Join Date: Feb 2014
Location: South Yorkshire - UK
Vehicle: 1997 SLK 230k
Other Toys: Jaguar X type 2,2 SE
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Major missfire at 2000 revs. Desperate for help now
Firstly, I apologise to anyone who has seen this issue in the introductions section, Im just hoping someone may have the answer if I open it up in the general section. Its a long one, sorry!!
The car starts first time everytime. It ticks over perfectly & will rev upto just before 2000 revs both when parked & when being driven. Then its like two cylinders shut down. It runs VERY rough, engine shakes etc. You can turn off the engine & immediately start it & all is well until the revs hit around 2000 revs again. No warning lights lit on the dash. No gearbox or ABS fault codes etc. Just the following codes - P0300, P0303, P0302, P0341, P1525.
This is how it started......
A couple of months ago now, I decided to sort the slight weep of oil from the front of the engine, I replaced the cam sensor magnet with a genuine one & fitted it with the genuine Merc sealant. The electrical plug that fits onto it was slightly damaged, so this was replaced & the breather pipe on top of the engine was also split, this was replaced too.
While the plastic cap on the front of the engine was off I thought Id paint it along with the cam & spark plug covers......so far so good!
Once the magnet & breather pipes were fitted, I took the car for a short run, only about a mile but it felt ok, I put the car back in the garage.
I went back to the car a few days later & the battery was totally dead. I fitted a brand new battery & the car started first time as usual. Ticking over nicely I reversed it out of the garage, no problems. I set off down the road, as soon as the car approaches 2000 revs the car runs really rough, engine shaking etc.
I didn't have time to do anything so put it back in the garage. Checked again a few days later & it started fine, reversed out fine, set off & same thing happened.
I had the codes read & it showed a missfire on cylinders 3 & 2 so I replaced the plugs, coil packs & plug leads. I also cleaned the MAF with electrical solvant cleaner. The codes were cleared & tried again. The car starts up perfect, ticks over fine but as soon as the car hits a certain amount of revs the missfire happens again.
I took it to a local garage who said the catalytic converter may be blocked, they disconnected the exhaust before the cat, no change!
They then thought the other cam sensor, the one on the side of the engine was at fault, this was replaced too, no change.
They now want to start taking the engine to bits but I have said no because the mechanic openly admits he has no idea what the fault is & opening up the engine is the next part in his investigation. I dont want to do this until we can at least confirm if the fault is electrical or mechanical. This garage has had the car a few weeks, he says his diagnostic equipment & his friends STAR equipment show the same faults. He also says the MAF is OK.
I dont have a local Indipendant near me that I know of & I cant afford a main dealer at the moment. Tax & MOT have now expired too.
Last edited by Slippy; 03-11-2014 at 05:01 PM.