Engine detonations - poor or rich fuel mixture?? - Alfa Romeo Forum
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  (Post Link) post #1 of 12 Old 28-06-08 Thread Starter
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Engine detonations - poor or rich fuel mixture??

What causes detonations in inlet collectors?
Poor or rich mixture....or both can do it.I'm still have some bang-bang when start cold engine, and i'm concerned about.
Here you can hear sound of my engine, started cold in the morning, and no touch of the throttle.
http://hitspaces.net/engine.wma
To explain what do you hear - when engine is on, revs are 600 - 800 and it seems like it will die instantly - this continues 10 - 20 sec.(you may hear first bang on 22 sec of this record) and then it's OK - 1100 - 1200 rpm, and working perfectly.
More - when i start cold engine and shut it down immediately after starting, and repeat this 2-3 times, on the 4 starting it's OK....no detonations. My fuel tank cap is not original, and there is no pressure in the tank at all, and i know that there must be some. Can this be a problem?
I changed 8 new Denso iridiums.New Bosch MAF and lambda!!!! No change.......
Thanks.
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  (Post Link) post #2 of 12 Old 04-08-08
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Re: Engine detonations - poor or rich fuel mixture??

i also get this with my car and would liek to know the solution?
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  (Post Link) post #3 of 12 Old 05-08-08 Thread Starter
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Re: Engine detonations - poor or rich fuel mixture??

TRy to measure fuel presure when engine's cold......
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  (Post Link) post #4 of 12 Old 05-08-08
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Re: Engine detonations - poor or rich fuel mixture??

I think you may find this is your pre-cat sensors if your car has the twin cans at the manifold outlet, your lamdas there are faulty.
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  (Post Link) post #5 of 12 Old 06-09-08
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Re: Engine detonations - poor or rich fuel mixture??

and what did you have to change ?
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  (Post Link) post #6 of 12 Old 06-09-08
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Re: Engine detonations - poor or rich fuel mixture??

When my old 'vette was fireing on the inlet side it was caused by the cams on the exhaust side wearing and refusing to let gas out, which then burst out of the carb. very dramatic
It could be a timing issue..Jumped a tooth on the t belt?
Hope you get it fixed
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  (Post Link) post #7 of 12 Old 09-05-09
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Re: Engine detonations - poor or rich fuel mixture??

Hello. I have exactly the same problem with my alfa 156 1.8 TS. When the engine is cold it works with large explosion. Boom in the inlet manifold and does not to press the gas pedal. Same sound as the sound file from the first post. When trying to run the engine first started working, he's in 1000 rpm and immediately stops. Run it a second time. Works with 1200 rpm and started banging and ringing of the impoverished fuel mixture. While working as idling engine speed fluctuate. It lasts about 30 seconds. Then the sound of the engine is quiet and everything is fine. I checked the following and are in compliance.

1. Throttle position sensor
2. Mass Air Flow Sensor
3. Coolant Temperature Sensor
4. New Denso Iridium Power Spark Plugs
5. Ignition coils - working perfectly
6. Fuel pressure 2.8 bar.
7. Fuel injector cleaned
8. I checked for air leaks after the MAF sensor - maintains 0.5 bar in the inlet manifold for about 15 minutes and there was no leakage of air.

What else should check out? Morning start the engine by the 3rd time.

Last edited by oem; 09-05-09 at 11:44.
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  (Post Link) post #8 of 12 Old 09-05-09
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Re: Engine detonations - poor or rich fuel mixture??

Replace hydraulic lifters
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  (Post Link) post #9 of 12 Old 09-05-09
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Re: Engine detonations - poor or rich fuel mixture??

Why? They can not hear tract?
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  (Post Link) post #10 of 12 Old 09-05-09
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Re: Engine detonations - poor or rich fuel mixture??

I' think you've had the belt done recently, the inlet cam asn't been tightened up and it's bent the valves allowing the ignition to backfire.

This means time for a compression test first. If that proves fruitful and all is OK, then change the knock sensor, it may be that telling the ECU lies and puting the ignition timing out.
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  (Post Link) post #11 of 12 Old 10-05-09
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Re: Engine detonations - poor or rich fuel mixture??

Sorry. I was not very good English and is not well understood the first sentence. If it comes to camshaft belt is changed and is gearing special tools.

Compression engine is good because it accelerates well. I have no cost of oil and a maximum speed reached 240 kilometers per hour on the speedometer.

I want to say that when declutch coolant temperature sensor ignition morning is good.

EDIT:
Problems with poor fuel mixture is only 30 seconds after the initial ignition. He expressed only after a long stay - 5 6 hours or more. Then everything is perfect.

The first fire was very bad. Engine fail immediately after starting it. Second ignition is good. Maintain turnover in 1200 as from time to time is unstable. Turnovers to fall in 1100 and started the engine off. Is called the sound of detonation.

I did AlfaDiag experience with the first ignition of the engine. I watched the angle of ignition. It was 3 degrees before TDC. By pressing the gas pedal angle of light changes to -3 degrees after TDC. After 30 seconds operation of the motor has stabilized and the angle of ignition in the range goes. Between 9 and 12 degrees after TDC.


All other data management engines were the norm.

1. Quantity air idling - 9 kilograms per hour
2. Air temperature - 27 degrees
3. Engine temperature - 30 degrees
4. Injection time 5 MS.
5. Lambda is cold and still not working.

Is it possible after a long stay in the car the fuel line to the tank back in the morning and having to gnaw engine light remains air. And the second is already starting to run normally?

Or is it possible to have a plunger which opens to the end?

Alfa Romeo 156

Last edited by oem; 10-05-09 at 20:04.
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  (Post Link) post #12 of 12 Old 11-10-13
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Hi, same problem for about 6 months maybe you know a solution?
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detonations , engine , fuel , mixture , poor , rich

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