your engine and pump original, or could it be older then 86?
 
That is a classic symptom of a diesel starving for fuel. They "surge" as the governor tries to correct.

Plugged filter (most common), air getting in the fuel, etc. Something is triggering that governor.

Allan
 
Check that rubber hose on the upstream side of the fuel pump.

They had a nasty habit of collapsing and shutting down the fuel supply.

Allan
 
Check that rubber hose on the upstream side of the fuel pump.

They had a nasty habit of collapsing and shutting down the fuel supply.

Allan
 
Thanks for the information. The engine is supposed to be the original one in the truck, BUT, it is 24 years old and a lot of time has passed since it left the factory.

I bought the truck from what was supposed to be the original owner, and it is supposed to have only 86,000 original miles on it. But who really knows. I picked it up because the body was in good shape and I like that body style for some reason.

I'm making a list of things to check over, will probably get to it this weekend I hope.
 
Thanks again to all of those that had input on my little problem, I did get a chance to check things out over the weekend and I believe I had two things working against me.

1st - The fuel lines were in pretty nasty shape and with a little messing around with clear fuel line found out that it did have air in the fuel, and quite a bit of it. Seems strange that it wasn't leaking when not running but maybe it was that much higher than the tank.

2nd - The turbo is spewing oil into the intake. Not a whole lot but it has some oil smearing around the whole thing then a clean spot where new oil has been washing the slime away.

So, as it sits right now it does run smoother and have more power. I figure I should swap that turbo out, gives me an excuse to get something bigger and newer....... Or just rebuild that one because it's just a 6.9 and does everything I want it to currently. Yup, the cheap guy in me says rebuild.
 
If the turbo is pushing oil DO NOT WAIT. Change it now or don't use it. Many an engine has 'run away' on oil drawn through the turbo... and been completly destroyed. Fix it or park it until you can fix it...

Rod
 
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