1984 Chevy Corvette my Chevy 350 Diesels every time I turn

WR3CK

MEMBER
1984 CHEVROLET CORVETTE
V8
2WD
AUTOMATIC
130,000 MILES

Engine: 350 Crossfire Injected (double Throttle Body Injection)

New OE style Autolight plugs (Hot Plug)

No vacume leaks found

engine idles great and runs fantastic

the engine is just driving me crazy with this dieseling.

every time I turn it off the engine diesels
does not matter if I run the vehicle for a hour or for 5 seconds. I even went out first thing in the morning with a totaly cold engine and started it and turned it off right away and the engine still dieseled on me.

I shot a can of intake cleaner down the motor while it was running to see if there were carbon deposits at the top of the cylinder turning red hot causing this engine to continue to try to run after I turn it off. I was hoping that a can of intake cleaner would break down any deposits so they would fall off. When that did not work I tried the cold start shut off on a super cold motor. I dont see how there can be deposits turning red hot in conditions such as that. So here I am. Stumped

thanks in advance for any help you guys can give

4 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Could be your idle speed is too high and throttle plate is not closing completely to shut off the incoming air, also the ignition timing could be off.

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Thursday, May 20th, 2010 AT 3:22 PM

WR3CK

MEMBER
3 POSTS

I have 2 of these cars. I forced open the throttle plates a little on the other 84 vette I have and it did not diesel. Also the idle is exactly the same on both cars warm and cold so I dont believe the timing is off either.

Not trying to dissagree off the bat but since I have 2 of these cars I just run out and try to replicate the issue on the other one if I can. So far. No dice :(

any other ideas?

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Thursday, May 20th, 2010 AT 6:45 PM

RASMATAZ

MECHANIC
75,992 POSTS

Lets try vacuum leaks, hot spot in the cylinders or excessive engine temperature due to an EGR inop.

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Thursday, May 20th, 2010 AT 7:25 PM

WR3CK

MEMBER
3 POSTS

I visually looked for vacume leaks however I will give it the ol'Carb cleaner try and see if I can get a RPM change shooting carb cleaner at the lines and around the intake.

As far as hot spots in the cylinders goes. Can it really get that hot when you only run the motor for like 3 seconds? That is what I was thinking at first. Hot carbon deposits. But I thought shutting it down the instant I got it started first thing in the morning and seeing it still diesel kind of killed that idea.

I know sometimes inferior plugs can cause a issue also. These are Autolight Plugs. Not exactly AC Delco quality in my book however I dont know that they could really be the issue due to the stellar performance when running.. Thoughts on that one?

And for excessive engine temp. Well this happens hot and cold. So I dont think that applys. The problem does not get worse cold or hot.

Tomorrow I get the car back from the paint shop (couldent stand looking at the old paintjob any longer) I will give the carb cleaner on the vacume lines and around the top of the motor a try and hopefully I missed something the first time over. If it does not work I will even give a link to video of the engine and the issue happening over and over.

This car does not just diesel for a second or two. Typically its 5-10 seconds of trying to continue running even after the key is out of the ignition (and yes the ignition switch is set correct. All power to everythig shuts down the instant the key is in off position)

more tomorrow. Thanks again for the replies. Hopefully we can get this figured out.

EDIT:
The paint shop screwed the pooch on the paintjob so I dont get the car back now untill Tues or Wed :(

so enjoy your Holiday weekend and hopefully we can get this squared away shortly after I get the car back.

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Thursday, May 20th, 2010 AT 9:19 PM