86 Firebird - Won't shut off


Old 09-25-05, 01:39 AM
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Join Date: Aug 2005
Location: Fort Worth, TX
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Unhappy 86 Firebird - Won't shut off

I have a 1986 Pontiac Firebird. If I drive for a bit (30 minutes or so), when I get ready to shut off the engine, the car acts like it wants to keep running. I have to turn the key back on, put the car in gear and give it gas and shut it off at the same time. Does this mean a carb rebuild or what? I have been TRYING to restore this car since I purchased it 2 years ago, but something ALWAYS seems to be going wrong with it.

During the Summer months, the car seems to be running at a higher temp than I like also. I am in Texas and after 11:00 AM the temp will get up past 225 - 230 in a hurry. I have done everything that I can think of, (changed out radiator, new water pump, new t-stat, new temp sensor in block, new fan motor & sensor, etc). It had, what I call an "idiot light", (goes on ONLY after it is too late), so I put in a guage which is where I am getting these temp readings. I know its pretty accurate as has been tested. When I do shut the car off, you can hear the water rumbling in the car and sometimes it boils out of the overflow.

I really don't want to keep throwing money in this car if it is just always gonna be a hassle. Any ideas?
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Old 09-25-05, 03:37 AM
Join Date: Jun 2002
Location: Long Island, NY
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You need to cover the basics first. Ignition timing could cause both problems. Also not related to running hot is idle speed too high, some engines have a solenoid to lower the idle on shut down.

Then I would look at the cooling system for the cause of running hot. I would check rad cap and fan clutch if equipped.
Old 09-25-05, 03:38 AM
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Location: Fort Worth, TX
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86 Firebird

Thanks, I will do that.
Old 09-27-05, 10:01 PM
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head gasket is a posablitlity

and the engine keeping on running problem can be the carb or even the compression in the engine

check the compression in each cylinder

pressuerize the coolant system and check for a leak down

check fuel pressure before starting, while running, after shutdown
Old 09-28-05, 06:28 AM
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Originally Posted by Cherry
the engine keeping on running problem can be the carb or even the compression in the engine

Sometimes it can also be caused by too low of an octane [gas]
Old 09-28-05, 07:51 PM
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Im thinking its the carb. Make sure that the carb is fully closing once the engine is shut off. If it is not, it will still pass o2 and gas through and the engine cannot shut off.
Old 09-29-05, 06:15 PM
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Quite possibly this is due to the engine timing being off.

It sounds like it might also be running a little hot, which could be caused by the timing being off.

You will need a timing light to check it, so if you don't have one, I would have a shop check it.

If the head gasket was blown, it would most likely run hot on the road, it might also have white smoke coming out the tail pipe, and you could see a lot of water/ oil mix inside the oil filler cap.

To be sure on the head gasket, I would first change the oil. If there is a lot of water in the oil, you might have trouble. You can also do a compression check on the cylinders.....but, do these first:

1) Drive it for the distance/ time you mentioned, with the heater on. This acts as a secondary radiator, due to water circulation and the fan blowing over the heater core. If it cuts off normally, it may be an over heating issue.

2) Check the water level - while it is cold.

3) Check the timing.

4) Check the fuel.....not impossible you have some bad gas (water.....which can be fixed with denatured alcohol).


Old 09-30-05, 05:02 AM
Join Date: Apr 2005
Posts: 242

sound like the timming, my 350 is doing the same thing but i havn't had time to fix it, i knew the timming was off because i had it set high but now it has started to run after it is shut off. It is a new motor, new distributer and new carb. I also recently put a new fan clutch and a 4 core radiator. I really need to reset my timming...............
Old 10-02-05, 09:13 PM
Join Date: Oct 2005
Posts: 25
All good suggestions. Here's my two cents.

If the carburetor is running lean, it will cause high running temperature. The run-on could also be caused by the temperature because the combustion chamber is so hot it continues to ignite the fuel after the spark is killed. High idle also causes run-on. If the engine has had any mods, like a larger profile camshaft, it may be running too lean. If it's a Rochester Quadrajet, rebuilds are easy. This is actually a good carburetor, and doesn't really deserve the name "Quadrajunk". The problem is that many people don't like the throttle response of the spreadbore's small primaries, and many people don't understand how the secondaries work. Oh, I almost forgot, check for vacuum leaks all over. Even small cracks in vacuum lines will cause problems when you have many lines with small leaks. If your system is sucking in air somewhere after the carburetor, it will make your fuel mixture lean. Propane is a good way to check for leaks. If the engine idles up when you pass the propane over a certain spot, you've found your leak.

The temps you mentioned are definitely too high. Another way to check for blown head gasket is to open the radiator up and look for air bubbles at the filler neck. Valve clatter during acceleration is also a good of a blown head gasket between cylinders and a compression check will help confirm that. If your engine oil looks like an almond milkshake, turn it off and don't run it anymore until you get it fixed.

This might seem like a silly question, but is your fan shroud in place? Sometimes people replace the factory belt-driven fan with an electric fan and do away with the shroud. Big mistake. The shroud is crucial in maintaining proper airflow and cooling through the radiator.

You could try backing your timing off by two degrees and then monitor the temperature to see if it drops some. You might have to use trial and error to get a good timing position that finds a balance between temperature and efficient running. But even if that helps, it might only be helping relieve symptoms of a separate problem.

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