'97 540 - Misfire issue

[Kirk930]

'97 540i, auto, 183,000 km, all stock. I've owned it about 5 years and put about 90,000 km on it. Never had any engine issues.

Car has started showing fault codes for misfires....random, and cylinders 5, 6, & 8

The CEL will only come on if I use full throttle on the car. If I clear the code and drive the car gently there are no problems.

Checked and changed the plugs (they had approx. 100,000 km on them). Two plugs were somewhat loose in the block, and two had the coil connector submerged in oil (looks like a valve cover leak). Plugs were pretty clean otherwise.

The other day I used full throttle and when the revs exceeded approx. 4000 rpm the CEL started flashing and the engine started cutting out. Letting off the gas, the CEL went solid and the car felt like it was firing on 7 cylinders. Rough idle, and from a stop if I took my foot off the brake the car would sort of lurch forward and stutter. At higher rpm the engine would smooth out.

Turned the car off for a while and cleared the codes. Car runs fine now, but no full throtlle blasts for the time being.

Coils look like they are original. Fuel filter has about 90,000 km on it.

Where to start? Swap coils around? Any way to test the coils?

Thanks.

[T.Dot_E30]

Was it the same misfire codes that triggered the last check engine light?
Sounds more like a maf/knock/crank/cam sensor type symptoms, but if you are only getting misfire codes start there. Swap coils and see if the mis-fires move to those cylinders.

Alternatively if you have the values from a Bentley Manual you can check to make sure they have the correct resistance with a multimeter that can measure Ohms.

[bmwm5lover]

I would say since you've replaced the plugs already to test the ign. coils. You can swap them around but you have 3 that sound like they might be gone. So swap side to side and see. Another way is, with the car running, gently lift the coil off the spark plug and listen for arcing, if there isn't any, then that coil isn't working. If you were closer I could have lent a hand.

Let us know

[Haggis]

It could be the CPS starting to go. Happen to my 98 540 after I did the timing chain guides. There's a way to test the CPS with the car on accessory so you have power to the CPS. With the CPS out of the timing chain case but still plugged in to the harness, strip the wire back on the CPS and there should be 3 wires, one is ground one is 12v constant and one is the signal wire. With power at the CPS take the leads of your 12v multi meter. Put one lead on ground and one lead on the signal wire and when you wave a metal pipe or a wrench you should have a voltage on the signal wire.

[Quack]

I had the same problem with my 98 540, but I already knew what the problem was before I bought it, turns out the cats were clogged, driving slowly with slow acceleration was fine, but everytime I put my foot down the check engine light would flash & the vehicle would misfire, once I restart the car or erase the check engine light the car would be fine again.

[Kirk930]

Hmm....cats are an interesting idea. I had trouble getting it to pass emissions testing recently. High NOx levels. Believe it or not the tech at Canadian Tire (yes I know....) cleaned the MAF and it passed.

The cam position sensor was replaced last year. When it failed all it caused was a rough startup. Never seemed to affect regular operation.

I have the Bentley manuals. I'll meter the coils and see what that shows. They are all original Bremi units as far as I can tell. Weird that 3 would go at once though.

[Kirk930]

Oh...and the engine codes were the same both times the CEL came on.

[Quack]

it could just mean that the cat on that bank is clogged, I ended up replacing the cats with hi-flo cats, the problem instantly went away.