hissing sound coming from rear under carriage
 

I noticed this yesterday on my 1990 190E. While my engine was running, I heard this hissing sound coming from the rear. At first I thought it was a tire leaking air. It wasn't. I went up to the front to see if it was coming from the engine bay. Not there either. When I stuck my head near the driver-side rear under carriage (near the rear tire), I heard the noise coming somewhere from there. I have no clue what it is or where exactly it is coming from. BTW, the hissing sound was noticed when the car was warming up from sitting in the garage for a few weeks. The hissing is only heard if I'm outside near the rear of the car. And very noticeable if I put my head down by the under carriage.

After driving my car and fully warmed, the noise was either gone or perhaps still there but not detectable. Anyone know if this is normal for a 190E or any Mercedes? I'm not too worried because I think the hissing has always been there, but I just recently took great notice of it.

It's the fuel pump.

They generally get noisier when they are failing, so if you've had the car for years and this is the first time you have noticed it, might be worth getting a new one before it fails and strands you miles from no-where.

Barry

E200 Wagon 1994 110,000 miles

Sounds like the fuel pump. Maybe the long sit had something to do with it's being louder than normal.

i agree it is the fuel pump-i own a 190e-18litre-uk spec-before you replace the fuel pump-could i ask when was the last time the fuel filter was replaced-a blocked filter can cause the fuel pump to be noisier than usual.

Thanks guys. Now I'm worried! Is replacing the fuel pump expensive (parts and labor)? I don't hear the hissing while I'm driving with the windows up and down. Is the hissing just a part of start-up? Would that be normal? Give me some good news! :) Sunil, I don't think the fuel filter has been changed since its last major tune-up--that was like 30,000-plus miles ago.

It may be nothing to worry about. It is quite possible that it hasn't changed in character at all but that you have only recently started to notice it. This happened to me. When I first "heard" it I thought I had a big exhaust leak! Mine is loudest in front of the right rear tire. Mine hasn't changed in volume or character for 75K miles.