Problems starting when warm
08-21-2003, 06:17 PM
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Problems starting when warm
I have an intermittent problem that seems to have cropped up. Car runs fine.. No problems while on the road for any length trip.. Problem arrises when the car is shut off. When I attempt to start it again, sometimes it will not start. Symptom is no spark. I thought it was antitheft related, but then why should it crank over at all.? So basically, when hot, sometimes, after I shut it off, it will not have spark again and will not start. If I wait until it cools some, it will start. Any ideas anyone? What should I check?
08-21-2003, 06:51 PM
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Re: Problems starting when warm
Are you sure the problem is spark?
Depends on model year. Later cars use a magnetic (presumably a Hall effect pickup) crank position sensor on the flywheel that's heat sensitive. Someone on this forum recently recommended a test procedure for this sensor. I gather that the cure if bad is replacement.
Older cars have a Hall sensor inside the distributor that replaces the points. I guess that this could fail with heat, though mine has worked fine.
Other than that, round up the usual suspects, especially the spark coil. When old, they can do some flaky things -- especially when heated -- in any car.
Depends on model year. Later cars use a magnetic (presumably a Hall effect pickup) crank position sensor on the flywheel that's heat sensitive. Someone on this forum recently recommended a test procedure for this sensor. I gather that the cure if bad is replacement.
Older cars have a Hall sensor inside the distributor that replaces the points. I guess that this could fail with heat, though mine has worked fine.
Other than that, round up the usual suspects, especially the spark coil. When old, they can do some flaky things -- especially when heated -- in any car.
08-21-2003, 07:48 PM
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Re: Problems starting when warm
I'd agree that a sensor could be the culprit. However, what is strange is that once running, there are no problems.. If the crank position sensor were flaky when hot, wouldn't the engine just sputter or die? The motor runs great until it's turned off. When I go to restart it just cranks forever. There is no spark.
Is the crank position sensor used all the time, or only during startup?
Is the crank position sensor used all the time, or only during startup?
08-21-2003, 08:00 PM
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Good question. i don't know the answer.
My older 5000 doesn't use one. Not sure about later 5000s. I think that I read that hot start fail is a symptom of a failing or failed sensor.
What year / model is yours? How old is its ignition coil?
What year / model is yours? How old is its ignition coil?
08-21-2003, 09:20 PM
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Re: Problems starting when warm
If I recall from your past post it is a V8. the V8 uses a crank sensor an engine speed sensor and a cam sensor and needs all three to start, once running it can run with a bad cam sensor but would trigger the check engine light. Seeing it runs fine and presumably isn't setting the light and just isn't starting it may be a relay (or even an ignition switch for that matter) that doesn't make contact when hot.
08-22-2003, 05:08 AM
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Just had the same problem!
I had the same symptoms and replaced the crank position sensor and RPM sensor. The condition is known has heat soak. Those sensors are real close to the exhaust manifold (also, the sensors are right next to each other). I'm sure audiqv8 can give you a great explanation of the condition. Basically, the car will start when its cool because the magnetic properties of the sensor is restored and the injector sequence is set. The ECU stores this information until the car is shut off (the crank position sensor is only used for starting). That's why it'll run fine until shut off. However, a bad RPM sensor will also cause the car not to start. Have you blinked out the codes? Check sjmautotechnik.com
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08-22-2003, 05:12 AM
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Re: Good question. i don't know the answer.
I blinked out the codes when I was having problems and only got the code for RPM/engine speed sensor. All along I thought it was the crank position sensor because it wouldn't start. Come to find out, a bad RPM sensor will not only make the car shut down while driving, but will also cause the car to not start up when hot. I changed both (lots of fun), no more problems. Also, no check engine light appears in either case.
08-22-2003, 05:53 AM
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Re: Is'nt the crank sensor used when the engine is running to tell the ecu the timing is right?
The crank position sensor is used by the engine when it is running, but will default to a value when the engine was started if it should fail while the engine is running. The engine will remain running. Once the engine is turned off the engine will not start until the sensor has cooled down. If the speed sensor fail then the engine will not run at all and if the engine was running it will die. Easy check for the speed sensor is to crank the engine and watch the tach. It should bounce when cranking, no bounce then the speed sensor is bad.
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