Hi.

I have a Fabia 2008 with 1.2 HTP petrol engine. I have really bad idling, it is running in 2 cylinders. When scanning with VCDS i keep getting the P301 error (cylinder 1 misfire).

During travel, car is running good but when idling the car enters limp mode and i have to turn on/off to have power.

I have replaced the spark plugs and moved the coils from cylinder 2/3 to cylinder 1. Still getting the same error (P301).

I have removed the connector from coil 1 to see the behavior of the Car, the car is running the same. I have disconnected the connector from Cylinder 2 and replaced with the connector from cylinder 1, car was running really bad (only in 1 cylinder).  

I have checked the wiring from the coils to ECU and wiring seems ok, all wires identified in the ECU connector.

I have measured the voltage inside the coil connector with engine on, but i have no voltage between ecu wire and black wire. For the other coils i have voltage.

I suspect that the ECU doesn't give signal to the cylinder 1 coil. Is there a way to check that?

 

Do you have other suggestions?

 

Thank you 

Do a compression test to see if cylinder 1 has much lower compression than cyls 2 & 3.

Thank you Breezy_Pete.

I will do that also. 

But, why is the difference in the lack of voltage? Lack of compression doesnt explain that. Also when I move the connector from cylinder 1 to cylinder 2 it transfers the problem to cylinder 2.

Is that not strange?

Thx 

If you move coil connectors around the sparks will not fire at the correct times.

If the ECU detects a problem with cyl 1 it may actively shut down fuelling/sparking to that cylinder.

Check that the black wire has 12V relative to earth (engine metalwork) with ignition on.

Ok. I will check that. Yesterday I have checked between black and green (signat wire from ecu) and it was 0v. For the other cilinder it was not 0v.

Thats why i suspect that its not getting signal from ecu.

When you say you swap the connection from cylinder one to cylinder 2 do you mean you swap the entire coil pack over? If so I would say you have a defective coil pack.

No. It is individual coils. I swapped the coonector from coil 1 to coil 2 to see if it firring the sparkplug from cylinder 2. Not sure if relevant but it resultjing in making the engine work in only one cylinder.

What I would do is unplug and remove the two coil packs, swap them over and reconnect the pack on cylinder one to the wiring for cylinder one and the same for cylinder two (I am assuming all the coil packs are identical). Clear any codes and run the engine.

If the fault still shows up as Cylinder 1 misfire then the fault is cylinder 1 related. If it now shows up as Cylinder 2 misfire then the problem is a defective coil. If you wish you can confirm this by moving it to cylinder 3.

I know that Audi coil packs had a high failure rate a few years back (garages ended up not being able to get spares quickly) so I would think it was common across all VAG marques.

Yes i have tried that first thing after changing the plugs. 

Swapped the coils between them, erase the code and start the car again. Missfire /code came back to cylinder 1.

 

I suspect you have low compression on cylinder one and the ECU is cutting both the coil pack and the injector as @Breezy_Pete has already told you...

Ok. Thank you for your feedback. I will do that next.

Can you please explain how does the ecu know that the compression is low and thus know to cut off the coil signal? Is there a sensor for that?

4 minutes ago, AdrianG123 said:

Can you please explain how does the ecu know that the compression is low and thus know to cut off the coil signal? Is there a sensor for that?

 

The ECU monitors the crank angle firing speeds via the G28 and the cylinder position by the G40, if it detects excess oxygen in the exhaust gases from the LSU 4.9 wideband oxygen sensor it can calculate which cylinder is at fault and shut down that cylinders injector to protect the cat from unburnt fuel.

I think BBM only has simple lambda sensors, FWIW.

 

It'll have a knock sensor which will pick up the misfire in milliseconds.

Update!

Just finished the compression test. Cylinder 1: 4bar cylinder 2 and 3: 11-12bar.

So thank you all for your help in diagnosing the problem.

12 minutes ago, AdrianG123 said:

Update!

Just finished the compression test. Cylinder 1: 4bar cylinder 2 and 3: 11-12bar.

So thank you all for your help in diagnosing the problem.

 

A head rebuild is the only real option I'm afraid, it'll be expensive and I'd replace the camchain and tensioner at the same time for complete peace of mind.