Archived ///// Flirting with diesel run away? ////

[AndrewKing]

HI All,

My 1997 Diesel Truck (Freightliner MT 45 step van...5.9 cummins, P pump, 4 sp allison Auto...300K miles, stock, nothing done except oil and fuel filter changes) had something happen recently that scares me a bit.

The other day a friend of mine was sitting in my truck (engine off) in the drivers seat....When I got back to drive, she moved over and I started the truck as usual but much to my surprise, the engine roared (high rpm)....Immediately I shut the truck off.

I cycled the pedal thinking maybe she had pushed the pedal and a linkage may have stuck.

I cranked the truck again and after a very brief higher than normal start up rpm the engine went to a more normal RPM.

I drove as usual....and have driven for days since this one episode.

Several days later (today...just now as a matter of fact)....I was driving down the road....foot off the accelerator coasting and it felt as though the truck was not slowing down as normal (going up a slight hill to my house).

I applied the brakes and could feel the truck trying to maintain speed (no cruise control just as though a foot was still on the accelerator pushing the pedal a bit).

Luckily the engine "pusH" could be overcome by the brakes....

I stopped the truck and put it in neutral (on the 4 sp Allsion auto in the truck there is no park position)....The engine roared...I switched off the truck and the engine shut off.

I popped the hood (well rather flipped it up and proped it open)....and checked the linkages....everything seemed free and the travel seemed fine.

So what is the problem?.....My guess is if everything outside (i.e. linkages) seems fine than it has to be an internal (aarg) issue?

I did think about the air filter that I have not changed in awhile (looks relatively clean but hard to see since it is in a canister but never really had black smoke except maybe a little if suddenly accelerating hard)....could a restricted air filter somehow cause oil to be sucked in somehow causing more RPM?...On the other hand if that were the case I would not have been able to shut the truck off with the key right?

I did several start / stop cycles (after cycling the linkage to free it up in case of sticking) but it still roars every time

Its my work truck so hopefully (with some help here), I can get it back on the road......I don't want to use it if it will run away...

Thanks in advance for any and all help.

Andrew

 

[mwilson]

Sounds like one of the plungers in the pump is sticking.....Seems to me one of Seth's previous 12 valves did the same thing. I don't remember the cure.

I will stroll out in a bit and ask.

 

[AndrewKing]

HI,

Thanks for the follow up....let me know what you find out.

Just a few minutes ago I went out to crank the truck up...I thought maybe since the engine is now cool maybe that could change something....Unfortunately, the same thing...Engine roared.....I started and stopped 2 times with the same results.....seems like whatever happened is here to stay until a fix is found.

Andrew

 

[RKula]

I would try disconnecting the vacuum hose to the cruise control servo (Plug the end of the hose that comes from the vacuum supply) and see if that helps. Something could be messed up there.

Bob

 

[AndrewKing]

HI Bob,

Thanks for the suggestion but the vehicle is not equipped with cruise control.

The best way for me to explain what the vehicle is doing is to pretend as though you were holding your foot on the accelerator pedal a bit and not letting off at startup through shutdown.... (fortunately only a moderate amount not wide open).

Andrew

 

[Tinman]

I doubt your looking at a near run away. If it were trying to run away, then shutting it down would not turn it off. Probably in the pump.

 

[mwilson]

Check for missing throttle springs, very common.

I will post more when I get to a computer. This was a Fed Ex unit as I recall. Do you have the last 6 of the truck vin at hand? If not the engine serial will get me to the chassis as long as it is the original engine.

 

[NIsaacs]

Any chance gas was put in the tank or a bottle of "Heat"?

Nick