W124 intermittent very bad running

[nmacc]

Hi folks,

Firstly I'd like to say thanks for all the help I've received from the forum and the car is nearly looking and behaving as a Mercedes should (except for the worn upholstery!).

Major problem:

1993 220TE automatic has developed a severe, but intermittent, rough running problem. When started the revs oscillate up and down as it tries to achieve a stable idle, frequently failing and cutting out. After idling for about 10 mins she may suddenly smooth out and run normally, but this smoothness will disapppear when driving. It makes the car very difficult to drive as she will cut out when slowing for a junction and lose steering power.

I initially thought it was an induction leak, but it's not exactly the same. It will smooth out with throttle, but it needs a LOT of throttle. Also it can appear when travelling; running steadily you will notice a slight loss of power. It's a bit like a misfire, but plugs and leads were replaced around 6 months ago. No visible or audible induction leaks.

I also notice some seriously sulphurous odours from the cat. it could be the varying mixture, but could it be a loose catalyst blocking the cat? No rattles from the cat however. I don't think it's overall fuel supply, as flooring the throttle brings a good response.

All suggestions welcome; thanks.

Niall

 

[jibcl500]

Could be the air flow meter, idle control valve needs a clean, van and breather pipes under the inlet manifold.

When was it last serviced.

jib

 

[kth286]

the first thing to always do in your situation is take it to a technician specialising in Mercedes of early mid 90's and get the diagnostic trouble codes read.

Let us know what codes were found.

 

[nmacc]

Thanks David, that isn't always as easily said as done. I have had occasion to approach the main dealers for Mercedes around here on far too many occasions in the past. Frankly their incompetence is of vast, nay of George W. Bush proportions. A small example from a long list:

I had a faulty steering rack replaced by them under warranty and they neglected to tighten the bolts; it fell out.

I brought it back and they tightened the bolts, but used the wrong bolts, so it fell out again.

Would you go to such a dealer?

It sticks in my craw to even buy spares off them so I'm damned if I'm going to pay them €150 and hour to mis-read the fault codes. Unfortuneltely reliable independents are thin on the ground around here.

But you do raise an interesting point - does a 1993 W124 record fault codes? If there is a standard serial interface available I'd invest in it myself.


Thanks for the suggestions Jib, I suspected the MAF, but of course I'd have to substitute it to check (although there's no obvious crud on the original). Can you tell me where I'd find the idle control valve? Are there many vacuum pipes under the manifold? I don't have the car to hand as my wife is out nursing it to her destination, but I didn't notice any on previous inspections.

I will be bringing it to an independent Merc specialist tomorrow morning, but I'd love to have some good places to start (such as the MAF, etc.)

Niall

 

[jibcl500]

There will be a diagnostics socket on your car, if you give me the first 6 digits of your chassis I will send some info via email if you could email me boss@mercanic.co.uk

Dirt wont stop a meter from working, they monitor air temp and air quantity they go out of spec which is enough to cause poor running, if the MAF was dead unpluging it would stall the engine, if its out of spec and unplugged you might find the car runs better as it will assume the settings.

Vac pipes and breathers are all around and under the inlet manifold, the idle control will have two large rubber hoses, one top one bottom.

jib

 

[kth286]

You do not have idle control valve it is all electronic engine, both fuel and ignition controlled by one main computer. That is why the codes are so relevant and important.

We need to know the codes.

Make sure they clear the codes as well. Then drive around for a few minutes and go back to read codes again and see what comes back. It is the second reading that is so important, and we need to know what those are. Have a pen and paper.

Some of the codes initially read may be very old and even as a result of wires disconnected from past work etc. so those not so relevant.

Obviously ask them what they think the problem is.

ALL of the above can be done within half hour labour charge and confirm there is a discount for older cars at commencement.

 

[nmacc]

Thanks for all the info guys, we'll see how we get on in the morning.

Jib: the VIN is WDB1240822F254100. I tried disconnecting the MAF at idle and it got worse briefly, then settled down to a bad, but functional idle; I didn't try driving it at that point to see how it behaved, but opening and then releasing the throttle caused the revs to drop back close to stall.

Reconnecting the MAF caused the revs to rise smoothly by at least 500 rpm. then smoothly drop back to an idle which was, alas, as lumpy and hunting as before.

N

 

[jibcl500]

I'd put my money on the MAF, it needs diags really to be sure otherwise you could end up spending a lot of money and still have problems.
jib

 

[nmacc]

Well, this morning hasn't brought any definite insights yet.

Drove her down to the indy this morning and the bitch behaved perfectly, despite being next to undriveable yesterday. I dropped a customer home for an 8-mile round trip in the hope of coaxing her to misbehave and she did, but by the time I got back, she was running smoothly again.

Of course by taking her out I missed my slot with the most experienced mechanic and they couldn't check the codes as the tester for that vintage is out on loan and won't be back until Thursday.

However one of the mechanics suggested a faulty throttle body and conveniently had a known good spare. I swapped them over and drove her home, about 6 miles. So far, so good.

I'll see how she runs for the rest of the day and I'll try and get back later in the week to check the codes when the tester has returned.

Niall

 

[nmacc]

Looks like a dodgy ECU

Evening all.

Thanks to all for the suggestions so far, but I seen to have a failing ECU.

As I mentioned previously, despite being almost undriveable on Sunday last, when I brought her to the garage on Monday, she behaved impeccably.

I swapped the throttle body for a known good spare and all was well until Thursday evening, when the fault returned. I was going to put back the original throttle body so that I could return the spare, when I had an idea.

Leaving the replacement throttle body in place I disconnected the plug under the manifold and plugged in the original throttle body which was, for the purpose of this test, simply sitting on the inner wing. Started the engine and then stopped it. Reconnected the fitted throttle body and re-started the engine - problem solved! She ran perfectly.

On Saturday I was able to confirm that the phenomenon was not tied to the throttle as the fault was back again Saturday. This time I disconnected the MAF, restarted the engine briefly; shut it down; reconnected the MAF and restarted. Once again, problem solved.

It therefore appears to be an ECU problem. I suspect leaky electrolytic capacitors, but someone out there may know better?

Can anyone tell me which of the three modules behind the battery is the ECU?

Thanks

Niall

 

[kth286]

and all this time you still have not had the codes read - you do like making work for yourself.

The quality of the Mercedes computer codes is system is second to none and are usually very reliable - just do it before you disconnect the ecu.

 

[nmacc]

Thanks David, you are of course correct that I need to obtain the codes. It is not simply a case of reluctance to approach the main dealer because of cost (although in my current impecunious state it is a consideration). I am convinced that if I bring it to a main dealer that they will break something.

This is not based on simple prejudice, but is a result of years of bitter and expensive experience. I also detest the condescension bordering on pity that is occasioned by bringing a car more than five years old to a main dealer.

I have made enquiries about a good independent and I have a lead that I'll be following up this week. When we have extracted the codes I shall immediately pass them on.

Does disconnecting the ECU clear the codes? Back to my original question: is the ECU the Bosch box nearest the battery, or is it one of the two smaller boxes lurking in the dimness behind?

Thanks,

Niall

 

[nmacc]

Problem found - now I'm really in trouble!

Well, what is it they say, life is what happens while you're making other plans?

I was planning to get the codes read, so I called into the garage this morning and presented my rough, hunting, 220. The mechanic asked if the MAF had been changed and then fiddled with the lead from same. Suddenly we had smooth running.

He headed off to check something and I examined the MAF cable; no physical damage, but it definitely felt strange, rather like rolling a dried-up cigar. Just then the engine stopped. I was about to switch off the ignition when the wiring loom melted and went up in smoke!

The fire diverted me from my first thought - to switch off the ignition, and instead I ran to get a spanner to disconnect the battery. That extra 30 seconds of current probably did most of the damage as now I have this:

Now I really have a lot of work to do. It's possible that the ECU and the overvoltage relay are buggered also, but I won't know until I've reassembled some form of a loom. Alas Haynes don't cover the 220. Would anyone out there have a wiring diagram available. Something with pin numbers and wire colours would be especially welcome.

Thanks

 

[television]

So sorry to see that but it was the cause of the bad running,,you can buy a repair kit from MB for this, not cheap but worth it in the long run. You will not know about the ECU until you fit the repair kit, OVP relay is unaffected

 

[roofles2]

i was told the 4cyl cars dont get the loom rot problem so it seems very unlucky but now you know whats needed .not the best way to find it ?

 

[television]

i was told the 4cyl cars dont get the loom rot problem so it seems very unlucky but now you know whats needed .not the best way to find it ?

Hello and welcome to the forum

 

[nmacc]

Thanks Malcolm,

Any idea what the kit is called, or exactly what is covered?

I notice the MAF connector is moulded on, so I can't readily rebuild it. As a quick-fix I'll hacksaw off the top and solder to the pins.

This is the first time that I've been let down by the electrcial engineers in MB. The cable in the MAF loom appears to be PVC (although sleeved in silicone) and therefore unsuitable for the high temperatures above the exhaust manifold that clearly caused the wiring to degrade. It should have been silicone of Teflon.

I'm going to start the rebuild tomorrow with soldering iron and cable, but there's a lot of wire involved. As for the ECU, there are a couple of marked pins on the right-hand connector (passenger side). These pins were clean the other day as I had the ECU out to check for damage.

The reason I mentioned the OV relay is that the wiring to the OV relay, the fuel pump relay and what I think is the A/C control relay, was all completely fried.

I've just hacked the lid off the ECU and there's no obvious damage; looks like I didn't let any smoke out, so I might be lucky. It'll obviously be a few days before I'm in a position to try it out.

 

[Bolide]

AFAIK the loom repair kit is just for the feeds to the coil packs. They run over the top of the engine where the heat is greatest

Nick Froome
www.w124.co.uk

 

[roofles2]

Hello and welcome to the forum

thanks for a warm welcome

 

[television]

AFAIK the loom repair kit is just for the feeds to the coil packs. They run over the top of the engine where the heat is greatest

Nick Froome
www.w124.co.uk

Thank you Nick.


Do the repair with heat shrink sleeving its so much nicer than anything else.

A link here may be of some help, I may know of one being broken up
http://www.mercedesshop.com/Wikka/M104WireHarness