Hypothetical Question
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Smokin
Joined: Jun 2006
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Hypothetical Question
Ok - So a question the pops and I were discussing last night...
we've heard stories about diesels that won't shut off...as you guys know a diesel will run forever as long as they have air and fuel. As I understand it, all a PSD does is shut off the fuel when you turn the key off. What happens if that fuel shutoff valve malfunctions, and the truck won't shut off? What would be the best way to get the truck to turn off, especially if you were on the road somewhere and had to be able to get it started again?
My dad has a Cummins which he claims has a mechanical fuel pump, so he could just disconnect his fuel line, I think. I'm wondering if I could try and do the same? Sort of a strange quesiton, but i'm curious because I've heard about this sort of thing happening to people. I think starving the 7.3L of fuel would be the wrong way to go about doing it.
Just curious what the experts thought...
we've heard stories about diesels that won't shut off...as you guys know a diesel will run forever as long as they have air and fuel. As I understand it, all a PSD does is shut off the fuel when you turn the key off. What happens if that fuel shutoff valve malfunctions, and the truck won't shut off? What would be the best way to get the truck to turn off, especially if you were on the road somewhere and had to be able to get it started again?
My dad has a Cummins which he claims has a mechanical fuel pump, so he could just disconnect his fuel line, I think. I'm wondering if I could try and do the same? Sort of a strange quesiton, but i'm curious because I've heard about this sort of thing happening to people. I think starving the 7.3L of fuel would be the wrong way to go about doing it.
Just curious what the experts thought...
Senior User
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quickest way to shut off a runaway is to block the intake air. Same should apply to a simple quietly running diesel that won't shut off. Other way would be to pull IDM fuse if you know which one it is or wires to whatever to keep injectors from firing, since they are electronically solonoid actuated. Actually I think the key off should be shutting off these electrical signals to the injectors anyway though.
Postmaster
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ANY compression ignition engine will run on air and the motors own oil alone. It doesn't matter what the type of injection is mechanical or electrical it can run on just air by using oil from the motor itself. Usally this happens on high modified trucks though. You can stop giving it fuel but lets say your turbo seal went out and now the oil is going into the intake, it will burn, causing a potential runaway.
The only way to stop it is to to block off the intake so it can no longer get air.
Im pretty sure the powerstroke stops by not allowing the injectors to fire no electrical charge to the injector = no fuel. Disconnecting the fuel line will start to mess things up, it can damage fuel pumps, injectors. The best way to stop it would be to stop giving it air.
The only way to stop it is to to block off the intake so it can no longer get air.
Im pretty sure the powerstroke stops by not allowing the injectors to fire no electrical charge to the injector = no fuel. Disconnecting the fuel line will start to mess things up, it can damage fuel pumps, injectors. The best way to stop it would be to stop giving it air.
Last edited by John311t; May 27, 2007 at 01:24 PM.
Posting Guru
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From: Plainfield, IL
Originally Posted by Benny2002
I have heard that the best way to shot off a "runaway" diesel is to cough it out, buy covering the intake for it to not get enough air.
More Turbo
Joined: Feb 2004
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From: Findlay, Il
Pull the fuse as previously mentioned or pull battery cables, need electricity to run (the computer age).
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No they dont need electricity to run, they need electricity to run on fuel. These motors can run off their own oil in the pan, you mix that with air and it will keep running. If it wont shut off on account of fuel, then yes stopping the running by pulling the fuse. Im talking about a runaway when oil is involved like stated a turbo that went and it dumping oil into the intake, the motor will run until there is no oil.
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Senior User
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From: Okeechobee,FL
If it's getting fuel/oil in the chamber,whether in the intake or past the rings or turbo,IT WILL RUN,,,Electroinic or not.I watched a detoit blow all to bits buy sucking oil by the rings.
all we could do was run,,,,,It went balistic.
Tom
all we could do was run,,,,,It went balistic.
Tom
Snowboard season cometh..
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From: Gulf Coast of Florida
So then the question becomes "How best to block the air?" Just off the top of my head, I'd say pulling the tube off the turbo inlet and having something sturdy & flat to seal up against it would thoroughly choke it and rather quickly.
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From: Okeechobee,FL
Originally Posted by papadelogan
So then the question becomes "How best to block the air?" Just off the top of my head, I'd say pulling the tube off the turbo inlet and having something sturdy & flat to seal up against it would thoroughly choke it and rather quickly.
The back side of a floor mat ,after pulling off the 6637.
Tom
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From: Fulltime RVer
I've never heard of a PSD not shutting off when you turn the key to off!!! The PCM will even shut off the engine with the key turned on, if the RPM drops below some magic #, which I can't remember exactly now, but it's not much lower than the typical 600 RPM idle. I've been told it's designed to do this because there's no crank sensor, and the signal from the CPS has a X2 less resolution, and is too inaccurate at lower RPM to provide reliable timing, and firing an injector at the wrong time can damage the engine, so the PCM just shuts it off as a safety precaution.
I came across this info over 8 years ago when I was having problems with the engine stalling just after installing my exhaust brake. It turned out that if I left the exhaust brake on all the way to a stop, the TC clutch would disengage and the RPM would suddenly drop to idle condition, and the extra load of the exhaust brake would drag the RPM just low enough that the PCM would shut off the engine. The solution was to disengage the exhaust brake above 15 mph because with the TC clutch engaged, the RPM is kept well above idle.
I came across this info over 8 years ago when I was having problems with the engine stalling just after installing my exhaust brake. It turned out that if I left the exhaust brake on all the way to a stop, the TC clutch would disengage and the RPM would suddenly drop to idle condition, and the extra load of the exhaust brake would drag the RPM just low enough that the PCM would shut off the engine. The solution was to disengage the exhaust brake above 15 mph because with the TC clutch engaged, the RPM is kept well above idle.