constant misfire

[bernsaudi]

hello, the last few weeks have been a pain.

went to a shop during a drive home across wales and upon return the engine has developed a contant misfire.
After 3 miles, the miss clearsand i get home fine.
ok for a day or two, and then whilst ticking over the miss returns and wont shift. tried a coil pack to no avail. i'm going to start it up with the injector wire off on the appropriate pot later to dry it out.
Are the coils independantly signalled from the ecu or is this wasted spark? Any tips to hunt this one will be greatly appreciated.
Bernie

[pixsaudisex2]

surely a coil what state are your wires in going to the coils..

[bernsaudi]

the wires arent very good, was thinking about putting one of the other coils on number 4 pot if it is a wasted spark system, but dont know.

[Bowlerwell]

Is it the POS?
Does the misfire move if you swap the POS positions?

[bernsaudi]

dont know what POS stands for

[Bowlerwell]

Power Output Stage.
There are 2.

They connect between the ECU and the coil packs.
Each POS has 3 channels (so one remains unused).

So, for example, if the middle channel on POS 1 is broken, you'll see the misfire in cylinder 2. If you swap the POSs over, you'll then see the misfire on cylinder 5.
The cylinders can be tested for misfire by removing the injector plugs one at a time whilst the engine is running. When you unplug the misfiring injector, the engine note won't change. If you remove the wrong one, the engine will become even more juddery.

[bernsaudi]

hello, fitted new coil to no4 pot, no difference.Found offending pot by removing injector wires. just had the coil pack up and with the help of a key turner have now got the definite on the problem-no spark on 4.

what bulkhead are these POS units on, ill swap em now to check it if theyre not too awkward.

[Bowlerwell]

You should just be able to follow the coil pack wires straight to the POSs. They're quite accessable at at the back of the engine compartment.
They are attached with 2 bolts each + thermal compound, so unless you have spare thermal compound, best not remove them.
But the cables should have sufficient reach to be swapped. Remember both the inputs and outputs should be swapped over, otherwise you'll end up firing in the wrong order.

[Fat Audi 80]

The POS are on the engine bulkhead Item 12 on the pdf compnent finder!

Cheers,

Steve

[Knight Rider S4]

Read this and go through the method of testing and it should point out your fault

http://www.sjmautotechnik.com/trouble_shooting/S4_Ignition.htm

Cheers

[Bowlerwell]

Was just about to post that link. You beat me to it.

[Knight Rider S4]

On my favourites

[bernsaudi]

thanks folks, i'll try it out in a bit.....
bernie

[Bowlerwell]

If you get stuck I have a spare I can send you.

What I ended up doing on mine was to make the broken POS channel the unused one . Did this by moving the position of the terminals on the plugs to use the 2 good channels. Hope that makes sense.

[bernsaudi]

i've just nipped out to see these, and lo there they are. I love the 'spare', how often do you find that in vehicles!!!!
i'm gonna swap the cables after a cuppa, cuz its cold outside. I hope this works.....
bernie.

the cars been great, ive had it about a year, done three sets of tyres so i wasnt really busted up when it picked up the miss. If this works it take quite a while to get the smile off( i'll solder it in the morning )