Ever since we had this new 383 stroker installed in my sons 67 Camaro it diesels when you turn it off if in park or neutral but if you turn it off in gear it turns off immediately. This is an automatic turbo 350. Why does it shut off in gear but not in park?
Why does a car not diesel when in gear?
Duneit
1 - 20 of 20 Posts
Joined
·
6,661 Posts
It is because the automatic transmission puts some drag on the engine halting the dieseling.
if it's 'dieseling' ...running on, in any gear there is a problem. 99.9% related to ignition timing. slightly too advanced, possibly too much vacuum advance. i'd look at idle speed, initial timing, vacuum advance and total advance to find out where it is when this is happening. make sure to make all your checks and corrections at full operating temp as i would assume it probably doesn't do that if you just start it up, pull it out of the garage and shut it down in park. just my assumption, correct me if i'm wrong, but it probably doesn't start the run-on effect until its hot. there are a lot of variables that could come into play but it all ALWAYS starts with ignition timing. poor fuel quality, too much compression etc etc can all contribute but most can be rectified with proper ignition timing. I'm going to guess that you probably notice a huge difference in idle speed between park and a drive gear. this is also likely related to ignition timing first and then fine tuning of the carb second.
you state that you're not too mechanically inclined when it comes to engines so i would find reputable shop that you trust and have them go through the timing and carb tuning. you may be surprised to have a completely different ride in all aspects, not just shut down.
just my opinion
you state that you're not too mechanically inclined when it comes to engines so i would find reputable shop that you trust and have them go through the timing and carb tuning. you may be surprised to have a completely different ride in all aspects, not just shut down.
just my opinion
Thanks for the advice. I had the engine built by a reputable machine shop here that has a dyno and they couldn't figure it out. They did the complete install too. A couple years later I took it to another shop who also couldn't figure it out. Your assumption is correct that it only keeps running after it's hot. Also my garage smells of fuel after I shut it off. I am looking for a good mechanic in the Sacramento area. I'll find one eventually. It's been over 7 years since this motor was built but it only has 4500 miles.
there's not too many shops in my neck of the woods with guys that really know their stuff on these carb / points style ignition motors any more. they all want to plug it in to a diagnostic machine and replace the bad sensor and collect their $1,000.00 . i'd hope in out in car country you can find a shop that specializes in these cars. my guess is that the combination of vacuum advance and initial timing is not correct and the previous shop tried to compensate with "carb tuning" by fiddling with the idle screw. (ask me how i know...lol) you likely have a combination of a few different issues going on but none of which are too tough to correct if the shop knows what they're doing. when you've got the car in park and the idle is likely much higher than in gear, with no load on the engine you're creating much more vacuum and probably over advancing the timing. then when you shut down she's still trying to fire. when you put it in gear and the idle and vacuum signal slow down, the degree of advance drops and it's ready shut down properly.
i thought i knew everything i needed about timing and tuning on these old motors until i had my new 406 sbc built. after 20 years of playing with these cars and having some really strong street / drag cars i came to realize that i may have been more lucky than good in some of my earlier engine set up's and tuning endeavors. some folks on this forum really helped me learn how much i didn't know. now the thing starts, idles, and runs like a champ. if i told my timing specs to a tech at a modern shop he'd probably tell me i was nuts and the motor's going to blow up. the ASE patch on the shop shirts these days doesn't mean much when it comes to these old non-computer controlled engines. keep at it, there's a ton of knowledge scrolling through these pages.
i thought i knew everything i needed about timing and tuning on these old motors until i had my new 406 sbc built. after 20 years of playing with these cars and having some really strong street / drag cars i came to realize that i may have been more lucky than good in some of my earlier engine set up's and tuning endeavors. some folks on this forum really helped me learn how much i didn't know. now the thing starts, idles, and runs like a champ. if i told my timing specs to a tech at a modern shop he'd probably tell me i was nuts and the motor's going to blow up. the ASE patch on the shop shirts these days doesn't mean much when it comes to these old non-computer controlled engines. keep at it, there's a ton of knowledge scrolling through these pages.
Agreed with suggestions given, and yes, a higher octane, is required.
The engine is being 'compression-ignited' after electrical power shut-down, hence the term 'dieseling' - diesel engines run/operate the same.
The dieseling engine is still creating a vacuum by running, and atmospheric pressure is pushing fuel into the vacuum to equalize the vacuum, Physics thing.
A temporary fix is shutting off engine in gear as this creates a load for the engine and it dies, it does not have enough compression to keep running.
Some times a lower idle RPM helps, and if timing is changed from the norm, then this will affect engine characteristics at normal conditions.
I hope this explanation is understood.
The engine is being 'compression-ignited' after electrical power shut-down, hence the term 'dieseling' - diesel engines run/operate the same.
The dieseling engine is still creating a vacuum by running, and atmospheric pressure is pushing fuel into the vacuum to equalize the vacuum, Physics thing.
A temporary fix is shutting off engine in gear as this creates a load for the engine and it dies, it does not have enough compression to keep running.
Some times a lower idle RPM helps, and if timing is changed from the norm, then this will affect engine characteristics at normal conditions.
I hope this explanation is understood.
Joined
·
2,284 Posts
I'll just throw this out there. Not sure how you drive it but sometimes carbon build up can cause hot spots that will ignite fuel after there is no spark. Idle too high and bad gas as stated above, timing can cause excessive heat too so...
Yes I'm running 91 octane only
I don't know what the rpm is at idle. It does not have a tachometer. I know it is a little high though because of the Vintage air the shop set it a little high so it wouldn't stall at stop lights.Vega$69 said:
Joined
·
12,374 Posts
Dave nothing rocket science about tuning points based ignitions. You could do it yourself and save the cash.
Buy a decent timing light and you then basically have what you need.
A vacuum gauge is in my opinion is a nice addition to the tune-up kit.
A dwell meter is also a nice tool to have.
All can be found at reasonable prices on-line, in shops and used on eBay and swap meets.
Then open the hood and have at it.
Buy a decent timing light and you then basically have what you need.
A vacuum gauge is in my opinion is a nice addition to the tune-up kit.
A dwell meter is also a nice tool to have.
All can be found at reasonable prices on-line, in shops and used on eBay and swap meets.
Then open the hood and have at it.
Joined
·
682 Posts
Add a idle stop solenoid like the factory did to solve that problem.
The car has an electronic ignition. Accel I believe is what it is
Joined
·
972 Posts
install a idle solenoid and have it come on with the A/C clutch. Set the idle at 700rpm with out the A/C on and 850rpm with the A/C and solenoid on. Or turn the idle right down to 500rpm and have the solenoid come on with the ignition on the run position at 850rpm when you will turn the ignition off the idle will drop at 500 and the engine will shut off. like this pic
Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
Joined
·
1,517 Posts
Dieseling is due to carbon build up on the piston heads. This carbon gets hot while the engine is running. When the ignition key is turned off, the battery to the coil/hei/other ignition system you have is eliminated, but the carbon on the piston head is what's igniting the fuel. With the transmission in gear, it effectively puts a load on the engine, and assists in stopping the engine.
Very common in the late 70's and early 80's. Auto manufacturers installed a solenoid on their OEM carburator's to shut off the fuel delivery to the main jet (aftermarket performance carbs such as Holley and Eldelbrock did not) that activated when the ignition key was turned off.
Even with 91 octane, you may experience this dieseling. Advanced ignition timing can aggravate it, low octane fuel, all lead to carbon build up on the piston heads. Some will add octane boost to the fuel tank at fill ups to help, some will "Seafoam" the engine periodically (pour Seafoam down the carb while holding a high idle to burn off the carbon buildup). These are temporary, as the carbon will eventually build up again on the piston head and dieseling will happen again.
Don't let it diesel! Leave the transmission in a gear when you shut off the engine. allowing the engine to diesel can lead to engine damage.
Very common in the late 70's and early 80's. Auto manufacturers installed a solenoid on their OEM carburator's to shut off the fuel delivery to the main jet (aftermarket performance carbs such as Holley and Eldelbrock did not) that activated when the ignition key was turned off.
Even with 91 octane, you may experience this dieseling. Advanced ignition timing can aggravate it, low octane fuel, all lead to carbon build up on the piston heads. Some will add octane boost to the fuel tank at fill ups to help, some will "Seafoam" the engine periodically (pour Seafoam down the carb while holding a high idle to burn off the carbon buildup). These are temporary, as the carbon will eventually build up again on the piston head and dieseling will happen again.
Don't let it diesel! Leave the transmission in a gear when you shut off the engine. allowing the engine to diesel can lead to engine damage.
Joined
·
1,290 Posts
While your original question has been adequately answered, other good tips on the cause and cure for run-on have been offered too. One other point that has not been mentioned (unless I missed it in the above replies) is the amount of transfer slot exposed below the throttle plates. Pull your carb and take a look. If you've had to adjust the curb idle screw in opening the throttle plates too far to ramp up the idle rpm so the engine will idle, you may have exposed more than the recommended 0.02" - 0.04". If you have too much transfer slot exposed, your carb will feed too much fuel from the slots when the engine is idling and this will definitely promote dieseling.
Thanks to everyone for your help and advice. I've found a mechanic who should be able to remedy my problems. He'll be looking at it end of next week or the beginning of the following week. I've told him all the great advice I've learned here. Hopefully he'll be able to fix it.
1 - 20 of 20 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
