Back Fire
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AutoX
Joined: Feb 2002
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Back Fire
I have my 89 C4 back after an extended stay with the shop for a top end rebuild after 91,000 miles.
I drove it few less than 10 miles today and when I attempted to restart, the engine back fired loudly and a puff of smoke appeared.
The engine would not restart for several minutes. I eventualy got it to turn over but it was missing badly and the timing was out of sync. I sound very sick.
I am planning on having it towed to back to the shop but I wanted to be prepared with some expectation as to the possible cause.
Exhaust valve stuck open?
I drove it few less than 10 miles today and when I attempted to restart, the engine back fired loudly and a puff of smoke appeared.
The engine would not restart for several minutes. I eventualy got it to turn over but it was missing badly and the timing was out of sync. I sound very sick.
I am planning on having it towed to back to the shop but I wanted to be prepared with some expectation as to the possible cause.
Exhaust valve stuck open?
Race Car
Joined: Jun 2001
Posts: 3,706
Likes: 10
From: Virginia Beach, Va.
Gill, it's hard to tell what that could've been. There's several things that could've caused the backfire...improper cam timing could very well be one of them. 
I doubt that an exhaust valve would be stuck open, although it's possible.
Your O2 sensor might have been bumped around a bit while the engine and its components sat around the shop, and it may make your engine run fairly rich...causing an intermittent backfire and running rough at idle. <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />
MY car does this after changing out the catalytic converter with a European Premuffler. I have yet to check it out, but it does smoke intermittently...like the O2 sensor goes in and out of working properly.
Please, by all means let us know what your mechanic/technician finds!
I doubt that an exhaust valve would be stuck open, although it's possible.
Your O2 sensor might have been bumped around a bit while the engine and its components sat around the shop, and it may make your engine run fairly rich...causing an intermittent backfire and running rough at idle. <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />
MY car does this after changing out the catalytic converter with a European Premuffler. I have yet to check it out, but it does smoke intermittently...like the O2 sensor goes in and out of working properly.
Please, by all means let us know what your mechanic/technician finds!
Addict
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Joined: May 2001
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Gil:
There's something that's not clear to me. Did you pick the car up and drive it less than ten miles and this occurred, or have you been driving it for a while but you drove it less than ten miles today and this occurred?
If you've been driving it for a while then you might want to check your distributor belt. Has this ever been changed? Is the distributor vented? Has the car run poorly since you picked it up?
There are really a lot of possibilites.
Good Luck
There's something that's not clear to me. Did you pick the car up and drive it less than ten miles and this occurred, or have you been driving it for a while but you drove it less than ten miles today and this occurred?
If you've been driving it for a while then you might want to check your distributor belt. Has this ever been changed? Is the distributor vented? Has the car run poorly since you picked it up?
There are really a lot of possibilites.
Good Luck
Thread Starter
AutoX
Joined: Feb 2002
Posts: 13
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Bill: I had it back from the shop and had been driving it without any issues before this happened. I was driving between my offices when the loud back fire occured.
The car has never done this before and the vent upgrade had been performed.
Are there any other signs that might indicate a worn distriubtor belt? Thanks
The car has never done this before and the vent upgrade had been performed.
Are there any other signs that might indicate a worn distriubtor belt? Thanks
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Gil:
There are some tricks you can use to test the distributor but the BEST way is to pull the dual distributor cap off and look at the belt. The reason I say this is because the belt has two modes of failure.
One failure mode occurs when the belt completely breaks. In most of these cases, the primary distributor (which runs off the engine) shoves all the remnants of the busted belt out of the way to the path of lesser mechanical resistance, and this is usually the chamber of the secondary (belt driven) distributor. This usually locks the secondary distributor in one position. If the secondary wiper gets locked like this, and the wiper position is far away from any of the distributor contacts, the problem may go undetected (a slight loss of power at the most) because the secondary distributor simply doesn't fire any of the plugs at all. The worst case would be where it locks the distributor wiper right over a contact. In this case, your primary distributor is properly distributing spark to all six plugs and cylinders, while the stuck distributor wiper is making all sparks that should be distributed to six plugs fire into a single chamber. This means, that it will fire during the intake, compression, and exhaust cycles. If the belt does break and the secondary wiper doesn't get "locked" by belt pieces, it can "free wheel"...sort of distributing spark to various plugs in a pretty haphazard manner.
The other mode is where the belt is severely worn or wearing out. In this case the belt can skip teeth, thus causing the secondary to fire at the wrong intervals. This is really almost as bad as if you had a timing belt and one of the cams jumped a tooth or two.
You could start pulling distributor "feed" wires to the distributor. The car should work with either the secondary or the primary distributor by itself. However, if your belt has skipped a tooth or two, using this tactic may hide the problem...the DME may be able to adjust the mixed up timing to compensate for it.
Like I said before...lots of possibilities, and not just the distributor.
Hope this helped.
There are some tricks you can use to test the distributor but the BEST way is to pull the dual distributor cap off and look at the belt. The reason I say this is because the belt has two modes of failure.
One failure mode occurs when the belt completely breaks. In most of these cases, the primary distributor (which runs off the engine) shoves all the remnants of the busted belt out of the way to the path of lesser mechanical resistance, and this is usually the chamber of the secondary (belt driven) distributor. This usually locks the secondary distributor in one position. If the secondary wiper gets locked like this, and the wiper position is far away from any of the distributor contacts, the problem may go undetected (a slight loss of power at the most) because the secondary distributor simply doesn't fire any of the plugs at all. The worst case would be where it locks the distributor wiper right over a contact. In this case, your primary distributor is properly distributing spark to all six plugs and cylinders, while the stuck distributor wiper is making all sparks that should be distributed to six plugs fire into a single chamber. This means, that it will fire during the intake, compression, and exhaust cycles. If the belt does break and the secondary wiper doesn't get "locked" by belt pieces, it can "free wheel"...sort of distributing spark to various plugs in a pretty haphazard manner.
The other mode is where the belt is severely worn or wearing out. In this case the belt can skip teeth, thus causing the secondary to fire at the wrong intervals. This is really almost as bad as if you had a timing belt and one of the cams jumped a tooth or two.
You could start pulling distributor "feed" wires to the distributor. The car should work with either the secondary or the primary distributor by itself. However, if your belt has skipped a tooth or two, using this tactic may hide the problem...the DME may be able to adjust the mixed up timing to compensate for it.
Like I said before...lots of possibilities, and not just the distributor.
Hope this helped.