Hey all,


Trying to sort out a little glitch with a 1700 Zetec-SE VCT. It general runs a bit rough, but when idling and generally driving round with not much throttle the engine runs and sounds fine, but under load or with more than a little throttle the engine sounds like its suffering from pre-ignition, reasonably loud (depending on how much throttle is applied).

Its not rev dependent (i.e. if you build up the revs with little throttle, i.e. with a bit of momentum or down hills etc. it is still quiet), its more throttle dependent.

Plugs were matte and the electrode was a caramel colour, but no signs of plug damage. They were NGKs but the wrong type (the were the normal LPN or something similar) so I have swapped them for platinum plugs which were listed for the engine.

OBD showed that the ignition was roughly 33 degrees advanced at idle, so I replaced the MAF as it was ford branded and probably on the engine since new (engine has done 113k and 11 years old). Left the battery off for an hour or so just to reset things.

So far, no difference. The codes previously pulled were:

P1131 (Ho2s not switching)
Diagnostics showed from start up on open loop that the HO2S started around 0.4v then dipped off slowly 'til it was around 0.02v. Wasn't switching either.

P0131 (cylinder one misfire)
Plug looked no different to the others to be honest.

Engine is reluctant to start, idles at 1k but is very lumpy.

The headgasket is leaking slightly on the chamber/coolant area, and I intend to do this as soon as possible but i'm looking to try and sort this ignition issue out before looking at a potential headgasket failure.

The Ho2s looked a bit aged but I'm not convinced that it could cause a lean condition enough to cause the pre-ignition/misfire?

Also not wanting to go down the route of 'why not try hi octane fuel' as i'm more concerned at why the car isn't running right on 95RON when it should?

Any advice/comments welcome as its getting to be a bit of a pain!!

Thanks