Cranking - but not starting.

[Rettopian]

Hi folks. Wisdom please.

My euro-spec E500 - build date approx. 09/1993 was running fine a few days ago - now refuses to start. It MAY have run out of fuel or the battery may have been low on charge. The battery has been on & off a few times over the past 3 months while it was at the body shop being fettled. Every time the battery was reconnected, it started & ran fine without problem.

It now has about 3 - 4 imperial gallons of fresh 98 octane fuel on board. Cranks fine, all the dash lights up as you would normally expect. No clicking from the fuel relay but equally - no noise from the fuel pumps and no fuel being delivered to the engine bay. New Bosch fuel pumps were fitted approx. 12 months ago so i doubt they will have failed. yet.

Could this be an immobiliser issue (if it has one?). What is the most likely cause? Failed relay? Fuse? LH module? Something else?

At the moment I have an expensive but really beautiful paperweight stuck at the body shop! I've waited 2 years to get to the point where I can drive him home but that day has not yet come

 

[gsxr]

If the fuel pumps are not running when cranking (and/or, not running for 2 seconds after the key is turned on), that's where to start investigating.

I don't believe the immobilisers were used on the 124 chassis, so that should not be the issue. If you have a spare LH module you could swap that in for grins, the LH module is what triggers the fuel pump relay to engage.

Also check the 30A fuse on the relay, located below the passenger rear seat cushion.

 

[R129 UK]

If you don't have a spare LH module, either put a 12V supply direct to the fuel pump (a bit of a PITA) or squirt some Easystart (easier) directly into the engine's throat.

 

[Rettopian]

If the fuel pumps are not running when cranking (and/or, not running for 2 seconds after the key is turned on), that's where to start investigating.

I don't believe the immobilisers were used on the 124 chassis, so that should not be the issue. If you have a spare LH module you could swap that in for grins, the LH module is what triggers the fuel pump relay to engage.

Also check the 30A fuse on the relay, located below the passenger rear seat cushion.

Great.

Thanks for the advice. No spare module I'm afraid. Presumably they can be repaired if difficult to obtain a replacement over here in the UK?

Also - terrible ignorance here - but is the LH module the sandwich-box sized lump tucked up by the passenger side bulkhead in the engine bay?

 

[Rettopian]

If you don't have a spare LH module, either put a 12V supply direct to the fuel pump (a bit of a PITA) or squirt some Easystart (easier) directly into the engine's throat.

Brilliant.

Thanks R129UK.

 

[Rettopian]

If you don't have a spare LH module, either put a 12V supply direct to the fuel pump (a bit of a PITA) or squirt some Easystart (easier) directly into the engine's throat.

Thinking about it, how will the easystart solution help? If its the LH module/relay/pump presumably none of those would function anyway?

 

[gsxr]

Great. Thanks for the advice. No spare module I'm afraid. Presumably they can be repaired if difficult to obtain a replacement over here in the UK?

LH failures are rare, and if it can't be repaired, there are replacements asily available.

Also - terrible ignorance here - but is the LH module the sandwich-box sized lump tucked up by the passenger side bulkhead in the engine bay?

That's the CAN box which contains the 4 main powertrain modules. The LH module is one of the modules inside that lump.

 

[gsxr]

Thinking about it, how will the easystart solution help? If its the LH module/relay/pump presumably none of those would function anyway?

If you spray starting fluid down the intake and the engine fires for 1-2 seconds and then dies, that mostly confirms you have a fuel supply issue, and not something else.

 

[R129 UK]

Thinking about it, how will the easystart solution help? If its the LH module/relay/pump presumably none of those would function anyway?

As mentioned by Dave above, if the engine fires with Easystart it will effectively eliminate any issues related to air, spark and timing leaving just fuel delivery (pump, relay etc.) as the root cause.

 

[Rettopian]

Thanks both. As there is no fuel getting to the engine I'll start with relay, move onto pumps and cross my fingers that its nothing more!

Really appreciate the steer, chaps.

 

[Rettopian]

OK - update.

Still cranking happily, and with reasonable speed. (Enough to build oil pressure)

Fuel pump relay clicks just once when the ignition key is at the second stage. Still not absolutely certain the pumps are running though. There may be a very slight buzzing noise but no 'whirring' that I would expect on my other 124's. No fuel seems to be getting from the tank (Now 1/3rd full) to the fuel rails. No apparent pressure in the fuel rail either - removed the brass nut/cap and depressed the valve on the front of the rail - no evident release of pressure and no fuel smell.

Battery is charged.

Other electrical systems seem to be fine as far as I can tell. (All dash lights light up when ignition turned. wipers, lights, horn etc). Central Locking works fine.

Radio (Original, I think) is flashing due to the battery having been disconnected and needing a code as expected.

On the dashboard where the rocker switches are for folding the rear head restraints, snow chains etc. about 3rd or 4th in from the left there is a small - presumably red light in the middle of a solid rectangle of. I believe this used to flash - alarm related. it doesn't seem to flash at all at the moment.

Also, what is this switch for - bolted in the engine bay on the wing ahead of fusebox? Original or aftermarket?

Cheers

Ian

 

[gsxr]

Also, what is this switch for - bolted in the engine bay on the wing ahead of fusebox? Original or aftermarket?

That switch is factory. Possibly for the alarm system?

 

[R129 UK]

The switch looks like it is a bonnet release sensor for an alarm - no idea if original or not. Check for an MB part number or other markings etc.

I think my earlier suggestion still stands, squirt some Easystart into the intake and see if the engine fires at all. The alternative is to hook up 12V to the fuel pump.

Have you checked for a spark while cranking?

The console button is also on R129s but the owner's manual doesn't clarify what the status of the lamp means what - you seem to know this already though based on your concern it is not acting as usual.

 

[Rettopian]

R129, Thanks - presumably that is simply a solid, flat faced plate with a red LED in the middle? I have no idea how it should function either. As things stand its not glowing/flashing.

Now you & Dave GSXR will have to be patient with me here but its about 2 year since I was able to drive the car while it was away being tended to. But my wife seems to recall that it wouldn't start shortly after I bought it. I may be mistaken here but somewhere in the instrument binnacle as opposed to the console - would there be a small red flashing light?

Also when thinking about the problem in the wee small hours I was wondering if the alarm is triggered in some way, would that cut the fuel pumps or simply the starter motor? Also, could the fuel pumps be cut if it thought it has been in an accident? (It hasn't been) Is that the box under the rear seats. If it has been triggered how would I reset the system?

Final thought was that I believe the car will start in Park or Neutral. Since the car wont start the guys at the body shop have had to put it in neutral and push it around to move it out of the way. Could this be a cause of some of the problems - if so in what way?

Cheers

 

[Rettopian]

That switch is factory. Possibly for the alarm system?

Thanks Dave

 

[R129 UK]

R129, Thanks - presumably that is simply a solid, flat faced plate with a red LED in the middle? I have no idea how it should function either. As things stand its not glowing/flashing.

Yes, that is correct, almost a blanking plate with a small red lamp in the centre.



Found a photo from an R129 on sale in the UK on eBay - my car doesn't have this "switch":



Now, my past (albeit limited) experience of relatively crude anti-theft devices from this era is that the lamp flashes when the system is active and monitoring. The fact you have no lamp illuminated is potentially a good thing imo.

Also when thinking about the problem in the wee small hours I was wondering if the alarm is triggered in some way, would that cut the fuel pumps or simply the starter motor? Also, could the fuel pumps be cut if it thought it has been in an accident? (It hasn't been) Is that the box under the rear seats. If it has been triggered how would I reset the system?

If the alarm is triggered, it would most likely cut power to the fuel pumps via the wiring "up stream" of the relay etc.

Putting 12V direct to the pump or using Easystart will soon tell you - why are you reluctant to try this?

I had exactly the symptoms you have earlier this year after removing camshafts etc. In my case I hadn't connected all the positive battery terminal wires - I was petrified of frying the R129's roof module so I tucked the cables well out of the away behind some trim and completely forgot they were there!! Anyway, squirting Easystart into the intake made the car fire up momentarily and putting 12V direct to the fuel pump made the car start instantly which was a massive step forward in my fault finding.

Regarding P / N for starting, I have no idea but my 98 R129 has some stupid rules like you must have your foot on the brake to remove the key from the ignition so anything is possible. I would be trying to start it in P personally.

 

[gsxr]

When the alarm is triggered on USA spec models, it does not cut fuel, it prevents the starter motor from engaging - the engine won't crank. Since it's cranking over fine, I doubt the alarm system is involved, since the 124 never received an immobiliser function (like the 129 and 140 did).

 

[Rettopian]

Yes, that is correct, almost a blanking plate with a small red lamp in the centre.

View attachment 198182

Found a photo from an R129 on sale in the UK on eBay - my car doesn't have this "switch":

View attachment 198183

Now, my past (albeit limited) experience of relatively crude anti-theft devices from this era is that the lamp flashes when the system is active and monitoring. The fact you have no lamp illuminated is potentially a good thing imo.


If the alarm is triggered, it would most likely cut power to the fuel pumps via the wiring "up stream" of the relay etc.

Putting 12V direct to the pump or using Easystart will soon tell you - why are you reluctant to try this?

I had exactly the symptoms you have earlier this year after removing camshafts etc. In my case I hadn't connected all the positive battery terminal wires - I was petrified of frying the R129's roof module so I tucked the cables well out of the away behind some trim and completely forgot they were there!! Anyway, squirting Easystart into the intake made the car fire up momentarily and putting 12V direct to the fuel pump made the car start instantly which was a massive step forward in my fault finding.

Regarding P / N for starting, I have no idea but my 98 R129 has some stupid rules like you must have your foot on the brake to remove the key from the ignition so anything is possible. I would be trying to start it in P personally.

Thanks for the pic's - that's the one!

No great reluctance. to putting a direct feed to the pump. Its simply that the car is sitting on the ground and I haven't yet been in a position to jack it up and try it. That will be a project for this week.

We have a spark, it turns over freely - its just that fuel wont move from the back of the car to the front!

 

[Rettopian]

OK - today we got some time on the car. We removed the fuel feed to the engine (at the engine) - no fuel.

Relay clicks as ignition turned and fuse is good.

It seems that there is no electricity getting past the relay though which you would think would be some sort of an answer BUT we also managed to get a direct 12 volt feed onto the terminals of the lower of the two pumps with a good live and a good earth - and nothing. Deader that the deadest dead thing.

We also had a spell where the engine wouldn’t crank but we would get about 20 seconds of clicking from the alarm controller in the passenger footwell. Managed to resolve that and got back to cranking but not starting.

Any ideas why electricity (ecu signal) isn’t getting past the relay?

Cheers

 

[gsxr]

What happens if you bypass the relay (forcing the fuel pumps on)... will the pumps run normally and the engine start?

If so, you need to figure out why the relay is not triggering. As mentioned back in post #2 above, The LH module is what sends the signal to trigger the relay. This is why it was mentioned to try swapping in a different LH module for testing...

 

[Rettopian]

So you wouldn’t regard hearing and feeling the relay click as it triggering?

Unfortunately I don’t have a spare LH module to test with.

 

[gsxr]

So you wouldn’t regard hearing and feeling the relay click as it triggering?

Generally, yes. However without the engine running, the relay should click twice.... once (energized) as the key is turned on, then again (de-energized) about 2 seconds afterwards. The pumps only run for 2 seconds each time the key is turned on. They should also run while cranking and of course while the engine is running.

Try swapping in a different relay next. If still no change you can try bypassing the relay entirely to force the pumps on and verify they are working correctly. Temporarily connect relay sockets 1 and 3 (terminals 30 and 87) with a short length of beefy wire. The pumps should run continuously while the jumper is in place.

 

[Rettopian]

Cool. Thanks for that. We’ll give it a go!

 

[nocfn]

I have a question and a comment. How long has the fuel Filter been in the car sitting, and was there climate control or just ambient air?

I had the media disintegrate on a fuel filter that plugged up the lines to the fuel distributor on my 560 SEC. The fuel rail has a small filter at the inlet that takes a pic tool to remove, it can be replaced. Perhaps you reverse flow some pressurized starter fluid or similar flammable product in the fuel rail. Or just inspect the filter as it sits and see if there is debris in there. Just to rule out the filter media blockage.

 

[Rettopian]

I have a question and a comment. How long has the fuel Filter been in the car sitting, and was there climate control or just ambient air?

I had the media disintegrate on a fuel filter that plugged up the lines to the fuel distributor on my 560 SEC. The fuel rail has a small filter at the inlet that takes a pic tool to remove, it can be replaced. Perhaps you reverse flow some pressurized starter fluid or similar flammable product in the fuel rail. Or just inspect the filter as it sits and see if there is debris in there. Just to rule out the filter media blockage.

Hi nocfn.

Both the fuel pumps and the filter were replaced about 15-18 months ago. I would assume that given they are not old they should be OK as its done no miles in that time either - perhaps 20 in total. And its always been garaged but in otherwise ambient air.

Thanks for the pointer on the fuel filter on the rail though.

Cheers

 

[Rettopian]

What happens if you bypass the relay (forcing the fuel pumps on)... will the pumps run normally and the engine start?

If so, you need to figure out why the relay is not triggering. As mentioned back in post #2 above, The LH module is what sends the signal to trigger the relay. This is why it was mentioned to try swapping in a different LH module for testing...

Going back to the LH module point. do you have a part number that is applicable to a module for a Sept. 1993 build car? If not from 124 cars will one from an R129 or S140 with the same engine be a suitable replacement? I understand that cars from 1992 need a different LH module, correct?

Also I see that the same part number 0015429619 returns results for fuel pump relay & OVP. In this case is it safe to assume that the terminology is interchangeable?

 

[gsxr]

Going back to the LH module point. do you have a part number that is applicable to a module for a Sept. 1993 build car? If not from 124 cars will one from an R129 or S140 with the same engine be a suitable replacement? I understand that cars from 1992 need a different LH module, correct?

Original will be 016-545-14-32. These are pretty rare failures so I'd diagnose further before buying one (although, it's handy to have a known-good spare for all 5 powertrain computer modules).

Installing a 1992 LH module in a 1993-up engine restores WOT enrichment and is good for a small power gain as detailed here.

Also I see that the same part number 0015429619 returns results for fuel pump relay & OVP.

In this case is it safe to assume that the terminology is interchangeable?

Nope. The fuel pump relay is a standard 30A fused relay, nothing special.

The OVP relay has multiple functions, and does not exist on the 400E/500E. That function was integrated into the GM/BM module which is the power supply for all powertrain computers. The OVP is used on all 4/5/6-cylinder 124 chassis, but not the V8.

 

[Rettopian]

Great. Thanks Dave. At the risk of pushing my luck a bit, do you have part numbers and descriptions of all the powertrain computer modules so I can try to track them down?

 

[gsxr]

Great. Thanks Dave. At the risk of pushing my luck a bit, do you have part numbers and descriptions of all the powertrain computer modules so I can try to track them down?

Easiest way is to remove the CAN box cover and snap a photo of the modules in your car now (this also helps confirm if they are correct, sometimes a previous owner/mechanic may have swapped in a wrong item).

More info here. If you buy any spares, swap them into your car (once it's running normally again) to confirm the spares are good. I'd leave the spares in the car and put the originals on the shelf as a "long term test" of the spares.

 

[Rettopian]

Grand idea! Cheers!

 

[R129 UK]

Grand idea! Cheers!

Did you manage to resolve your issue?

 

[Rettopian]

Hi Chap.

Sadly not but thanks for asking. I currently have a very large, shiny paperweight!

It seems that power gets to the fuel pump relay but no further. We managed to get a direct 12v feed to the pumps as well - still nothing. So will get those off in due course but can't believe new Bosch pumps will have failed after no more that 5 miles of driving.

Interestingly, that blank switch with the red LED in the row is now flashing when the car is locked so I'd guess that means the Alarm is activated. Also its gone back no not turning over but this time there is a regular clicking from the passenger footwell that seems to be an alarm module? We disconnected that but it made no difference so its currently plugged back in. It's all a bit of a bugger really!

 

[R129 UK]

That’s a bit crap.

Regarding the fuel pumps, if you have eliminated everything else, whatever remains is the cause regardless of how unlikely it seems.

Can you hook a supply direct to the starter motor on your car?

 

[gsxr]

It seems that power gets to the fuel pump relay but no further. We managed to get a direct 12v feed to the pumps as well - still nothing. So will get those off in due course but can't believe new Bosch pumps will have failed after no more that 5 miles of driving.

Are you certain they were Genuine Bosch, and not counterfeit Borsch/Bocsh knockoffs? What part number was installed? Photos would help too. New Bosch pumps absolutely should not have failed immediately after installation, unless there was debris in the fuel tank which seized the pumps (unlikely, but theoretically possible if the [NLA] tank strainer is missing).

Note that power for the fuel pumps comes directly from the battery to the relay. Make sure you are properly sending +12v power to the pumps. Click here for the pump schematic.

Interestingly, that blank switch with the red LED in the row is now flashing when the car is locked so I'd guess that means the Alarm is activated. Also its gone back no not turning over but this time there is a regular clicking from the passenger footwell that seems to be an alarm module? We disconnected that but it made no difference so its currently plugged back in. It's all a bit of a bugger really!

The alarm system can prevent the starter from engaging. Disconnecting the alarm module will not allow the starter to engage, unless you also short out / jumper two sockets on the connector which plugs into the module. Search the forum for more info on this. Some people have disabled the alarm system and it requires a permanent jumper at the connector once the module is removed.

 

[Rettopian]

That’s a bit crap.

Regarding the fuel pumps, if you have eliminated everything else, whatever remains is the cause regardless of how unlikely it seems.

Can you hook a supply direct to the starter motor on your car?

That’s a bit crap.

Regarding the fuel pumps, if you have eliminated everything else, whatever remains is the cause regardless of how unlikely it seems.

Can you hook a supply direct to the starter motor on your car?

Ha! Very Sherlock Holmes! The starter motor is fine. Pretty convinced its something alarm related.

 

[Rettopian]

Are you certain they were Genuine Bosch, and not counterfeit Borsch/Bocsh knockoffs? What part number was installed? Photos would help too. New Bosch pumps absolutely should not have failed immediately after installation, unless there was debris in the fuel tank which seized the pumps (unlikely, but theoretically possible if the [NLA] tank strainer is missing).

Note that power for the fuel pumps comes directly from the battery to the relay. Make sure you are properly sending +12v power to the pumps. Click here for the pump schematic.



The alarm system can prevent the starter from engaging. Disconnecting the alarm module will not allow the starter to engage, unless you also short out / jumper two sockets on the connector which plugs into the module. Search the forum for more info on this. Some people have disabled the alarm system and it requires a permanent jumper at the connector once the module is removed.

Great. Thanks Dave.

The car is going to be transported back to the workshop next week. I'll let Tony go through it then. Pretty certain they are genuine Bosch. Again Tony sourced them but I've used him for 20 year & and trust him 100%

 

[R129 UK]

Ha! Very Sherlock Holmes! The starter motor is fine. Pretty convinced its something alarm related.

Glad you got the reference, good luck with the next round of your investigation.

 

[TerryA]

Interestingly, that blank switch with the red LED in the row is now flashing when the car is locked so I'd guess that means the Alarm is activated.

@Rettopian,
I’ve never heard this before. I’m curious, you say you have an E500. What LED flashes when your alarm is activated? Is it an aftermarket alarm system?

Nothing like that in my 500E that I’m aware of.

 

[gsxr]

@Rettopian,
I’ve never heard this before. I’m curious, you say you have an E500. What LED flashes when your alarm is activated? Is it an aftermarket alarm system?

Nothing like that in my 500E that I’m aware of.

Terry, the alarm system was standard in USA as of model year 1993. Your 1993 500E should have the alarm, the LED is in the row of switches above the HVAC controls. Photo below.

However, if your car has an ASR defeat added, often the ASR defeat switch is installed in place of the alarm LED...

 

[Rettopian]

It’s just like the pictures posted by R129 UK - a flat plate with a red led that flashes in the centre. It sits just above the heater controls just to the right of the hazard warning switch from memory. This was a car delivered to Germany and seems to have been an MB ordered car.

 

[Rettopian]

And by Dave.

 

[Rettopian]

Glad you got the reference, good luck with the next round of your investigation.

Thanks. I've read a book or two in my time! Just not the right books to help me sort out the Merc! Such a pity they didn't make a 320hp E230!

 

[R129 UK]

You had a running car recently before creating this thread so you aren't far away from the fix.

Just keep it to the basics, work methodically and change one thing at a time and you will make progress.

 

[TerryA]

Terry, the alarm system was standard in USA as of model year 1993. Your 1993 500E should have the alarm, the LED is in the row of switches above the HVAC controls. Photo below.

However, if your car has an ASR defeat added, often the ASR defeat switch is installed in place of the alarm LED...

View attachment 198758

I’m pretty sure my alarm works but I’ve never seen the red light flashing. Maybe I just haven’t noticed it. I only lock the car when I’m out of it. I guess I need to check it out.

 

[Rettopian]

You had a running car recently before creating this thread so you aren't far away from the fix.

Just keep it to the basics, work methodically and change one thing at a time and you will make progress.

Yeah. True. Just very frustrating as it’s been a long time coming, looks great but doesn’t do what a car should!

 

[Rettopian]

Just a question regarding sourcing a replacement LH module. Does it matter if it comes from an R129 SL500, (Or a 5 litre W140?) and does it matter if that was a US or European spec car? That is to say would a US spec module result in performance differences?

Cheers

 

[gsxr]

Just a question regarding sourcing a replacement LH module. Does it matter if it comes from an R129 SL500, (Or a 5 litre W140?) and does it matter if that was a US or European spec car? That is to say would a US spec module result in performance differences?

Generally, no, it doesn't matter. The R129 and E500E shared identical part numbers, the 140 had different part numbers but the modules are functionally equivalent. There was no performance difference between USA and ROW modules.

Early modules have WOT enrichment, later modules do not. There is a small power gain when an early module is used in a late engine (details here) and there would be a power loss if a late module was used in an early engine. The Wiki has most of the part numbers, click here.

Your E500 can use early or late modules, but the early ones will provide the small power gain at full throttle.

 

[Rettopian]

Generally, no, it doesn't matter. The R129 and E500E shared identical part numbers, the 140 had different part numbers but the modules are functionally equivalent. There was no performance difference between USA and ROW modules.

Early modules have WOT enrichment, later modules do not. There is a small power gain when an early module is used in a late engine (details here) and there would be a power loss if a late module was used in an early engine. The Wiki has most of the part numbers, click here.

Your E500 can use early or late modules, but the early ones will provide the small power gain at full throttle.

Great! Thanks Dave.

 

[Rettopian]

Just to provide a brief update.

The car is running once again.

It seems it did run out of fuel and looks to have dragged a little water through to the pump. a light tap with a Brummagem Screwdriver and she's away again. (It's OK I was born in Birmingham, still regard it as home and am very fond/protective of the place!) So in the end, it really wasn't complicated at all - I'm just annoyed that given my roots, I didn't try this first!

Now I need to resolve the non working rear fog lights and number plate lights and it can get an MOT and I can then get to enjoy it a bit.

So thanks for all your help, and suggestions folks. It has been appreciated.

 

[doolar]

I’m pretty sure my alarm works but I’ve never seen the red light flashing. Maybe I just haven’t noticed it. I only lock the car when I’m out of it. I guess I need to check it out.

I don’t know if it’s been mentioned, but the easiest way to test the original alarm is to put the driver window down, close and lock the door with the key, and after that, reach inside the car and open the door from inside.

If the alarm is working, you will know by the blaring siren. Close the door and lock with the key and the alarm should turn off.

The LED in the centre console may be dead, or VERY weak after all these years, but the alarm rarely fails.