HELP !!Buzzing after engine turned off
 

Ok, i think I've got a ghost in the back - tonight after i turned off the car from a 30 minute normal drive, i kept hearing a mechanical buzzing sound from the engine compartment. It seems like it is coming from the area of the fuel filter/accumulator. I restarted the car, turned off again . . . no change. Still buzzing after about 5 minutes.

I don't mind getting my hands dirty (and like it in fact) and have done a couple of small projects so far, but I don't have a huge amount of experience, so if you can offer any help, I'd apprecitate it.

The dog of it is that I just returned my leased car and decided to use this as my everday ride for a month while looking for another car . . . .ugh!

Thanks in advance - Adam

i had this happen too. It goes away when you pull the key out of the ignition.

thanks for the uquick answer - but it kept going afgter the key was removed - not just turned to the off, but out of the ignition totally.

oh then you got me. No clue.

Mine comes from the ebrake blinker noise maker that when i turn the car off it keeps buzzing; when i remove the key it turns off

what kind of buzzing? like 2 wires crossed or like a humm from a flourescent lightbulb

ok, after 30 minutes of key out of ingnition, the buzzing was continuing; i was able to restart the car, ran a little rough, then flattened out ok - ran for 2 minutes, turned off and the sweet sound of silence.

so my real problem: what am i looking at? is this an accumulator problem? safe to drive? reliable to drive?

Any thoughts?

humm of flourecent bulb - butt much louder - only other thought was that the passenger side foot well was pretty wet from being left out of the garage for last 5 days parked at my dad's house . . . any chance that might have affected teh CIS module under the passenger's seat?

that could be true that it messed with the box. But shouldnt that stop when the ignition is cut because no power would go to the box?

My friend has a sub and amp in his car and whenever the amp wiggles the wire to the ground causes a hum until he fixes the wire. Maybe something is not properly grounded that is connected to the battery.

maybe a stuck relay for the heater blower motor. put your hand on the motor and see if it's running. the relay is the black round thing on the rear electrical panel. pull it out if the blower is running.

Hmm, very odd especially with the ignition off. Could be a short in the cutoff to the fuel pump. The pump makes a pretty definate "buzz" when the key is "on"... I'd check it, unless you can pinpoint the buzz. Could also be a stuck relay somewhere. First thing you need to do it find out exactly WHAT is buzzing. No way to trouble shoot based on "I have a buzz in the back". Needs to be more specific. "DME relay is buzzing after I turn off the car". Then we could help trace the cause.

Here's a thought.
 

I looked at the Bentley wiring diagram (#970-9). It appears the ignition switch actually consists of two separate single pole double throw switches. One set of contacts supplies power to the fuel pump via a yellow wire. The second set of contacts supplies power to the CDI unit. A red/black wire leaves pin 15 of the second switch, goes through the fuse box where is it tied to a solid red wire that leaves and goes to pin 15 of the CDI unit. Why they didn't just go straight to the CDI unit is beyond me. Maybe there was a fuse intended to be there at one time and they changed their mind.

Anyway, from your description of the noise source, it sounds like the CDI unit, which is located near the fuel filter, is still running with the key removed. It is feasible, since the two sets of switches that make up the ignition switch are independent, that the switch that supplies power to the fuel pump is opening as designed when you remove the key, but the other switch is sticking. If so, the car would stop, but the CDI unit would still be humming. You could have an intermittent sticking switch. If it later became unstuck, the humming would stop.

To check this theory, locate the red wire at pin 15 of the CDI unit and check for 12 vdc when the key is removed. If you have 12 volts there, you need a new ignition switch. Of course, you can also check for the unwanted 12vdc at the switch itself by checking the red/black wire there.


Good luck

i've re-started the car 4 times, letting it run a while each time, then turned the car off, hoping (kinda) to recreate the problem so that i could try the heater blower relay or the ignitition swith to the CDI unit. Since i can't replicate the problem again, I guess that i'll have to wait and see if this happens again and then try to huntit down - unless anybody has any other way of diagnosising the problem (?)

Thanks for your help!!!!!!!!

hard to diagnose if it ain't doin it.

One short-isolating trick is to pull the negative battery connector, put a volt-tester in between, and pull fuses until the light goes out. It doesn't explain why, just shows the general circuit.

Try this.
 

I assumed the buzzing noise you heard was your CDI based on your description of the source of the sound.

You should get the same sound from an energized CDI just by turning the key to the "on" position and listening in the engine compartment. If this is the sound you hear on an intermittent basis with the key off, you then know the source.

You're a wise man JW. :D

ok, tried the key in the ON position, but motor off and the noise was definitely different - the noise (presumably from the CDI) is a much higher pitch - more like a whine then a buzz

car has been on and off half a dozen times since problem last night and has not resurfaced hmhmhmhm don't you love the intermittents:D

Noah - the sound was definitely coming from the left side engine compartement - right near the cdi / fuel accumulator (?)

Thanks