Clyinders 5+6 B misfire
 

Hi guys,
Have just been out in car and noticed the engine management light come on and it was real lumpy and poor respose to accelaration.....
I had a friend who ran diagnostics on the car and found that Cylinders 5+6 were misfiring on B. He changed the leads over and swapped the coil pack for a new one both with no joy.
We (well he) ran a test on the MAF and that was showing ok i think it read 16 which is ok on the M112 engine ( needs to be between 12-20 i think ).
He reccomended changing the plugs as this was the only thing left, now im not to sure as i would need to replace all of the plugs and according to the servoce these were only change around 1-2 yrs ago (from what i recall).
Has anyone had any problems like this with a similar fault does anyone know what could cause this?????

Regards,

Raj

SL320 misfire
 

guys,
Have been looking on the net for similar faults and found some guys in the states who who similar symptons, and put it down to water in the fuel? now i would normally think there cant be that much water or crap the would mess up the car surely, But apparantly if the tanks at the garage are emptish there is supposed to be loads of goo and water at the bottom.
Now i got this problem after i stuck in £55 worth of BP petrol and recall a big fuel tanker parked up that was re filling the tanks or getting ready too and th pump did make a odd noise half way through the fill.....
Im not sure if im being para but could this maybe be a cause, i started again today and the revs are ok just if i rev high it drops like its going to cut out and there is a weird smell from the exhaust as i went by back of the car????

any suggestions???
Raj

anybody????
 

no body had any similar problems???? and suggestions????

Raj

looks like cats
 

Right not good news, been to my mechaninc, redone the diagnostics and now cylinder 4 is out so that 4,5 and 6 and 3 is on its last legs, this leads them to think its the cat breaking up!!!!!! not going to be cheap fix then !!!!

Any ideas or suggestions on replacement cats? do you go with dealer parts of aftermarket..... i have bought aftermarket for the c class but did notice a bit more noise and is raspy..... if anyone has replaced cats on SL could you please advise me on which ones you used

Regards

Raj

I went with OE cats from the dealer. There are a load of posts about whether to go for dealer or aftermarket and the general consensus is dealer.

It can be very expensive if the cat has broken up and somehow gone upstream into the engine.

I'd be surprised if bad fuel were to blame. In 15 years and 300,000miles of motoring I've never encountered really bad fuel. Plus, petrol stations and pumps are pretty heavily regulated these days.

i feel that what you say is right and the best way would be mb cats but they are double the price of aftermarket ones.....
i hope that it hasnt gone too far as that i know will be utterly expensive...
fingers crossed

Raj

doubting the cats
 

mmmm now after a long discuaaion with my mechanic and klp 92 they are doubting the cats..... and will be checking again.... i feel the same scenario coming along with what happened when i first got car and went into limp mode..... a long long story...

Not your model but on my 560SL US version. I had an annoying miss in a cylinder. Found the spark plug wires were going bad. 2 of the cylinders I pulled off the sparkplug wire and the unit spatted. So I had a gap that the spark had to jump on its way to the spark plug. A new set of wires and it ran smoothly.

Check your spark plug wires. The dealer had it 3 times for this and $1200 later it still ran rough. Got a full refund. And I started the diagnosis.
Spark plug wires.

Dave

plugs/wires
 

thanks dave, i have already checkd this, all one bank on my v6 is now down, so its seems more and more like a collapsed cat stoping the fumes out...thus causing the misfire

Raj

cats look smaller?????
 

hi got the cats from GSF and they look really small compared to the ones on the car????

what should i do? fit them or not?

Raj

Are they Mercedes Benz OEM cats or are they aftermarket?

GSF = German, Swedish & French car parts, an aftermarket parts supplier here in the UK. I imagine the cats are aftermarket. I wouldn't fit them.

How old is the car? You should get 60k to 120k miles out of your cats; they are a long term wear and tear item. You wouldn't fit cheaper and smaller brake pads just to save money, so why fit cheaper and smaller cats?

General opinion on this forum and all the others is (1) aftermarket cats are smaller and as a result don't last as long as OEM and (2) the car will never run right with aftermarket cats because, being smaller, they behave differently and send different signals back to the engine.

I tried a set of Aftermarket cats on my 300TE once. I will never do it again. They cause too much back pressure, killed 2 o2 sensors, and continually triggered my check engine light...

new codes
 

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got new star diagnostic, po300 and po306 error codes on cylinder 6..... new cats on there aswell,

update
 

Hi guys another update, found that the fault is originating from cylinder 6, have had the faults wiped from the car and ir revs and drives fine for about 5 mins then starts to misfire. It seems that cylinder 6 is out as a test was done on star and showed it runnibg a 3.95 to 4.65 all the other cylinders ran at
-0.22 or 0.00 the tolerance on the cylinders is 2.95.

They are now thinking it could be a faulty injector causing the misfire as it is fine when the faults are all wiped the error codes are showing as a capital F aswell?????

any suggestions or ideas???? is it the injector?

Raj