Rattle under load when engine is hot

I have a GL 1996 with 209k and I have the same problem.
Also had the same problem in many other older cars I,ve owned.
It's called either piston slap or big end knock, or both.

As the engine wears clearance get bigger, when you accelerate at low revs and under higher gearing, fuel charge is larger, wants to force the piston down faster but because of the high torque the result is all the clearances are taken up at once, hence knocking sound.
You often hear this when people take off from the lights in a manual car,when they don't have enough revs.

BTW GLs are ment to run on 95-96 ron. I've run 98 and 95 and there is no noticable difference (except the price)
Trouble is they are replacing 95 with e10 so we will have to use 98 in the future.


Ross.

Quote:

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Originally Posted by RossB

I have a GL 1996 with 209k and I have the same problem.
Also had the same problem in many other older cars I,ve owned.
It's called either piston slap or big end knock, or both.

As the engine wears clearance get bigger, when you accelerate at low revs and under higher gearing, fuel charge is larger, wants to force the piston down faster but because of the high torque the result is all the clearances are taken up at once, hence knocking sound.
You often hear this when people take off from the lights in a manual car,when they don't have enough revs.

BTW GLs are ment to run on 95-96 ron. I've run 98 and 95 and there is no noticable difference (except the price)
Trouble is they are replacing 95 with e10 so we will have to use 98 in the future.


Ross.

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ethanol boosts the octane rating anyway ;-)

his car has pretty low mileage for it to be caused by piston slap - and a very uncommon occurrence in vw's anyway - with regular oil changes plenty of dubs get past 300,000km without pistons/bores going out of spec. its rare to find wrist pins out of spec at any mileage unless there's been oil system problems.

Yeah its not engine wear at 100ks. The car is immaculate and has been looked after. I reckon knock sensor.

Quote:

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Originally Posted by jmystaki

Does anybody know the torque setting for the knock sensor?

- 2.0 8v Mk3

I don't have a workshop/service manual... I think it is mentioned in there...

Cheers

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The tightening torque of the knock sensor to cylinder block is 20 Nm (15 ft-lb)

(From Bentley)

Geez maybe I should check my knock sensor:)
Although I suspect mine is due to the car having had a hard time in its previous lives!!!

Ross.

Thanks guys !

I have found a local source for the knock sensor Volksbard - $165 for Bosch part number: 0 261 231 077 (which is the aftermarket part number for my car)

I have found a shop in the US that will sell it for $55.91 USD + shipping.

www.impartsol.com

I intend to get this in the next week or so...

Also thanks for the Knock Sensor torque settings... I will try this out as well...

Gee... (i really need to get a manual !)

Cheers

Ok, I am 95% sure that the problem is solved.

I originally purchased a number of the Subaru decarbonising cans and followed the process to decarbonise the head via the intake manifold.

3 cans later the only real difference was early torque and acceleration.

Still pinging...

The day before yesterday, I removed the spark plugs (after the engine was really hot) and filled up each cylinder with the remaining can of the decarbonising spray.

I let it sit for 2 hours, reinstalled the plugs, left the leads off, cranked the motor to flush the liquid down the exhaust, reconnected the lead, started the car and took it for a drive.


NO PINGING !!!!!

I tested today (given it is hotter today, ran the AC and loaded up the engine) no issues !

Thanks for all the interest and help !

Quote:

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Originally Posted by jmystaki

Thanks for the advice re: testing knock sensor. I hope to get my cable in the next day or early next week.


Hi Biggles - I will be using Ross-Tech - http://www.ross-tech.com/

Cheers

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Thanks Jmystaki.

Quote:

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Originally Posted by jmystaki

Ok, I am 95% sure that the problem is solved.

I originally purchased a number of the Subaru decarbonising cans and followed the process to decarbonise the head via the intake manifold.

3 cans later the only real difference was early torque and acceleration.

Still pinging...

The day before yesterday, I removed the spark plugs (after the engine was really hot) and filled up each cylinder with the remaining can of the decarbonising spray.

I let it sit for 2 hours, reinstalled the plugs, left the leads off, cranked the motor to flush the liquid down the exhaust, reconnected the lead, started the car and took it for a drive.


NO PINGING !!!!!

I tested today (given it is hotter today, ran the AC and loaded up the engine) no issues !

Thanks for all the interest and help !

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Could also be the plugs you put in were not right and the decarbonising cans has affected them.

Is it still ok?

nope.... pinged the next day ( the hot one... after the car really got hot...)

I have purchased 2 more decarb cans today, and filled the cylinders up and will leave it over night.

It def has a major improvement... but still pinging....