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Discussion Starter · #1 ·
This problem occurs in my '77 coupe. When I turn off the engine and pull out the key, the fuel pump continues to run -- I can hear it humming. I have to put the key back in the ignition and turn it until the alternator comes on (to the ON setting, I believe) three or four times before the hum stops.

I realized there might be a problem when my one-year old battery died. I think maybe the fuel pump had been running overnight and drained my battery.

I'm thinking it could be 1) the fuel pump relay, 2) the fuel pump itself, 3) the ignition switch, or 4) the fuel pump cutoff contacts in the AFM.

The AFM is a refurb I bought from Motorsport in July, 2000. TPS and all of the temp water sensors have been replaced.

(Of course, the car's been at my mechanic's shop for four days, and they haven't been able to replicate the problem. Imagine that.)

Any and all advice will be appreciated. Thanks in advance.
 
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Gene,

I apologize for not having a direct answer to your question. However, I read your post and wanted to remind you to check your oil. You may have watered it down with gas. Just pull out the dipstick and take a wiff. If it smells like gas you are going to want to change the oil and start again with fresh oil after you resolve the fuel pump problem. Good luck to you. John.
 

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It sounds to me to be one of two problems with your fuel pump.
It either sounds like a faulty ground maybe a short to the ground. Or it is in your ignition switch through all the years of Z cars there ignitions were not the most reliable. I know on allot of the Z cars you can use any key to start the ignition.
They used the same design as did GM in the early 70s and 80s.
But my first culprit to check would be a short to ground on the wiring on, or leading to the fule pump. If it were a Relay it would be constant, relays 99% of the time just crap out and do not work sometimes usally they do or Don't.
 

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My guess is you have a sticking FI relay. I've had the exact same problem before. Turning the key to off and on will not affect the AFM switch, and that is the only control on the early 77. Some later 77s used the 78 scheme, which uses the oil pressure switch and the alternator to control the fuel pump.

Try unplugging and plugging the FI relay. See if the hum stops.

If yours is a later 77, check your alternator/oil pressure switch for proper operation.

BTW, unplugging the FI relay (easy to do) is an effective way to prevent your car from being stolen.
 

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Discussion Starter · #7 ·
Re: Engine is off, but fuel pump runs UPDATE

Well, it turns out the problem was a bad fuel pump relay. I had it replaced and now the fuel pump is behaving correctly.

Which is good, because it had gotten to the point where the fuel pump would begin turning itself on by itself twenty minutes *after* I had turned off the car and pulled the key out. And the fuel pump was buzzing like a horde of very angry bees, too.

The relay cost about $100.

Thanks to everyone who offered advice.
 
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