Multivalve Diesel S124 Starting Issue

chilsta

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'94 S124 E300D
Sometime in the summer I had a couple of times when the engine would start, but immediately die again.I had to turn over the engine many times before it would eventually start, with periodic glows inbetween.
After those couple of times it seemed to rectify itself & was fine.

Until a couple of weeks ago, when it started to not start every time that I tried in the morning. It gets to the point where the battery has pretty much drained and just as I think it's not going to, it will start to fire again. Once it's started it runs absolutely fine and will restart immediately even after sitting for 9+ hours while I'm at work.

So last week it went into my local mechanic. My initial thought was that it was probably a leak in one of the injector line seals at the top of the injector pump (I had this on a 201 years ago). Over time, air bleeds in and the fuel bleeds back to the tank.

The mechanic wasn't so sure, or was the Mercedes guy over the road from him. They both suspected glowplugs. They also spotted that there was damp coming from at least one of the lines on top of the injector pump.

So the inlet manifold came off, new Bosch glowplugs fitted, new seals and O rings fitted on the injector lines.

On reassembly it started fine, they MoTd it for me (no advisaries after replacing the light switch so it didn't pull off when trying to switch on the fogs) and dropped it back to me. I was away so it sat for around 5 days until Monday when I used it for work. It took maybe a turn or two of the engine to start (it normally starts immediately, but I put this down to the fact it had just had work done and had sat for 5 days). It started up immediately 9 hours later after work and I was fairly satisfied that all was well.

I didn't use the car yesterday, but this afternoon I went to start it and was gutted to find the same thing happened- started straight up but almost immediately died. After nearly cranking the battery to death it started and all was well. I turned the engine off and restarted a few times after that while running errands and it was fine each time.
I spoke to the mechanic and he's at a loss, but said he'll take a look.
I'm still of the opinion that air's getting in somewhere, but really don't know where that could be now. He's suggesting that we change the fuel filter housing. I've not heard of this being an issue before. Is this likely to help?

Anyone have any ideas where air could be getting in, or another solution to this?

Many thanks in advance
 

carat 3.6

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There are 6 clear plastic pipes around the diesel pump and fuel filter area, these are a good suspect for air leaks. Change them all.
 

SilverSaloon

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the fuel is draining back to the tank in the lines because of an airleak.

you need to also replace all the orings on the pre-filter housing, not just the clear pipe orings. Also worth swapping out the main filter too. Take out and clean the pre-filter at the same time.

if that fails, then i'd suspect the delivery valve seals too.

until its fixed, just park the car on a slight hill with the nose pointing downwards - this should help as the fuel wont drain back to the tank.

is the car run on diesel or veg?
 
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chilsta

chilsta

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There are 6 clear plastic pipes around the diesel pump and fuel filter area, these are a good suspect for air leaks. Change them all.
Fantastic stuff, thanks carat. I've known of those pipes but didn't know they could be a cause of leaks. They will be swapped out...

Do the pipes come as a kit from MB? Any kind soul have a part #?

you need to also replace all the orings on the pre-filter housing, not just the clear pipe orings.
Thanks a million SilverSaloon. Did some digging on the o-rings and found a previous post where you'd mentioned these- thankfully they're still on eBay 3 years later...
MERCEDES DIESEL VITON FUEL ORING SEAL KIT E300D,E300TD,C250TD,124,210,202 O-RING | eBay
A lot of money for some O-Rings, but a bargain for reliable starting. Have just ordered. If anyone's looking in the future and the above link's dead, try this link to the seller and search their items for 'viton'.

The eBay listing states 'This kit includes replacement orings to replace worn out, leaking standard orings on your fuel system's clear piping.'

...any idea where I'd get the additional housing o-rings you mention?

Also worth swapping out the main filter too. Take out and clean the pre-filter at the same time.
I did change the primary 6 months ago & the pre a year ago (did about 1k a month over the last year, which has thankfully now significantly reduced) and carry spares of both in the back. I'll change the primary & check the pre (the one it replaced was spotless a year ago.)

is the car run on diesel or veg?
I did run on a couple of 50/50 tanks of WVO in the summer, just before the first case of the non-starting after sitting overnight. It's been regular dino since then.

I also ran it almost exclusively on Bio over last winter. Having read the description of the viton seals, that could be the cause of the standard o-rings deteriorating, although my last 124 and the 201 before that didn't seem to mind...
 

SilverSaloon

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if you have run any veg oil then that will of cleaned the fuel tank and brought all the stuff to the filters - they will need changing ASAP. Dont forget the strainer inside the fuel tank too.

After that, replacing the orings should help, hopefully you wont need to replace the clear pipes. these can just be swapped over for standard hose (but you wont see any bubbles though then)
 

bolide

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I don't see any reason to replace the pipes. They are not leaking - the O-rings are. So just replace the O-rings

With the money you save you could replace the front ARB Bushes - they always improve a W124

Nick Froome
 

carat 3.6

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The thing that most people don't realize with those pipes, is that they can also leak air in where the end fitting's are pushed inside the pipe itself. They are only plastic and do deteriorate with age, the pipes on the newest w124 will be 20 years old shortly so it is worth the cost if your keeping the car.
 

Smiley

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When you replaced the pre filter did you fit a new o ring to it? You have to buy the o-ring separately - it does not come with the filter (stupidly).
 
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chilsta

chilsta

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'94 S124 E300D
I don't see any reason to replace the pipes. They are not leaking - the O-rings are. So just replace the O-rings

With the money you save you could replace the front ARB Bushes - they always improve a W124
The thing that most people don't realize with those pipes, is that they can also leak air in where the end fitting's are pushed inside the pipe itself. They are only plastic and do deteriorate with age, the pipes on the newest w124 will be 20 years old shortly so it is worth the cost if your keeping the car.
Thanks Nick & Carat - To keep grief down and avoid removing the inlet manifold for a third time in a couple of weeks, we decided to only replace the o-rings that are accessible without removing the manifold and see what happened.
One of the pipes that he did almost fell off it was so loose, whereas the others required some force to remove. It's been a week now and no more starting issues, so I'm hoping that's the end of it for now. I'm keeping the spare o-rings safe and the next time the inlet manifold comes off will get all the pipes and remaining o-rings swapped as preventative measure for peace of mind. The pipes are about £45 from MB, so worth doing IMO. Will add the ARB bushes to the list...

When you replaced the pre filter did you fit a new o ring to it? You have to buy the o-ring separately - it does not come with the filter (stupidly).
I didn't. I'll need to replace that, thanks Smiley!
 
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chilsta

chilsta

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An update on this. Shortly after my last post, it started not starting again. I checked and the top pre-filter O-ring had been changed (it was part of the eBay set), so I tried changing the lower O-ring on the pre filter. After that it was fine for 2-3 weeks. Until we drove up to Newcastle for xmas. Was to be a taxi on xmas morning for S/O's family and guess when it decided to not start?! Since then it's not started more often than it has. It's booked in to my mechanic's for tomorrow morning where I've asked him to replace the remaining o-rings which weren't accessible without removing the inlet manifold. I'm also going to replace the clear pipes while he's in there. Having read this post, I'm considering replacing the clear pipes with regular fuel lines, which I like the idea of for cost/longevity reasons, but I'm not convinced about having to use PTFE to get them to fit properly. The following post about using a banjo on the IP sounds promising though. I'm going to show those posts to the mechanic and see what he thinks.
Really hoping this saga is at its end...

Am probably going to fit a hand priming or electrical fuel pump just to avoid caning the battery in case of starting issues due to air in the lines. I'd still know there was a problem and have to get it fixed, but run less risk of being stranded with a dead battery from re-priming the system with the starter motor.
 

a111r

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You haven't mentioned the fuel shut-off valve O ring. Deforms over time and prevents starting. It's a ten minute job.

As all of the above 'extra work' shouldn't be necessary with new pipes, O rings and some basic skills.
 

Druk

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If your mech is a bit inventive get him to replace the fine mesh filter with one of these. Also has a hand primer pump so gets rid of air in a second.





.
 
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chilsta

chilsta

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'94 S124 E300D
You haven't mentioned the fuel shut-off valve O ring. Deforms over time and prevents starting. It's a ten minute job.

As all of the above 'extra work' shouldn't be necessary with new pipes, O rings and some basic skills.
I no longer have a fuel shutoff.
Shortly after buying the car the fuel shutoff was leaking fuel, pretty badly.
As this is a multivalve it has a screw on the top of the filter housing to let air in rather than a lever on top of the IP (the inlet manifold covers the top of the IP).
I couldn't see a way of taking the valve apart & got an extortionate price from MB for a replacement. I ended up buying a new top filter housing bolt for a pre-multivalve from MB. If I ever need to kill the engine, I'll loosen that bolt, or pull a hose or something...
 
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chilsta

chilsta

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If your mech is a bit inventive get him to replace the fine mesh filter with one of these. Also has a hand primer pump so gets rid of air in a second.
Interesting- is that the pre-filter in the main filter housing that you're referring to?

I do have a heated aux fuel filter that I've kept from a 1 tank Elsbett bio-fuel kit that I had installed on my old 109D 2.5 (which was the original reason for me getting into old MBs 13 years ago)- it's arrowed here:



I'm intending to have that filter added to the 124 at some point, but with the Elsbett kit I believe it was inline just before the main filter. There was a separate hand priming pump, which I'd also like to reinstate (or possibly an electrical pump, need to research this further before making a call on which).

Would that arrangement achieve the same as you're thinking? What's the benefit as far as the air leak is concerned?
 
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chilsta

chilsta

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Last Thurs I had the clear pipes replaced. I've used the car every day & haven't had any issues since.
All fairly straightforward apart from one pipe in the replacement kit having a banjo connection whereas the one that came off was the pushfit type. This post was very helpful in discovering that the IP will take either type, so we just had to get the banjo housing and that was sorted.

Only down side was that the pipes came with the standard MB o-rings fitted and the mechanic decided to go with those rather than fitting the Viton ones I'd got from eBay. He'd thrown the ones he'd already fitted in the bin- I got him to get them back and will keep the set in case of any future issues.

Next day I was getting a nasty knocking at gear shifts and I noticed a piece of rubber seal hanging out of the NS engine mount. So it's back in now and having new genuine MB engine/gearbox mounts fitted tomorrow.
Hoping that's it for spending out for a while...
 
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chilsta

chilsta

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An update on this- it's now been 6 months and no further starting issues. Replacing those clear pipes was definitely the solution.

Regarding the knocking while shifting that I mention at the end of the past post- the mechanic had left off a vacuum line. The engine mounts were shot though, so their replacement improved shifting and general smoothness.
 
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chilsta

chilsta

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Sadly marking this as unsolved as this has come back to haunt me.

The first time was early August, on a ferry from Denmark to Germany. Was one of the first cars on, so was parked right at the front of the boat with the nose slightly up the off-ramp. Only an hour or so crossing. I think it fired then died, then took over a minute or two to start- felt like an hour with a line of cars stuck behind us.

Was OK after that until late Aug when I parked on a steep hill for a couple of hours, again with the nose up. It didn't fire at all initially. Started after a couple of minutes.

This week I was parked on a very slight incline, again with the nose up and it happened again, this time starting then immediately dying. I had to get a spare battery to get it started as the internal one went flat.
This time, as soon as it died I checked the clear lines and they all were full of fuel.
Everyone I've spoken to is out of ideas, although one person is wondering about the shut-off system (the vacuum activated one, not the emergency one).

I'm booking it in with a local diesel specialist this week.
 

carat 3.6

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Sadly marking this as unsolved as this has come back to haunt me.

The first time was early August, on a ferry from Denmark to Germany. Was one of the first cars on, so was parked right at the front of the boat with the nose slightly up the off-ramp. Only an hour or so crossing. I think it fired then died, then took over a minute or two to start- felt like an hour with a line of cars stuck behind us.

Was OK after that until late Aug when I parked on a steep hill for a couple of hours, again with the nose up. It didn't fire at all initially. Started after a couple of minutes.

This week I was parked on a very slight incline, again with the nose up and it happened again, this time starting then immediately dying. I had to get a spare battery to get it started as the internal one went flat.
This time, as soon as it died I checked the clear lines and they all were full of fuel.
Everyone I've spoken to is out of ideas, although one person is wondering about the shut-off system (the vacuum activated one, not the emergency one).

I'm booking it in with a local diesel specialist this week.
It only does this with the nose up? Not when parked downhill?

That sounds like air moving to the highest point in the system, which would be the fuel filter on a 606.
 

rorf

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I had a C250 diesel which had a similar problem. To listen to the radio when stationary the ignition key had to be in accessory position and after an hour the car wouldn't start.

Found out the electric diesel line valve was connected to this circuit and therefore diesel drained back into the tank.

Crazy but true - made even worse when the car was parked on my steep drive way:crazy:
 

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