Engine keeps running after ignition shutoff
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Junior User
Joined: Sep 2012
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Engine keeps running after ignition shutoff
Hey everyone, I'm looking for some ideas on where to start with this issue. I'm running a '79 F150 with an I6. The issue is that when the engine is hot (after driving for 15 minutes or so) when I just the ignition off the engine keeps wanting to run. It doesn't make pretty sounds, it is kind of a loping and banging for a few seconds before it will die. Usually if I've driven for any significant amount of time it'll eventually stop, shudder, and make a wheezing sound.
Now, I'm pretty sure its not an issue with the vacuum as I've replaced most of the lines and made sure I'm not losing vacuum all over the place. I don't think it's electrical because it only happens when the engine is hot. This leaves me with thinking it has to do with my carb (of which I've been hesitant to mess with yet). So, any ideas or thoughts on where to start would be appreciated.
On a side note i've got an offy intake, headers, and a 500cfm carb all waiting to get put in. Just haven't had the time to really open everything up.
Now, I'm pretty sure its not an issue with the vacuum as I've replaced most of the lines and made sure I'm not losing vacuum all over the place. I don't think it's electrical because it only happens when the engine is hot. This leaves me with thinking it has to do with my carb (of which I've been hesitant to mess with yet). So, any ideas or thoughts on where to start would be appreciated.
On a side note i've got an offy intake, headers, and a 500cfm carb all waiting to get put in. Just haven't had the time to really open everything up.
Freshman User
Joined: Dec 2012
Posts: 32
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From: Saint Paul, Mn
This is called dieseling and is not very good, as you can maybe tell from the sounds it makes. Basically whats happening is the cylinders are getting really hot inside, which lets it keep firing without spark, much like a diesel engine needs no spark plugs. Im afraid to tell you that you are more than likely going to need to adjust the carb because it is running to rich or lean. If it keeps going this way you will build up carbon and that could also be a source of ignition. Hope this helps.
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Junior User
Joined: Sep 2012
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Thanks, guess I'll pull the carb out and clean and rebuild it this weekend. I have a bad feeling it might be related to the EGR which only makes me want to put the new intake manifold and carb in there sooner to eliminate it.
If it is just running too rich, that would make some sense since I'm only getting about 9 mpg at the moment.
If it is just running too rich, that would make some sense since I'm only getting about 9 mpg at the moment.
Freshman User
Joined: Dec 2012
Posts: 32
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From: Saint Paul, Mn
Another thing with these carbs is sometimes the choke will stick or stay shut without enough heat, which happened to me making a richer mixture than normal. I thought i fixed it but then it just stayed shut and stuck a screwdriver in it, works fine now 
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Senior User
Joined: Jul 2011
Posts: 151
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From: Nanaimo BC
Slow down. Don't touch that carb yet. LOL!
Your idle is too high. Slow it down. Idle adjustment screw is on drivers side.
If that doesn't slow it down then hook your vacuum advance to a manifold source. Motor will speed up cause of more timing then turn idle down.
Your idle is too high. Slow it down. Idle adjustment screw is on drivers side.
If that doesn't slow it down then hook your vacuum advance to a manifold source. Motor will speed up cause of more timing then turn idle down.
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Junior User
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Thanks for the info, and this might seem like a bit of a new question because I'm still new to carbs if you haven't guessed. If I'm just adjusting the fast idle, that won't help if I'm running rich all the time right?
Otherwise I guess if the choke is sticking open, you said you just stuck a screwdriver in there? I'm not even sure I understand what good that would do short of a temp fix. Maybe it just needs cleaning out?
Heh the carb disassembly diagram still has me a bit scared to really open it up and get in there.
Otherwise I guess if the choke is sticking open, you said you just stuck a screwdriver in there? I'm not even sure I understand what good that would do short of a temp fix. Maybe it just needs cleaning out?
Heh the carb disassembly diagram still has me a bit scared to really open it up and get in there.
Tuned
Joined: Nov 2012
Posts: 253
Likes: 51
From: billings mt
its not the "fast idle" you want to adjust. that would be associated with the choke, usually the opposite side of the carb. turn your main idle down some, and maybe retard your timing a couple degrees. no more dieseling
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Elder User
Joined: Jul 2003
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[QUOTE=evilci;
On a side note i've got an offy intake, headers, and a 500cfm carb all waiting to get put in. Just haven't had the time to really open everything up.[/QUOTE]
evilci,
IMHO, I suggest\strongly recommend you install all of the new hotrod parts that you have, then get back with us if you have any issues. Making them all work together properly can sometimes be an art. Some lucky people just bolt em on and go..LOL
On a side note i've got an offy intake, headers, and a 500cfm carb all waiting to get put in. Just haven't had the time to really open everything up.[/QUOTE]
evilci,
IMHO, I suggest\strongly recommend you install all of the new hotrod parts that you have, then get back with us if you have any issues. Making them all work together properly can sometimes be an art. Some lucky people just bolt em on and go..LOL
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New User
Joined: Dec 2012
Posts: 12
Likes: 1
From: North Dakota
Yes this. Start with idle speed. I had same symptoms on a 250 chevy. Turned out one of the return springs on the carb was in the wrong place. If it still does it then retard the timing a tad bit.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
High idle speed can exacerbate the underlying issue, but the real problem is heightened combustion chamber temperatures because of a lean, overly-advanced setup. My guess is your EGR system is long gone (engines that are factory-equipped with EGR are jetted lean and use a steepened timing curve to account for the different combustion mixture; with the system removed the resulting setup often causes the engine to ping and diesel). Also, at one time your engine likely had an idle stop solenoid to help close the throttle plates at shut-off, which may have been removed too.
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Junior User
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fmc, thanks for the info. Luckily having to mess with the idle and timing just motivated me to take the leap and start with my upgrades. No sense in doing all that tinkering and having to do it all over again in a month or 2. Started another thread with my progress so far. New intake manifold, headers, 500cfm carb and such. And saying bye-bye to the EGR so thats not a problem anymore.
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