One for the mechanics and mechanically minded

d123

I’ve come across a rather strange fault on an ‘04 Focus 1.6. The car runs absolutely normally most of the time but if it’s driven down a hill in gear and no throttle applied (running against the engine compression) it will give an engine rattle/pinking and a small cloud of white smoke when beginning to accelerate again from a low rpm (usually in 2nd) at the bottom of the slope.

I could get this to happen reasonably consistently when I tested it down a longish hill nearby that has an upwards incline after the downhill.

Bizarrely if you fill up with premium petrol it will not do it, even dropping the revs/using a higher gear where the car will start to shudder and stall but I haven’t been able to get the pinking or white smoke a single time when running on premium.

Any ideas what could be the cause?

I’ve suggested a start with a change of plugs and plug leads but it’s puzzling me why premium fuel is completely eradicating it, after all it’s only an old 1.6 Ford, it shouldn’t need premium fuel.

angrycrow

Very stem oil seals on the way out. Eventually it will start doing it every time you pull away from traffic lights. Try going up one oil grade.

d123

angrycrow wrote: »

Very stem oil seals on the way out. Eventually it will start doing it every time you pull away from traffic lights. Try going up one oil grade.

I had thought of valve stem seals but the almost pure white smoke confused me.

Any guesstimate on what labour should cost/hours required for the job?

Goudy

Pinking is pre detonation, there is fuel igniting too soon in the cycle.

White exhaust smoke can be a sign of coolant in there, but white or grey smoke is usually a sign of an excess of unburnt fuel in the exhaust.

As it's pinking on the over run, ie down hill when there shouldn't be much if any fuel injected and you're getting the white smoke when accelerating after, I would hazard a guess you have injector issues, perhaps one that is stuck open.

You don't need a spark to ignite petrol in an engine, under high enough pressure in a hot engine it will go bang all by it's self, the higher the octane the more pressure is can withstand before auto igniting, so goes bang later.

So the higher octane fuel is masking the fueling issue as it can withstands higher pressure before auto-igniting, so goes bang later.
Lower octane petrol will self ignite under lower pressures, so earlier in the cycle causing the pinking.

First off pull the plugs (but keep them in order) and see if one looks different or more mucky than the others.
Is so, swap that cylinders injector over to another cylinder, clean the plugs and run the car for a few days.
Pull the plugs again and see if the mucky plug moves with the injector.

I think valve stem oil seals or the worn valve guides will result in blue smoke on the over run, not white or grey.

d123

Goudy wrote: »

First off pull the plugs (but keep them in order) and see if one looks different or more mucky than the others.

All the plugs appear to be burning properly, a nice slightly off-white look.

Goudy wrote: »

I think valve stem oil seals or the worn valve guides will result in blue smoke on the over run, not white or grey.

That was my understanding as well, it was why I discounted them initially. The smoke is almost pure white when it happens (it’s going to be at least a week before I can see it again, there’s half a tank of premium in the car now).

The frustrating part is there are no other symptoms, No warning lights and the car is smooth and powerful when running on premium :huh::huh:

Ganga

For peace of mind why not keep running on the premium fuel and adjust your driving to increase your MPG so you are not out of pocket.

d123

Ganga wrote: »

For peace of mind why not keep running on the premium fuel and adjust your driving to increase your MPG so you are not out of pocket.

That is likely the most sensible choice, it’s an old car not worth extensive work, so a few pence extra per litre is a lot cheaper than a lot of mechanical work.

ANDY597

I'd try a full tank and a tin of injector cleaner as a cheap first step.