# backfire and smoke from my air intake ????



## kevin203 (Jun 5, 2009)

i went to start my car and it backfire every time i would go to start it backfire then if it did start it would run roughly and shake the whole car.


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## germancarnut51 (Mar 23, 2008)

*Re: backfire and smoke from my air intake ???? (kevin203)*

Camshaft and/or ignition is/are seriously off, or the crankshaft position sensor has failed.
Have you replaced the camshaft timing belt or played with the ignition lately?
If not, my guess is that the camshaft timing belt has stripped teeth or gone slack and jumped timing. Bent valves are now an issue.
Don't try turning the engine again until to verify that the timing belt is intact, and timed correctly. My guess is that if you check, you will find the camshaft timing is way off.


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## bearing01 (May 27, 2004)

*Re: backfire and smoke from my air intake ???? (germancarnut51)*

You can't set the ignition timing on this car. Spark timing is set by the ECM by using the crankshaft sensor.
Is it an exhaust backfire or intake backfire? Exhaust backfire occurs because you have unburnt fuel in the exhaust manifold that combusts when fresh air hits it. Common on carbureted engines that had a smog pump (called SAI on VW's) with a non-functioning intake anti-backfire (intake air-bleed) valve. Taking your foot off the gas chokes off air to the carb. The sudden rich charge doesn't burn but goes out the exhaust. If the smog pump's anti-backfire valve doesn't bleed some air to the intake manifold, for a second duration after closing the throttle, to burn off this pooled fuel, you get an exhaust popping noise on decelleration.
I guess if the cam was severely retarded then you could get an intake backfire if the intake valve was still open a bit while simultaneously having spark timing too advanced (for some reason?). This would also cause the very rough idle like you're seeing. It would never improve as the engine warms up.
I don't think your car has SAI. Even if it did, it doesn't run like the old smog pumps. It only runs on cold startup of the engine, to help incinerate any unburnt fuel in the cat due to rich startup mixture. 
I would:
1) make sure the spark plugs, distrubutor cap & rotor and coil are all working properly. If you have misfire that could be putting unburnt fuel into your exhaust, causing the backfire.
2) Make sure the engine timing is correct. If the cam is retarded it could cause your problem.
3) Check to see if you have a leaky fuel injector. It would put fuel in the intake port while sitting overnight. On startup it could end up in the exhaust and could burn there. It could get the air to burn by an exhaust manifold gasket leak. Therefore, also check your exhaust manifold or where it connects to the head for any leaks. Leaky fuel injector can be determined by a fuel pressure residual pressure test or by removing the fuel injector rail (with injectors attached) and powering up the fuel pump (by unplugging the relay and electrically bypassing it) and watching the injectors for dripping fuel.


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## bearing01 (May 27, 2004)

*Re: backfire and smoke from my air intake ???? (bearing01)*

I just found these... may interest you
http://en.wikipedia.org/wiki/Back-fire
http://www.2carpros.com/first_...e.htm


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## germancarnut51 (Mar 23, 2008)

*Re: backfire and smoke from my air intake ???? (bearing01)*

Ignition timing can be off if the camshaft timing belt is not installed properly, because it drives the intermediate shaft and the distributor. The distributor can be out of time, even though the car has electronic ignition because the distributor relies on the properly thing of the intermediate shaft and the camshaft for it to be set correct inorder to send the correct timing information to the ECU, which controls the spark.
If the distributor timing is off, then ignition timing will be off because the ECU will not have the correct position of the camshaft, or pistons.


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## benzboyracer (Aug 5, 2003)

*Re: backfire and smoke from my air intake ???? (germancarnut51)*

Actually, Motronic 2.9 and 5.9 both use the crank position sensor to determine timing. That's what the whole 60 teeth -2 is about. The crank tells the ECU where the pistons are at- not the dizzy. The dizzy does point the rotor at the correct cylinder at the correct time, but the actual timing of the firing of the plug can be anywhere along that arc. Disconnect the hall sender and watch that the motor still starts and runs. That signal from the hall sender is used for timing the fuel injector events and nothing else.
For the original poster- check your cam timing for sure. Also check that there's not any air leaking in anywhere- from the brake booster hose, or evap line or anything like that. I remember forgetting to connect my booster hose one time and the resulting backfire had everyone in the shop ducking for cover.


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## mrdub27 (Mar 25, 2002)

*Re: backfire and smoke from my air intake ???? (kevin203)*

check plug wires.. have you done any recent tune up work.. also check timing belt it may have shaved a few ribbs off and skipped and screwed the cam timing up..


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## kevin203 (Jun 5, 2009)

the only thing that happen before this is my thermostat went and 
were i pour the antifreeze into started to leak.i was like 3 miles away from home and just put antifreeze in and drove home.


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## bearing01 (May 27, 2004)

*Re: (kevin203)*

are you saying your engine overheated? Did the engine boil over and you lost coolant out of the coolant ball lid?


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## kevin203 (Jun 5, 2009)

*Re: (bearing01)*

yeah


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## bearing01 (May 27, 2004)

*Re: (kevin203)*


_Quote, originally posted by *kevin203* »_yeah

There's a good chance your cylinder head is warped. I would run a cylinder compression check.


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## ognjen28 (Jul 8, 2009)

*Re: backfire and smoke from my air intake ???? (kevin203)*

Head gasket. If you overheated most likely that is the problem. next time watch the temperature gauge.


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