HELP - Fuel pump buzzing

gshiwota · 12-13-2007, 09:20 AM

The car is a stock '82 911SC

I noticed last night that my car just started making a loud buzzing sound coming from the engine compartment AND under the front of the car when the key is in the on position. The sound is quite loud and sounds very metallic. I think it's the fuel pump because when I pull the fuel pump relay the sound goes away. I also noticed that my car is harder to start now after sitting... it used to start in about 1/2 crank.. now it takes several cranks to start.

Has anyone had this issue? I'm particularly confused about the sounds coming from the engine compartment. Is this just the sound traveling down the fuel lines and echoing in the engine compartment? It certainly seems like a single issue since it goes away completely when I pull the fuel pump relay.

If it's the fuel pump, which pump should I get. Many sites show the OEM pump for $250+ while there's an Universal Fit Bosch unit that looks the same for under $150. Anybody have experience with the Universal Fit Bosch unit or another cheaper unit?

My family calls this car "the money pit" so I'd like to get the cheaper pump if it fits.

Thanks!

Gabe

Sunroof · 12-13-2007, 09:25 AM

Rebuilt fuel pumps do very well, especially with a warranty. You can save $$$$ on the rebuilds. I do not believe the replacement would be too difficult to perform.

911quest · 12-13-2007, 10:09 AM

One other thing when and if you replace the pump check the screen in the tank these pumps get noisy if they starve for fuel thats what lubricates them so while your in there.....

boyt911sc · boyt911sc's Garage

Gabe,

At normal condition, your fuel pump should NOT be running when the ignition switch is at ON position. One reason it could be running now is the air sensor plate (air meter switch) having a gap or opening. This could cause fuel flooding in your manifolds resulting to difficulties in your starting. Your problem is electrical.

Don't even think of replacing CIS components like an expensive FP without checking the delivery pressure or performing related tests. Replace only when confirmed defective. If your pump could deliver a 65-70 psi fuel pressure range, SAVE it. Just my two-cents.

Tony

gshiwota · 12-14-2007, 09:27 AM

Tony - Thanks for your input. What you're saying makes a lot of sense.

In fact, there is a loud buzzing sound coming from the engine compartment as well which first led me to believe it was an electrical problem. Any idea what could be buzzing in the engine compartment? I haven't had time to look closely however it sounds like it's coming from the upper left-center side of the engine - perhaps near the CIS stuff. The buzzing goes away when I pull the FP relay so it must be on the same circuit. Is there another relay or switch on the same circuit that may cause this noise?

Thanks again!

Gabe

boyt911sc · boyt911sc's Garage

Gabe,

Do you have a spare fuel pump relay (911.615.108.01 RED) you could use? It might be a simple bad relay or open ground for #85 terminal (relay). Keep us posted and will figure out what's your problem. Good luck.

Tony

JP911 · JP911's Garage

You may very well have some buildup around the air sensor plate that is hanging it up, which would cause the fuel pump to run before turning the key. This would also lead to the sound of the injectors spraying without the engine running, which is a buzzing sound.

Tom '74 911 · 12-14-2007, 11:45 AM

Quote:

Originally Posted by boyt911sc

Gabe,

At normal condition, your fuel pump should NOT be running when the ignition switch is at ON position.
Tony

An '82 SC may be different than a '77 2.7 CIS, but my fuel pump runs w/my key in the "on" position.

Tom

tcar · 12-14-2007, 01:05 PM

Quote:

Originally Posted by Tom '74 911

An '82 SC may be different than a '77 2.7 CIS, but my fuel pump runs w/my key in the "on" position.

Tom

'73.5 911T -'83 all used the same CIS injection system.

gshiwota · 12-14-2007, 01:25 PM

Update..

I ran home at lunch today to try replacing the FP relay and to check the air flow plate.

1. I replaced the red relay with a brand new black relay and nothing changed. There is still a buzzing sound from the engine compartment and humming sound from the FP area.

2. I took off the air cleaner to check the air flow plate. I moved the plate with my hand while the key is in the on position and heard the injectors activate. It's a different humming noise when the plate is opened then the buzzing noise I'm hearing - the buzzing noise didn't change when the plate was moved. Plus the plate appears to close completely when the engine is not running. Therefore, I think I have ruled out the air flow plate.

So, the buzzing sound from the engine compartment is loud and sounds almost like an electrical buzzing sound. Any ideas on what can be buzzing - it may or may not be on the same circuit?

Thanks again!

Gabe

Jim Sims · 12-14-2007, 01:29 PM

"'73.5 911T -'83 all used the same CIS injection system."

Incorrect. They all used a CIS system but it was far from being the same. For example a '73.5T doesn't have an air flow safety switch while a '76S does. There are numerous other differences.

tcar · 12-14-2007, 01:45 PM

Quote:

Originally Posted by Jim Sims

"'73.5 911T -'83 all used the same CIS injection system."

Incorrect. They all used a CIS system but it was far from being the same. For example a '73.5T doesn't have an air flow safety switch while a '76S does. There are numerous other differences.

I guess I was being too general re: his question.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by tcar

'73.5 911T -'83 all used the same CIS injection system.

'73.5 US models don't have TTS like those of '74 to '83 US models. '77 to '83 US models with fuel pump relay should not have the fuel pump running when ignition is at ON position based from the factory wiring diagrams.

Tony

911Freak · 12-14-2007, 03:49 PM

It is possible you are hearing the "Frequency Valve", check section 240-30 in your Bentley Repair manual. you will also find smart troubleshooting guides there too!

911Freak · 12-14-2007, 03:59 PM

IE: Frequency Valve: Bleeds off fuel pressure in the lower chamber in the fuel distributer

Based on input from the oygen sensor, the ox sensor control unit corrects the fuel/air mixture by varying the frequency valve duty cycle...

To quickly check the Frequency valve:
Start the engine and place a finger on the valve. It SHOULD be BUZZING.

If valve isn't buzzing, check the ohm resistance ( 2-3 ohms)-( 78-83 CSI )

Again run a few Fuel system electrical diagnosis and make sure everything is working properly before you start buying a component at a time....(never works, just ask me! )

A little time spent troubleshooting and familiarizing yourself with the fuel system and all it's components will save you time and money!

squelch · 12-18-2007, 10:06 AM

Where is the best place to buy a rebuilt fuel pump?

I am having the same buzzing sound on mine. Here are two other threads about the same thing:
#1 & #2

Please let us know if you solve the problem. I won't be able to get to mine until after Christmas.

sean m · sean m's Garage

Guys,

My 77 2.7 had the same "buzzing". Got a fuel pump from Pelican Parts, followed Wayne's direction on page 98 - 99 of his book....about 30 minute project from jacking up the car to starting it back up. Works like charm.

I wasn't having any problem with the pump working, just annoying buzzing noise. Just my .02..

Sean

RoninLB · 12-18-2007, 11:36 AM

FPs get old.

If it has 75-100k on it get ready to r&r pump, intake line, clamp, and gas seal washers at connectors. Sometimes the FP will start making more noise than usual and last another 5k miles.

gshiwota · 12-18-2007, 09:45 PM

It's been raining on and off here in sunny Southern California so I haven't had a chance to check the frequency valve. I did get a few minutes tonight to try to track down where the buzzing in the engine compartment is coming from.

It now appears to be an intermittent electrical problem (don't you love intermittent issues?) and is coming from somewhere high up on the engine. Now, sometimes when I turn the key to the "on" position I hear what sounds like a relay clicking on/off a few times - each time it "clicks on" I hear the buzzing sound from the rear and the fuel pump hum from the front. Once the key is in the on position the buzzing in the rear will intermittently cycle - no consistency, it just sounds like something is shorting at random in the rear. I looked under the deck lid at night and see no sparks or tell-tale signs of electrical shorting, so I'm guessing it's a electrical switch or relay acting up.

I'm going to try to isolate the location once I have some time later this week.

gshiwota · 12-18-2007, 11:28 PM

Ok... it's still raining and I decided I'd better go out and check the integrity of my targa seals to make sure that my car doesn't become a fishbowl after sitting outside tonight.

Apparently my front windshield seal has a small leak on the passenger side. The floor is wet and I noticed that water is collecting under the pass seat... Wait, isn't the CIS computer under there???!!! Now I'm starting to put two and two together...

I have water collecting under the pass seat after it rains or I wash the car. I'm hearing a relay clicking / shorting inside the car along with loud buzzing from the engine near the CIS and the fuel pump coming on simultaneously. Could the relay or CIS computer be shorting out due to moisture causing these symptoms? I'm going to wait for my car to completely dry out before firing it up again just to make sure I don't fry anything. So far, the car is still running well.

I also noticed in the maintenance log that the prior owner just had to replace the computer under the seat fairly recently. Do these things crap out on their own or are they typically drowned to death?

Looks like I need a new windshield seal at a minimum.

Thanks again!

Gabe