C200 (W202) ECU problems, Ignition Coils test, Guide and help

dolle39

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Hello everyone! I have got the famous ECU failure problem on my Mercedes C200 -96. One day I was driving and suddenly the engine was only driven by 2 cylinders. I left the car to a car repair and they tried to change spark plugs and ignition coils but without success. I have read alot about this know and is about 95% sure that it is the ECU (PMS) now.


Anyway I am looking for an ECU but that is not the problem I want to adress here first. When you change ECU you must make sure to test or even change the coil packs before inserting the new ECU or you take the risk of blowing that one up aswell. So, first I want to do here is take out the ignition coils and measure the resistances. I am pretty new to cars so I want to have so help on my mission here.

I started of by removing the air inlet duct and then opening the top of the camshaft cover. Inside I found this (see attachment). So my first questions here are, I realise this is probably not the ignition coils as I hoped, they are probably located on the right side somewhere on the picture (can you perhaps further explain where)? What is it that I see? Is it only the spark plugs?
Second when trying to remove the air inlet duct it still sticks to the cylinder block (see lower arrow in picture). Can I remove this with more force? I am really scared to do something dangerous so thats why I am asking.

Also on the backside of the air inlet duct (see arrow also in picture) there is some electric cable, perhaps some air measuring transducer? Can I remove that aswell?

I start with these questions now. Help appreciated.
 
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Pendragon

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If you are changing the ECU it will probably have to be programmed and what makes you think its the ECU at fault anyway ?

I would also be looking for a garage who are more competent as changing the coil packs etc' is not a difficult job at all even if they have never been remove before.

Get a STAR diagnostics done on it before you do anything at all.

Keith
 
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grober

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The ignition coils are located on bracket/s under the inlet manifold- fiddley to get at but not impossible. That electrical connector you refer to is a air inlet temperature thermistor- You remove it by squeezing in both sides of the connector which disengages the small locating catches on either sideallowing you to pull it back . On cars of that age you release the cross engine duct by releasing its connection to the throttle body and sliding it sideways towards the steering column side of the car . There are 2 flat "hooks" that engage on the underside of the duct via rubber sleeves- careful not to lose them.
 
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Pendragon

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That will do it then.....I only said probably as I wasn't 100% certain but no evidence that ECU has got pear shape ?

Keith
 
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dolle39

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Thanks for quick response and answers!

Well first, Pendragon since the mechanic tried to change coil packs and spark plugs without success and he feared there was something more complex to this problem I am pretty sure about this after having read multiple threads about this that the ECU is the most likely problem.

Grobber what about the small rubber attachment to the engine, close to the oil cap (lower arrow in picture). Can I detach that one? What is it for?

And what about these four red things in my picture, are these the spark plugs?
Btw, if they are can I measure here to see where I get a spark. I have a pen to detect AC. Would I detect a current in these cables? Anything to be aware of in case of a trial?

And if I would do such a measurement I guess I have to set the air duct back in place. That is not a problem but just out of curiousity, what would happen if I dont. I mean what is the purpose of this vent duct. I guess it contains filtered air, but is it pressurized or is it just atmospheric presure? This is the air for the ignition in the cylinders?
 

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grober

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Thanks for quick response and answers!

Since the mechanic tried to change coil packs and spark plugs without success and he feared there was something more complex to this problem I am pretty sure about this after having read multiple threads about this that the ECU is the most likely problem.

Grober what about the small rubber attachment to the engine, close to the oil cap (lower arrow in picture). Can I detach that one? What is it for?

And what about these four red things in my picture, are these the spark plugs?
Btw, if they are can I measure here to see where I get a spark. I have a pen to detect AC. Would I detect a current in these cables? Anything to be aware of in case of a trial?

And if I would do such a measurement I guess I have to set the air duct back in place. That is not a problem but just out of curiousity, what would happen if I dont. I mean what is the purpose of this vent duct. I guess it contains filtered air, but is it pressurized or is it just atmospheric presure? This is the air for the ignition in the cylinders?


First don't be offended but your questions reveal you are pretty much a novice at this game so proceed with caution to avoid damaging the car or yourself!

The rubber attachment is a camcover breather pipe feeding into the inlet and can be safely removed temporarily.
the "4 red things" are the insulated connectors to the plugs deep in the cylinder head- they sometimes need a great deal of persuasion to come off!!

On a PMS system the cross engine air duct just leads from the air filter [ there is no MAF] and is not strictly necessary

BUT you shouldn't need to remove it as you can access each lead as the picture shows ! Get a hold of a timing light that has an inductive pickup clamp and attach it to each plug lead in turn [ don't get a shock by touching the plug lead!!] with the engine running- each active lead will fire the light. one coil fires 1+4 plugs the other 2+3

ps its probable one of the ECU ignition channels or its associated coil wiring has gone faulty leading to the loss of 2 cylinders. The ECU is NOT REPAIRABLE and must be replaced by a new or second hand part. You are correct often this occurs due to a faulty coil or its LT wiring and this must be rectified/checked before the new ECU is deployed.
 
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dolle39

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It's cool Im not offended. As I stated in the beginning I am very novice so I really appreciate the help.

I will be gone now for a few days, unfortunately, but as soon as I am come back I will try to measure and confirm which cylinders not firing.

But if there is no air mass flow (I guess this air is for the combustion) how does the cylinders fill up with air? Suction when the piston moves back?

I did read the following thread: http://www.mbclub.co.uk/forums/engine/143950-c200-w202-ecu-problems-ignition-coils-test-guide-help-new-post.html
and a guy there tried to open up the ECU and from what I understand it is not a good idea since the ECU is well sealed and as I can see on mine there are screws to unscrew. Also he states the the components inside is really fragile. And from the picture he shows it seems to be som transistor that has melted and it does not seem to be a standard component. But when you say that it is not possible to repair, I guess you mean for a normal person. I saw for example ecu-repairs.com offers repairs for 350 £ + VAT for these models. I hope they are not just defrauding people and taking 50 £ for test and then says its unrepairable.

Anyway that is probably not an option anyway since if I cant find an ECU at a junkyard I will probably buy one from Nielrr.
 

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Take it to a good indie.
Where abouts are you?
 
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dolle39

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I am back now and will try to measure which cyinders that not fires. However, I have some things that I want to discuss before I do so. Im not very familiar with electricity and wants to be careful. If I touch one of the leads when the engine idles I hope to see it light up. As you already sad that will work but is there any chance to brake the AC pen. I mean if there is a voltage of approx 40-60 000 volts from the ignition coil I guess a pretty large voltage will be induced in the pen aswell. But that is perhaps nothing to worry about. Can I just safely take my pen and hold it against the cable without hurting myself of damaging the pen?
 
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dolle39

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I came back now and was trying to put the old ECU back again but I was not able to connect the cables (see the pictures attached). I was trying for over 30 minutes without success. How does these actually work, I feel so stupid. Should I just use more force? I am worried to damage the cables or the pins. The back of the plug goes in easy but I can not get the whole plug in the right place. Any tips how to do this?
 
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grober

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Usually these type of connectors "hook in" at one end and then you rotate the plug downwards
 

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They are quite tight too.
 

neilrr

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In the first picture where we can see your hand, you need to move the shiny metal locking bit about 80 degrees to the left, approx where your hand is.

Then place the plug in the slot, black plastic prongs on the bottom right first, making sure they are all the way in. Moving the shiny metal locking bit all the way to the right should push the rest of the plug down & home.

Don't force it.
 
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dolle39

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Ah thanks. Was able to fit it today. I did not pull the plug far enough back.

However, I tried to detect a spark with the AC-pen but that did not work. Perhaps the pulse is to short for the pen to detect such voltages. Anyway there are other methods.
 

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Put a spark plug in the end of a lead and earth the the plug and then turn the engine over.

Be careful not to get any shocks. Use insulated plires.
 
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dolle39

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Yep, I did that and now I verified that there is no spark at cylinder 1 nad 4 but on 2 and 3. The mechanic also tried replace the ignition coil but without success so thats only narrows it down to the ECU I think. I will buy one form Nielrr now. However I was interested in taking out at least one ignition coil, the one that doesnt get signals from the ECU, and measure it. However, when opening the hood and looking down for the coils, they seem to be very hard to get to.

I know that I already asked about this but please guide me from the following pictures. I have located one of the coils as I marked in the pictures. But how in the whole world should I get it out of there?
 
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Dec

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Another picture to assist, cant help regarding removal of coil, I had intended to change a coil but then discovered that replaceing the HT leads solved my fault.

Top right of picture is a coil (insert picture)
Could you swap the leads around to see if that makes any difference, I think, from memory, that all 4 leads are different lengths.


Dec

 

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