Cylinder 2 misfire - plugs and coils replaced - still lumpy and powerless
 

Hi,

This is my first post, so bear with me.

I have a 2004 231 with 38k miles. It has had the uprated starter motor and has not had any issues before.

I started it the other day with no probs, but almost instantly the car was very juddery and was suffering with a lack of power. Then the engine light came on permanently. Got it plugged on a machine, which showed a cylinder 2 misfire, so the car was towed to the garage and the lead coil replaced.

The car ran fine for a week, then suddenly lost revs whilst idling and cut out. Restarted fine, but again loss of power and shuddery, then engine light came back on. Returned to garage, where the trailing coil on the same cylinder was changed and again the car started up fine. However, I asked the garage to replace all plugs and remaining coils, to be safe, given the mileage. They managed to flood the engine, as they moved the car a very short distance then turned it off and back on again very quickly. They pull started to de-flood and then replaced the plugs/coils as requested.

However, despite a full set of brand new plugs and coils, I am having the same problem. Drove the car around the block to test it and it was lumpy, with poor power. Then the engine light started flashing intermitently.

I am now thinking of getting new HT leads to complete the ignition set, but I am not convinced this is going to work.

Does anyone have any ideas or have had something similar? I am worried that the flooding may have done some further damage?

Any help very welcome as I love this car and want it working asap!!

Thanks :)

I'd guess from your terminology that you are in the UK?

Correct, when you replace the coils and the plugs, you should also replace the leads. If the leads are bad, the coils can't get the charge to the plugs, and coils loading up that can't discharge will die very quickly, even if new.

There are some other causes for misfires, though with your symptoms if it's not the leads then I'd next point my finger at the e-shaft sensor. It's a magnet with wires coming off of it down next to the front main pulley that keeps track of where in the rotation the engine is. If that has gotten fouled with a bit of metal or general gunk, it can have trouble telling the engine when to fire the spark and when to inject fuel. It's hard to get to, but you can clean it off with a rag. Nothing special needed.

Once you do that, you should reset the e-shaft profile by doing the 20-brake-pedal-stomp reset.

Key to on but not start, start pumping the brake pedal enough to light up the tail lights, watch the oil pressure gauge. Stop when you see it sweep to the right. Should take around 20 stomps. Key to off, wait at least a minute and then fire it up. It may stumble around for a bit at idle until it relearns the fuel trims.

You guessed correctly, I'm English!

Many thanks for your detailed reply, I will definitely do the leads and go from there. I didn't know about the e-shaft sensor, so thank you for that info, will turn to that if the leads fail to make a difference.

Much appreciated :)