W140 S500 engine electrics expert needed in Hertfordshire

[Lambo911]

Hi all,

I need some help please.

I have a 1994 W140 S500 Coupe with an intermittent misfire. I have a 10 page thread on Benz World about the misfire I have on my car. It makes interesting reading and I've changed lots of parts. I thought it was fixed as it had been ok for a while but it is misfiring again.
s500 engine misfire when warm - Mercedes-Benz Forum

I've got to the stage where I need an expert with some monitoring kit to track down what is happening before I lose the plot and drive the car into a lake !

Is there anyone that can help me? I really need a garage/person I can work with to track down the fault without changing every sensor and component, I tried that and so far nothing I have replaced has made any difference.

Cheers

 

[Codger49]

You could try Philip Tutt at WelwynMerx.

It seems he was a MB Diagnostic Engineer, so should be able to help you.

Phillip Tutt - Welwyn Merx Limited

 

[Codger49]

If the lake wins, there's another around:

MERCEDES-BENZ S CLASS 5.0 S500 2dr For Sale in Bolton - Moses Gate Car Sales

Looks rather nice and I would be tempted myself, except the boss has laid down a moratorium on 2 door cars at the moment.

 

[Codger49]

Just read your thread on the other place, you have all my sympathy.

I think I would be heading for the lake right now.

Did you actually change the crank position sensor? That must be a player in ignition issues and seems to mentioned quite often in problems with more recent engines on this forum.

PS I haven't used Welwyn Merx myself, but found them as my son is contracting in Welwyn at the moment and wants someone to look at his CLK500. My own indy was a MB Diagnostic Technician and has tackled all my problems in his stride so I told him to try there in the first instance. I see from his CV that this Philip Tutt also has a degree in auto electronics which may (or may not) be useful.

PS His profile on LinkedIn shows a couple of interesting overseas assignments with MB, one setting up and running the MB New Zealand Technical centre.

 

[Doodle]

PCS are very familiar with M119s.

However, 2 observations from the thread, one of which has already been mentioned:
You've got the wrong plugs - the 119 should not run resistor plugs. It's a common error by retailers, main dealer will supply F8DC4s at a good price. The rest of the ignition system (plug leads, distributor, rotor arm) have inherent resistance designed to work in line with non-resistor plugs.
There's no mention of having changed the insulation disks behind the rotor arm mount, again these are often overlooked.

 

[grober]

TRY K6JRF's PAGES K6JRF Auto Page
based on symptoms I would have said EZL module and or wiring insulation as you are in the correct time band.

ps You say you have swopped EZL units but have you tested the replacement in another car?

 

[Lambo911]

Thank you for your replies. I've booked it in with Welwyn Merx on Monday for him to have a look at it.

TRY K6JRF's PAGES K6JRF Auto Page
based on symptoms I would have said EZL module and or wiring insulation as you are in the correct time band.

ps You say you have swopped EZL units but have you tested the replacement in another car?

Hi, yes I did replace the EZL from a car that had been driven to the breakers. It was the first thing I did but the symptoms were exactly the same so I discounted it. It is very unlikely I'd have two EZL's with the same fault?

PCS are very familiar with M119s.

However, 2 observations from the thread, one of which has already been mentioned:
You've got the wrong plugs - the 119 should not run resistor plugs. It's a common error by retailers, main dealer will supply F8DC4s at a good price. The rest of the ignition system (plug leads, distributor, rotor arm) have inherent resistance designed to work in line with non-resistor plugs.
There's no mention of having changed the insulation disks behind the rotor arm mount, again these are often overlooked.

Wouldn't the plugs give a problem all the time? The fault I have is intermittent.
I didn't change the insulation disks. They did look ok but I can check them again.

Did you actually change the crank position sensor? That must be a player in ignition issues and seems to mentioned quite often in problems with more recent engines on this forum.

I didn't change the crank sensor, it looked pretty new. I had sort of discounted it as the symptons of this failing tend to be problems with starting. My car starts up straight away all the time. This was something I did want to test though.

 

[Doodle]

Wouldn't the plugs give a problem all the time? The fault I have is intermittent.

Ignition systems usually have a positive temperature coefficient of resistance, i.e. it increases in line with temperature.

 

[Lambo911]

Hi All,

It's fixed !

I had the car booked into Welwyn Merx on Monday but thought I would have one last search on the net for an answer.

I came across this Intermittent misfire | Mercedes W140 S-Class V8

and I remembered I hadn't actually changed both rotors as I one of the hex bolts had rounded off and I couldn't get it off. The one I had changed looked fine and so I thought it would be ok. A big mistake !

I read the article and though I would have another go at the stuck rotor bolt. I had to get a punch on it to loosen it off but eventually I undid it and sure enough the rotor looked exactly like the one in the article!

So I fitted a new one, took the car out for a long run and it is perfect !

Thank you for your suggestions.

If I had persevered with the bolt and changed the rotor in the first place I'd have saved myself a whole lot of hassle. Lesson learned !

Now is anyone looking to buy a nice W140 Coupe ??