No fuel pump and buzzing relay

Jim · Aug 7, 2013

I need some advice please...

When I turn the ignition on I have a buzz coming from the "central" rectangular relay (1/92) in the relay box behind the fuses; also the fuel pump does not run. The engine cranks but does not fire up. I have cleaned all the fuses but there does not seem to be a fuel pump fuse.

I have not pulled codes yet.

Anyone recognise these symptoms?

gsxr · Aug 7, 2013

Check all the fuses first. The fuel pump has a relay below the rear passenger seat, and the relay is triggered by the LH module.

:detective:

Jim · Aug 8, 2013

I carefully cleaned all the fuses and checked for continuity.

I removed the relay under the seat. I tested the coil at 55 Ohms. The relay pulls in OK and switches the contacts.

I do not see 12 volts on the 30A feed to the relay.

I swopped the LH with my other car no effect.

The buzz in the relay box stops when fuse 6 , (horn, signal and outside temp gauge) iis removed.

I need to find the feed to that relay under the rear seat.

gerryvz · Aug 8, 2013

I would recommend looking at the W124 electrical diagrams. You can find them posted online by MB at this URL: http://www.startekinfo.com/StarTek/outside/12264/?requestedDocId=12264

Jim · Aug 8, 2013

Thanks Dave &. Gerry, I looked at the diagrams and realised that the feed to the fuel pumps is direct from the battery...when I took the car from storage I just pushed the positive terminal on without tightening up the clamp. Hence the fuel pump feed was only making intermittent contact. So it's running now...but the fuel pump relay is clicking and clicks faster when the car engine speed is increased...is it supposed to do that and you just cannot hear it under the seat?

So always check the simple things, especially when some one (me) has "worked" on the car. As I let it warm up I realised I no oil pressure....in fact no gauges....this was due to poor fuse contact. The fuses and their contacts really are in poor condition. So I endorse the recommendation for some regular cleaning on the fuses and their sprung loaded contacts.

Still not sure about the buzzing relay in the box in the engine compartment.

Nice sunny day here in UK so good for car TLC.

gerryvz · Aug 8, 2013

It sounds like the relay could be defective, and is probably worth a replacement from a breaker. Talk to Mercman.co.uk in the southwest of England ... they sand a daily parts truck to London and/or will ship anywhere in the UK rather quickly via Royal Mail. Relays shouldn't buzz as far as I know.

Cheers,
Gerry

bing · Aug 8, 2013

Now that you got it running try swapping the LH module again and see if the relay clicking stops.

gsxr · Aug 8, 2013

If the relay clicks, the LH module is defective. A different LH module should fix the problem. We've been hearing more about this problem in the past few years, as the modules pass ~20 years old...

:runexe:

Jim · Aug 9, 2013

Thank-you Dave, I changed the LH for my spare, started up the engine and the fuel pump relay stopped clicking.

Given that we know the symptom, i.e. clicking fuel pump relay; I wonder is the removed LH repairable?

superstar · Aug 9, 2013

had the same problem, a new LH should fix it.

Jim · Aug 9, 2013

Just to close this out...it seems that the Volvo Community have identified this common fuel pump control failure in the LH 2.x.

As yet I have not found a repair shop for the defective and now removed LH module part number 012 545 6232.

ADMIN EDIT: The Mercedes / Bosch LH-SFI system is version 4.x, similar but not identical to Volvo/Porsche/etc.

tcg1122 · Aug 27, 2013

The problem with the LH module is the crummy Frako electrolytic capacitors the Germans liked to use. Replace all ( believe there are 7 ) Frakos with Nichicon high temp caps. It will require a pretty good soldering Iron because the ground plane on the modules contain a lot of copper.
I have a 92 500E which had the chattering fuel pump relay problem. After I replaced all the caps the problem went away.
When I see a Frako, I replace it. Mercedes, Revox, Bang & Olufsen, dosen't mater. CHANGE THEM.

Jim · Aug 27, 2013

Welcome tcg...way to go for a first post.

I asked a 928 Guru where to get my module repaired and He recommended ATP Electronics. I wrote to them on 9th August and so far have no reply. With the information provided by you I can perhaps do it myself. Thanks again.

Jim

tcg1122 · Aug 28, 2013

Go for it Jim.
If I can help, let me know.

Tom

gsxr · Aug 28, 2013

Tom, do you have a recommended source for the Nichicon high temp caps?

:apl:

tcg1122 · Aug 28, 2013

Nichicons cap can be purchased from:
www.mouser.com
www.digikey.com
and www.alliedelec.com
Get at least the same voltage rating. Not a bad idea to get the next higher voltage. Buy the same uF (micro farad) value. These caps are aluminum electrolytics.
I was talking to a friend today and he thinks the Panasonic caps have a very long lifespan. He also likes the way they sound. Not too relevant in a engine management system. Of course the Frakos lasted 20 years. I can't imagine the nichicons not lasting longer.
My advice is when you see a frako, replace it! I have a Bang & Olufsen Service Center and I restore quite a bit of 20+ year old equipment. The bulk of the problems are the frako caps.

Tom

Gmach · Jan 8, 2015

tcg1122 said:
The problem with the LH module is the crummy Frako electrolytic capacitors the Germans liked to use. Replace all ( believe there are 7 ) Frakos with Nichicon high temp caps. It will require a pretty good soldering Iron because the ground plane on the modules contain a lot of copper.
I have a 92 500E which had the chattering fuel pump relay problem. After I replaced all the caps the problem went away.
When I see a Frako, I replace it. Mercedes, Revox, Bang & Olufsen, dosen't mater. CHANGE THEM.

Hi Tom...I'm game to try to replace those caps myself. I've taken the unit apart but am stuck on how to lift the PC board that has the caps on it. Do I need to remove the black plastic end piece first to "unplug" all those connectors (the ones that go to the plugs) so I can flip the board up. Or do I need to desolder ALL this pin connectors from the board itself? Thanks
I also PM'd you but thought it maybe helpful posted here for others who want to try and replace those caps.
Brian

Gmach · Jan 25, 2015

Replaced all the caps....pretty easy...and the car has never run as well. Starts and idles like a new car. Thanks for your help.

Glen · Jan 25, 2015

Gmach said:
Replaced all the caps....pretty easy...and the car has never run as well. Starts and idles like a new car. Thanks for your help.

Did you take any pix, by chance? Would love to see the process...

Gmach · Jan 26, 2015

No..sorry. But it isn't that hard if you have a good soldering iron for electrical work. Use a solder wick as opposed to sucker to remove the old solder.

lowman · Aug 31, 2015

Does someone have a picture of this procedure ? Very interesting

Jim · Aug 31, 2015

There are how to videos available for using a solder wick.

This one
https://www.youtube.com/watch?v=htrcZuK_ZsY
is pretty good at 1.50

It's a matter of identifying the capacitors and replacing them all on whatever PC board you are working on repairing.

I have to own up as never having done it.

lowman · Aug 31, 2015

Jim said:
There are how to videos available for using a solder wick.

This one
https://www.youtube.com/watch?v=htrcZuK_ZsY
is pretty good at 1.50

It's a matter of identifying the capacitors and replacing them all on whatever PC board you are working on repairing.

I have to own up as never having done it.

thank you very much.ill dig into that one right there

got to talk to a company here in norway ..who does repairs on ECU"s...and got a quote on checkup and repair on the LH unit..so..but i think i want to open the LH unit myself..and have a look..
and...i got a dudes phonenumber today..and i got to borrow his LH ..and BM..and any module that i wanted..so im pretty excited to see if my car starts today..
if im very unlucky...the car starts today withouth having done anything..so im really hoping it doesnt start before i change the LH unit..and Bm module..that would be shitty cause then i dont know "what is wrong" ..hehe

lowman · Aug 31, 2015

Gmach said:
Hi Tom...I'm game to try to replace those caps myself. I've taken the unit apart but am stuck on how to lift the PC board that has the caps on it. Do I need to remove the black plastic end piece first to "unplug" all those connectors (the ones that go to the plugs) so I can flip the board up. Or do I need to desolder ALL this pin connectors from the board itself? Thanks
I also PM'd you but thought it maybe helpful posted here for others who want to try and replace those caps.
Brian

did you find out "HOW" to take the module appart?

Jim · Aug 31, 2015

lowman said:
did you find out "HOW" to take the module appart?

This may give some generic help. Nothing about capacitor replacement but some good tips on where and what to look for.

https://www.youtube.com/watch?v=zY2pVnhHgR8

Jim

samiam44 · Aug 31, 2015

I've always used Panasonic caps in my amplifiers, but they are not in the signal path. Tube stuff.

Frako? At least they are not mexican made Mallory Twistloks from the 50's and 60's.

If you are going to the effort, verify all resistors and replace the diodes if any.

Michael

Eno · Apr 6, 2017

I didn't know where to post this, so this old thread seemed appropriate.
My midnight blue '92 500E has this fuel relay
001 542 59 19 under the rear passenger seat which had some 'direct' wire repair.

But when I ordered fuel relays from MB dealer a few weeks ago they ordered these below different numbers.
Maybe they are replacement numbers?

I am about to tackle the fuel system as there is no power going to the fuel pumps.

So I started with relays, fuses, and next will be LH module.

Sent from my iPhone using Tapatalk

gsxr · Apr 6, 2017

The green relay would be a correct replacement for the old relay.

The fuel pump relay receives the turn-on signal from the LH module, if the car runs fine with the relay 'hot wired', it's pretty likely your LH module is at fault. If you have a spare LH module to test with (from any M119 LH) you can prove this one way or the other. If you have trouble finding a replacement LH module, I should have one available for sale if you need it...

:detective:

Eno · Apr 6, 2017

Thank you always Dave for the quick reply and advice.
I already have a spare '92 500E LH module but not here where I live, it's in my garage back in my home country [emoji853]

Sent from my iPhone using Tapatalk

DarkStar · Aug 14, 2021

My pumps quit the other day leaving me stranded on the road downhill from my driveway…

I just hotwired the pins 30 & 87, pumps turned on immediately.
So now how to test relay? Apply 12v across
the trigger pins 85/86?
The circuit diagram shows a fuse on 87, is it internal or where would I find it?
I’ve got some water intrusion that may be a factor based on the corrosion on the relay socket.

DarkStar · Aug 14, 2021

Testing voltage at 85/86 when key goes on I am seeing voltage, so I think the LH module is sending the signal.

DarkStar · Aug 14, 2021

So relay failed miserably…
Light clicking when 12v applied across it. Didn’t close contacts.

DarkStar · Aug 14, 2021

Are Vemo relays ok?

gsxr · Aug 14, 2021

Relays are a rare failure, usually it's the LH module at fault.

It's a standard cube relay, used in other locations as well, if you want to temporarily swap one out for testing.

Vemo would not be my first choice, especially for something that could leave you stranded. I'd install a used OE/OEM relay before a new Vemo but that's just me.

:shocking:

No fuel pump and buzzing relay

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