No fuel pressure 500SE

[Svein R]

Hello guys, I have a problem with my 92 500SE (euro model) the car has been sitting in my carge for a while now. I drove the car out of my garage and parked it outside to the next morning, when I came out next day and should take it for a spinn it won’t start. There are no sound from the pump at all and no fuel pressure. I have 12V on pin 30 on my relay, I have tried to bridge the relay from 30 to 87 but still no pump is running. Can some of you help me please?

 

[Kridre]

Probably your pumps are dead if they were never replaced. Dont cheap out on them, bosch is my go to for the pumps. When replacing the pumps also do every rubber line in the system as preventive maintenance if they are original to the car.

 

[gsxr]

Yup... if you have confirmed +12v to the pumps and they aren't running, the pumps are top suspect. I'll second the recommendation to only use OEM Bosch and replace all the rubber hoses with OE/Genuine while you are in there.

 

[Svein R]

No 12V on pump, but there are 12V on pin 30 on relay

 

[gsxr]

The relay is triggered by the LH module. However if you have bridged 30+87 and the pumps still don't run, that may indicate bad pumps. But you also need to verify there is no fuse upstream. There's none on the 400E/500E AFAIK but I'm not certain about the 140 chassis.

 

[Svein R]

I must have taken the wrong socket when I bridge the relay, now I have ohmed and I have founf the right cable and the pump is running with my jumper cable.

 

[Svein R]

When I jump 87-30 my pump starts up and the eninge runs fine. I have constant 12V on 87, shouldn’t be on 30? When I switch on the ignition there is 12V on 86. I have replaced the relay but same problem(no power to pump). Could it be the LH module that causes this problem?

 

[gsxr]

LH module triggers the relay. If the relay is not energizing when it should, the LH module is suspect. Do you have a spare to test with? Even a 4.2L module will work for this test.

 

[Svein R]

My fuel meter doesn’t work either

 

[gsxr]

My fuel meter doesn’t work either

Do you mean the gas gauge on the instrument cluster, or the fuel economy meter that is part of the optional trip computer?

 

[Svein R]

 

[gsxr]

View attachment 172908

OH... sorry, this is a 140 chassis. That "economy" meter is just a vacuum gauge, isn't it? I'm not familiar with Euro-spec 140 instrumentation.

 

[Svein R]

Yes it’s a W140 500SE, I think it’s a vacuum gauge but now it don’t work

 

[Svein R]

I will try to replace the LH module first

 

[henboy1]

Interesting post.I am learning everything on this post