AU 6cyl Misfiring. Any ideas??

brissyonetonner · 10-05-2007, 03:50 PM

Hi everyone. I have an AU ute, 6 cylinder. For some strange reason it has started misfiring at idle and under acceleration.

Now heres the really strange bit. Shortly after it started showing these problems, the exhaust gave in and now its got a leak. When that happened it stopped doing it for a while and now has come back to misfiring.

Any ideas or advise would be appreciated. The new muffler is on it, but its still missing.

DODDO · 10-05-2007, 04:17 PM

Hi,
How many KM on your ute? Do you know how to use a multi-meter? If you can, read on...
The first thing that you can do is test the resistance in the ignition leads. You can do this with a Multi meter and you should be able to find the specs somewhere on the Forum? You will have to remove the air intake pipe and airbox to gain easier access to the coil pack side of the leads.

The next (and most common) thing it could be is your coil pack has packed it in or is starting to. There is a method for testing the coil pack assembly, i have done it before, but off the top of my head i cant remember the terminals that have to be probed in the wiring loom. I will get back to you on the terminal numbers and locations.

Or it can be something even simpler, like a dud spark plug.
Hope i have helped and goodluck!

Cheers!

Cobra · 10-05-2007, 04:56 PM

Most common thing would be the leads. You can visually check the leads to see if theres any white marks on them where they may have been arcing. If no then the other check is what was said above, if you have a multimeter set it to ohms and check the resistence.

Because you have a coil pack you wont need to remove the leads from the coil pack to check their resitence. You can just remove the leads from the plugs and check them in sequence by probing #1 and #6, then #2 and #5, then #3 and #4. T

he resistence should be about 25k ohms. If it's a little bit more or less don't worry, as long as they are all constent with each other. If one has got an open circuit probably won't get a reading, or it'll show something dodgy.

DOHC-DJ · 10-05-2007, 05:19 PM

yer start by checking the basics, the resistance in the leads should be roughly 3000-8000 ohms per 300mm of ignition lead. or just check the like cobra said. check for plugs arent fouled or oil soaked and possibly regap them. then maybe clean your throttle body, they tend to get a carbon build up and can cause a miss at idle.

bodes-sh · 10-05-2007, 08:04 PM

i think the first question to ask would be when were the plugs and leads last replaced?

brissyonetonner · 10-05-2007, 11:22 PM

I will do those things. I cranked it up in pitch black shed and could see any leads arcing, which is usually something ive been able to see when ive had leads fail on other cars.
This problem seems to be intermittant. now it is idling better, and will miss when revved hard and sudden, but if you open the throttle slowly, it wont miss. When its under load it will miss too.

The car has 160,000 KM on it, and has always had Ford log book services, although it has been a while since it has had one, as it doesnt get used all that regularly. I do know how to use an ohm meter, but i dont have one in handy access, and i dont own one.

I just had to replace the power steering pressure line, $380 for the part alone - excluding labour. The ford dealer i go to charges like a wounded bull for repairs, so i really dont envy taking this down for him to diagnose.

Apart from leads, plugs, coil pack is there anything else that it could be? Do the AU's have a 02 sensor? I've seen those fail before (on my chev camaro) and it ran it so rich that it missed like nothing else. Are the plug leads and coil packs something that can only be bought genuine parts (like the PS hose i just bought?)

bodes-sh · 10-05-2007, 11:33 PM

plug, leads and coil packs you can get from pretty much any parts store, repco, etc... au's do have an o2 sensor, but they only control the mixture when the engine is at operating mixture, and i've never heard of anyone having a miss caused be a faulty o2 sensor on an au... personally i'd start by replacing the plugs and leads and go from there, probably also wouldn't hurt to replace the o2 sensor with that many km on it, they are usually only apparently good for about 100,000km