shutdown problems
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Senior User
Joined: Mar 2002
Posts: 147
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From: USA
shutdown problems
Hey guys. I have a 78 f100 with a 300 six, and sometimes when I turn the ignition off, the engine doesn't shutdown right away. It sputters and this and that and then finally quites. Anybody know what the problem is? My knowledge of how a carbed engine works exactly is very limited, so any help would be great. Thanks.
Posting Guru
Joined: Jun 2002
Posts: 1,288
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From: redding U.S.A.
shutdown problems
thats called dieseling.
Turning the ignition off stops the sparks from firing. Hot carbon deposits can still ignite the fuel mixture though, and sometimes when the spark doesn't go, they'll ignite it and keep the engine sputtering.
Try running some carb cleaner through the engine. You probably have a bit of carbon buildup.
I've hear that this may have something to do with ignition timing, but i couldn't see why...
Turning the ignition off stops the sparks from firing. Hot carbon deposits can still ignite the fuel mixture though, and sometimes when the spark doesn't go, they'll ignite it and keep the engine sputtering.
Try running some carb cleaner through the engine. You probably have a bit of carbon buildup.
I've hear that this may have something to do with ignition timing, but i couldn't see why...
Posting Guru
Joined: Jun 2002
Posts: 1,288
Likes: 1
From: redding U.S.A.
shutdown problems
I was also just reading a thread about spraying some water down the intake... its an old method and it actually works pretty damn good for some people. Its really cheap too 
Anywho, If the carb cleaner doesn't work, i would try spraying some water out of an old spray bottle or something down the carb after the engine is heated up. Rev up the engine and spray a bunch more down there, it should stumble a bit, and hopefully clean out some carbon deposits.
If that doesn't work, i'm really not too sure what to do. Hopefully one of these methods will help you out though.
Anywho, If the carb cleaner doesn't work, i would try spraying some water out of an old spray bottle or something down the carb after the engine is heated up. Rev up the engine and spray a bunch more down there, it should stumble a bit, and hopefully clean out some carbon deposits.
If that doesn't work, i'm really not too sure what to do. Hopefully one of these methods will help you out though.
Posting Guru
Joined: Dec 2002
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From: peoria, az
shutdown problems
I usually clean out the carbon by running down the freeway in 2nd gear for about 30 sec's and they usually blow a nice cloud out the back after that. Timing causes dieseling too if it is too far advanced. It gets your temp up too high. Even backing off 2-4 degrees can make a difference.
Senior User
Joined: Dec 2002
Posts: 112
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From: Newark,DE
shutdown problems
yea i have the same problem. mine diesels when i shut it down.
till i feel like adjusting the timing, i just keep it in first shut of the ignition and let the clutch out a bit and it shuts right off...i hat epulling up to the supermarket and having that thing diesel!
till i feel like adjusting the timing, i just keep it in first shut of the ignition and let the clutch out a bit and it shuts right off...i hat epulling up to the supermarket and having that thing diesel!
Senior User
Joined: Sep 2003
Posts: 497
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From: Houston TX
shutdown problems
I use ATF trickled in the carb while revving to clean carbed engines. Follow it up by a shot of carb cleaner to melt some cheese in the carb. Then take it out and blast it out on the road.
For FI, I often use a mix of ATF, injector cleaner, and carb cleaner fed directly into the throttle body vacuum port while revving. FI engines usually get worse than carbed engines. A bad case, I'll get the engine good and hot, and then spraya bunch of cleaner mix into the TB, and shut it off and let it sit for an hour. May have to repeat until clean. Usually will add some techron to the gas tank too. MK
For FI, I often use a mix of ATF, injector cleaner, and carb cleaner fed directly into the throttle body vacuum port while revving. FI engines usually get worse than carbed engines. A bad case, I'll get the engine good and hot, and then spraya bunch of cleaner mix into the TB, and shut it off and let it sit for an hour. May have to repeat until clean. Usually will add some techron to the gas tank too. MK
