Engine shake and noise after turning off - Team Camaro Tech
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post #1 of 5 (permalink) Old May 3rd, 15, 08:00 PM Thread Starter
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Engine shake and noise after turning off

Hey guys,

I just had my distributor and a new carb installed yesterday. Car started up great, drove fine, but when i got it home from the shop, I put it in park and shut it off. The engine proceeded to shake pretty hard, and make this repeated loud grinding sound for about 20-30 seconds. When it stopped, the car let out this really strong burned gas smell.

Any ideas what the problem could be? Prior to installing these new parts everything was fine.

The carb is a 670 Holley Street Avenger with electric choke and vac secondaries. Motor is a 5.7 350 crate.

Thanks
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post #2 of 5 (permalink) Old May 4th, 15, 06:52 AM
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Re: Engine shake and noise after turning off

Quote:
Originally Posted by cozen89 View Post
Hey guys,

I just had my distributor and a new carb installed yesterday. Car started up great, drove fine, but when i got it home from the shop, I put it in park and shut it off. The engine proceeded to shake pretty hard, and make this repeated loud grinding sound for about 20-30 seconds. When it stopped, the car let out this really strong burned gas smell.

Any ideas what the problem could be? Prior to installing these new parts everything was fine.

The carb is a 670 Holley Street Avenger with electric choke and vac secondaries. Motor is a 5.7 350 crate.

Thanks
Sounds like it is "dieseling" or also known as "run on". It occurs when the ignition is killed but the engine continues to run due to enough heat in the combustion chambers to fire the incoming air fuel mixture (thus the term "dieseling"). The shake is due to the firing of the air fuel mixture being out of proper time, but close enough to keep it running until the chambers cool enough that it finally stalls. Some reasons for this can be but are not limited to: too high of an idle speed, timing too far advanced, spark plugs too hot of a heat range, excessive carbon in the chambers. Any one or combination of these and a few other things can be contributing factors.

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post #3 of 5 (permalink) Old May 4th, 15, 08:08 AM
DjD
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Re: Engine shake and noise after turning off

To add to what Scott has said run-on is more often than not caused by the carbs throttle blades being open too far. The idle could be right on but if there is not enough initial timing at idle then opening the throttle blades more than necessary to set the idle will cause run-on.

This could also be caused by the secondary throttle blades being opened which is a trick guys use when having problems getting the engine to idle properly. This is also a sign of not enough initial timing at idle.

There are a lot of caveats and cautions and since you had someone install the dist and carb for you I recommend you take it back to the him! It's not as simple as cranking up the initial timing, it may require re-curving the dist so you have more initial without effecting the total timing.

It could also be as simple as switching the vacuum advance from a metered source to a manifold source. If you used an experienced mechanic he will understand that increasing the initial timing will raise the idle and then you can close down the throttle blades. He will also understand that raising the initial idle to solve the run-on may cause pinging at WOT because it also raises the total timing unless the dist is re-curved.

...Dennis

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post #4 of 5 (permalink) Old May 4th, 15, 01:17 PM Thread Starter
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Re: Engine shake and noise after turning off

I did use an experienced mechanic, I spoke with him today and he said to bring it back in, but doesn't have time until the end of the week. Is it safe to drive like this?
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post #5 of 5 (permalink) Old May 4th, 15, 03:08 PM
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Mark
 
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Re: Engine shake and noise after turning off

Quote:
Originally Posted by cozen89 View Post
Is it safe to drive like this?
Yes, just turn it off in gear if an auto and if it's a manual and idling too high just ease the clutch pedal up to get the RPMs lower then shut it off.

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