Petrol Pump W107 300 SL

[spannerman]

Stopped at a gas station today to fill up and when I tried to restart... nothing, well one little fire on one or two cylinders and then nothing. Let it sit for a few minutes and the same, but if I kept cranking .......absolutely zilch.

The petrol-pump had been getting a little noisier lately and I thought...that's it gone now. Turning on the ignition and listening for the usual humming until pressure is up.......nothing.

So I get rescued and soon I'm underneath, drain down the tank, and have the pump off. So I though I'd test it on the bench (so to speak), actually it was on the ground with a battery pack, and lo and behold.......... what you don't really want at a time like this........she buzzes away like something demented.

So I get under the car with another pump and hang it there, and put the two leads on it, switch on the ignition and.........nothing.

What happened at the switch off at the gas station, coincidentally or otherwise ?????

I know it's probably something really stupid.

 

[paulcallender]

Fuel pump relay?






Immobiliser???

 

[spannerman]

Hi Paul,

Definitely not immobiliser, but you could be right about relay. I''ll have to figure out which one it is. It's the same setup as the 289/300 E W 124 so if you have an pointers I'll be very grateful.

The car has't given one minutes bother in ten years, and only recently gave the first little glitch with the aircon/heater blower motor...new brushes fitted and away we go. I hope this is not the beginning of the bad times

 

[spannerman]

I could only find two relays over the fusebox in the side of the footwell. Both are identical, silver in colour, and with round pins ,and swapping them around didn't help.

Any suggestions?

 

[Mid_lfe_Crisis]

The realy u need is behind a plate in the glove box at the back

 

[spannerman]

Thanks for that info.

There's two in there at the back with identical numbers.

 

[Mid_lfe_Crisis]

hmmmmm well one is the idle control at the front and pump realy at the verry back of my 1986 420 sl 107. but if as you say they are the same then u could swap them and see what happerns



Ps the fule pump realy is a two stage realy one for normal running and one bosting on cranking i think

 

[spannerman]

Halleluia !!! Praise the Lord and pass the tamberine ! She's going like a mouse chewing paper.

I switched a relay, and then was puzzled as to why I was only getting three seconds of power at the pump leads (not connected to pump at this stage). Scratched my head, cursed a bit (quite a bit in fact), thought about it some more, and then decided to fit the replacement pump, thinking that perhaps she does only buzz for a few seconds before she fires up.

The old pump had been whinning her head off for a while, and probably wasn't building too much pressure.

Anyway, on with the pump, connected the two pipes, then into the driver's seat (left hand side in this instance) like a kid on christmas morning.
Turn the key, splutter splutter, turn the key again.......and .....vroom vroom.

She's a bit lumpy at idle, and around 1000rpm, probably needs a bit of tuning, maybe as a result of different, albeit stronger, pressure from the pump, since it's far more modern that the one that came off.

All's well that ends well.