I have this rattle in my car that comes and goes, it sounds bad. I notice it when my wife starts the car, it will rattle for alittle bit then stop, then rattle alittle more then stop. The noise stops when you push on the gas peddle. This has been going on for about a week, she started it this afternoon and the rattle was alot louder than usual and it was steady. I told her to turn it off, timing chain? vacuum pump? It sounds bad. Where should I start? I took the valve cover off to see if I cuold see anything and nothing looks bad. I think I have the motor at tdc and the marks on the pully look like about 3 deg. look at the pictures and see if I am doing this right. Thankyou. The pointer is pointing to a mark on the pully that looks like a capital T? What does that mean? 0 is just a few marks to the left.

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Is it a metal on metal knocking sound? I'd start by looking at the serp tensioner arm. Simple test, remove the serp belt and see if the noise goes away.

-Jason

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

You can start the motor without the belt?

If there is coolant in the motor and it is stone cold you can start it and let it run for minutes. More then long enough to see if the sound goes away.

-Jason

Well took the belt off and started the car the noise was gone, put the belt back on and the noise was still gone. What is going on?

My guess is that the serp tensioner arm is defective. I went through the same thing on my car... when you take the belt off it moves the bearing around on the pivot and the sound goes away for a while. Replacing all the parts of the tensioner is not expensive. Remove the shock and the spring, and see if there is any play in the tensioner arm. It should not be able to move to and away from the engine, only rotate on its pivot.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Thanks, I will look at it tomorrow it is dark now. Yours was making a rattling sound too? That noise really scared me. I thought it was timing chain or the vacuum pump.

Mine made a metal on metal knocking / rapping sound. I also thought it was the timing chain or the vacuum pump, and replaced the $$$ vacuum pump only to have the sound persist!!!

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

So what all did you replace?

The tensioner arm: 6012001773
The roller: 6012000930
The shock absorber: (don't have the PN for this at hand )

-J

Thankyou