V6 misfire

[DrH]

I have W210 E240 with 105K and a misfire.
The diagnostics suggest cylinder 1 - is the coil pack the first thing to try, rather than leads etc.?
It had new plugs 5K ago & it's not the Air Mass meter (is that MAF in merc-speak?).
It seems to be in limp-home mode permanently -would the coil cause that?
It has LPG fitted, but it's running on petrol ATM.

 

[Miffy]

Try swapping the leads from your suspect coil pack to another, and see if the problem moves with the swap

 

[television]

As Mark above,,it should just be a coil pack,and they are known to do this

 

[jberks]

As its twin spark, you would need 2 leads and plugs to be down at the same time. Possible, but unlikely.
Mark's suggestion will prove it one way of the other.

That said, a new set of leads (if they're over 3-4 years old) would probably be beneficial to the general running once this issue is resolved. Mine never lasted more than 3 years before starting to missfire. I noticed the deterioration as I'd had it from new. Most people buy them with a slight miss so they often don't know how smooth they can run.

 

[DrH]

Update

I replaced the coil pack on cylinder 1 without noticeable effect (assuming cylinder 1 is on the RH bank).
The next plan was to replace all 6 from the wife's C240 (W202); unfortunately they are not backwards compatible (the actual metal connector blades are wider on the 202's).
I have tried each of the suspect ones, in turn one at a time, on the 202 which seemed to run perfectly with each one. I didn't road test as I figured it would get too hot to change them if i did.
I broke (careless!) one of the leads trying to remove it from the replacement coil pack, so that is the only thing that was not tested on the 202 but was present whenever the 210 misfired. I thought I would change all the leads, but GSF won't have them until Monday (dealer price £24 each).
Am I missing something and what would be the next thing to try?
I'm wondering about another £30 for a diagnostics printout, but the last one wasn't conclusive (to me at least ) -mostly cyl#1, but also 5 & 6, and a couple of improbable sensor readings.
Thanks & sorry for the essay
Richard

 

[Alex Crow]

lead failure is a common problem. the best diagnostic test is using das actuations to shut down a and b coils in turn (each coil pack is actually two seperate coils, one for each lead). the function monitors smooth running or missfiring at the same time making it easy to isolate specific leads. i know that coil replacement is common and said to be the probable cause, but we generally find the leads at fault - even if the test out ok on the multimeter.

severe missfiring will put the engine in limp home, and with p0300/0301 etc codes but no o2 sensor or adaptation codes i would definately suggest an ht fault. also the recent plug change may even be the cause! i`m sure you have now noticed how hard it is to get the leads off........

 

[LYNALL]

17mm spanner under the tin bit on the lead and they come of a treat.

Look on e bay for leads.

Changed leads on both mine and the wifes car and they did make a difference.

My leads where pretty shaggy over 100k, wifes seemed pretty good 70k.

All checked with multimeter and i had 3 out of range, all wifes were okay.

Tin bit has got the ohms reading stamped on it.



Lynall

 

[colinspain]

Hi, Maybe you can help me.
I have a C240 2002 model W203. I am about to change the spark plugs (12) but have been told the battery must be disconnected first, is that correct and what would be the reason for this. Appreciate any assistance before I start.
Thanks
Colin

 

[jberks]

Hi, Maybe you can help me.
I have a C240 2002 model W203. I am about to change the spark plugs (12) but have been told the battery must be disconnected first, is that correct and what would be the reason for this. Appreciate any assistance before I start.
Thanks
Colin

With the ignition off (obviously) I don't see why. Its a common safety step that people recommend for everything down to a bulb change, but I wouldn't bother for a plug change.

 

[DrH]

Problem solved!!
New HT leads fixed it - with the original coil packs.
Many thanks to all who replied.
Richard

 

[Top Cat]

On twin spark ignition, does one coil pack feed both plugs of any given cylinder?