Need to find out whats wrong with my M816. It has developed this problem slowly over the course of a few months. Basically, if you let the truck idle for a while (ie, when using the crane), when you go to accelerate again the engine will want to run away for a few seconds. At first it was only if it idled for an excessive amount of time, but now even 5 minutes idling and the engine will want to drive itself for a couple seconds. Doesn't sound healthy when it does, sounds like one cylinder is doing the running away. Makes plenty of white/grey smoke when it happens.
Engine seems to run good, it gets the heavy truck down the road alright. Only real "issue" is that it sounds a little noisy, like if the valves were out of adjustment.
I have worked on my fair share of light/medium duty diesels but I have NO experience with engines like the 250.
If anyone has any suggestions, or could get me pointed in the right direction it would be much appreciated!
What RPM's does the engine put out when it "runs away"? If it is just going up on the governor ( like around 2300 rpm I think), then it might be your IP or governor not working properly.
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Area52's answer to most questions:
The O-rings in the fuel selector switch are notorious for drying out and allowing air to be sucked into the system.
That would be my first suspect. I had that problem on my 816 and had to bypass it.
Damaged O-rings and "runoff" situations have also been caused by "magic" fuel containing paint thinner...or so I've heard!
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White smoke usually means an injection timing issue, i.e. air introduced into the fuel, air compresses, fuel don't. Timing can't slip on one of these, it's done with a hefty cam key and shims under the cam boxes. When an injector is removed from an 855 and another installed, at start up it had a pretty good fuel knock and lets out a good size cloud of grey smoke, that smoke isn't a timing issue, just a case of waayy too much fuel in the cylinder that isn't atomized. You might have a split cup on an injector. That would give the engine a funny sound like maybe a marble in one cylinder, the heavy whitish grey smoke and the RPM hanging up after idle. Split cups happen from incorrect adjustment, fuel tanks higher than the cylinder heads or restricted return lines. Try running the engine out of and into a bucket of fuel and see if it runs the same, that will eliminate the fuel lines and let you know if you need to check the chassis or if it is an engine issue.
Also, these engines have little holes in the heads, under the rocker boxes that run into the intake. If you have too much oil in the engine or there is an issue of the oil not getting off the head fast enough, like a broken rocker shaft, it will suck the oil into the hole and the engine will uncontrollably run away. very uncommon, but I have seen it. Since your engine runs OK going down the raod though, I don't think this an issue.
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Sixspeed, like the others said, maybe your oil level is too high and oil is being sucked out of the crankcase, effectively giving it more fuel.??
After reading wreckermans horror story of his runaway, i keep the air cleaner mushroom cover loose and a board by the drivers seat to block off the air......just in case!!
Also, when offroading my 818 and creeping down a steep hill mine will tend to start accelerating on its own, then i blip the throttle and behaves again, not sure what thats about, throttle linkage?
Runaway Wrecker
