W124 E200 Estate starting fault.

[hannay]

W124 E200 Estate, ’96, 210K miles, always looked after, always utterly reliable. Except ……

VERY rarely – 4-5 isolated times in the past 3 years – the engine has failed to “catch” just on the key. It catches perfectly fine with a blip on the throttle at the same time and will rev fine, but come off the throttle and it dies, won’t idle. It might take just 2-3-4 turns and 10 seconds to then start normally, or might take 30-40 tries across 10-15 mins, but it has always started fine at some point soon after that initial little hiccup and settled to a smooth steady idle perfectly normally. It doesn’t ever cut out, simply doesn’t fire on the odd occasion

There has not been an obvious pattern of weather, temperature, time of year, from-cold or from-hot, etc. No other powered system has been affected/unusable that I have noticed.

Virtually impossible to catch/predict/replicate/sustain/explore.

Checked in isolation the fuel/pump/delivery/system is fine, ditto electrics/spark etc. Seemingly those two systems just occasionally don’t speak to each other except when encouraged/overridden by a tickle on the throttle, though at some point it self-corrects anyway.

It has occurred on each of the past three days however after 5-6 months clear, and is now more than an overlookable little sporadic nuisance after embarrassingly stranding me temporarily at a client’s premises.

Is this symptomatic of a known fault/failure please? If not, is anything in particular indicated? I have reached the limit of my awareness of internal combustion engine general-principles, and am still learning of M-B specific wizardry/systems. More-informed thoughts and opinions would be appreciated.

With thanks

 

[television]

I have read your post and am thinking

 

[hannay]

I have read your post and am thinking

Appreciated .... thank you.

 

[jibcl500]

Could be the crank position sensor. Might be worth checking the condition of the engine loom as they do have a problem with the plastic shield cracking and allowing the wires to short.

jib

 

[jibcl500]

Actually over protection relay next to the battery!!! its the one with the fuse in the top of it.

jib

 

[hannay]

Actually over protection relay next to the battery!!! its the one with the fuse in the top of it.

Thank you ... would you know if there a means of checking the relay, or is it a matter of replacing it and seeing the outcome? I have done a quick search here before replying to try and find that out, but can find no mention of a check-process thaough I can recognise one or two of the conditions central to other posts where the relay has been a central suspect. None mention that "their" firing problem was easily overcome by a blip of the throttle however, which I would have thought might not have been overlooked if occurring ..

But anyway I can take a look in a couple of hours time when I get home as it didn't fire this morning quickly either and I didn't want to labour it so left it there and got a lift instead - I am in and out of here from the office just now.

If a replacement is indicated, is there a source I can turn to to find the part number if it is not not clear on the unit itself?

Again thanks for the pointer and I have my fingers crossed ...

 

[television]

If the OVP relay was at fault you would have the ABS lamp on

 

[hannay]

If the OVP relay was at fault you would have the ABS lamp on

... first thing I'll check, thanks.

 

[jibcl500]

BAS lamp doesnt come on, didnt on my dads 320 coop, he had starting problems, fitted the OVP with battery connected and the car started.

Easier to just replace the relay. £58 from mercedes I think.

jib

 

[hannay]

ABS lamp operating perfectly normally, lit with ign and goes out when it fires.

OVP relay externally undamaged and clean, sound, pins clean, fuse intact, nothing loose when (gently!) shaken …

Engine still fires instantly with a throttle-blip but not at all without, and revs smoothly, but dies with no throttle, won’t idle.

Can the OVP relay be bypassed/eliminated in order to check its functioning/non-functioning? Some other check?

Or does bypassing it interrupt the starting-process anyway, or perhaps leave a door open for damage to result even from a brief test?

Is the OVP relay the prime suspect still, as I can’t readily afford to throw away the replacement cost if it is not at fault.

A couple of the posts I read earlier this afternoon when researching previous OVP relay-related comments where starting/idling had been a problem, found the simple cure in checking/cleaning/replacing the distributor cap … however I wasn’t even able to locate that or the cables etc when looking around generally after the OVP inspection didn’t seem to throw anything up. Is that a valid line of thought for the behaviour I have described? If so how deep in the very busy under-bonnet area do I have to dive to find it – presumably ign IS still provided by plugs and leads in an injection system also, and my inability to see them was simply down to the dark/cold/torchlight nature of my exploration ….

I do need to take care of this urgently now as I have a special event happening at the weekend that would become very awkward otherwise, so any focus that someone feels able to introduce to cover some good ground would really be appreciated.

Thanks!

 

[television]

You do not have a distributor on your car

http://www.detali.ru/cat/oem_mb2.as...+++717.413&CT=M&cat=19K&SID=15&SGR=060&SGN=03


Re the OVP relay, to be sure the only thing would be to check the 12 volt live feed to the engine ECU.

Its could be worth looking under the bonnet at night when its dark to see if any high voltage leads are leaking and its easy to see the spark

 

[Ellsy Tanners]

I have read your post and am thinking

I could Hear the cogs ticking here on MARS

 

[television]

I could Hear the cogs ticking here in ESSEX

Its OK I only do that on Thursdays :-?

 

[hannay]

Thank you Malcolm.

You do not have a distributor on your car ....

I had just about come to that conclusion once my brain began to warm-through again and logic eventually began to trickle back as well last night after those evening-hours outside under the bonnet checking everything I could think to check in addition to following yesterday's good advice here. The only thing I simply wasn't able to get on to was Jib's thought about the crank position sensor, though in any event I have neither the equipment or the expertise/knowledge to take that much further anyway.

I did give myself a little pat on the back just now however on seeing your further words about noticing any sparking/leakage in the dark, which at least is one diagnostic step I managed to come up with unaided before brainfade reached 10. None was apparent.

I think I am sensing some bullet-biting coming up .... hmmmm, wonder if I can get the OVP relay on sale or return ... doubt it ... mumble mumble ...

I could Hear the cogs ticking here on MARS

Its OK I only do that on Thursdays :-?

I had put that down to the clock here on my desk, henceforth to be referred to as Malcolm

 

[The Crooner]

At 190000 on my 230 TE W124 I found excessive wear in the accelerator cable linkage in the engine bay - its a quite complicated mechanical component with pivots, ball joints and springs.

Buying £20 worth of parts from the dealer made my cars idle and general driving experience better. The position of the linkage determines the movement of the parts in the fuel distributor, if the link is worn, the position will have moved from the position it was set at from the factory.

I'm not saying yours is worn, and I'm by no means an expert, but it might be worth a look...

Tony

 

[hannay]

An interesting thought Tony, to be checked though well worth bearing in mind to explore in any eventuality I would think - thanks.

 

[television]

What makes these faults hard is that there are so many ECU modules, without knowing the part numbers and the exact system used it makes searching very difficult, added to this is the slow disappearance of the documents for these cars.

Sadly the average owner driver cannot give this information so I could sit here and search for a few hours and all for the wrong system or ECU. When I am working on a car it is easy to see what the cars has and get references to that car.

Going back to the OVP relay, we know that a faulty unit will give rough idle on the later cars, but starting I am not convinced. All of these cars use a fuel enrichment device for cold starting. As the sensor (2) have been running for some 14 to 18 years, replacing them is a good start and recommended by Auto Data. Most faults on cars are still basic electrics, and finding them you do need some test equipment so that you can test one thing and move onto the next, knowing that part X is good and working, some experience is also needed when looking at instruments to
interpret what you are looking at. Its not an easy subject with electronics,, nothing moves it is all just signals and voltages being at the right place at the right time

 

[jibcl500]

Hannay
Where are you in the UK, I have a complete 93 E220 ready for breaking car complete.

My guess for you car would be

1 air flow meter
2 Engine loom
3 OVP
4 Oxygen sensors, the one on the manifold is a service item!!! should be replaced.

jib
07730 777596

 

[hannay]

Very relevant observations Malcolm, thanks. I have the same view and concerns precisely, though as a tinkerer at best I can only express it simply and basically - I can cope with good honest nuts and bolts even without too much of the theorey, often improving knowledge in the process, but black boxes come from Mars.

I am already past my limit, and the OVP is a minor black-box on an increasing path that makes no sense for me to travel down beyond maybe this first step if indicated.

And right there is the first dilemma already. Both on this forum and the US counterpart there are contrasting opinions about whether the ABS lamp is a valid indicator of the OVP's wellbeing. With equal certainty that is frequently based in direct experience, one view states that the ABS lamp going out indicates that the OVP is operating properly, whilst the other states that the lamp can go out with a faulty unit and does not automatically mean the OVP is fine.

I would have loved to find that my ABS lamp remained on, at least it would have indicated some sort of fault somewhere: However, it goes out perfectly normally when I *make* the engine fire by blipping the throttle as it spins. And this makes step-two nothing more than a coin-toss .. replace in hope or not? I can tell myself almost convincingly that it is justified as a reasonable (?) move to make in the elimination process, though I can't justify the £60+VAT that I have been quoted this morning with absolutely nothing beyond suck-it-and-see for a reason.

And on the surface all seems so simple - blip it on starting and it fires, don't and it doesn't .... there's someone somewhere to whom this makes simple sense and who knows which tyre to kick where for the dislodged blip-widget to fall back in to place.

Honestly? I have my doubts about the OVP but there seems as much for as against and who am I to judge when it isn't something I can fix just by tightening it with a suitable spanner. Remember spanners? Things with corners once they went all high-tech and got double-ended, that needed an oily rag to stop gouging chunks out of your palm, things you always chose the longest one you could get on to the nut so you would get best leverage, balancing the extra torque against the knuckle-skin inevitably to be lost in the resultant tight spaces when it slipped off ... and as for a torque-wrench? Pah, a proper mechanic can do it entirely by *feel*!!

A question please just as a precaution ... if I do replace the OVP in the absence of something else becoming the obvious best-move, does the battery need to be disconnected in order to avoid frying something before even being able to do anything?

 

[television]

Take the OVP relay out and bridge pin 30 and 87 then it will be out of the circuit

On some cars they have 7 and 9 pin relays, but the extra pins are used for ASR and other thing that your car does not have.

The OVP relay is a safety device, and its first main action is to safe guard expensive things like the ABS pump, this was extended on later cars to parts of the main engine ECU that makes it complicated without know the exact chassis.

The device its self is a pair of 7.5 volt zenor diodes that crowbar in the event of a over voltage caused through jump starting and reverse polarity.

The ones made in Ireland are much better than the Austrian counter parts.

There is a fuse on top that can blow with jump starting.

This OVP relay often gets blamed for other faults like a low voltage battery, when you turn the key to start, the ABS requires 12.5 volt in order to set, and once the engine is running it swiches over to the cars running system, this is why it takes a few seconds for the lamp to go out,,if a low voltage was logged at starting, then it cant be re set without restarting, and they often do on a re start.

Cars with ASR need a more complicated version that has a further 2 outputs and 9 pins to drive these circuits.

Most faults are down to dry solder on the PCB, they were wave soldered from new and the solder can disapear on some of the joints rendering it US.

I have soldered up loads of the things but others prefer to buy new, at around £50 to £80 to replace