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runaway then wont start

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Jkinney
Join Date: Nov 2003
Posts: 21 maine
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2003-11-16          68928

I have a 7274 I use commercially with 1600 hrs I lit her off today to do a few chores for myself, around the yard.
She started to run away while still in the barn, I shut her down with the key,restarted and let her Idle at 1200 backed her out of the barn and let her run for 15 min. I then got on her to move some soil and she ran away I turned the key off and she continued to run away I jumped off the seat and turned the fuel off and killed the engine. Turned the fuel back on, lit her off and she ran away again, again had to shut the fuel off to kill her. I tried to start her again and she wont start. I have cleaned the bowl primed the fuel system. no Luck I have bled the fuel system many times on this tractor with no problems. A diesel mech I know said the selenoid on the fuel pump might be bad. I can hear it click (lightly) when I try to start it, it clicks loudly when I turn the key off. any suggestions?


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loghouse95
Join Date: Jul 2003
Posts: 87 missouri
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2003-11-16          68930

Sounds like you might have a broken governer spring in the injector pump also Have you checked the governer on the throttle ....

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jkinney
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2003-11-16          68932

Checked the throtle, all springs, cables attached and operating the selenoid my friend refered to is on the injection pump. Im gona hate to load this on the trailer and haul it to the dealer. ....

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Art White
Join Date: Jan 2000
Posts: 6898 Waterville New York
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2003-11-17          68946

Often when a diesel is just about out of fuel it will run up on rpm's. I would think that if your shutoff was about to fail that might be the culprit as it might have just about closed the fuel off before but not quite. Now it might have closed it off well. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-11-17          68949

I'd guess that the mechanic was saying that a faulty fuel solenoid may cause the failure to shut down when the key was turned off but not the run away problem.

If 7274's use a jerk pump type system, the run away problem sounds like a governor or control rod problem. Many pumps and governors are the same unit and these units aren't serviceable except by trained techs. That sort of limits self-help and do it yourself repair.

You might check if the throttle lever moves when the hand throttle is changed and if the throttle lever operation is smooth and free throughout its range when the governor linkage is disconnected. However, chances are that knowing what the problem is still going to take a trip to the dealer for a new pump assembly. There is some potential for self-help. For example, there's a small chance that some lube on the counter-weight pivot points or replacement of broken internal governor springs fix it but you'd need a manual to know.

If the pump is shot there's a chance that a diesel shop may not need the whole tractor to repair or replace a pump as long as you were willing to do removal and installation. Installation would require setting the timing. Anyway that's another possibility for some self-help. I guess there's no chance the tractor was operated around propane or natural gas leaks when it ran away. That'd be a rare event but taking in propane would cause a run away and even shutting off the tank valve may not shut it down. ....

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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2003-11-17          68955

From your description of what happens the mechanic and Art maybe right. If the diesel is in starved fuel mode then the diesel will often run up. Normally this is a run up and then the motor quits as it runs out of fuel.

If the fuel solenoid is not closing properly and possibly leaking air in then the run away condition could persist. I am not sure if it can damage the pump?

As the problem is related to the shut down. The shut off solenoid is the first place I would look. The relay connecting the solenoid to the switch is the second area. ....

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kwschumm
Join Date: Feb 2003
Posts: 5764 NW Oregon
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2003-11-17          68965

I'm a newbie to diesel engines and I don't understand how a diesel engine can runaway if the fuel is being starved. It seems to me that when fuel is starved the engine will run lean and quit. What phenomenon causes the engine speed to run up? ....

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Art White
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2003-11-17          68971

To lean out any engine the first thing that happens is rpm gain. ....

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kwschumm
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2003-11-17          68973

Thanks Art, I did not know that. I knew that lean mixtures resulted in hot running, burning valves and damaging pistons but I didn't know about the RPM gain. ....

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jkinney
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2003-11-17          68978

The tractor went to the dealer today, FM Abbotts in Waterboro Maine. He spent about 15 minutes looking at it and is not sure of the problem. Regardless of a runaway he does not yet understand why she would not shut down when I turned the key off because he states the key shuts off the air valve.
He thought he will have an answer in a couple days.
His first check will be the selenoid. ....

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Art White
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2003-11-17          68982

From time to time we do have problems with those shut-offs. Never seen one make or style that has it happen more than the other, just happens. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-11-18          68998

I'll be interested hearing the outcome. I think of a run away diesel as one that goes to max no-load rpm or beyond and stays there irrespective of hand throttle position. I didn't think fuel starvation would do that but maybe 'run away' means something else.

While there are a few things on a governor/pump that would switch operation to fast idle (max no-load) there's still the problem of why it wouldn't shut down or start again so that explanation would have to be have separate problems in both the pump/governor and the solenoid. Separate malfunctions that produce one problem is a stretch.

The problem with a solenoid explanation is that it has to both fail to open completely and then fail to release when the key is off. I read Art's comment after posting mine and now I'm thinking that a solenoid that is weak and sticks at just the right place and then won't release and finally sticks in a fuel off position might be a more reasonable explanation--at least it's all the same malfunction. If the tractor was stuck at fast idle I'm still not sure how likely a fuel starvation explanation is but maybe I'll learn something. ....

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jkinney
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2003-11-19          69082

I hope everyone understands that I shut off the fuel valve because there was no other way to stop the engine as it raced past 2800 rpm in a no load situation. In the Coast Guard I ran diesel small boats for 24years. Of those 24 I had two run aways both were jimmy 671's

The dealer took my injection pump off the timing rack was stuck in the closed position and it did not want to slide back and forward. The pump was sent out to a shop for rebuild. The dealer feels something else is broke in there but does not know what. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-11-20          69154

Thanks for getting back. Yes, that's how I understood the problem and what you did. In my mind it was very likely the pump/governor that caused part of the problem.

There's still the question of why it wouldn't shut down with the key. My understanding of a conventional solenoid/relay system is that it takes power to hold the solenoid open. Without power the solenoid closes to shut off the fuel. Maybe the system works differently, or maybe fuel flow at full throttle was enough to keep it from closing. I wouldn't think it should work that way. I think they're supposed to act as safety features to prevent what actually happened.

One thing I'd do is get an explanation from the mechanic for why it didn't shut down. If there isn't a good one and solenoids tend to go bad around 1600 hours I might replace it on principal. It's always a serious stretch explaining a problem by coincidental malfunctions in independent components but maybe that's what happened. If I hadn't thought that 'run away' meant sticking at fast idle I'd probably guess the solenoid because at least you can get an explanation for the whole problem in one component. ....

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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2003-11-20          69168

I think some machine work a little differently, when you turn the key off the solenoid then moves and causes the fuel to dump back into the return line.

They do it that way so that they can utilize the existing mechanical kill system just by adding a solenoid to activate it.

Best of luck. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-11-21          69218

Thanks for the detail Murf! Somehow it never seemed quite right that they'd be simple line shut-offs. A line shut-off would cavitate the pump each time the engine shut down unless there was something to change the pump to no-delivery at the same time. It'll still be interesting to hear why the solenoid didn't shut down the engine when the key was turned off. ....

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jkinney
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2003-11-21          69295

The dealer has told me the pump is repaired and is being shipped back via brown to his shop. Sounds like I will have my tractor home sometime tuesday I will pop the question of why the key did not kill it.

I like my tractor alot I just wish bolts, nuts etc did not loosen up or fall out like they do. ....

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jkinney
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2003-11-25          69581

I got my tractor back last night 527.00 for the injector pump to be rebuilt. 3 hrs from the dealer for his mechanics time. The pump was a total rebuild. The rack had stuck in the open position and the selenoid could not pull it back. However when I did shut the fuel valve off, The lack of fuel some how pulled it to the closed position. I guess it was just worn out and was sticking. Im greatfull it happened at home, home is where I rarely use my tractor. ....

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TomG
Join Date: Feb 2002
Posts: 5406 Upper Ottawa Valley
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2003-11-25          69625

Thanks and it's good to have the tractor back I'll bet!

I've got the idea now, the solenoid set the pump to no-delivery, which means that it overrides the governor/throttle, but it couldn't if the pump was stuck. That idea was brought out in one of Murf's comments. Whether the solenoid also acts as a line shut off I don't know.

Shutting off the tank valve would have cavitated the pump and caused max suction side vacuum. That's what likely moved the pump to no delivery where it stuck again. I'm happy I've got an explanation good enough for my purposes and I hope we all learned something. Sorry about the repair bill though. ....

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