W202 ?? C280 Straight Six Misfire

[Phantom Mark]

Hi there guys, please forgive me if I managed to get the "W" code wrong

Just picked myself up a 1996 C280 Auto "Elengance"

Have a couple of small problems I hope you guys can help me with.

First of all I am not savvy with MB cars at all, this is my first, i'm afraid I know more about BMW's lol.......

First problem.

Whilst idling smooth with no nasty noises the car has a misfire, when driving you can hear it heavily backfire through the airbox.

With my BMW experience first things I am going to look at are......

1. Plugs
2. Leads
3. Coil Packs

I can't find the damned plugs/coil packs, I have admitedly spent all of 5 mins looking in this cold weather, I am guessing they are maybe hidden under the top cover maybe ??

Other possibilitys I am considering but outside my DIY ability is injector / harness faults, any other ideas you experienced guys can throw at me please, seems like a nice engine if I can get it running on six properly.

Looks like a nasty weep of oil from the front of the engine where I would guess the water pump is, again I have no experience with these engines and just a guess, is this common and something to worry about ??? also the dipstick is loose as an old hookers pants, worth worrying ??

When driving the car home I also noticed that indicated temp climbed to sub 80c ?? the heater was blowing nice and warm however, could that be a sign the thermostat is shot ?? or normal for these cars in this weather ?

Car has a full stamped history to current mileage of 105k, 4 owners and in really nice condition, no signs of oil in the expansion tank etc, everything else appears to work with no problems.

Bit of TLC and a little tidy up should make a nice cheap classy motor hopefully....

Help appreciated - thanks.

Mark.

Power is nothing without control !
www.VXR8.com

 

[grober]

Misfire probably due to plugs/plug extensions/coils [3?]/ low tension supply loom. All buried under the plate on top of the cam cover-will require a allen or torx key to open it after you remove the cross engine air intake duct. Start at the plugs and work back. Don't ignore this as a fault in this area has a habit of blowing the ECU ignition output transistors. You could of course have a leaking CHG but seems unlikely. The oil leak might just be the front crankshaft pulley seal-very common but there are one or two places on the front timing case leaks can occur also- if its not bad you can maybe live with it?

ps your 6 ZYL engine is essentially the same as fitted in the earlier E class W124 and early W210 series- lots of posts about it on here.

 

[Phantom Mark]

Cheers mate, thanks

Was gonna do the usual swapping plugs/coil pack thing and see if I can track down the rogue part first of all.

The car had new plugs at it's last service (a while ago but not done any miles since?)

Just out of interest what kind of reputation do these particular engines have ?

Fingers crossed it does not end up costing a bomb !

Thanks again

 

[bennesspipers]

Hehe like your loose dipstick description, thats personal experience is it ??
Listen to Grober, knows what he's talking about

 

[bennesspipers]

They do have a habit of blowing head gaskets

 

[Mark300SL]

Isn't 1996 still in the "loom issues" timespan ?

I completely destroyed my Loom/Coilpacks/Ecu jsut by removing the plugs - and this has just had a plug change which moves the loom in the coil cover just the same amount.

The loom deteriorates and all the cables enter the head area through a solid rubber bung - nine shorted in here taking out the coilpacks and the ECU


I would be very very careful taking it apart - and for the record my loom looked fine until it developed a missfire and then a reluctance to start immediately after the "cleanup"

 

[grober]

Isn't 1996 still in the "loom issues" timespan ?

I completely destroyed my Loom/Coilpacks/Ecu jsut by removing the plugs - and this has just had a plug change which moves the loom in the coil cover just the same amount.

The loom deteriorates and all the cables enter the head area through a solid rubber bung - nine shorted in here taking out the coilpacks and the ECU


I would be very very careful taking it apart - and for the record my loom looked fine until it developed a missfire and then a reluctance to start immediately after the "cleanup"

I think you may well be right the car does fall within the correct "danger" period so it may require a new upper engine wiring loom. A careful inspection/dissection of the loom sheathing should reveal all. The M104 is pretty strong if looked after. The bottom end cast iron block goes on for ever and cylinder head gaskets are the only major weak spot.

 

[w124coupe]

If you "just picked it up" can't you get some redress from the seller? (or was it sold described as "running poorly")?

Even private sales have redress if the car is not "as described"....

Susprised its backfiring through the airbox - these cars shut down the injectors if a misfire is detected (to protect the cat in the exhaust from unburned fuel). This detection is via the ECU measuring the voltage and current taken by the coil to make a spark so COULD fail if the loom is shot I suppose?

(backfiring through the airbox will risk damage to the MAF by the way so get it sorted before you add another £180 to the bill!).


I would:

1. check the loom condition before anything else (and before you ruin MAF and/or cat). Open up the outer insulation on the wires leading to the low tension side of the coils (where they run through a groove between inlet manifold and coils) and check for rotten insulation on the individual wires. The loom rots generally but seems to be worst affected near the intense heat. New loom is about £550 plus fitting!

2. if the loom is OK, get the codes read to see if the misfire is contained within one coil pack or generally across all cylinders.

3. if contained, swap two coils and see if the fault moves - if it does, change the coil.

4. check the plugs and also the "boot" under each coil pack - these boots are cheap and often break down because of the heat. Make sure the correct plug type is fitted - this is VERY important to avoid fouled plugs and misfires!

5. general misfire can be down to MAF and/or O2 sensor problems and will often show up with large "fuel trim" values - here the key is to get the car "live data" analysed (on Star) to see what's going on during the misfire....

Unless you are keen on the DIY, a good independent specialist with Star is the way forward (after checking the loom) to avoid "spend & hope" diagnostics.

 

[Phantom Mark]

Thanks for that.

Small development today.

I took off the air intake etc and top cover to have a visual on the coils and leads etc, all "looked ok"

I started the car and no missfire, but now thinking back I am starting to wonder if the car developed the missfire once it had warmed up ??

I bought the car at a local auction so no comebacks

Just been made redundant and looking to make this a cheap run around (a nice driving one anyways) in case I have to sell my HSV.

So anyways, it now looks possible the fault may be related to when the car has warmed up, will get the car up to temp tomorrow and see if it then develops that missfire, any thoughts on my running temp observations btw ?? sub 80c indicated on the dash ?? possible thermostat ??

Also, a faulty MAF on a BMW at least would not cause a bad missfire like this, my missfire is rough as hell It would cause heavy fuel consumption and rough idle, and probably down on power throughout the rev range....pulling the plug on the MAF would force the ECU into using a same pre programmed "default" ??

Cheers, and hope you all had a nice Christmas

 

[w124coupe]

If the misfire stops with the cover off you may have tracking from the leads....try cleaning them up?

(often a good idea to run the car in the dark and look for tracking sparks)

 

[Phantom Mark]

Great idea thanks

Will give it a run tonight, cheers mate.

Only got little globs of time to play around with the car atm because of trying to entertain my lit tle girl

Any of you hardcore guys live local btw ??? Sleaford Lincs here ???

If I cannot trace this one down myself would happily throw a few quid in the direction of someone who knows their stuff on these cars, I hate main dealers with a passion, especially if they are anything like BMW Main dealers !!! Can't afford to be ripped off by these scam artists at the moment !

 

[bennesspipers]

I'm not far from you,but i'm not a proper mechanic,mind you,been messing with cars for 40 years.

 

[w124coupe]

Great idea thanks

Will give it a run tonight, cheers mate.

Only got little globs of time to play around with the car atm because of trying to entertain my lit tle girl

Any of you hardcore guys live local btw ??? Sleaford Lincs here ???

If I cannot trace this one down myself would happily throw a few quid in the direction of someone who knows their stuff on these cars, I hate main dealers with a passion, especially if they are anything like BMW Main dealers !!! Can't afford to be ripped off by these scam artists at the moment !

With a problem like this one and the budget situation you explained you are in, I would suggest doing all the cheap/free cleanup and fiddling yourself but then not to buy anything significant without getting fault codes and live data read by a good independent garage.

Yours is not a car to take to the main dealer - they will find thousands of pounds of work that "needs doing" and will expect you to pay £100 per hour labour for diagnostic work needed to determine the misfire fault.

Start with checking the loom - open up the outer insulation where the LT side of the coil leads come together into a bundle - if the inner wire insulation is cracked/dusty then you will have endless problems until you replace the loom as the important engine sensor readings will be misread by the ECU or just shorted out).

I'm miles away from you but I'm sure someone will recommend a garage in your area if you want to go that way.

If you ran the car with the coil/lead cover off then presumably the air cross-pipe was off as well? If so, this means the MAF reading will have been ignored by the ECU as "implausible" and so it will have used a default map.....

 

[w124coupe]

If you do decide to have a fiddle yourself, post again and we can take you through the likely areas to check (for free) - there are quite a few!

 

[Phantom Mark]

I have the plastic top cover off but I popped the air pipe back on as I noticed two round holes which appeared to need sealing, didn't wanna risk oil or debris getting in or out

Gonna run the car in a min and see if I can see any shorts/sparking going on in the dark, will take a look at the loom tomorrow if nothing obvious shows tonight.

Is there a cheap way to fix the loom ?? starting to wonder if I made a mistake with this car, which is a real shame as on the surface it appears to be a really nice motor for the money I paid for it.

Check back in later with results, thanks again guys.

 

[w124coupe]

Some people have stripped and repaired the loom but you will need a fair amount of time on your hands to do it properly (if it needs it).

The issue is that the shorts cause damage to the ECU (in particular the output stages driving the coils) if not fixed.

You may well be fine but for this age M104 its a sensible first check.

Hopefully the previous owner was scared by a loony quote from a Merc main dealer and it will turn out to be plugs/boots/leads or something nice and easy.

 

[w124coupe]

I have the plastic top cover off but I popped the air pipe back on as I noticed two round holes which appeared to need sealing, didn't wanna risk oil or debris getting in or out

Gonna run the car in a min and see if I can see any shorts/sparking going on in the dark, will take a look at the loom tomorrow if nothing obvious shows tonight.

Is there a cheap way to fix the loom ?? starting to wonder if I made a mistake with this car, which is a real shame as on the surface it appears to be a really nice motor for the money I paid for it.

Check back in later with results, thanks again guys.

The two holes are part of the crankcase breathing system and sometimes are a source of air leaks (unmetered air after the MAF).

 

[Phantom Mark]

Ok, last update for the day after battling with the MB Security system lol.......

As I said earlier, think I have found a consistant link now.

Car runs smooth as silk from cold for a couple of mins, then drops into the missing problem, so as I see it, could be a plug or lead breaking down or maybe something to with the fuel injection system ?? Based on how I know a carb car works it's like when the choke is on too long etc, may explain the back farting through the airbox if it's choked up ?? Could this be related to my suspected thermostat problem ?? Ie: Fuel injections version of "choke" not turning off and fouling a plug etc ?? or of course it could simply be a plug fouling up as it gets warm because its knackered, however I do know for a fact according to service history the plugs were changed very very recently, in the last 10k in fact ????

Sorry for long winded stuff, I know as much detail as possible is valuable normally right ??

Cheers

 

[Phantom Mark]

Ps.

The fact that the car will run smooth on all cyls is a positive sign no ?? Even if it is only for a couple of mins from cold ??

 

[grober]

Make sure you have the correct heat range plugs fitted. Even the plug manufacturer lists can be reproduced wrongly! The recommended plugs were listed on the front slam panel originally but the label might be gone. These engines don't like the multi electrode design but prefer the simple single electrode type. I prefer Bosch or NGK=BCP6E/BCP6ES You may have an inlet manifold/associated pipework air leak = the car runs fine on a rich mixture but as it leans off with increased engine temp the misfire starts.