Strange noise...fuel pump??

saxony_wu · 07-30-2013, 06:31 PM

Hi gents,

Lately a sharp humming noise developed after the car is fully warmed up and driven for half an hour or so. The noise comes and goes for few seconds. Little vibration can also be felt through the steering wheel with the noise. Only happen when the car is idling; not in motion.

The noise sounds like coming from the front or underneath the car. Since the car has no power steering, I was thinking maybe the fuel pump. But I was told if the pump is failing, it makes noise consistently.

Car is 88 Targa with 50K miles.

Any idea or suggestions?

Thanks....Steve

porwolf · 07-30-2013, 07:07 PM

I would stop when you hear the noise and try to listen with your head low to the ground near the front wheels. If you think the noise come from there it could be the fuel pump. The fuel pump can get noisy when the fuel flow into it is disrupted by junk in the tank, like rust, and the tank fuel filter is compromised. Also the pump can get noisy when the fuel level is low and the engine has been running hot for a while. Then the gas in the tank, being constantly circlated by the pump, also is hot. Filling up with fresh gas would quiet down the pump. I would go through these motions to get some idea about the fuel pumps culpability in creating the noise.

saxony_wu · 07-30-2013, 07:55 PM

Hi Porwolf,

Thanks for input.

I've tried that in underground parking a few times. Problem is the noise came and gone in few seconds and not consistent. By the time I got out of the car the noise was gone and everything sounded normal again!

Also the noise doesn't seem to have anything to do with gas level. It also acted up after fresh fill up.

My concern is if the fuel pump is making noise, why would the steering wheel vibrates a little simultaneously?

Discseven · Discseven's Garage

Steve,

Not sure if you have AC... and if you do if an 88 has a front condensor and blower.

I know first hand the impeller in the blower can rotate out of round and hit the housing. What does not make sense is for it to make noise and then not... but strange things do happen!

Aside from the fuel pump, this is the only other thing that spins up front that I'm aware of. (I'm referencing my '80.)

porwolf · 07-30-2013, 08:27 PM

Quote:

Originally Posted by Discseven

Steve,

Not sure if you have AC... and if you do if an 88 has a front condensor and blower.

I know first hand the impeller in the blower can rotate out of round and hit the housing. What does not make sense is for it to make noise and then not... but strange things do happen!

Aside from the fuel pump, this is the only other thing that spins up front that I'm aware of. (I'm referencing my '80.)

Or could it be the blower motor bearing? Bearings, I think can make that noise and vibrate at the same time. And then appear normal again. Just a guess, if you have air conditioning and it is turned on.

Discseven · Discseven's Garage

Quote:

Originally Posted by porwolf

Or could it be the blower motor bearing? Bearings, I think can make that noise and vibrate at the same time. And then appear normal again. Just a guess, if you have air conditioning and it is turned on.

Hmmmm... possible the bearing(s) could be it. The blower motor is relatively small so how much vibration rotted bearings would create seems questionable.

If there is something awry with the blower --- and Steve has one --- it's easy enough to feel the blower (AC on) and sense whether it's vibrating more than seems reasonable.

What else spins up front?

saxony_wu · 07-30-2013, 09:19 PM

Car has AC which I seldom use. Most of the time I drive with the top off. The noise is there without AC or blower on. That's why I figure those are out. Problem is the noise is quite irritating but not consistent. It is much harder to diagnose.

The only thing I can think of is the fuel pump. Maybe I should order a replacement to see what happen.

Thanks guys for your info.

porwolf · 07-30-2013, 10:45 PM

Quote:

Originally Posted by saxony_wu

Car has AC which I seldom use. Most of the time I drive with the top off. The noise is there without AC or blower on. That's why I figure those are out. Problem is the noise is quite irritating but not consistent. It is much harder to diagnose.

The only thing I can think of is the fuel pump. Maybe I should order a replacement to see what happen.

Thanks guys for your info.

The fuel pump is not cheap. But in the worst case and the pump was not the problem you have a spare pump. That is a good insurance on the road. I carry one, just in case. If you do change the pump I would also check the in-tank-fuel-filter that screws into the tank from the bottom. That filter is supposed to keep any debris in the tank from reaching the fuel pump. It is not too expensive, less than $50.-.

frannyB · frannyB's Garage

Hi Steve,

I'm going through this right now... Almost sure it is your pump. Mine would get very mouthy when warm so I replaced it and the filter in the engine bay ('86). That helped, but I still got the buzzing noise a bit so I drained the tank and pulled the plug on the bottom to clean the screen. There were a few large clumps of crap that came out. Also, my filter screen had separated from the plug so I had to order a whole new plug and filter. If you do pull the plug, don't forget to replace the rubber "O" ring seal on the plug. Our host has that too. The one I pulled off was hard and flat and probably would have leaked if I tried to re-use it.

The pump flows quite a bit more fuel than the engine needs and the rest is routed back into the tank. This allows the fuel to cool the pump. If the screen in the tank is clogged, then the pump may pull enough to supply the engine, but it will start to over heat due to lack of cooling.

Sounds like you are right at the beginning of an issue. I would replace the filter and clean the screen and see if that get's it. If not, replace the pump and hold the old one as a backup.

Good luck, Franny

Jerome74911S · 07-31-2013, 07:53 AM

I like to start simple, because that's all I can do . . .

It's not impossible that the pump is simply loose in its mountings. If so, it might vibrate somehow, then quit after it shifts a little.

Worth a check before you start spending $$

frannyB · frannyB's Garage

Good call Jerome... I forgot to mention that my bottom skid plate was bent just enough to be touching the fitting at the end of the pump or something... Just thump it or pluck it and see if it buzzes.

Franny

saxony_wu · 07-31-2013, 10:38 AM

Thanks everyone for your meaningful inputs and suggestions.

I remember my last 88 coupe started making the same sound just before I sold it 3 years ago. Didn't get the chance to address that. I did mention to the new owner and advised him maybe it was fuel pump issue.

Sound like a little weekend project for me. It's OK as we have a long weekend coming in Toronto.

Steve