M103 Fuel Pump Relay bridged, primes and dies on removal after start

[isobars]

Hi All,

I've had a good browse, but can't find a solution.

My 89 300E has been a sporadic starter for a while, but relay twiddling has usually solved the problem - I don't use the car for long periods.

This week I couldn't get the pumps to prime with the one second 'buzz', (no buzz), so jumped relay holes 87 and 30, then starts the continuous buzz of the pump and off she starts; trouble is when I remove the jump, the car stops immediately. I've adapted the pin-jump so that the rest of the relay remains in place in case the pumps need a signal from a running engine via the relay.

It's a mystery to me and I'd be grateful if anyone could offer advice.

Cheers,

Paul

 

[Stratman]

You may be setting up a dangerous situation by jumping the relay.

The relay should be de-energised in the event of a crash, so neat fuel isn't pumped on a hot exhaust or doesn't make a pool under the car.

Have you tried a new relay yet, or measured to see if the coil is getting the correct voltage?

 

[isobars]

Hi,

Thanks, yes, good advice, I wouldn't take it out with a bridge, I just used it to start the bugger and hoped when I removed it that it would continue to run.

Does the pump make the same priming noise when running, or it is higher to prime. I don't ever remember hearing the pump at that sound level, but if it only kicks-in when the engine starts after the prime, perhaps that's the same noise, but the engine drowns it?

What tells the pump to start after the prime, is it in the OVP relay?

Cheers,

Paul

 

[optimusprime]

I used a bridge on 7 and 8 to the fuel relay .Are you working on the right relay .Can you pop a picture in the post of your relay ~?.

 

[optimusprime]

This is your relay location , and the right relay that fitts your 300e And the bridge .

 

[isobars]

Hi,

Many thanks for the images, mine is identical save for the number 24 being 93 on mine and the pins being named differently, though they are in the same place and the jump makes the buzz.

There must be a signal to the pump from the engine that it is turning over which is cut on engine stop - perhaps?

Cheers,

Paul

 

[optimusprime]

I would check it out., all ican find for your m103 is 24 not 93 my check finds no fuel relay with 003 545 93 05 and my M 103 is the same number .

 

[optimusprime]

To help me find if it is the right fuel relay yoiu need to post a picture .
I searched for an hour to find nothing with that number you put in the above post.

 

[isobars]

Hi Optimus,
I'm so sorry, and I thank you wholeheartedly for such an effort.
Typo, I'm afraid, you image idea would have prevented that!

 

[optimusprime]

That is not for your m103 should read 003 not 002.But i will now check out and you did say the only change was one numberr change the 24 like mine to 93 but you now say on yours it is a 002 545 93 05 .

 

[optimusprime]

Paul Well i have come to the conclusion that it is the right relay .I was confused when you said it was a 002 .The one in picture is the same part for your car only one number out but the listing said it was for the 300e m103 so yours is original . Can you hear it rattle inside if so chuck it in the bin and replace it .Do replace this with a good original Mercedes relay no other will last .

 

[isobars]

Hi Optimus,
Thanks for the info and all your help, it's well shot. I'll take your advice and get an OEM.
Cheers,

Paul

 

[optimusprime]

Paul dealers is the best they will sell you the right relay to fit your car.

 

[isobars]

Thanks Optimus.

 

[optimusprime]

Any news on this Paul ?