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Discussion Starter #1 (Edited)
Hello,
Been driving the 164 a lot lately, no issues except Friday night at a stop light I started to hear a mechanical whirring noise from the rear, sort of left side of the car. It's coming from outside the car, not interior. It's not the antenna motor, but it's near there, underneath the car. It does it whether moving or not. It doesn't change pitch with throttle. It makes the noise with engine off and in the ON ignition position as well as running.
I am thinking fuel pump. Any other guesses or help? Thanks!
 

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Probably fuel pump but if car wired as designed from factory pump should not run with key but on engine not running. Could somebody modified wiring OR a stuck on fuel pump relay located on top radiator support rail near ignition coil. Remove black cover closest to coil and remove non-red stripped relay and pump should stop. That relay should only be grounded to energize fuel pump when engine running.

Report your findings please.
 

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Discussion Starter #3
Hey Steve,
Thanks for your suggestion. So I found the relay near the radiator, I will try to attach pictures.
Key in the ON position, engine not running, you can hear the whirring noise from the fuel tank area for sure.
When I pull the relay, it stops. The relay is brown and the previous owner wrote "Fuel" on it in sharpie, probably indicting that the P.O. rewired / changed /monkeyed around with it for some reason.
There also is no black cover over this set of relays on the left, maybe I am looking at the wrong set of relays?
There is another set to the right of these with a black cover, however in that set there isn't a red striped relay. I took the black cover off and inside there are 2 black relays. Pulling them while whirring noise is occurring with engine off and key in ON, does nothing. These relays don't effect the pump it seems like.
Pulling the brown relay all the way on the left of the 4 relays, stops the pump. (if this noise is the pump that is).
 

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Discussion Starter #6
In second pic, that brown relay closest to the camera is the FUEL labeled relay that stops the noise when I pull it.
 

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OK so you have what year/model 164? From picture I am guessing you have a 24v V6 USA spec 94-95?
If so you have the later model relays. The 15A fuse near relays on that model is for fuel pump and 3A fuse is power for motronic computer ECU. There should be another 7.5A fuse for O2 sensor heater nearby, too. The other two black relays nearby are for the low/high speed cooling fan speeds.

Can you read part numbers on the brown relays? I see ++1019 on relay cover for computer.

Fuel pump should not run with key on motor off. Swap brown relays and see if pump still runs with key on engine off and if not see if engine will start.

Report your findings.
 

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Discussion Starter #8
Hey Steve, sorry for not adding what I have. Yes, its a 1994 164LS with the 24V Busso, USA Spec.
I will dig into what you said and report back soon. Thanks!
 

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Discussion Starter #9
Yes, I have those fuses right nearby. The 15A and the 3A. I see the 7.5A fuse as well, its hanging nearby.
I can not read the part number of the other brown relay. One is ++1019, the other I can not read. It's Bosch and Made in Portugal. The writing on top is really worn down.
I swapped brown relays, the other relay has "ECU" written on it in Sharpie by the PO. So we have ECU and Fuel on them. I swapped them, still has the noise from the back in ON ignition, however the sound/pitch has changed slightly. It's now more of hissing noise then a mechanical whirring noise. I pull the brown relay, it stops. Relay in, engine starts, runs fine. If I pull the relay while engine is running, immediate stall. If I pull it while in ON with engine off, noise stops but engine does NOT start. Nothing occurs when key is turned to start, just nothing.
 

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Hard to say why fuel pump runs with key on but if swapping relays it still runs with key on and engine off then not stuck relay. As for excessive fuel pump noise could be pump going bad or rubber hose in tank going bad.
 

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The only moving things (circular motion) back there are antenna ( you SURE its not that) and the fuel pump. There’s nothing else back there.
 

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Fuel pump noise is one thing to investigate but also why it runs with key on and motor off is another thing to investigate. Fuel pump relay normally is grounded by white wire going to pin 85 of fuel pump relay socket when grounded by ECU ONLY when engine turning over/running.

If somebody hard wired the pin socket 85 white wire to ground then relay would be energized as soon as key turned on. It is a safety feature for pump not to run unless engine running in case of car accident.
 
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