W124 Fuel Pump Relay Doing My Head In - Girlfriend Not happy

[Mick65]

Can anyone help resolve please?

For past couple of months my E300D has been intermittently cutting out. After searching on forums, I narrowed it down to fuel pump relay. Each time it happens, I find that taking out the offending relay, applying liberal WD40, sharply hitting it and re-placing it a few times resolves the problem. I bought a spare secondhand relay and sometimes just for good measure find that i have to swap them over.

Also my drivers door electric window stopped working.

After several weeks of it getting so bad (and a very disgruntled girlfriend who thought that latest break down on a quiet country lane was a very badly timed attempt to compromise her virtue), I can hardly risk going out.

I spent yesterday carefully cleaning the connector block. Only found very small amount of perished relay gasket. Removed it. And voila. 10 miles trouble free run last night

Alas today - we konked out half mile down road :-(
Wiggle, WD40, quick prayer and we're fired up again.

Got home, left engine running, removed relay and WTH, engine carried on running. Stopped and restarted and the car ran fine without the relay. Then, lol, my electric window started working again - a joy in the heatwave we're currently having.

My girlfriend now won't go in my car and insists that she drive us to the pub in her car, so I have to drink whilst the poor girl only has coke.

But this all feels like a pyrrhic victory.

Please can someone help me avoid insanity (and more importantly regain my girlfriend's trust) What is going on? Why would it work without the relay? Is the door window motor linked?

And is the relay that I'm now on first name terms with really the fuel pump relay? What does it do? It's the small one behind battery - Labelled D-Kickdown 003 545 48 05.

Desperate of Chester

 

[dinoy]

i believe it control the fuel pump but not sure in diesel version if has more intellegence have checked your filters are clean pls

 

[Dec]

Open the relay to have a look at the PCB.
Guide, as an example of what might be at fault, see… N10 Relay, Soldering Repair, Wiper - Indicators & Hazards - Rear Window Demister. - Mercedes-Benz Owners' Forums

Dec
Picture… Vis innlegg - RamboEinar

 

[carat 3.6]

It wont be the fuel pump relay as a 300d doesn't have one. Which begs the question, what relay are you messing with?

 

[grober]

You may have an electrically controlled vacuum fuel cutoff valve to stop the diesel from continuing to " run on" on switch off---- perhaps that's the problem, the ignition switch itself or you have a vacuum leak

 

[Mick65]

Thank you for helpful comments.

Quick update.

I had been messing around with the relay marked Kickdown shown in the pictures which i believed from other forum posts to be the fuel pump relay. It is located just in front of bulkhead behind battery.

Replies from Carat and Grober made me think that this might be red herring. So I tried the vacuum pipe on the fuel pump. Disconnected it to disable auto-cutoff. Car ran great for 24 hours and i was about to celebrate until this morning when it cut out again.

Tried various prayers, waiting, Wd40 on relay (this has now become a religious act for me), opened fuel cap in case fuel tank was under vacuum. Nothing. Then, I thought i heard a relay click somehere in the engine bay, cranked her over again and she started.

So in summary I haven't got a clue.
It's definitely fuel being cut off. It's not the fuel pump vacuum cut-off. Fuel filters are all clean and new (only one not tried is strainer in tank but seems unlikely to me as it starts again without anything in tank being touched).

Help please

 

[JohnBell]

Sorry dude can't help with the relay but i can make your girlfriend happy ;0)

 

[grober]

I am begining to think that you may have some sort of fuel cutoff relay present which is non standard [ perhaps part of an aftermarket alarm system??] Does the car turn over on the starter but not fire? or is it dead when this happens?

 

[grober]

Does the glow plug light illuminate on switch on and then go out after several seconds?

http://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/70010.pdf

 

[WG M-B]

Maybe get the car on a star machine? It could be anything

 

[carat 3.6]

And is the relay that I'm now on first name terms with really the fuel pump relay? What does it do? It's the small one behind battery - Labelled D-Kickdown 003 545 48 05.

If your car was a petrol model that would be the fuel pump relay, on the diesel models it controls the gearbox kick down facility and is also linked to the air con.

You've ruled out the vacuum stop system, so I think your problem is likely to be the tank strainer or air being drawn in somewhere.

Graeme's suggestion of an aftermarket fuel cut off somewhere is also a possibility.

 

[Bellow]

Just to add, while you are changing relays, time passes, things cool...

 

[Mick65]

Thanks all.

Yes, engine turns over and glow plug light comes on and off as normal. I know its fuel cutoff as pre-filter is bone dry when it happens.

I'm going to try to investigate vacuum switch off on pump - have heard there are a couple of o - rings under flange that can fail. Might be interesting trying to access it !!

 

[roadhog]

I wouldn't bother with the vacuum switch off for now. If your pre-filter is running dry the problem must be further upstream. Check the tank strainer and make sure the fuel line from the tank to the filter is not clogged whilst you're there.

It might be helpful if you put up more details of your car i.e. age, what engine etc. The later (OM606) fuel pumps have different controls.

 

[optimusprime]

W124 300D See first post

 

[roadhog]

W124 300D See first post

I got that far thanks, couldn't see whether it was OM603 or OM606. I'll keep looking...

Edit: Not that I think it makes any difference in this case.

 

[bolide]

E300 Diesel W124: no fuel pump relay as there is no electric fuel pump

Cutting out on a 606 pretty much has to be a fuel feed problem - once the engine is started it'll run even without a battery and needs intervention (via the shutoff valve) to stop the engine

Some cars were retrofitted with an electrical non-return valve in the fuel system. I don't think this is likely to be the source of your problem

Look for air leaks and anything that can stop fuel flow - blocked strainer, filters, etc

Nick Froome