Misfiring problem
 

Hi,

I've had an ongoing misfiring problem for a while - would welcome some advice.

The engine codes are P0300 and P0306 - misfiring, and misfiring in cylinder 6. First, we replaced the spark plugs and then, the coil pack on cylinder 6. We've flushed through some injector cleaner.

MAF and Air Filter were replaced some months back.

There are a few things which are curious:

- It only happens below 2000RPM and when you put your foot down. If you gently rev through 2000RPM and then put your foot down, there is no misfire.
- It is much worse in the wet.
- ABS and PSM lights come on sometimes (probably unrelated?)
- The CEL sometimes flashes for a few seconds and goes to solid. Then, it will turn off a day later.

I'm not really sure what the logical next step of things to replace is and would really appreciate any ideas.

Thanks!

John

Check the crank position sensor
Check the cam position sensor
Check the cam timing
Check the O2 sensor on that bank

If its much worse in the wet, it sounds electrical...
Did you replace the coil pack with a new one or one from another cylinder?
As you probably know, it only takes a minute crack in the insulation that can cause tracking when wet, so check the coil pack & connection again carefully - or to be doubly sure, install a new one.

Thanks, yes I replaced it with a brand new Beru coil. The old one did indeed have a minute crack in it, barely visible to the eye.

I'm going to replace the other 2 coils in the bank, plus the spark plug tubes and O-rings. That sounds like a sensible next step.

Rain was really bad yesterday - torrential - and the car was even misbehaving at idle. Very unhappy camper. I double checked and it's definitely the same cylinder which is misfiring. You should have seen me taking my driving test in it!

Thanks for the advice.

John

John, before you go throwing money at the problem;
1) Try swapping the #6 coil pack (I know, again) with another cylinders coilpack just see if the fault follows the change over.
2) If the fault is still on #6 after above, while the wheel is still off run the engine after spraying water (from a hose) over the suspect coil pack and see if the engine stumbles more or if you can see and hear the spark tracking to ground.
3) Changing plug tubes and O rings won't help the missfire unless they are leaking - oil is a reasonably good insulator unless wet.....
4) If above tests are negative, then you are going to have to dig deeper as thstone recommends above....

Thanks for the reply :-) So I'd already ordered a coil pack by the time I read this, so figured I may as well install it.

Now with new packs on cylinders 5/6 the problem is WAY better. Under load, at low revs - most commonly when slowing down for a corner in 3rd gear and then speeding up, uphill, you get a machine-gun style misfire.

I got a flashing CEL briefly when testing, but it went off again.

That's a different misfire to before - hard to describe, but it's like a machine gun, before it would just be... muddy, when you put your foot down.

Is this just that all 3 coils in the bank had a hairline crack and moisture is getting across the bank? I'm thinking that if I replace the coil on cylinder 4, it should be all good?

It's worth noting that the weather is dry right now. I live in an apartment building so getting a hose to test is tricky!

Check the electrical plug that connects to the fuel injector.