1997 W202 Misfire

[DuFFmAn]

Well.. i still want to keep her... Im thinking of changing the air sensor after reading the other posts... but im confused...

Some people are mentioning MAS and some are mentiong MAF... Which one is which etc? are they the same thing? how can i do a quick test... someone said i should disconnect them and drive in limp mode??

 

[willy]

Well the HT leads were apparently done the last time this problem occured...

Its wierd because the spark plugs fixed the problem but now about 5% of the problem has creeped back .. (its 95% better)...lol

i would not rule out the ht leads especially if cheap unbranded ones have been used.

i once had a pug that has misfiring problem, changed the leads and its was okay for about 5k then the problem turn out to be the cheap replacement ht leads. see if u can borrow ht leads from another c class to try out

 

[Muller]

i agree with willy, same problem with my 260E, it kind of burbled and spluttered, but when the HT leads were changed it ran fine

 

[Wully]

The issues discussed match the same as those i had in my C180 auto.
After searching all the various forums i came up with four possible problems:-

1) Spark Plugs
2) MAS
3) Coils
4) HT Leads

Now going with the cost in mind (what can i say I'm a Scot) i ended up doing the following:-

1) Spark Plugs
At the same time i replaced the air filter, when doing so i disconnected the battery and reset the ECU. Result or so i thought, car drove fine for a few days and the problems came back.

Next!

2) MAS
After much searching of the chairs in the living room i decided on the MAS, got a new Bosch one on eBay and again disconnected the battery and fitted. Result, nope wrong again!

Next!

3) Coils
Now everything is pointing to ignition so decided on the coils. Result? Yes for again a few days then back to the problems!

Next!

4) I was finally about to take it to the stealership when i thought about the HT leads. Pulled them out again and i honestly couldn't see any issue with them but i thought compared to the cost of putting the car in to be checked i might as well try! Result i bet you ask, you better believe it car drove great and still did when i sold it the other week, even the guy who bought it commented on how well it drove.

My advice try the leads then the coils or both if you think your budget will stretch.

 

[Shude]

My advice try the leads then the coils or both if you think your budget will stretch.

To add to your list:

crankshaft sensor
fuel pressure problem (check with gauge)
fuel pump problem

I think there is a throttle position sensor or sender too, which I have suspected for a while.

 

[DuFFmAn]

Ok... Well the last owner said he had already did the HT leads a few days months back so i prefere to leave that a while...

Is there anyway of testing the MAF? I heard you can test it by disconnecting it and running in limp mode and see if it still pops??

 

[DuFFmAn]

Shude: I've read your previous posts and it sounds like to me that me and you have pretty much the exact problem... Poping when the pedals to the metal in gears 1 and 2 (manual)???... Have you replaced you MAF yet?

 

[Shude]

Shude: I've read your previous posts and it sounds like to me that me and you have pretty much the exact problem... Poping when the pedals to the metal in gears 1 and 2 (manual)???... Have you replaced you MAF yet?

What mine does is misfire when the pedal is about 50% down in any gear and then continue to do so until the engine is restarted. This includes trying to climb a hill in 5th gear at 50mph, try accelerating or even maintaining the speed and it suddenly loses half the power (actually just one cylinder). Makes for some interesting overtaking! What's annoying is that the gearbox thinks I want to drop a gear when the pedal is about 55-60% down, so I tend to shift into 4th or something manually by knocking the lever to the right, once the revs have built up I can pop it back into 5th and carry on as usual.

If the MAS were faulty it wouldn't have anything to do with the position of the gas pedal or the engine load, AFAIK the MAS would also make it misfire when driving "normally" or idling, which mine doesn't do unless provoked.

The MAS is still on my list of things to replace though, at 150k miles and original MAS it's probably on borrowed time as it is.

 

[DuFFmAn]

Yeah... Thing is, mines a Manual so i don't have problems with the gearbox...

Does anybody know where i can get a cheap MAS from?? I heard someone picked one up for £60... Ive just been finding prices at local motor factors for £160 :| ... its a W202 1997 Preg...

Also... Does anybody know how to tell if mine is the facelift one or not???

 

[KLP 92]

Have a look on ebay, they are cheap enough!

 

[DuFFmAn]

Ok... So following Wully's list...

1) Spark Plugs (Done) Result!! Car runs 100% but then about 5% of the problem has come back.. Car misfires under heavy acceleration in first and second gear (manual)... Not sure about 3rd gear..

2) Maf... Disconnected this to check if it will still misfire in limp mode... and yes it does misfire so it can't be this...

3) HT leads... Personally havn't checked but the previous owner says that he got this done about 4 months ago so assuming for the time being that this is okay...

4) Coilpack... Havn't the smallest clue about this... Going to inspect it for visual damage etc... Can anybody help me on this?? Never really looked at coilpacks before so im walking in blind...??

..ps.. Have i missed anything off the list

 

[Dieselman]

The misfire could be a result of a weak mixture so check for vacuum leaks but it could be a weak spark.

You can buy a cheap spark tester to test the power of the spark. A weak spark would give stuttering under load.

 

[Wully]

The coils are quite easily removed, they are held in place by 2no 6mm bolts.

When you remove the cover hiding these, check the wiring harness that comes from the back of the engine and clips into each of the coils. Where these terminate onto the coils check the small caps that hide the solder joints, i had to tape the covers on mine as they kept coming off.

When you remove the coils check the condition of the rubber connections to the bottom of the coils, if you do replace the coils replace these at the same, these are only around £2.

Best of luck!

 

[KLP 92]

The car will continue to misfire sometimes even with the MAS disconnetced, may be even worse. Only 100% way to check is to replace.

 

[Valps]

My E240 had almost identical symptoms when I bought it. I drove it round the block under light throttle conditions - all fine. I parted with my cash drove onto the motorway put my foot down and pop, bang splutter - nothing. Anyway nursed car home at about 50mph, read this fine forum and replaced the MAF, MAS, oh the thing that seems to affect most Mercs at sometime in their lives, and it absolutely transformed the car. Took ten minutes to change and cost £80 - best money I ever spent. Oh apart from on the wedding, in case the missus should stumble across this site

 

[DuFFmAn]

Im still bamboozled between the coil pack and the MAS...

The AA guy came around yesterday and i let him have a crack at it...

He started the engine up, and pulled the HT leads out one by one listening for a "clicking" sound... ( he can only access two of them)

One of them didnt work so he swapped it with the other one and then they both started working .. He reckons its the coilpack and didnt mention anything about the MAS... He also didnt hook it up to his laptop which i hoped he would've...

So what do you guys reckon?? Coil pack or MAS?? I don't have access to another C180 so can't swap em around etc...

 

[Shude]

Im still bamboozled between the coil pack and the MAS...

The AA guy came around yesterday and i let him have a crack at it...

He started the engine up, and pulled the HT leads out one by one listening for a "clicking" sound... ( he can only access two of them)

One of them didnt work so he swapped it with the other one and then they both started working .. He reckons its the coilpack and didnt mention anything about the MAS... He also didnt hook it up to his laptop which i hoped he would've...

So what do you guys reckon?? Coil pack or MAS?? I don't have access to another C180 so can't swap em around etc...

I was told by my stealership that they tested the electrics and they're fine, but I'm not sure that I believe them.

Having thumbed through my receipts I see that I have paid about £100+VAT so far for various tests and so far we know it's not the sparks or the ht leads etc, but I'm not sure that I believe them!

I will probably have this work done:
Fuel pump/pressure test/filter change, then coils, ht leads, MAS, then possibly crankshaft sensor/sender and throttle body assembly/sensor.

If that lot doesn't do it then I don't know what's left! Injectors/valves? *shudder*

 

[DuFFmAn]

Coil packs will cost me £50 and Mas meter will cost £60ish... Not sure which one to do first... lol... Any seriously mechanically minded people wanna make a money related decision for me ???

 

[DuFFmAn]

Ive finally got full access to my car as I've been away for a while..

Just a note... I disconnected the MAS and took the car for a spin and have actually found no change in performance :s ... Is this normal?? I heard its meant to go into limp mode but it doesn't even do that :S..

The misfire happens at low revs and when I put my foot down... This kinda points me towards the coil pack as I reckon its not sparking under heavy load at low revs... and it also doesn't misfire at idle or motorway speeds.. (above 3000 revs??)... Can anyone comfirm my thoughts or do I have to let my Bank Manager know ?

 

[Dieselman]

Your diagnosis could well be correct, a weak spark will cause poor running under load.

You can buy a small tool from Gunsens for testing spark strength accurately. The tool is a few pounds and definately works. Basically it's a caliper with a graduated scale reading between good and bad spark output.