Clicking sound at idle or low rpm while driving.

[Noah]

Hello, i have the following issue with my '92 500E
When at idle or driving like 10km/h i hear a tapping sound coming from the fuel tank/trunk area. I know it's RPM related as i hear it synchronised with the engine sound.
When revving to 1000rpm it's gone.
Note: it's not the sound of the green relay under the the RH rear seat.

Thanks!

 

[gsxr]

It's almost impossible for any noise in the trunk area, to be related directly to engine RPM. Are you 10000% certain it's not the green relay under the rear seat? Because that can occur at idle and go away above 1000rpm, if clicking. Is there a CD changer in the trunk? And it's not related to the power antenna?

BTW, welcome to the forum!

 

[Noah]

Its almost impossible for any noise in the trunk area, to be related directly to engine RPM. Are you 10000% certain its not the green relay under the rear seat? Because that can occur at idle and go away above 1000rpm, if clicking. Is there a CD changer in the trunk? And its not related to the power antenna?

BTW, welcome to the forum!

Hi, thanks for the reply. I've checked again, and it really sounds like something is hitting inside the fueltank. Perhaps the sender unit? The green relay is clicking but not that loud. Should it be totally quite? Can any of this be caused by a faulty wiring harness? I'm thinking of replacing both wiring harnesses too.

 

[nocfn]

I'm with Dave - clicking in the trunk is a CD unit or antenna. The fuel stack should be observed with car running. The fuel pump relay should not click. Are any of the modules warm after sitting all night.... that four letter word "test" strikes again.

 

[gsxr]

Hi, thanks for the reply. Ive checked again, and it really sounds like something is hitting inside the fueltank. Perhaps the sender unit?

Nope. The sending unit cannot make noise, and it would be random based on vehicle movement / bumps, not engine RPM.

The green relay is clicking but not that loud. Should it be totally quite?

It should be silent. The root cause is a faulty LH module. You can replace it with a good used module, or repair it by replacing the 6 capacitors inside (search the forum, there are details on this issue).

Can any of this be caused by a faulty wiring harness? Im thinking of replacing both wiring harnesses too.

No, the wiring harnesses would not cause the issue(s) you describe. Check the date code on the upper harness, see if it's already been replaced (or, look for insulation crumbling off the wires at the injectors / cam advance solenoid). If defective, new ones are available from the dealer at reasonable cost.

The lower harness goes to the alternator, starter, and oil sensors for the instrument cluster. This harness is NLA but you can buy a repair harness from Kurth Classics.

 

[Noah]

Nope. The sending unit cannot make noise, and it would be random based on vehicle movement / bumps, not engine RPM.

It should be silent. The root cause is a faulty LH module. You can replace it with a good used module, or repair it by replacing the 6 capacitors inside (search the forum, there are details on this issue).

Thanks for the reply, i will check the module.
As for the sending unit, it's strange because i filled the fuel tank and the knocking sound is gone. Maybe it was shaking due the bad stationary running...

 

[gerryvz]

Any update on this?