Fabia 1.2 Misfire at idle

[zenman]

I have a Fabia 1.2 (40kw) with detectable missfire on the center cylinder, but only at idle. Fault code p0202 circuit defective sporadic comes up on the Bosch KTS 540 and I can see the missfires being counted in live data.
One step at a time I:
Swapped 1 & 2 spark plugs
Swapped injectors
Swapped coil packs.

Misfire is still on the middle cylinder.
Anyone come accross this before?

I have to leave it now, but I plan on scoping the injector switching (amps and volts), then doing a compression check. tomorrow (Sunday) or later in the week.

Cheers for any help or ideas.
I'll check here before I start with the spanners!

[A4 Lad]

mmm

[zenman]

Update
I have removed the ECU, checked the continuity of the injector earth (switched side to ECU) OK.
Cleaned up the contacts and refitted the ECU (it was out for 4 days until I obtained some contact cleaner spray).
Guess what.... Its now worse than ever.
Different fault code now.
injector faulty, but its not..., because I swapped it with one of the others.
I'm going to check compression, then cross over the wires from Inj 1 - 2.

I'll keep you posted (it takes me a week to get motivated) teenagers!

[A4 Lad]

..

[zenman]

Cheers,
It's bit more serious than that, I have diagnosed that the ECU is not switching number 2 injector. I will do that if it detects a missfire.
Electrics OK.
Compression test showed -
11bar Number 1 cylinder
7 bar Number 2
12 bar number 3

Cylinder leak test was inconclusive, so it's engine out today.
I only want to remove the cylinder head, but to remove the timing chain I will have to remove the sump.
A bit more work than I wanted, but it has to be right.

Selected photos and before and after test results will be posted, (as soon as I get time).

[paulstewart]

Hi,

I am having exactly the same problem with a 1.2 Skoda Fabia.

Did you ever get this problem sorted?

Would appreciate any advise as trying to get this problem fixed at the minute.

Thanks,

Paul

[zenman]

You might not want to hear this!
New exhaust valves sorted it, a compression test showed number 3 to be down by about 20%, the ECU stops delivering fuel to the injector.
The golden rule is: always check the mechanics before the electrics!
I took the engine out to do the valves, but you don't need to. I did make a tool to remove the valve springs and a tool to position the camshaft on reassembly, and I used VW liquid gasket on the rebuild. A big job but quite simple. Timing chain drives the counter balance shaft, with a position mark.
I'm glad it was that, cos I'd checked EVERYTHING else!
Good luck, PS Someone who worked at VW said this engine is a bit prone to this fault.
D

[zenman]

Sorry, should read number 2 cylinder, thinking about a Vauxhall!

[Crasher]

I have diagnosed that the ECU is not switching number 2 injector.

All you have diagnosed there is the ECU doing is EU4 job, when the ECU detects an emissions problem it identifies the offending cylinder and shuts off the injector. You have low compression on that cylinder and the head will have to come off for a rebuild with new exhaust valves and guides, this is becoming meat and two veg work for the garagre trade on the VAG 3 cylinder 1.2 engine, especially the 6 valve version.

I can see you have done this but for anyone else with a 3 cylinder petrol and a misfire, before wasting any time, get a compression test done.

[zenman]

As I said "The golden rule is: always check the mechanics before the electrics!"

[paulstewart]

Cheers zenman,

I had narrowed it down to the second cylinder miss firing because of a sticky valve but have been trying to avoid taking the head off.

I have flushed the whole engine (engine and new oil) and have been running forte engine flush thought it on BP premium petrol. The forte stuff used to fix the sticky valves on the Zetec engine.

The problem seems to be getting worse now with the forte but I only hope this is the stuff working, removing the carbon stuck on the valves.

I still have another tank to run through the engine and then if no better then the head has to come off.

I am lucky enough to know a mechanic who said he would replace the valves for £360. That is take the head off, 4 new valves, skim head, all back together.

It was his mate a got the car off so feels a bit responsible I think.

Will let you know how it gets fixed!

Thanks guys for your helps.

[Crasher]

3 new valves, not 4. It will be a burnt valve with a worn guide so you will have to replace the exhaust guides as well, if you don't the new valve will fail again in around 20K miles.

[paulstewart]

I was going to replace all the values on cylinder 2. So 4 values per cylinder (12 valve). As cylinder 2 is the only problem (thinking about it, may only do the 2 exhaust valves now).

I have heard that it is heat not getting away from cylinder 2 that causes this carbon build up, so cylinder 1 and 3 are usually fine.

I hadn't thought about replacing the valve guides, I am only doing this to sell the car as it is sitting doing nothing.

Thanks.

[Crasher]

I have heard that it is heat not getting away from cylinder 2 that causes this carbon build up, so cylinder 1 and 3 are usually fine

Of the last four we have done that I can remember, one had a number 1 failure, one failed on number 2 and one failed on number 3 so that shoots that theory down in flames! If anything, number 3 will run hotter on the 12 valve due to the EGR valve port being there.

1 on 1

1 on 2

2 on 3

[A4 Lad]

Of the last four we have done that I can remember, one had a number 1 failure, one failed on number 2 and one failed on number 3 so that shoots that theory down in flames! If anything, number 3 will run hotter on the 12 valve due to the EGR valve port being there.

Thats only 3 lol :D

[Crasher]

Doh! I was editing it so that the car was alpha and the cylinder number numerical and I cocked it up!

[A4 Lad]

lol