W124/M104 engine issues

[MB-tex]

Hi All

My old 96 e280 5sp auto estate is now well over 300,000 miles and still going strong-ish. Still my daily driver and a rolling restoration when I can afford the next bit that needs doing. Have all the parts now for a total refresh of front axles, redid the whole rear subframe 4 or so years ago and had the rusty rear cargo windows welded up and rear section resprayed last year. Also head gasket 3 years ago. So in many ways she's in fine fettle apart from jacking points, inner front arches (2 old inner arches in shed) and an ongoing front end oil leak...
So onto the problem I am on here for help with. It is intermittent and my regular mechanic cannot figure it out, partly cos he couldn't get it to perform when he had it in... When I accelerate from a junction there is a (sometimes dangerous) lag before the power comes on. Its like the engine is holding its breath before it bursts into life again. It sometimes happens when accelerating when already moving along too. It is also often accompanied by a popping sound from under the bonnet that could almost be described as a backfire. It had new fuel filters 2/3 years ago. It had a new fuel pumps too around the same time. New fuel pressure regulator too. Spark plugs are all ok and air filter is pretty new. Dirty injectors? Wiring loom? Any advice gladly received.

Thanks

Tom

 

[Smiley]

If the engine wiring loom has not been replaced then that would be where I would look first. Start looking at the wiring near the coils.....and be ready for a heart stopping moment when you look at the individual wires. I assume that you have seen photos of how it can degrade.

 

[MB-tex]

If the engine wiring loom has not been replaced then that would be where I would look first. Start looking at the wiring near the coils.....and be ready for a heart stopping moment when you look at the individual wires. I assume that you have seen photos of how it can degrade.

Thanks Smiley

Is there anything in particular about the symptoms that point towards the loom? Electrics are a bit of a mystery to me. I suppose the loom will probably cause problems eventually. It is the original still in place. I'm always super careful when changing the plugs. But its an expensive fix - hoping it is something cheaper?!

 

[carat 3.6]

Thanks Smiley

Is there anything in particular about the symptoms that point towards the loom? Electrics are a bit of a mystery to me. I suppose the loom will probably cause problems eventually. It is the original still in place. I'm always super careful when changing the plugs. But its an expensive fix - hoping it is something cheaper?!

If the loom is original that's a breakdown waiting to happen, also be aware that the longer you drive the car like that you run the risk of damage to the ecu. An easy way to check the condition of the loom is at the front of the engine, look at the plugs for the temp sensors and the camshaft magnets, if you see bare copper the loom is toast.

There are companies that can rebuild your loom rather than buying a new one from the dealer, I would advise that you have the small wiring harness to the throttle body rebuilt at the same time.

 

[Bellow]

Thanks Smiley

Is there anything in particular about the symptoms that point towards the loom? Electrics are a bit of a mystery to me. I suppose the loom will probably cause problems eventually. It is the original still in place. I'm always super careful when changing the plugs. But its an expensive fix - hoping it is something cheaper?!

Inlet backfires are usually associated with overly lean mixtures and/or delayed combustion - but not misfires. Late ignition timing or possibly, ignition weak enough to delay the onset of ignition but not deny it.
The lag is maybe a clue. Ignition failures on the high tension side are worse under load (throttle open). Or it may point to (momentary) fuel starvation. If this were mine, I'd provoke it and then immediately stop and pull a plug and see if wet or dry. If dry - fuel starved. Wet/sooty - ignition problem.
If the loom is falling apart though....

 

[RichardF]

Silec is the goto for looms.

I thought mine was OK but it seems the coils had new wires spliced into an old loom.

Have you read the codes?

 

[Smiley]

I've heard of all sorts of problems caused by the loom - and you are either very lucky or you are on borrowed time with an original 1996 loom and 300k miles - they don't like the heat from the engine so it has done very well to get this far - maybe you have the one good one! In your position I would be finding out how best to get it refurbed before disturbing any of it - because you may find that disturbing it is the final straw and the car won't start at all. If the car is a keeper then it is definitely worth inspecting and, if needed, fixing and especially before it does more damage eg to the ECU.

 

[MB-tex]

Thanks for replies and advice. I suspect you're both correct and it is down to the loom and I now have to decide what to do next. Part number of my loom A124 440 3433. So Sileck electrical quote £450 for loom restoration and £70 for throttle body. Both + VAT and postage. I think this has gone up a bit since I last enquired. On eBay the R129 co. is charging £650 for exchange remanufactured harness. Kurth Classics in Germany are charging €750 for same thing. I'm not even going to ask my parts guy at Merc. Anyone know of anywhere cheaper? Or have one in the shed?! Sileck is my first choice as they come highly recommended and have a quick (week) turnaround but money is a bit tight this month! Old cars are great until...

Tom

 

[MB-tex]

I tried to make one of those blink testers a while back, but like I said, electrics are a bit of a mystery to me and it never worked. It is the original loom. Its 26th birthday, according to the sticker on the wire, will be on 15 Nov this year! Pretty good eh?

But I can't afford to get it fixed right now and I don't want to let it sit because it starts to look more and more like a car waiting for the breakers yard. It is a keeper but how long can I keep saying that?! And I think driving it (though it seems to be fine most of the time) risks further damaging the electrics...

I'll work something out and she will fly again...

 

[colinallcars]

Thanks for replies and advice. I suspect you're both correct and it is down to the loom and I now have to decide what to do next. Part number of my loom A124 440 3433. So Sileck electrical quote £450 for loom restoration and £70 for throttle body. Both + VAT and postage. I think this has gone up a bit since I last enquired. On eBay the R129 co. is charging £650 for exchange remanufactured harness. Kurth Classics in Germany are charging €750 for same thing. I'm not even going to ask my parts guy at Merc. Anyone know of anywhere cheaper? Or have one in the shed?! Sileck is my first choice as they come highly recommended and have a quick (week) turnaround but money is a bit tight this month! Old cars are great until...

Tom

Don’t be afraid to ask Mercedes nor be afraid to ask for discount. Depends on the part but I often get 40% off list for SLK R170 items.

 

[MB-tex]

I get 10% at merc but they stubbornly won't go any higher despite my requests. I emailed merc to get a price. I'll let you know what they say...

I need to sell some parts that I have lying around. If anyone's interested:
Rear cargo side windows x2
Rear cargo window seals x2
Hirshman Auta 6000KE electric aerial
1 kidney (52000 miles) one careful owner.
All for S124 except kidney

Let me know if anyone is interested.

Tom

 

[colinallcars]

I get 10% at merc but they stubbornly won't go any higher despite my requests. I emailed merc to get a price. I'll let you know what they say...

I need to sell some parts that I have lying around. If anyone's interested:
Rear cargo side windows x2
Rear cargo window seals x2
Hirshman Auta 6000KE electric aerial
1 kidney (52000 miles) one careful owner.
All for S124 except kidney

Let me know if anyone is interested.

Tom

I’d try a different dealership to see what they offer.

 

[Bellow]

I get 10% at merc but they stubbornly won't go any higher despite my requests. I emailed merc to get a price. I'll let you know what they say...

It'll be interesting to see what they come back with. Often, the price isn't as steep as expected. On mere parts for a recent model that is...

 

[grober]

Sounds like as sticky throttle body plate- which might be dirty or more than likely the internal wiring is gone as suggested. your symptoms suggest increased fuelling without a corresponding increase in air flow=faulty throttle plate position signal to ECU

Dont bother with MB dealers--they wont carry parts for that age of car in UK---have to special order from Germany- where periodically they will get replacement batches made up from third party specialist remanufacturers such as Sileck!!

 

[colinallcars]

Sounds like as sticky throttle body plate- which might be dirty or more than likely the internal wiring is gone as suggested. your symptoms suggest increased fuelling without a corresponding increase in air flow=faulty throttle plate position signal to ECU

Dont bother with MB dealers--they wont carry parts for that age of car in UK---have to special order from Germany- where periodically they will get replacement batches made up from third party specialist remanufacturers such as Sileck!!

Why leave that stone unturned? The OP has nothing to lose by asking.

 

[grober]

Why leave that stone unturned? The OP has nothing to lose by asking.

Just trying to save the OP time and money but happy to be proved wrong. Historically the dodgy wiring was provided by one JOE LUCAS -the idea being it would biodegrade once in landfill- unfortunately it degraded faster than that!

 

[MB-tex]

Thanks all

I might try getting the throttle body rewired and cleaned first. That might cure it and save me £450+VAT! - But I know the loom is on the fritz - sections needed repairing when head gasket was done a while back. So it'll have to be done sooner or later if I am to keep the car. I've been avoiding it.

I'll let you know what price Mercedes Brighton give me for a new loom. My parts guy is generally pretty good at digging out parts for me and only rarely do they fail. W124 front lower control arms for instance - now NLA! I may try some other dealers too - Rivervale in Brighton have started selling merc parts again and Inchscape seems to get mentioned as a good parts department. I suspect though it will be way more expensive than Sileck...

No takers for the 124 parts?

Tom

 

[poormansporsche]

Just out of interest did all w124 m104s come with the bio degradable looms ? My 1996 w202 c280 had the the updated (Delphi?) Non bio degradable loom and I know that some 96 w202s didn't have the upgraded loom ? Pretty sure all early w210s with the m104 had the updated loom ?????

 

[MB-tex]

Rear window seals just sold on eBay. £75 for the pair. The coffers are filling...

 

[grober]

Just out of interest did all w124 m104s come with the bio degradable looms ? My 1996 w202 c280 had the the updated (Delphi?) Non bio degradable loom and I know that some 96 w202s didn't have the upgraded loom ? Pretty sure all early w210s with the m104 had the updated loom ?????

At that time Mercedes used to introduce the new models or engines after the August/September factory break. The biodegradable LOOMS were introduced in mid 1994 with the introduction of the new M111 and M104 engines in W124 models [this excludes the previous 300-24V 104 engines which had distributor based ignition and CIS jetTronic KE injection] the new engines with the dodgy wiring continued with the 95 facelift models but this was changed in early 96- by this time the saloons had been replaced by the W210 series. The W124 models continued in coupe/convertible/estate versions till mid 96 and had the improved wiring. IIRC?
That said even with the improved insulation the idea of mounting the HT coils and associated wiring effectively an enclosed oven on top of the cam cover of the M 104 was not a good idea in the long-term!