yourSpecialisT

Just finished changing a headgasket on my car which overheated. Car runs good, pulls good vaccum, compression is good but my knock sensor is getting faint readings on the engine. I can only describe it as piston slap. When the head was off, one of the pistons seemed a wee bit loose to where I could move it a tiny bit it I pressed it hard enough. Is piston slap enough to make the knock sensor go off on the AEM?

JohnBradley

iTrader: (30)

Yes. It is only looking for amplitude of noise expressed in Volts.

aaron

barneyb

The ECU supposedly does filtering of the signal it gets in an effort to discriminate between knock and normal noise. On the other hand, I noticed that when I dropped the hood on my engine last night, the idle momentarily dropped.

yourSpecialisT

So assuming it is Piston Slap, would it be safe to still drive and boost the car? Everything checks out perfect except for the annoying noise.

GG06MR

iTrader: (9)

How does it check out perfect if you've got that much free play? I can't imagine your bearing tolerances are within spec.

yourSpecialisT

I'm not 100% sure it is piston slap without tearing apart the motor again. I just meant the general vitals are all good. ie. compression, vaccum, etc... I'm gonna get a stethoscope and try and pinpoint where the noise is coming from.

JohnBradley

iTrader: (30)

While what you said is true (and caused by your MAF by the way) this is an AEM so the knock control is unfiltered and just runs vs voltage.

So did you inspect the following?

Piston skirts to make sure they hadnt collapsed from the heat/lack of lubrication

Rod bearings

Valvetrain noise

I wouldnt run full power before you take it and log some low boost pulls. Since this an AEM I would be interested in seeing what the knock voltage actually is

barneyb

Sorry, some day I hope to learn to read.