306 1.8 petrol pinking under medium load

Honest John Back Room » Technical matters
View Threaded
Thu 1 Sep 2005 15:12
306 1.8 petrol pinking under medium load - SjB {P}
The engine in my wife's 306 1.8 SR Sedan has started to pink under the transition from light load to medium load at medium revs. A typical situation is pulling away from the 270 degree navigation of a mini roundabout in second gear or leaving a 30 limit in third gear. After a few seconds the pinking ceases. It does not pink under any other operating regime. The plugs are a perfect colour, fuel consumption is as it always has been, the air filter is still clean, there are no induction blockages, and the problem has been prevalent over many (many) tanks of branded 95 octane petrol. This genuine 37k miles car still burns the same faithful 1 litre of oil per 2000 miles that it always has. I have not yet tried a tank of super unleaded. Of course ignition timing is taken care of by the ECU so I haven't even tried to check it.

Can any BRer with experience of the XU7 engine with Magneti Marelli 8P control systems share advice please; is this likely to be a knock sensor problem?

I know the difference between knocking and pinking and they are not the same, but given that the car pulls and runs otherwise perfectly well, I can't think what else the problem could be.


TVM.
Reply | Report as offensive | Link
Sun 4 Sep 2005 19:24
306 1.8 petrol pinking under medium load - SjB {P}
Whipped the 5k miles old V-groove NGK plugs out and found all four insulators to be ceramic white on the 180 degrees that face the flame front and normal 'digestive biscuit' colour and texture on the other 180 degrees. There was also a fair amount of excess carbon deposit on the bent electrode and around the base of the plug body. I guess this is from driving the car for a few weeks with a duff lamda sensor (now replaced). Gap was the correct 0.8mm.

Anyway, I cleaned the plugs with a stiff wire brush, checked the gaps were still correct, and refitted.

Pinking totally banished, including leaving the engine to heat soak at idle and then make it pull with wide open throttle in third gear from tickover. Problem solved.

I do however now have an idle problem! (unrelated to plugs and see separate post)
Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide

Real MPG enables you to register the fuel economy you are actually getting against your make and model of car, its engine and type of transmission.

Every time you enter an average consumption figure against your car, the overall average automatically adjusts to reflect it.

Real MPG