450 fuel pump relay

[Oversize]

Can someone tell me where the hell it is??? Why are MB manuals great for schematics and wiring diagrams, but poor when it comes to component location?

 

[Helmet]

If not in the back of the fuse box , its behind the RH kick panel .

 

[SEL_69L]

I had a rather frightening experience with a failed fuel pump relay in my 6.9 about 5 years ago.

Being an electrical item it started to fail intermittenly. Some times, the engine would simply refuse to start. Come back five minutes later and all was well.

It was deduced that the fuel pump was playing up, so a new one was installed.
Problem remained.

I was driving in the fast lane of a motorway, when the engine suddenly cut out.
No power steering at 100 km/hr!
Adrenelin kicks in. You need to be a gorilla to wrestle with a 6.9, with that big cast iron engine over the front wheels.

Somehow managed to change through three lanes and pull to the side of the road.
Waited for five minutes, until some reasonable complexion returned to my face.
Started the car again, without trouble, and drove home in the slow lane, prepared for more trouble. Managed to get the beast back into the garage.

Next day, attempted to start the car. No go.
Called in an N.R.M.A. road mechanic to my home address.

He checked down two lines if testing:
A) Spark.
B) Fuel supply.

Spark OK
Disconnected the fuel supply line: No fuel
Two reasons for this: Fuel pump not working - told him it had been replaced.

Therefore no electrical supply to the fuel pump.

Failed relay? Pulled it out and tested it. Problem found.

He hot wired past the relay and told me to take the car to an auto electrician.

Cost of a new relay? Minimal.

No problems of this sort since.

 

[WGB]

The fuel pump relay should be in the fuse box under the bonnet.

There will usually be two relays - sometimes three and if you check the wiring diagrams you will see the correct colours plus the relay will be labelled with a number on the wiring harness.

I think I uploaded good versions of the early and late 6.9 wiring diagrams onto the site here but if I didn't PM me with an e-mail and your chassis no and I will send you the correct one (there are two for early or late).

If the motor is running it is easy enough to pull the relay and if it is the fuel pump one the motor will die immediately.

Bill

 

[Oversize]

Yes there's a main and fuel pump relay that work in tandem. I did get a diagram from the net but it appears it's the wrong one. When I bridged 2 terminals to see if the pump was working the engine started cranking!!! One of the terminals bridged was supposed to have constant power and yet it had none. It was supposed to come from a fuse, but a fuse for the fuel pump relay isn't listed on the lid. Are there any other fuses located remotely???

Anyway I got my mate's car going, but it seems the fuel pump's fried. And after going through some old E-bay ads today I discovered where he got the car....

http://www.topklasse.org/forums/showthread.php?t=3900

Advertised as a 6.9 no so long ago!! Needless to say he didn't pay the advertised price for the car... Small world eh?

 

[Michel]

http://www.topklasse.org/forums/showthread.php?t=3900

Advertised as a 6.9 no so long ago!! Needless to say he didn't pay the advertised price for the car... Small world eh?

Nice colour....

 

[Styria]

It has now been established, beyond doubt, that the fuel pump relay is, or should as a rule, be located inside the fuse box on the r.h. side of right hand drive cars. Regards Styria

 

[Oversize]

I can confirm the fuel pump relay is the rear one closest to the firewall & bridging the terminals will only work with ignition on. There's provision for another relay below the two at the top but on an Aussie 6.9 it's just an unused plug. I'll advise which terminals to bridge soon so there's no doubt & no one will set fire to their car...

 

[sean sherry]

After the Horse has bolted.... To ensure the reliability of my 107 S.L. First thing I did was to replace ALL the Relays plus the Fuel pump. Also the aluminium Fuses. Not trying to be a smart arse , just realizing the joys of older Cars.

 

[Oversize]

I was getting frustrated cause I couldn't find the answer quickly on the net! So I worked it out myself & posted it here for future reference. Simple things like this can be the difference between happy ownership & a mental breakdown!

 

[Oversize]

I've also heard if you disconnect the blue plug on the fuel distributor you can run the pump via the ignition without any engine cranking. I assume it'll work if the relay is operating ok but I have tested the theory yet....