Misfire

[wowhestall]

My wife has a 69 Grandland X 1.2 Petrol with about 30k on it. The other evening on the motorway it developed a misfire and later flagged an EML for cyl 2.

I swapped coils that evening but cyl 2 still caused issues. I had a look at the coolant and noticed it was low and a little murkey (black). I thought it might be the head.

Performed an exhaust gas check on the coolant, nothing. Whipped the plugs out and cyl 2 had lost it's earth tab and some ceramic insulator. It was clearly covered in soot from the poor ignition. Compression test also passed with flying colours.

Replaced the spark plugs and the car runs a little better but still feels low on power and sluggish under load. I'm concerned what the cause of the damaged plug is?

My first guess would be an injector with a lean burn, though I'm getting no fault codes for knock (or any other codes).

Any suggestions? I'm a willing victim.

[Vauxhall Owners Club]

Well firstly it sounds like the earth electrode has been eroded away without leaving any material in the cylinders causing piston or valve damage
As long as the compression is okay then there is half a chance of rescuing the engine if little else has occurred

I would scan the injectors to see what duration and pulse width they have to determine a faulty injector on that cylinder and replace if necessary
Once running then see how the spark plug fairs after a run and look at the colour of the electrodes on all cylinders for a comparison.
 

[wowhestall]

On 8/25/2023 at 12:49 PM, Vauxhall Owners Club said:

Well firstly it sounds like the earth electrode has been eroded away without leaving any material in the cylinders causing piston or valve damage
As long as the compression is okay then there is half a chance of rescuing the engine if little else has occurred

I would scan the injectors to see what duration and pulse width they have to determine a faulty injector on that cylinder and replace if necessary
Once running then see how the spark plug fairs after a run and look at the colour of the electrodes on all cylinders for a comparison.
 

Thanks for the help. I'm using a cheap ELM unit with Torque Pro, not many options for injector pulse widths.

Today I whipped out the coils, plugs and injectors. All looked identical. Checked the tops of the pistons. Cyl 1 & 3 have a layer of carbon deposit. Cyl 2 is very clean, indicating a hot burn to me. Both the injectors looked identical.

I've swapped injector 2 & 3 to see if the misfire moves / the top of the piston cleans up.

Not sure the car has been trying to compensate with extending the duty cycle but would be cool to see that sort of info.

[Vauxhall Owners Club]

Well time will tell if you have shifted the issue from one cylinder to another

Please keep us updated on how it pans out

[wowhestall]

Aye, got my hands on a picoscope to see the injector timing, but I've not had time to play yet.