The Phantom Misfire is back!

[Welly]

Woooo hoo. I'm so happy my car is misfiring again.

Not.

Any ideas anyone?

Started weeks ago when it was randomly misfiring on one cyl only (didn't know which one), and only when on full boost. No Fault codes. Changed spark plugs. All good. .

Two days later, misfire is back . One cyl again (Still no idea which one). Took coils out, had a look, all OK, put coils back, tested, all good .

A day later, misfire back. . Decided one coil must be dodgy so bought a pair since 2 of them are obviously newer than the others. Collected and fitted them (not genuine). Tested. All good .

(See a pattern emerging here)

Three days later, misfire back - but worse this time and doing it on idle. . Swapped coils about and eventually found it to be one of the new coils. A pain, but not the end of the world. Phoned and ordered replacment. . Replaced with old Audi coil as temp measure.

A couple of hours later, misfire back! . Swapped Audi coil and second new coil around. Now OK. Found a break in the main power wire sheath to Cylinder 3. Stripped back and insulated.

At this point it all seems to be centering around cylinder 3. Left second new coil in cylinder 3. Cylinder 3 kills this coil as well.

Order second replacement from a p*ssed off motors factors!

Collected them Wednesday and fitted. Driving fine. Thought it might be sorted this time. Good as gold yesterday. Coming back from work today, misfire back. Deep joy. . After shouting and screaming at the car I give up.

It MUST be something else. But what? Help. Before I kill it.

If I change out the coil in cyl 3, I'm sure it will be fine for a while an then start all over again...

Bad earth maybe? Faulty injector?

 

[Welly]

Just to add, still no sign of any Fault Codes or engine lights....

 

[badger5]

genuine coil packs?

all 4 new?

coil wiring cracking up and "potentially" shorting is getting more common.
plug gaps being too large can also bring demise of tired coil packs

presumes coils are the issue... swapping injectors across cylinders may assist the diagnosis

 

[Welly]

genuine coil packs?

Nope

all 4 new?

Only two. Two look reasonably new so thought I would only replace the old ones. I replaced these 2.

coil wiring cracking up and "potentially" shorting is getting more common.

I did strap up the crack in the wire in cyl 3, but I guess it's worth stripping it all back and having a look.

plug gaps being too large can also bring demise of tired coil packs

They are NGK plugs, but was considering replacing with Super 4's. Maybe worth swapping the plugs from cyl 3 to cyl 1 for example and seeing if the problem follows?

presumes coils are the issue... swapping injectors across cylinders may assist the diagnosis

The only thing is that if injector related, why would it behave itself for a short while after changing coils about?

F**king car!

 

[Welly]

Also, a point to note is that I'm using NGK BKR7e plugs.

I never checked the gap before fitting, so I guess I should now *cough*.

0.7mm? Not sure what the would be out of the box...

 

[badger5]

07 should be fine

I would be suspecting the coils.. if not changed for original NEW ones

 

[Welly]

OK. Have been working on this today in the lovely cold

Have removed plugs and shortened gap from 0.9mm to 0.7mm.

Have also stripped and inspected wiring loom itself and found some serious issues - pics below:

I have sealed all the sheath fractures for testing with bodge (electrical) tape and re-sealed the loom itself. I will now leave to test for a few days.

Good shout Bill, having done some reading on other forums I see that this is becoming a fairly common issue.

Does anyone have the part number of this part of the loom, I have seen them on websites in the states but can't find one on the web in the UK.

 

[jonny87]

what would cause this to happen mate, sheathing cracking under the extreme temperature changes that go on in the engine bay?

good effort finding it though, especially in this lovely weather we're having atm

lets hope this is the end of it for you

 

[Welly]

Extreme heat I would imagine due to the wires running across the top of the Rocker Cover.

New loom fo me....!