symptoms: loud humming sound (loud enough to hear inside the car) coming from near or just below the front passenger-side fuse box. The sound only occurs when the engine is running...no sound with just the electrical systems on. I've done searches that might point to either a failing fuel pump or a brake pump, but there is nothing definiative on this.

I'm doubting a fuel pump issue because I would think I'd get the sound with the electrical systems on. Not sure then how to test whether its the brake pump.

suggestions?

 

Probably the fuel pump. Mine does the same thing and is really loud and annoying. I am planning to replace it soon rather than get stranded somewhere. You will have your share of R-listers chiming in to assure you that the noise is 'ok', but my first 993 (with 110K miles!!!) had a quiet fuel pump as in - you could NOT hear it. I'm going to go so far as to 'guess' that the PO ran crappy, water-logged gas all the time and the pump has had to work harder and harder to pull the gas thru sludge and water that has probably accumulated in the tank around the fuel pickup. I am actually considering having the tank removed, drained and flushed as part of the pump R&R. Maybe overkill, but ya' never know till ya' know.

 

Isn't the fuel pump under the car? in a little box with a cover over it? I'd say ABS? Power steering?

C/

 

Yep - but your hear it in the front boot and cockpit. Power steering pump is mounted ON the engine. ABS could be the noise, but I don't have it so it is not in my equation.

 

Just another idea, It could also be the high speed fan that the climate control utilizes located in the dash.

ZP44

 

thought about the fan, so I shout it off...was able to hear the humming sound even more clearly.

if the ABS, would simply pulling the fuse diagnose the issue, presuming there is a fuse for the ABS?

 

Yes, you could pull fuses to confirm. It's unlikely to be the ABS and most likely it is the fuel pump (been there, replaced it). However, I thought you said it was only loud when the engine was running? If so, you can't pull the fuse for the fuel pump and expect anything other than the car dies. The fuse for the ABS (speedometer too) can be pullled with the car runnning, you'll just have no ABS and no speedometer.

 

I have the same Hum from the rear slider.... except its the rear fuel pump, going to replace it its very annoying.

JERRY

 

Tom - did you do the pump yourself? Looks pretty easy on the DIY scale.

 

No. My wife and I have an agreement that I get 10 track weekends a year. She views time spent doing DIY stuff as counting against that track time. So, I'm lucky and am able to pay a pro to do my work and not have to worry about DIY stuff.

 

Coo - el. I'm leaning towards letting the pros do it as well. Ten years ago I couldn't get enough of working on cars. Not so much any more although I still can do it...just other things to do in the spare time I have.

 

follow up - so I pulled fuse no 16 for the ABS and still had a humm. Then pulled fuse no 26 for the fuel pump and the humming stopped...the engine almost immediately started to stumble, so I put the fuse back in....engine picked up again and so did the humming. so it would seem I'll be replacing the fuel pump soon.

my question is does the humming mean an imminent failure?

 

The only time I ever had a fuel pump failure was in a 1979 911SC (my 2nd of four earlier 911's). I was bragging about how great the car was to a buddy in the right seat and the engine promptly 'died' on the San Diego freeway. Luckily I was able to glide down an exist ramp for the tow. It was the pump.
When you replace the pump, replace the dme relay also - if not already and keep the old one as a spare.

 

had a 79 SC as well with an ill-timed fuel pump failure as well...loved the car, but it left me stranded by the side of the road way too many times. Good thought on the DME.

 

It is an electric motor... it is supposed to hum. The only issue is how loud. If you can't hear it with the trunk lid shut it is OK.