Engine knock - Alfa Romeo Bulletin Board & Forums

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post #1 of 9 (permalink) Old 05-19-2017, 08:24 PM Thread Starter
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Engine knock

I own an alfa 75 turbo evoluzione, I resently changed my broken aftermarket manifold to a much nicer aftermarket manifold. The old were leaking at a number of places and the engine never felt good because of this(vibrations and such). Now my engine runs nicer, but I have had a few ignition knocks. First time was low speed, low rpm up a hill. But I have noticsed some knocking from acceleration in 2 gear, fulltrottle at 3500-400 rpm on level ground.

The don't have much documentation but I I believe they have used a TS throotle body and custom TS looking plenum, and a large FM intercooler. Stock ECU but the car has a max of 0.9-1.0 of boost. Ignition was adjusted by reputable tuner on a dyno by previous owner.

The car didn't do this before I change manifold and downpipe.

What can be done? I've ordered a new knocksensor to se if this helps and tried 3 different sets of plugs. Bosch, NGK BP6ES and NGK BP8ES.

Can you adjust the ignition on a 75 turbo engine(I know the previous owner told me, but how?)?


Last edited by panzhar; 05-19-2017 at 08:27 PM.
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post #2 of 9 (permalink) Old 05-20-2017, 02:21 PM
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Are you sure it's Pre-ignition engine knock? The reason I ask is that changing headers would probably not induce this situation. Now, potentially you have always had this knock, but just couldn't hear it due to the noisy previous set of cracked headers.

Just throwing out ideas.


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post #3 of 9 (permalink) Old 05-20-2017, 03:25 PM Thread Starter
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Well, it's a rattle like wrenches beeing rattled or loose exhaust piece or something like that. The old header was working good actually under these conditions. The engine was very smooth on boost and lots of rpm. The new header is of equal length pipes and a larger diameter downpipe.
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post #4 of 9 (permalink) Old 05-20-2017, 04:58 PM
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I would first check the install, bang on the exhaust with a rubber mallet, make sure it is all sound and no rattles are coming from the exhaust/headers...start there


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post #5 of 9 (permalink) Old 05-20-2017, 08:51 PM Thread Starter
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Doubt it's coming from the exhaust. That would be to easy :-) Can this be caused by running to lean? But how would the header cause this? Anyway I drove 150 km or so before noticing anything.

Old vs new manifold:

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post #6 of 9 (permalink) Old 05-21-2017, 01:20 AM
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Quote:
Originally Posted by panzhar View Post
The new header is of equal length pipes and a larger diameter downpipe.
Perhaps just becouse the downpipe is larger is playing avoc with your FI
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post #7 of 9 (permalink) Old 05-21-2017, 02:17 AM
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You may have some false air leaks in the induction system or misreading MAF. That will lean the fuel amount and the engine will knock.
Check all the air tubing for cracks.
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post #8 of 9 (permalink) Old 05-21-2017, 10:45 AM Thread Starter
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My hoses are all good. Is there a good way to check the ancient MAF?
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post #9 of 9 (permalink) Old 05-22-2017, 05:14 AM
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You could clean it - the flap gets dirty over time and he electric windings. Use a usual degreaser product for the flap and contact cleaner for the windings.
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