One cylinder no ignition

[MickyPo]

Hi everybody ! 

 

I have an issue with cylinder 2 not getting spark

I've changed the sparkplugs, leads and the ignition coil pack.

For some years now I had intermittent no2 misfire, now it stopped altogether.

I've put a spare lead and sparkplug "in the air" and on cyl 4 it gives spark and cyllinder 2 it doesn't.

I've checked the wires going from ECU to the coil pack: 

-the four thinner ones  measure (2-3 ohms) with no short to ground or positive.

-of the two thick ones: one is 2-3 ohm but one is 30 ohm ...  ( Short from battery terminal to coil input) and 30 ohm from battery terminal to ECU output and 30 ohm from coil input to ECU output.

Question: 

1 Is this supposed to be a straight wire from ECU to ignition coil?

2 Does anyone know where to find the detailed wiring diagram for the ignition system ? 

3 anything that I might be able to check that will cause the ECU to not send signal to only one cyllinder other that faulty ECU ? ( I removed and opened the ECU and I haven't seen any signs of corrosion etc) 

 

Any help would be greatly appreciated !! 

Oh forgot to add it's a Octavia MK1 2003 estate

[Breezy_Pete]

Engine code is required to find relevant wiring info. Letters ahead of engine number on V5c ownership document, or on boot build label.

[MickyPo]

If I understand correctly the engine code is the 8th digit on vin !?

That would be U 

[Breezy_Pete]

No, that's a code for the engine code, the real code will be 3 or 4 letters.

I don't have the ability to decode your 'U'.

Please see one of the links in my signature (view on computer not phone) for other places to find it, if you've tried both of my suggestions without success.

Edited 1 June, 2023 by Breezy_Pete
Sp

[varooom]

The 5th Character is the start of your engine code, but not the value we need (it will show the cc/type only)

 

C - 1.4 ltr./55 kW/petrol engine
E - 2.0 ltr./85 kW/petrol engine (does not apply for India)
E - 2.0 ltr./82 kW/petrol engine (applies for India)
G - 1.9l TDI/66 kW/diesel engine
H - 1.4 ltr./44 kW/petrol engine
J - 1.6l/55 kW/petrol engine
K - 1.6 ltr./74 kW/petrol engine
L - 1.8 ltr./110 kW/petrol engine
N - 1.9 SDI/50 kW/diesel engine
P - 1.9 TDI/81 kW/diesel engine
R - 1.8l/132 kW/petrol engine
S - 1.9 ltr. TDI PD/74 kW/diesel engine
U - 1.9 ltr. TDI PD/96 kW/diesel engine
X - 1.6 ltr./75 kW/petrol engine

 

As written, it will be 3 or 4 characters, if you post a VIN, it can be decoded.

[MickyPo]

Thank you for that 

The 5-8 characters are : 

e41u

[varooom]

Probably one of these...

AEG APK AQY AZH AZJ

 

But, might need exact code for correct wiring diagrams (from VIN)

[MickyPo]

Please find attached a photo with the vin

 

Also: 

The coil pack input has 6 wires 

1 and 6 are thicker 

And 2-5 are thinner 

The thicker ones are positive and negative 12 v.

Am I right in assuming that the thinner ones are for signal for each piston ? 

What I find courious is that pin 2,4and 5 have 0v on them with ignition on but the pin 3 which I assume corresponds to cilinder 2 signal has 3.4 v on it ? 

[Breezy_Pete]

Right, nice one, your engine code is AZJ.

Brown on pin 1 of coilpack connector is earth, black/lilac on pin 6 is the switched 12V feed, live when fuel pump relay is energised (e.g. engine running).

Pins 2, 3, 4 and 5 go to engine ECU pins 102, 95, 103 and 94 respectively. These will be pulsed earth (or positive) triggers, I think, for each cylinder's coil driver, energising spark plugs no.1, 2 ,3 and 4.

 

Edited 1 June, 2023 by Breezy_Pete

[MickyPo]

Thank you for that! 

So pin 3 (cyllinder 2 - the bad one ) being at 3.4V whils the other ones showing 0V indicates a ECU problem I guess.. 

I'll look for a test/repair shop for that, if anyone has any good suggestions it will be much appreciated 

 

Once again many thanks and I'll keep you posted on the progress 

 

 

 

[Breezy_Pete]

Is that 3.4V with the connector not plugged into the coilpack?

If so I tend to agree. First step - maybe - look for water ingress in connector(s).

Then if no telltale corrosion found, see if anything has got inside the ECU's case.

 

 

[MickyPo]

Yes that is 3.4v with the cable connected on ECU side but not coil pack side.

The connectors look dry and clean, I've opened the ECU also and it is clean, closely inspected solder joints and they all look good with reasonable confidence. 

I've traced the traces a fair bit back towards the processor and they have continuity as far as I can trace them 

 

[MickyPo]

If it will help anyone in the future I found this to be an easy way of removing the ECU :

[Breezy_Pete]

I'd be happy to have a look at it, but have no experience of engine ECU repair.

[MickyPo]

Thank you for that, I've ordered a used one, hopefully by the end of next week I'll get it working. 

I'll keep you posted

[MickyPo]

Update: 

Got new ECU and had it cloned of the old one.

I've installed it and to my surprise gave the same issue on cyl 2 - no spark.

I took the old coil in the house and connected the plus and minus to a spare battery and that allowed me to give an impuls to generate spark.

I could get a spark on all of them.

 I've installed the old coil connected to the new ECU and now it runs on all pistons.. 

what's surprising to me is that both the old ECU and brand new coil pack have issues on cyllinder 2 !?

 

Once again, many thanks for your support, it's much appreciated ! 

 

[Breezy_Pete]

Inspect cylinder 2's wire between coil and ECU for damage/exposed copper/corrosion maybe?

Probably easier to run a new wire in parallel with existing, spicing in close to connector at each end?

Or are you saying all's well now?

[MickyPo]

I didn't do a test drive but as of now it is working well - it starts and runs on all cyllinders without fail where before I could not get the cyl2 to fire at all.

 

I did check the wires as well as I could ie continuity and for short to both positive and negative whilst puling on them in within reason and they all look good. 

 

I will test the new coil (not working coil) on the bench tomorrow for confirmation.. 

 

[MickyPo]

All working as it should.

New ECU with the old coil pack.

 

The new coil pack does not work on cyllinder 2 and has a big crack on it on coil no2. 

I don't know what caused it - either bad copy or my loom has an intermittent fault which I could not find.

 

Of course time will tell but for now it's working.