W208 CLK 320 - Some engine issues

[mbenz1]

Play can't be checked. It's a visual check.

Just pull the lead off the plug and coil to check it. They are plug and play. No coding required.

Ok, I will tell the mechanic to visually check them... I don't know why I said play tbh

I have learnt that to pull the plugs off, there is a special tool called a 'boot removal tool' or something along those lines. Is this really needed or can all 12 leads be pulled off by hand?

 

[markmifsud]

Someone here was selling the correct device to aid plug lead removal in the Items for sale section

 

[mbenz1]

Someone here was selling the correct device to aid plug lead removal in the Items for sale section

I will just pop down to my local hardware shop...he sells everything and anything I know how the boot removal tool looks like - I had learnt about this from Mercedessource in one of Kent's Spark Plug inspection videos.

 

[mbenz1]

Update 6:
The mechanic cleaned the throttle valve with Brake cleaner and unfortunately the shaking has now increased to how it was with the previous NGK spark plugs.

I am losing my patience now and opting to change the plug leads. I had a look at the plug leads and the leads towards the end of the engine bay are really hard to access, let alone removing them. Due to that I was not able to check the lead resistances.

I have seen a set of 12 plug leads for the M112 engine online at ECP for £60. It doesn't mention which brand they are.

Is it recommended to go for genuine MB plug leads or are aftermarket plug leads suitable?

Thanks

 

[rorf]

It is easy to remove the plug leads with a 17mm open spanner, but first loosen the coils and move them out of the way before attempting.

Those plugs have a lot of unburnt oil on them - think you need to start having a cylinder compression test and a cylinder leak down test done, the traditional way. Unfortunately these modern engines can only really be diagnosed on a Star Machine due to all the electronics controlling all the engine parameters.

You could also have a multitude of vacuum leaks due to brittle hoses on the cylinder head covers - the list can go on and on.

 

[mbenz1]

It is easy to remove the plug leads with a 17mm open spanner, but first loosen the coils and move them out of the way before attempting.

Those plugs have a lot of unburnt oil on them - think you need to start having a cylinder compression test and a cylinder leak down test done, the traditional way. Unfortunately these modern engines can only really be diagnosed on a Star Machine due to all the electronics controlling all the engine parameters.

You could also have a multitude of vacuum leaks due to brittle hoses on the cylinder head covers - the list can go on and on.

Thanks for the tip of using a 17mm spanner. I couldn't figure out how the lead is removed from the coil pack. Is it simply pulled off or does the coil pack have to opened to disconnect the lead?

I told the mechanic at local MB indy but since STAR is showing clear, he is not recommending anything besides cleaning the catalytic converter (?!) now. I don't want to take my car to a normal mechanic because they don't know these engines very well.

 

[mbenz1]

Getting the 12 plug leads changed tomorrow. Wish me luck! If it doesn't sort the problem.out then I will be really disappointed. The car only does about 220 miles per tank and CLK 320 owners are reporting around 250-300 miles, which seems right since 220 miles corresponds to under 16 mpg. This pins the problem down to an ignition issue or a air/compression leak.

 

[gbjeppm]

The car only does about 220 miles per tank and CLK 320 owners are reporting around 250-300 miles, which seems right since 220 miles corresponds to under 16 mpg. This pins the problem down to an ignition issue or a air/compression leak.

I comfortably get 30mpg on a 30 mile run, I have seen 35 if driving very carefully, so something is not right.

Good luck

 

[mbenz1]

I comfortably get 30mpg on a 30 mile run, I have seen 35 if driving very carefully, so something is not right.

Good luck

30 mpg is excellent. It just goes to show what a great engine the M112 was back in the 90s and even today. I have only used the car for town driving since purchase but after the plug leads are changed I'm hoping the shaking at idle dissapears and the fuel economy improves significantly.

I observed something interesting just today. On the 12 old NGK plugs that were removed from the car (and replaced with genuine MB plugs), two plugs had some green/white dry residue on the tips of the metal that.connects to the plug lead. I'm thinking that the residue came from the plug leads (no idea where from) onto the plug connecting tips, which may have caused a bad voltage signal to the plugs??

I just hope the new plug leads will sort the issue out. I will keep the thread updated

 

[mbenz1]

Here is a picture to show the residues:

 

[mbenz1]

Picture of residues

 

[My320CLK]

Ive only skim read this thread but mine went from having a slight engine shake to running on what felt like 4 cylinders shaking itself apart and it was the HT leads failing, never had it happen on a car before now but believe these engines are "really really" sensitive to them all 12 !!! - nothing showed on diag just said cat issue and random misfire, after the best it had every driven so smooth - I also did the plugs at the same time, good luck and i hope it cures all your issues, on a good run any thing from 32 to 35mpg (30miles plus I think cold start kills the MPG and mines a heavy soft-top so even worse)

EDIT: I had white powder and green discolour in the plug ends,

 

[mbenz1]

Ive only skim read this thread but mine went from having a slight engine shake to running on what felt like 4 cylinders shaking itself apart and it was the HT leads failing, never had it happen on a car before now but believe these engines are "really really" sensitive to them all 12 !!! - nothing showed on diag just said cat issue and random misfire, after the best it had every driven so smooth - I also did the plugs at the same time, good luck and i hope it cures all your issues, on a good run any thing from 32 to 35mpg (30miles plus I think cold start kills the MPG and mines a heavy soft-top so even worse)

EDIT: I had white powder and green discolour in the plug ends,

Thanks for sharing your experience. I really hope changing those 12 HT leads will solve the shaking - tbh I'm really confident they will since many on this forum have mentioned that the HT leads seem to be the main culprit. Yes, I had the car in for a service about 3 weeks ago and I'm so disspointed that it didn't cross my mind to get the HT leads changed at the same time as the plugs were changed and neither did the mechanic suggest it. I hope those new plugs are not filled up with black crud because the old HT leads are still is use - the plugs costed under £80 I think.

My mechanic suggested that a CAT clean may solve the issue but I'd rather change the HT leads (although I'm not a mechanic) because he even cleaned the air intake for me and that made the shaking worse suprisingly.

I have no idea what that white power and green residue is - it could be either due to a bad HT lead or a bad voltage signal but that's just me guessing.

 

[My320CLK]

Could be water ingress not sure, I'm sure the leads are classed as routine service items but I guess due to the cost no one replaces them mine came from GSF about £80 for a set I think, the Bosch ones are a lot more, as someone else pointed out could also be a vacuum leak, I know when mine was playing up we'd move the leads around it would sometimes idle go for a drive and the shaking would start again,

 

[Ted]

It sounds like the deposit you used to get on the terminals inside a distributor cap where the spark jumped from the rotor arm to the HT contacts in the cap.
If this is the case, my guess would be a poor connection/HT arcing.
Just a guess.

 

[mbenz1]

Could be water ingress not sure, I'm sure the leads are classed as routine service items but I guess due to the cost no one replaces them mine came from GSF about £80 for a set I think, the Bosch ones are a lot more, as someone else pointed out could also be a vacuum leak, I know when mine was playing up we'd move the leads around it would sometimes idle go for a drive and the shaking would start again,

I got the lead set from GSF also - they were £80 but I got a 25% discount so ended up paying circa £65. They came in a sea-through polythene cover and its appears as a german brand. When you say a vaccum leak, do you mean a vaccum leak within the HT leads?

It sounds like the deposit you used to get on the terminals inside a distributor cap where the spark jumped from the rotor arm to the HT contacts in the cap.
If this is the case, my guess would be a poor connection/HT arcing.
Just a guess.

It could well be the case.

Everything seems to be pointing at the HT leads now, so time will tell. Can't wait till tomorrow tbh - I really find that shaking annoying. Its such a great car to drive besides that annoying problem.

 

[mbenz1]

Really disappointed now.

Mechanic changed the plug leads and I then drove off and stopped a minute after and the shake at idle still remained.

10 minutes after driving the car, I noticed a tapping noise from engine in the cabin. Upon checking, it appeared to come from the right engine block. Took it back to mechanic and it turned out that 1 of the plug leads were loose. It was then put back in and taping noise stopped. I drove off.

After 5 minutes of driving, the shaking at idle became significantly bad - my body was literally shaking with the car and the rpm needle was fluctuating alot (up and down between a 2mm distance). The car felt like it was about to cut off and the trip computer display and headlights were 'slightly' dimming as the rpm was fluctuating.

I popped into a local garage (turned the car off) and the chap test drove it by going through all gears, boosting it and letting it idle. Chap returns back and he did not notice any problem with the car.

I drove the car back home and the shake at idle had reduced very very significantly and rpm fluctuation became significantly less also.

Where do I stand now?

The mechanic at my local MB indy did not suggest changing the HT leads so he changed them on my authorisation.

Either the HT leads are loose or not been installed properly or are wrong (which I doubt since they look identical to the previous leads) or the problem is not the HT leads.

I have the old set of HT leads with me currently.

My.main concern is whether that really bad shake at idle does not come again...

Please advise. Thanks

 

[mbenz1]

^^

 

[mbenz1]

Bump

 

[My320CLK]

Hmmm thats a shame - the leads are they 100% correct in terms of fitment on the a and b on the coil packs and are they on the coil packs fully, they are the same ones I bought in a clear bag,

I know when I fitted them my brother went over them again and a good few weren't fully mounted on the coil packs even though didn't feel loose, really tight fit,