alexanderfoti

Hi all

Having now fixed my power problems (will update other thread shortly). I now have misfire events under full throttle above 5000 rpm.
Plugs are new, insulators are new, and show no signs of arcing.

It is very repeatable and is always on one bank. The codes that are logged are different every time though.

If I repeat the process 5 times I get the following:

misfire on 7,11,12
misfire on 7,8,9,10,11,12
misfire on 10,7,11,23
misfire on 7,11,12
misfire on 7,8,9,10,11,12

Obviously this side is the issue. I have opened the ignition transformer and it all looks good in there, no burns etc, or obvious failure of components.

To add as well, On smooth running when cold, cylinder number 10 misfires for 30 seconds on cold start. So there is obviously and issue with the mosfet/coil on this a or b side (b I think as ionic current measurement shows 2v at idle.)

My plan for when this occurred was to rebuild the ignition coil on the misfiring cylinders, but I was not planning on having a whole pack show as misfiring .... I have a large set of spare coils and parts that look good.

Any guidance much appreciated.

Thanks

alx

alexanderfoti

Many thanks, I will do that now.

Russell Ormerod

Common issue, replace that coil pack

alexanderfoti

I have replaced the 7-12 side pack today and now I have same thing, but also constant misfires on number 8 @ idle:





This was a rebuilt pack from INPOST on ebay.

Am I right in thinking that its still the pack and that this one is faulty, or is it possible its the ignition transformer?

Russell Ormerod

The transformer won't affect 1 cyl. The transformer can be tested by measuring its output too. It's possible it could be the coil pack. It could also be a mechanical issue with the engine, or even A spark plug, you need to dig deeper, or test that coil pack on another car

alexanderfoti

I would be surprised if there was a mechanical issue with the engine, I will put the old pack back on and check the plugs again. These plugs are new so unless they are damaged its something else.

Could be a blocked cat but...

Russell Ormerod

Nope, blocked cat can't effect one cyl, and to be that blocked the engine will be ruined by now

alexanderfoti

I thought that! I meant the misfires on the whole bank rather than CYL 8 misfire, its obvious that the rebuild coil I bought was junk.

Russell Ormerod

Ok, in all of the v12 motors i have had misfires on it 99 percent of the time the coil pack, I think once I had a transformer fail.

alexanderfoti

Something interesting.

On the old pack, when it misfired it was very soft, barely felt it, and the check engine light would go on. The dumping of boost through the divert valves was louder.

With the new faulty pack, when it misfired it was very violent and obvious.

Anyway, new pack still hasn't arrived. Wait and see.

alexanderfoti

New pack finally arrived.

Installed and fired up. Interestingly I had smooth running counter count up to 16 right away on cylinder number 10, once warm it goes away. Im slightly concerened there is mechanical damage on this cylinder as this is with a new coil pack and new plugs. The old (6000 miles) plug was quite carboned up but dry. Possibly bad spray pattern from injector?

Anyway, car is waiting for new brakes so cant tell whether the car still misfires under load or not, will know by next week. Stay tuned for our next instalment.

Russell Ormerod

Take it out in the open road and drive it hard, then cruise with the revs up, like 3rd gear. Then see how it runs the next day

alexanderfoti

Right. In rather typical fashion with me and this car.

2 x new coil packs.

Took it out today, still misfires all along one bank above 4000rpm full throttle. (7,8,9,10,11,12)!!!

Ignition controller?

Its a very soft misfire, not aggressive like an actual misfire. It just puts the check engine light on and turns off one bank.The first passenger side coil pack I fitted misfired on hard acceleration too, but it felt like a real misfire. This one, if it weren't for the light coming on and limp mode, you wouldn't have known its misfired.

Russell Ormerod

Are All Plugs New And Correct as Per MB?
Red tubes in coils new?
New genuine mb coil pack?

alexanderfoti

Yes to all three.
Correct ngk plugs too.

Russell Ormerod

Check the transformer if its one bank

alexanderfoti

I had initially ruled out the transformer as it was only on hard acceleration.

Will try a new ono from my mate with an mb garage

Russell Ormerod

Have my doubts but worth a try

Russell Ormerod

Also make sure the power supply to the coils are good

alexanderfoti

The ignition transformer is the power supply to the coil packs??

Russell Ormerod

It still needs 12v supply and check transformer supply

alexanderfoti

Considering it only misfires above 5000rpm @ WOT. Under all other conditions the car runs on 12 cylinders, so the 12v supply must be present. The only way would be to check the 12v supply and transformer supply (which are the same thing) under misfire conditions, which would be rather difficult?

Richard Wraith

I wrote this on another reply but sounds all the same. Hope this helps
Check the coil packs as they tend to get small fracture's & cause the spark to find an earth. So what you have to do is pull the coil packs out, check for very tiny fractures/cracks & insulate them with Self amalgamating tape or clear nail polish, even silicone, just make sure they're insulated & it will work fine.

alexanderfoti

Thanks but the car has had multiple new coil packs with multiple new insulators, issue isn't with the coils.

I have gapped plugs down a tiny bit and have also sent injectors off for testing/cleaning. They came back all good but 2 tested as stuck open before cleaning.

I fitted them back to the car and 2 injectors dumped fuel into the inlet like a hose so I am thinking there are 2 faulty injectors that cannot be revived by cleaning. 2 new injectors on their way

I'll post up the whole procedure when I fix the problem