Arrie

Today noticed an engine noise that does not sound good at all. This is with warm engine at idle. I do not hear it inside the cabin when driving and car seems to drive fine but this noise is just awful.

The sound seems to come from the rear part of the engine. I was thinking of the rattling timing chain but think the noise would come from the front of the engine and I have not heard of chain rattle problem other than right after cold start-up. Car has 74000 miles on it.

MBENZTECH

That sounds like the High pressure fuel pump. How many miles on the vehicle?

Arrie

Oh, I hope it is the pump, but how would that make a noise like this?

74k miles.

Arrie

Yes, it is the pump. Now the question is if I can keep driving it or should I have it replaced?

I see comment from various places that these pumps are noisy but mine was not until yesterday when it suddenly started making that noise.

MBENZTECH

They are noisy and they get noisier as the mileage goes up. As long as the car drives find, nothing to worry about.

Arrie

Well,

done some reading about the pump and find out it is lobe driven by the exhaust cam shaft. Lobes drive the pumps like the valves, i.e. press the pump actuator against a spring.

More noise, like mine, most likely comes from the lobe losing contact with the pump actuator. Now this can be because parts wear but my noise comes and goes so it cannot be wear. I suspect the pump is probably dirty / sticky inside and does not allow actuator to return fast enough with the spring force and loses contact with the cam.

I have ordered both high pressure pumps and will replace them as they arrive. If it is still noisy with new pumps, then I know I have new parts with noise and can trust it a bit better.

BenzV12

Best of luck with that , I trust you will be satisfied with the results as well

Arrie

Engine sound with new pumps. Quite a big improvement.

And I don’t think the noise was coming from the pumps themselves. I think it is from the roller lifter that runs on the cam. One of them had worn a little dimple in the area where the center of the spring loaded valve comes in contact with it. This probably made more clearance that allowed the roller to bounce around.

Well, if it is the pumps or the lifters the bad sound is gone with new pumps and roller lifters.