WHY is my car dieseling when I turn it off - happens every time....

[MrY]

This is and older Ford 1946 with a newer 350 Chevy engine Wieand intake and a Holley carburetor and HEI ignition

 

only way to turn it off is to put the car in reverse and kill it quickly OR it will huff and puff for a minute and sometimes the engine runs backwards it feels like before it finally stops .....

 

WHAT is the cure ?    What is the cause ?   

gunk in the combustion cambers that is glowing ?  

It should not get any more fuel or spark when ignition is shut off

Pulling the heads off is the only solution ?

Buying expensive fuel injection cleaner liquid is like to pouring money down the drain I feel like...

 

Any advice or comment are appreciated

thx

[ABear]

Term is called "dieseling", which basically means your engine is self igniting (preignition) air fuel in the cylinders by compression and cylinder temps..

 

Generally, causes can be poor fuel quality (IE too low of Octane rating) for the compression ratio of the engine, excessive idle speed, carbon build up in the cylinders increasing compression ratio and creating hot spots in the cylinders.

 

Generally the main fixes are to lower the idle RPM and/or try higher Octane rated fuel.

 

Long term, may need what is called a "dasher" to be added to your carb. The dasher basically is a little 12V solenoid which is mounted to your carb holds the idle setting when running. When ignition is turned off, the dasher solenoid retracts, the carb plates close dropping the idle speed which helps to arrest dieseling.

[carbking]

Try readjusting the idle with a bit more mixture, and a bit less throttle.

 

Jon

[Bloo]

Do you have your ignition timing curve and carb jetting all worked out yet? If you don't know yet what the initial (static) timing is going to be when that is all done, you are just chasing your tail trying to solve dieseling now.

 

If you have worked that stuff out, consider this. One of the classic fixes is ignition timing. How can that be? The ignition is off while it is dieseling. To run an engine needs air, fuel, compression and ignition. If the engine is running with the ignition off, you have sufficient compression and ignition for the reasons already mentioned in a previous post. Why do you have enough air and fuel to keep it running with this lousy accidental ignition?

 

I remember reading articles when I was a kid probably where people would intentionally create carbon hot spots to make jeeps run underwater. The ignition happens at the wrong time, is unreliable, etc, but was enough to keep the jeep moving. They had to drill holes in the head and let them fill with carbon to make it happen. In short, it works but runs terrible. If it worked well nobody would bother having an ignition system. As it is your car has enough "ignition" to keep running with ignition off. It must have more air and fuel than it really needs with the ignition on.

 

That brings us back to ignition, and why timing is often given as a "cause" of dieseling. If the timing is such that the engine is idling less efficiently than it could be, it will need more air and fuel to keep running at idle. When you take the spark away, there is still enough air and fuel to keep it running. Fuel, already mixed with air comes from the idle jets in the carburetor. More air comes around the throttle and mixes with it, controlled by the throttle stop screw. More initial timing makes the idle more efficient, requiring less throttle angle and less air/fuel mixture from the idle jets.

 

Malaise era pre-computer cars were terrible for this. Retarded initial timing was used to help control emissions, and that meant the throttle needed to be open further at idle. The hot carbon and poor octane served as ignition. The extra air/fuel kept it running.

 

I have seen cases where you have to drill little holes in the throttle plates over the idle jets because enough throttle angle (air) to keep the engine idling uncovered a bit of the transfer slots, and the ported vacuum (distributor) port too. The idle jets won't adjust because the transfer slots are partly uncovered. **Don't do this preemptively**. It's an edge case, and when it does happen, it is usually on engines with really hot cams that barely idle at all. It shouldn't be necessary 99% of the time, and when it is necessary you figure that out after getting everything else right and finding you still have too much throttle angle to cover the ports properly in your particular carburetor.

 

Edited April 17 by Bloo (see edit history)

[dodge28]

I think the engine has the incorrect combination of parts. The Chev engine needs a 4 barrel Carter Carb and needs to run on 93 Octane. I owned one of those in the 70's. Worked great until this 10 percent Ethanol was introduced in the fuel.

[ABear]

28 minutes ago, dodge28 said:

I think the engine has the incorrect combination of parts. The Chev engine needs a 4 barrel Carter Carb and needs to run on 93 Octane. I owned one of those in the 70's. Worked great until this 10 percent Ethanol was introduced in the fuel.

Got it wrong. Needs a "Ford" engine in that Ford..

 

As far as a Carter carb on a Chevy, no, Holley WILL work perfectly fine and most likely a better carb than a Carter for tuning.

 

Needing 93 Octane? That all depends on how much the compression ratio is, 100% stock for older engines not so much, now running 8.5 - 10.5:1 then 93 is pretty much a given to keep preignition ping at bay..

 

Adjusting timing back some might help a little, doing so will automatically drop RPMs at idle, but in doing so may lose performance and fuel efficiency in the process.

 

Best to start with the obvious place, set idle speed a bit lower, if it calls for 850, try 800 RPM, shouldn't take much.

 

If lowering idle helps some and OP is using 87 Octane, then try next available grade up, may not need 93 Octane but may need more than 87 Octane.

 

Dasher may be the real fix.

[intimeold]

You didn't mention, if the idle speed adjustment is controlled by a screw adjustment; or an electric solenoid.

 

If the idle speed is controlled by some sort of mechanical screw or like item; when you turn the ignition off the idle falls back to the hard setting of the screw.  Which may be holding the idle just a bit too fast.

 

On the other hand; if there is an electric solenoid controlling the idle speed; when the ignition key is turned off, this allows the solenoid to collapse, thus allowing a much lower setting .

 

  So when you energize the key and solenoid; the solenoid is controlling the idle speed.   Turn the key off and the adjusting screw, (that we talked about earlier) can be set much lower to actually stall the engine. 

 

Send a picture of your throttle linkage at the engine; and we can get a better idea of what you have.

 

And the solenoid can be used on fuel injection or carbureted vehicles. 

 

I purposely, jumped past all the other things that should be checked too; and only focused on the base idle adjustment.  

 

intimeold

[carbking]

A bit more information concerning the engine would gain more useful answers.

 

Jon

[Angelfish]

Just the Ford grousing about that Chevy engine.

[TTR]

I would recommend finding/hiring a mechanic who knows how to properly diagnose the cause.

Everything else, including asking about this here or in any other forum is likely waste of time, both your own and of those trying answer/help, including me.

 

[ABear]

10 minutes ago, TTR said:

I would recommend finding/hiring a mechanic who knows how to properly diagnose the cause.

Have you considered that the OP most likely DID try finding/hiring a mechanic that is able to properly diagnose the problem AND failed to be to "find" one that can?

 

The reality is, very few auto repair shops actually have mechanics that have the knowledge to troubleshoot and solve the issues without OBD2 ports and/or shotgunning with thousands of Dollars worth of parts and thousands of Dollars in labor..

 

I know myself, after getting burned for well over $4K in parts and labor on a MODERN OBD2 equipped vehicle just how frustrating and expensive it can be and yet have the same problem plus more bad mechanic induced problems. The fix to the problem I had, found it doing a Internet search and then a few Youtube searches plus a can of throttle body cleaner were were back on the road and off to the races. Yeah, $6 for a can of throttle body cleaner and only took two good squirts to clean the sticking computer controlled throttle plate.. Yeah I raised heck with the dealer shop supervisor, total of no less than 8 times returned back to them and they returned it still broken.

 

Sometimes one can find some nuggets of wisdom on Internet forums and that most likely is why the OP asked here..

[Ronnie]

Try an old drag racer's trick and see if it helps prevent dieseling. Instead of cutting key off at idle, rev the engine up and cut the key off while the rpm is high.

[TTR]

2 hours ago, ABear said:

Have you considered that the OP most likely DID try finding/hiring a mechanic that is able to properly diagnose the problem AND failed to be to "find" one that can?

 

The reality is, very few auto repair shops actually have mechanics that have the knowledge to troubleshoot and solve the issues without OBD2 ports and/or shotgunning with thousands of Dollars worth of parts and thousands of Dollars in labor..

 

I know myself, after getting burned for well over $4K in parts and labor on a MODERN OBD2 equipped vehicle just how frustrating and expensive it can be and yet have the same problem plus more bad mechanic induced problems. The fix to the problem I had, found it doing a Internet search and then a few Youtube searches plus a can of throttle body cleaner were were back on the road and off to the races. Yeah, $6 for a can of throttle body cleaner and only took two good squirts to clean the sticking computer controlled throttle plate.. Yeah I raised heck with the dealer shop supervisor, total of no less than 8 times returned back to them and they returned it still broken.

 

Sometimes one can find some nuggets of wisdom on Internet forums and that most likely is why the OP asked here..

I absolutely considered, but since OP didn’t indicate having done that hence my recommendation.

Besides, had OP found one he/she wouldn’t have a need to ask about it here.

Apparently you failed to find proper one also.

[ABear]

18 minutes ago, TTR said:

Apparently you failed to find proper one also.

Yeah, last ditch effort before considering trading in for a new vehicle, I started searching the Internet with the symptoms I was getting and low and behold up popped the solution..

 

So, in the end, I discovered that I was the "better" mechanic than the so called "professional" mechanics and I didn't cost $160 per hr mechanics rate the dealer charged me at that time. Haven't been back to the dealer for many yrs, instead for modern vehicles the first tool I grab is my HF OBD2 scanner and the second tool is Internet search engines..

 

Older vehicles, I rely on a lot of lessons learned working beside my Dad on back then modern vehicles with carbs and points ignitions. He taught me a lot and I like passing on old knowledge to others when possible.

[TTR]

52 minutes ago, ABear said:

Yeah, last ditch effort before considering trading in for a new vehicle, I started searching the Internet with the symptoms I was getting and low and behold up popped the solution..

 

So, in the end, I discovered that I was the "better" mechanic than the so called "professional" mechanics and I didn't cost $160 per hr mechanics rate the dealer charged me at that time. Haven't been back to the dealer for many yrs, instead for modern vehicles the first tool I grab is my HF OBD2 scanner and the second tool is Internet search engines..

 

Older vehicles, I rely on a lot of lessons learned working beside my Dad on back then modern vehicles with carbs and points ignitions. He taught me a lot and I like passing on old knowledge to others when possible.

First, based on your description of the events, I wouldn’t consider you being a “better mechanic” than one you contracted to diagnose and fix the problem, but rather that you just got lucky after spending several grand (according to you) for nothing.

And of course there’s alway a possibility you not disclosing everything that actually transpired, but that seems fairly common, especially on internet forum problem solving inquiries, so nothing to be taken personally.

Second, I’m surprised that based on your supposed experience in leadership position you failed to recognize the dealership shop & mechanic weren’t up to the task before submitting your vehicle for their care.

How did you found them and decided to let them work on it ? Internet reviews ?

 

P.S. I’m not defending “professionals” per se,  as there are plenty of bad or less than good ones in any field, but compared to DIYs, the ratio is probably nowhere near as dramatic.

Heck, here in SoCal,  I’m surrounded by a large variety and quantities (= thousands upon thousands or more) of automotive related businesses of all types, but let’s say within 50 mile radius, there’s not many I would do business with, let alone recommend to someone else
Yet most of these “professional” shops seem to stay in business and some have for decades.

 

 

Edited April 18 by TTR (see edit history)

[ABear]

31 minutes ago, TTR said:

First, based on your description of the events, I wouldn’t consider you being a “better mechanic” than one you contracted to diagnose and fix the problem, but rather that you just got lucky after spending several grand (according to you) for nothing.

And of course there’s alway a possibility you not disclosing everything that actually transpired, but that seems fairly common, especially on internet forum problem solving inquiries, so nothing to be taken personally.

Second, I’m surprised that based on your supposed experience in leadership position you failed to recognize the dealership shop & mechanic weren’t up to the task before submitting your vehicle for their care.

How did you found them and decided to let them work on it ? Internet reviews ?

 

P.S. I’m not defending “professionals” per se, regardless of their field as there are bad and good ones in any,

but compared to DIYs, the ratio is probably nowhere near as drastic.

 

Well to put things into perspective, you would have to understand how we got there.

 

First, my job was a 1hr each way daily commute.

 

It was my wifes vehicle 1 hr away from my work.

 

It was in the winter and wife just left work at 4:30 PM, pickup daughter from baby siter.

 

Proceeds to drive home and tow miles from home no more throttle, dead pedal, engine barely running.

 

Did I mention WINTER, well yeah, it is dark, it is below zero and I am 1 hr away from being able to help..

 

Wife with young daughter had to sit on the side of the road until I was able to get home..

 

Last ditch effort to get said vehicle home, I turned off the ignition and restarted it.. Yea, no more dead pedal..

 

Ran fine for a week and dead pedal.. Lather, rinse, repeat.

 

Since I wasn't able to get home until after 5:00 PM and then grab a bit to eat it left me with less than 3hrs to diagnose and work on said vehicle until I had to go to be so I can drag my behind out of bed in the morning at 5:00 AM to get to work the next day.. Some of us slobs have to punch real time clocks and management gets real trigger happy if you do not clock in promptly 10 minutes before shift each day. And no management wasn't real happy if you left before end of shift and that triggered an unsheduled out even when you have PTO to use.. Too many unshceduled outs and by by job..

 

Reality sets in, vehicle needs to be looked at by a "professional" who's main job in life is diagnosing and repairing newish said vehicles.. Where best to take it, well, since it was a make designed and built THEY the dealer surely has some guy there that has at least read a couple of service books while using the restroom every day one would think, right? Yeah, how did that work? Not too god to say the least..

 

Did I mention, that the dealer service doesn't open until 9:00 AM and they close promptly at 4:30 PM, yeah, howd that work? Not to good..

 

After the 8th time back and forth to the dealer garage with a lot of NPFs on papers (No Problem Found) I decided that I was going to be the one to figure the mess out. One of those NPFs was for strong gas odor in the vehicle, yeah, they couldn't smell that stomach turning strong odor like someone splashed 10 gallons of fuel in the vehicle.. I discovered by Internet search that loose plugs can cause fuel fumes inside the vehicle.. First plug I checked was only engaged by one thread.. All 8 plugs were loose.. Yeah, that was a "profesional" induced bad side effect from return to dealer number 2 Yeah, Howd that go, not to good.

 

When I wanted to take time off, I was subject to calendar rules, to many people off, nope can't get those days, had to schedule my life and PTO around open spaces on company calendar..

 

The reality is not everyone is entitled to have a lot of leisure time to mess around troubleshooting vehicles that they depend on for daily life, not everyone has money to burn to have spare backup vehicles so sometimes one must turn to a mechanic or dealer service bay.

 

Spent 22 yrs working that job, let a lot of things slide that needed work done around my house and property because when you are up at 6 AM and get home at 5 PM and go to bed at 9 PM there isn't much time left to tear into things before you have to reset for the next day..

Edited April 18 by ABear (see edit history)

[Str8-8-Dave]

If it's got a GM late model engine with a Rochester or Edelbrock carburetor put an electric idle solenoid on the carburetor and use the adjustable plunger in the solenoid to set idle speed. These were used on almost all GM cars from late 1960s, my Pontiac 1969 Ram Air IV GTO had one on the 4MV Quadrajet carburetor and it never, ever dieseled.   With engine off, solenoid not energized, back off the original throttle stop screw until throttle butterflies close completely, then screw the stop screw in just far enough to prevent throttle plates from closing completely and sticking in the throttle bores.  Ignition on, throttle solenoid on, ignition off, throttle solenoid deactivated.  Now you have a setup to adjust the idle speed with the plunger in the solenoid and when you turn the ignition off throttle butterflies will close enough to stop the park diesel.