Caprice won't turn off - Chevy Impala SS Forum
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post #1 of 12 (permalink) Old 03-13-2015, 03:03 PM Thread Starter
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Caprice won't turn off

Hi I recently purchased a 89 box caprice with a 350 in it, but the previous owner said that sometimes it won't turn off and will just rough idle because the timing is off. But my friend said that it's most likely the ignition switch, but this doesn't happen all the time and only happens like once every other day. Any ideas on what I should check? The vehicle also has a kill switch but this does nothing when i turn it on. And when the key is turned all the way off it sounds like its going to die. Thanks!

-Azzar
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post #2 of 12 (permalink) Old 03-13-2015, 08:09 PM
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Just a guess, but I have seen where the alternator wiring is messed up, so you get a power feedback keeping the ignition energized even when the key is off. To test this, unplug the plug on the alternator. With this plug disconnected, the car is running entirely off the battery(be careful driving it like this, since your battery will go dead with no charging system). If it still does it, it's not alternator feedback.

Until you get it figured out, shut the car off with it in gear. Since you say it is already running rough when it does this, the extra drag might be enough to cause it to die.

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post #3 of 12 (permalink) Old 03-14-2015, 07:19 AM
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shut off.

The car is "dieseling".
Set timing correctly.
Set idle correctly.
There might be a detent (solenoid that holds idle up when running, then drops off when shut down). It must be operational and set correctly.
Use some "GM top cleaner" to clean the carbon from the pistons. The carbon stays hot and acts like a spark plug when shut off.
By shutting it off in gear, this works because the idle is held lower.
It has nothing to do with the ignition switch.

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post #4 of 12 (permalink) Old 03-14-2015, 10:09 AM
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Quote:
Originally Posted by Charlie Costello View Post
The car is "dieseling".
I didn't realize '89's were still carbed. If they are, then I agree, it's dieseling. Get the timing set right and it should go away.

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Last edited by Bugman; 03-14-2015 at 10:12 AM.
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post #5 of 12 (permalink) Old 03-14-2015, 11:30 AM
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shut off

That might be my bad. I read it as 86, sorry.
Still need to check timing and idle.
Still need to run good / better gas.
Should still run some top cleaner.
Also, if idling too high, the throttle body gasket could have a leak, allowing non-registered air. Sorry for any confusion.

Charlie Costello
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post #6 of 12 (permalink) Old 03-15-2015, 06:01 AM
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The wagons were carbed all the way to the last year of 1990. They came with the olds 307 & 2004R trans.
1988 was the last year of sedans with carbs. 89 & 90 came TBI.
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post #7 of 12 (permalink) Old 03-15-2015, 11:00 AM
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Quote:
Originally Posted by wytltng View Post
The wagons were carbed all the way to the last year of 1990. They came with the olds 307 & 2004R trans.
1988 was the last year of sedans with carbs. 89 & 90 came TBI.
It's hard to believe GM stuck with carbs up until 1990 on those cars when almost everything else was fuel injected. Guess they had a leftover stockpile of carbs that needed to be gotten rid of.

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post #8 of 12 (permalink) Old 03-15-2015, 11:12 AM
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From a brief search, it seems that EFI was an option after '86. From a performance and economy standpoint, the early TBI didn't really gain you much over the computer controlled carb. I used to get 25mpg highway in my '86 carbed Caprice, and that was with 175K on the odometer.

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post #9 of 12 (permalink) Old 03-15-2015, 11:37 AM
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Quote:
Originally Posted by Bugman View Post
From a brief search, it seems that EFI was an option after '86. From a performance and economy standpoint, the early TBI didn't really gain you much over the computer controlled carb. I used to get 25mpg highway in my '86 carbed Caprice, and that was with 175K on the odometer.
I believe the main benefit to TBI was better emissions and driveability, especially in cold weather. Temperatures got down to the single digits this winter (lowest being 1.5*F), yet my L03 fired right up every time. Would a carburetor equiped engine done so as well? I'm too young to remember cars with carbs, but my father has plenty of stories to tell of the trouble he had with his carb equiped cars during some of the brutal winters he went through in the '70s. He wasn't an auto tech like I am, so that might have been part of it.

'91 Caprice Classic sedan L03 170xxx miles all stock

"Mods? I'm too busy trying to keep the old girl running to have time for that."

Last edited by Madmachine; 03-15-2015 at 11:41 AM.
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post #10 of 12 (permalink) Old 03-15-2015, 02:16 PM
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Quote:
Originally Posted by Madmachine View Post
I believe the main benefit to TBI was better emissions and driveability, especially in cold weather. Temperatures got down to the single digits this winter (lowest being 1.5*F), yet my L03 fired right up every time. Would a carburetor equiped engine done so as well? I'm too young to remember cars with carbs, but my father has plenty of stories to tell of the trouble he had with his carb equiped cars during some of the brutal winters he went through in the '70s. He wasn't an auto tech like I am, so that might have been part of it.
That's a big part of it. EFI is "turn key, car starts." Late model carbs were almost that good, but not quite. IIRC, my '86 only didn't start for me once even in the bitterest cold, but not all carbed cars are like that. Older cars in particular often had a "procedure" for cold starting you had to figure out. My '86 was pump the gas once, hit the key. My Corvette is two pumps of gas and hit the key. My '55 Plymouth is 4 pumps, hit the key and hold the pedal at 1/2 throttle. Then there's learning how to feather the gas so it doesn't die until the choke opens up. And if you flooded it in the cold... Every carb is a bit different, it all depends on how worn the motor and carb are, how well it's tuned, etc. EFI doesn't have those problems. From a starting standpoint, it's much more consistent and reliable.

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