83 F60 very intermittently dies while idling……kind of.

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So here’s the issue, and why I think it could be ignition related. The problem I’m having is it’s done it twice now, both times at stop lights in traffic, and I can’t duplicate it idling in the garage for correct diagnosis. Hoping someone will chime in and be like “oh ya, mine was doing exactly the same thing, here’s what my issue was…”.

83 FJ60 2F, factory carb, smog intact. 130k.
I’ve owned the truck for 4 years. 97.5% of the time I’ve owned it it’s run flawlessly. After 15-20 minutes of 50-60mph driving, I’ll come to a stop light. It doesn’t die while slowing down, or even when I first stop. But at some point while I’m waiting on the light, it’ll die…sort of. It will just essentially start dieseling. Throttle input does absolutely nothing, shutting the key off does nothing. It’ll continue to diesel. I’ll put it in 4th and let the clutch out to kill it. It will restart right away and may run perfectly or may just just do the weird diesel limbo thing. I popped the hood (at the intersection), disconnected and reconnected the fuel cut solenoid, disconnected and reconnected the igniter connector, and made sure the distributor connector hadn’t come loose. Fired right up and drives completely normal. Several drives later and it’s running fine without a single issue. Then, same deal. Cruising along and come to a light, boom, dieseling with no response to throttle. Hop out at an intersection and make the same checks. Fires up and is fine.
I’ve tried disconnecting things in the garage to duplicate a similar response. Disconnecting the fuel cut solenoid will make it idle like garbage, but it will respond to throttle input and rev normally. I took the coil and ignitor off and will bench test them at work. Fuel filter is a year old, fuel pump (oem) is 2 years old. Cap, rotor, and plugs (OEM) are 2 years old. Base timing is set to about 10° BTDC.
I’ve pulled the primary and secondary main and slow jets out to verify no restrictions. Accelerator pump works normally. EGR is bypassed. I have approx 18Hg of vacuum at idle (sea level). The ONLY thing I’ve done to even remotely duplicate the issue is disconnect the igniter connector in the garage. It will die, kinda diesel a bit and fizzle out, much faster than it does while it’s actually acting up. Anyone have any suggestions or ideas on what would cause that?

Edit: I have a sniper on order from Mosley Motors but they’re back ordered until mid august-ish. Plus if it’s ignition related, fuel injection isn’t going to fix it anyways.
 
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OSS

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The very first thing to do is install a vacuum gauge in the cab that you can see while driving, like the example shown below.

Keep an eye on the vacuum gauge the next time it starts to sputter at idle. If the vacuum goes really low while the engine is gasping it’s last breath - there’s a vacuum leak opening up somewhere.

Rule out that the problem isn’t vacuum related. If it’s not, suspect ignition. But typically ignition malfunction can happen at any RPM, not just at idle after a highway run.

An igniter malfunction (I’ve heard) is a go/no go affair. Either the engine will run or it won’t.

Dieseling at an unplanned shutdown seems like the engine ignition is still active (fuel cut solenoid still open) but the engine simply ran out of fuel.

Something should happen if frantically pumping the gas pedal before the engine conks out. Since you say nothing happens, that’s hinting towards the carburetor is completely dry.

Take a look in the sight glass of the carb (until you get the sniper) after an unexpected shutdown and see if the float bowl is dry.

78761539-936C-4C97-8B1C-6A0BE7972911.jpeg
 
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The very first thing to do is install a vacuum gauge in the cab that you can see while driving, like the example shown below.

Keep an eye on the vacuum gauge the next time it starts to sputter at idle. If the vacuum goes really low while the engine is gasping it’s last breath - there’s a vacuum leak opening up somewhere.

Rule out that the problem isn’t vacuum related. If it’s not, suspect ignition. But typically ignition malfunction can happen at any RPM, not just at idle after a highway run.

An igniter malfunction (I’ve heard) is a go/no go affair. Either the engine will run or it won’t.

Dieseling at an unplanned shutdown seems like the engine ignition is still active (fuel cut solenoid still open) but the engine simply ran out of fuel.

Something should happen if frantically pumping the gas pedal before the engine conks out. Since you say nothing happens, that’s hinting towards the carburetor is completely dry.

Take a look in the sight glass of the carb (until you get the sniper) after an unexpected shutdown and see if the float bowl is dry.

View attachment 3047065
Good points. When I say it starts right up, it starts literally right back up with a half a crank of the motor. I’d think if the carb were dry it would crank a bit.
I’ve also been thinking maybe it isn’t ignition related. I had one occurrence where I had to put it in 4th to kill it, and it started right back up but did the same thing, immediately from the get go. I could see ignition cutting out while running and it dieseling on its own without spark, but there’s no way it would restart with the same symptoms (or period) without spark. I can say with certainty there was fuel in the filter, but I can’t say for sure if the sight glass had visible fuel. Kind of a bummer it happens so infrequently and at the most inopportune time. Like I wish it would do it as I’m pulling into my subdivision or something, where I can safely inspect some things. Not in the middle of an intersection with a line of cars behind me.
 
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OSS

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Yes, infrequent random shutdowns that can’t be duplicated easily can be real head scratchers. Can be tricky to find the cause.
 

klinetime574

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You didn’t mention the spark plug wires. Have they been replaced? How does the distributor look under the cap?

Dieseling is normally something that happens when you shut the ignition off and the engine continues to “run” which is why I’d say you suspect ignition related. A misfire seems more likely but the engine would actually still be running and respond to the gas pedal. I’m sure you know and thought of this, but I’m writing and thinking. I’d have to agree with @OSS that it doesn’t have enough fuel when feathering the pedal during these events.

When you say 18” at idle is that a steady reading? Thinking valve adjustment would be worth a check, if not steady.

I’m just as perplexed as you are. Just some thoughts so we can figure this out with ya.

EDIT - I will add that my engine would bog out and die intermittently after coming to a stop. Ran fine otherwise. My float had a pinhole in it and filled with gas which tricked the carb into thinking it didn’t have enough fuel. This carried on for longer than I should admit until the float no longer floated and gas was literally dripping on the ground one day. Replaced the float and moved on with life. Now I’ve got two mostly complete carburetors in the garage in a box and Sniper EFI happily sitting on the intake. All that to say. Could the opposite be happening to you? i.e. Float level too high.
 
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You didn’t mention the spark plug wires. Have they been replaced? How does the distributor look under the cap?

Dieseling is normally something that happens when you shut the ignition off and the engine continues to “run” which is why I’d say you suspect ignition related. A misfire seems more likely but the engine would actually still be running and respond to the gas pedal. I’m sure you know and thought of this, but I’m writing and thinking. I’d have to agree with @OSS that it doesn’t have enough fuel when feathering the pedal during these events.

When you say 18” at idle is that a steady reading? Thinking valve adjustment would be worth a check, if not steady.

I’m just as perplexed as you are. Just some thoughts so we can figure this out with ya.

EDIT - I will add that my engine would bog out and die intermittently after coming to a stop. Ran fine otherwise. My float had a pinhole in it and filled with gas which tricked the carb into thinking it didn’t have enough fuel. This carried on for longer than I should admit until the float no longer floated and gas was literally dripping on the ground one day. Replaced the float and moved on with life. Now I’ve got two mostly complete carburetors in the garage in a box and Sniper EFI happily sitting on the intake. All that to say. Could the opposite be happening to you? i.e. Float level too high.
Plug wires are Yazaki replacements, not done by me. I’d have to look thru the receipts for a date, but IIRC they’re not that old. Definitely not more than 15k on them.
Also something worth mentioning, both times this has happened, I’ve never actually felt it “die”. The last time it happened, I was on my way to meet a buddy for dinner. I’m sitting at a light and I actually thought to myself “I hope it doesn’t die, it’s been running great” and I gave it a small/light rev to make sure it was still alive. It was, and a few seconds later when the light changed and I went to go I had nothing. Super weird deal for sure. Obviously I’m totally over thinking things, but it feels ignition to me. Distributor is/was clean inside, but I haven’t looked at it since I did the cap and rotor a couple years ago, so I’ll recheck that. It’s a used OEM from SOR replacement from many years ago so I don’t know the mileage on it- or why the original was replaced. I just have a receipt for it prior to my ownership.
 

OSS

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Maybe set the idle speed faster - like 750-800 RPM. The 2F is never that happy at spec 650 RPM. Especially when hot.
 
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Maybe set the idle speed faster - like 750-800 RPM. The 2F is never that happy at spec 650 RPM. Especially when hot.
It is. It’s at about 800. A/C idle up at about 1100. But both times it’s happened the A/C has been off.
 
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So I checked the coil. Secondary is 13.5k ohms, spec is 11k-16k.

Primary is 0.8ohms, spec is 0.4-0.5. I’m wondering if that’s a pretty normal number for a 40 year old coil, or should I condemn it?

I can’t find the specs for the igniter on Alldata. Anybody have them by chance?
 

OSS

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Also I’ve read on this forum that the fuel pump can develop a faulty diaphragm and sometimes not pump fuel adequately at idle.
I’ve personally never experienced it so I can’t comment on the exact symptoms.
 

2mbb

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To me the interesting point is that the engine is running fine, then starts misfiring (?), but continues to misfire/diesel when the ignition is turned off. To me this indicates an electrical problem like a short circuit some place. There is no mention that the truck diesels on other occasions so I assume the truck will stop if the sparking is stopped. somehow the sparking continues when the ignition is turned off.

check the electrical components per the manual. Also check (or better replace) fuses and fusible links.
 
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Also I’ve read on this forum that the fuel pump can develop a faulty diaphragm and sometimes not pump fuel adequately at idle.
I’ve personally never experienced it so I can’t comment on the exact symptoms.
Fuel pump is only 2 years old and OEM. plus I’d think the diaphragm would either be faulty or not, meaning if it were faulty I’d have issues all the time, not randomly once a week or so.
 
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To me the interesting point is that the engine is running fine, then starts misfiring (?), but continues to misfire/diesel when the ignition is turned off. To me this indicates an electrical problem like a short circuit some place. There is no mention that the truck diesels on other occasions so I assume the truck will stop if the sparking is stopped. somehow the sparking continues when the ignition is turned off.

check the electrical components per the manual. Also check (or better replace) fuses and fusible links.
Dieseling is a result of engine run-on without spark. Whether or not I lose spark is kind of the basis of the diagnosis/questions. The trick is I need to get it to happen again somewhere other than a busy intersection. And it’s misfiring as a result of either a fuel or spark issue. It’s not the cause of it dying, it’s a result.
 
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So after browsing the FSM, the igniter voltage test is kind of vague. I’m under the assumption that the service manual is assuming I’m testing the igniter because I have no spark. So the only check it gives is to use a battery and then check the coil. No resistance checks or anything. Ugh.
 

OSS

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Yeah - the igniter was a concern on really long trips into the boonies. Luckily they have a history of being extremely reliable.
My original igniter never failed me after 32 years & 290K miles, so I don’t have a personal reference for what a failure is like.
I was told by Marv Specter that if an igniter goes out, the engine won’t run. It’s all or nothing.
There’s a thread here somewhere on mud (can’t remember) where a guy replaced his igniter with a different one.
 
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Yeah - the igniter was a concern on really long trips into the boonies. Luckily they have a history of being extremely reliable.
My original igniter never failed me after 32 years & 290K miles, so I don’t have a personal reference for what a failure is like.
I was told by Marv Specter that if an igniter goes out, the engine won’t run. It’s all or nothing.
There’s a thread here somewhere on mud (can’t remember) where a guy replaced his igniter with a different one. Also installed a bigger heat sink. It worked.
Good to know that they’re generally either all or nothing on the igniters, not intermittent.
 

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