Fuel Pump Noise?

[Halm]

I have finally gotten my electrical issue with the fuel pump circuit on my SC fixed. But now, I think for the first time in almost 3 years ownership I can hear the pump run before the starter engages. As part of the electrical troubleshooting, the gas tank was drained and inspected, and a new screen filter installed. It was sometime after this I started noticing the fuel pump.

Maybe it is because I am listening for it for the first time, or maybe because coincidental to fixing the electrical issue it is going bad?

How loud, if at all, should the pump be? Is it a Hummm sound or more mechanical?

Thanks.

[RWebb]

a CIS fuel pump can be heard but it isn't really loud

mine is behind the R. wheel - where is yours?

[spuggy]

PET's a little confusing on the topic. My '77 has the pump under the tank. Thought they moved it back there a few years earlier.

The fuel pump on a later car shouldn't run with the ignition just switched on; the switch on the AFM needs to provide a circuit, which usually only happens when the plate moves off the rest - e.g. because the motor is turning over or running. Perhaps the switch is broken or disconnected? Or the relay jumpered?

As far as "loud" is concerned, they can be pretty darned noisy... I switched the original out for an 044 motorsport - and that sounded exactly the same. They sound - well, like a pump that's got a significant current rating and moves a lot of fuel at high pressure.

Maybe being located up front it's easier to hear in the cabin? Mine sounds like it's just behind the gauges

[RWebb]

I have a '73.5

could be that the rubber is stiff on yours... or the pump could be going bad

change the fuel fiter; flush the old one with WD-40 for a bit more safety, and cut it apart to examine the filter media

[porwolf]

I replaced my 79 SC Bosch fuel pump a couple of years ago because the original pump was frozen because of stale gasoline when the care was stored for many years. Because of possible old fuel debris still left in the tank I replaced it with a $ 50.- Walbro pump. That pump initially was very noisy. I don't remember hearing anything from the original Bosch pump before I put the car into storage. But now, even the new Walbro pump is quiet. Especially with a full tank of gas. Because of the Techron gas additive I only use Chevron gas now. I think That eventually cleaned out the fuel system and keeps the pump quiet. I understand cavitation can cause fuel pump noise and cavitation can be caused by restricted input to the pump. The pump, I understand, transports a lot of fuel, more than the engine needs, the rest goes back into the tank.

[ossiblue]

Originally Posted by Halm

I have finally gotten my electrical issue with the fuel pump circuit on my SC fixed. But now, I think for the first time in almost 3 years ownership I can hear the pump run before the starter engages. As part of the electrical troubleshooting, the gas tank was drained and inspected, and a new screen filter installed. It was sometime after this I started noticing the fuel pump.

Maybe it is because I am listening for it for the first time, or maybe because coincidental to fixing the electrical issue it is going bad?

How loud, if at all, should the pump be? Is it a Hummm sound or more mechanical?

Thanks.

You have an SC. If the engine/CIS is proper for the car, you should not hear the pump running before you start the car. As mentioned in an earlier post, the switch on the intake manifold could be the problem--either the wire to the switch is disconnected, the switch itself is bad, or the plunger is not coming to rest at the proper location--or the fuel pump relay is faulty. Since you are hearing the pump, it should be a humming sound, not high pitched and not metallic. You probably notice it because you appear to have a fault in the electricals to the pump which you did not have before and you hear the pump when the rest of the car (engine) is quiet. CIS cars up through 75 had the pump start with the ignition simply "on." From 76 on, the pump only runs with the starter and a running engine.

[Halm]

Great info here guys. Thanks!

[Jerome74911S]

My pump (under the back seat, on the left) was noisy. I did two things: I ran some Techron through the fuel system and remarkably this did quiet down the pump a lot. The second thing is, I remounted the pump, in the same location, but cushioned in some closed-cell rubber. This stopped noise transfer to the tub.

[RWebb]

Originally Posted by ossiblue

You have an SC. If the engine/CIS is proper for the car, you should not hear the pump running before you start the car.

doesn't the pump come on briefly to pressurize the system, before the safety relay turns it off?

[theiceman]

no.

i cis fuel pump for an sc ONLY pumps when the key is in the start and run position. i have heard of some cars that have been "wired" to have the pump run in the on position, but usually this is done to cover up some other underlying issue

[RWebb]

when the key is in the run position is what we are talking about - the question is whether the engine is turning over or not

[Nickshu]

Mine was buzzing loudly and when I investigated I found that the PO had hit something and the skid plate was bent just enough so the pump was contacting the underside of the plate and vibrating against it. The stock clearance here is very small so it does not take much of a bend to hit the pump.

[boyt911sc]

Originally Posted by RWebb

doesn't the pump come on briefly to pressurize the system, before the safety relay turns it off?

RWebb,

It does for the early CIS ('73.5 - '75). But not for the later CIS ('76-'83) that have AFS (air flow switch).

Tony

[Halm]

Here is a quick update to my situation. The noise I am hearing is not the fuel pump. I was hearing the noise when in the car and in garage. I turned the key to the “On” position, stepped out of the car and there was zero sound coming from the fuel pump.

So as per L.R.’s post I also opened the engine lid and listened. I did hear several sounds there, including the CDI whine. Car runs and drives fine, so I now suspect I was just overly cautious / paranoid about what I thought were new sounds.

[midlife]

On my car the pump only runs while cranking. It is off when the key is on but the engine is not running.

Not CIS though.

[wayner]

A new pump is cheaper than a tow truck ride. I replaced mine just in case.