My UK97 has developed a hesitation on full throttle which seems to have got a lot worse following a service that included a plug change.

I can get full boost on lower throttle positions without problem.

What I have noticed is when it happens my DIY AFR gauge changes from rich to lean for a fraction of a second.

I am suspecting a poor spark on the ignition system unable to fire up under full throttle but the AFR fluctuations have me a bit worried. Would the unburnt fuel/air cause the AFR meter to indicate lean?

The garage has offered to change the plugs again but I want to fit a new set of leads first.

I cleaned the MAF, checked all hoses and got no error codes from the ECU.

Any other ideas while I'm waiting for the leads to turn up?

Cheers

Rich

 

I've sort of ansered my own question:

searching the net I found a good description regarding the operation of the lambda sensor, looks like no spark will cause the AFR symtoms above

Quote:
An air leak in the intake or exhaust manifold or even a fouled spark plug, for example, will cause the lambda sensor to give a false lean indication. The sensor reacts only to the presence or absence of oxygen in the exhaust. It has no way of knowing where the extra oxygen came from. So keep that in mind when diagnosing oxygen sensor problems.

The web page is here if anyone is interested:

http://www.picotech.com/auto/lambda_sensor.html

Cheers

Rich