I drive 1.8 Mondeo Duratec petrol its done 160,000 miles and up until about 3 weeks ago it was operating perfectly and acceleration was fine.

However, when you put your foot flat to the floorpan (on the accelerator) in third gear (it is most noticeable) it revs up to 4000rpm swiftly and smoothly, but then it only creeps up to 5000rpm, and you can feel it holding back. If you keep your foot in there planted, it gradually arrives at 5000rpm, then it seems to overcome the problem and revs cleanly again almost to 6000rpm (redline @6250 or 6100 ish)

When you get up to say 5,500/6000 rpm and then change up into 4th gear it dies again and loses its power, but then regains it again once it breaks through the 4,500/5000 rpm sector.

Furthermore, at much lower speeds, when say approaching a roundabout with a reasonable amount of roadspeed but low revs on the overrun in third, and then when you see the road ahead is clear you accelerate away, it starts to Pink momentarily.

I have replaced a short piece of vaccum pipe, replaced the spark plugs and the leads, but still it persists.

There is a vacuum unit sat just behind No:4 Cylinder which has a nylon knuckle joint mounted vertically just under the coil area, how likely is it that this unit (if the diaphragm has split) could be a contributor ? It is a sealed unit and can not be dismantled as far as I can tell, the body is made of plastic.

Thanks - Anybody got any bright ideas. ??

Id try a good fuel injector cleaner first and if the fuel filter hasnt been changed recently, I would do that as well.

As above me change the fuel filter, if this doesn't solve your issue then it may be worth getting a garage to check the fuel pressure within the fuel rail. They do this by plugging in a little gauge and then checking results compared to what they should be. Quite easy to do yourself but not without the gauge and equipment. This would be helpful to check as your injectors could be getting starved of fuel when they need it the most. Faulty injectors could also cause the problem, but this is all based on whether there's something a miss that side of things. You've made sure there's good spark, fuel side of things seems the best way forward and the second place to check for an issue.

The vacuum unit you describe sounds familiar to a PCV valve (positive crankcase ventilation) which will be fully open at higer RPMs so the engine can burn off blowby gasses produced by leakage on the piston rings. If something is wrong here you'd usually experience the engine stalling and even oil burning - essentially as it causes an air leak and foces the engine to run too lean paricularly on idle. That of course is assuming it is the PCV valve, I think mine is located near cylinder no.1 (timing belt end).

Ultimately if you can't find any issue on these things then a garage will be able to do a compression test for you, wet and dry. This will help find any issues inside the combustion chambers (valves, piston rings, even headgasket) before going any further with the fault finding.

Hope that's of some help and let us know how ya get on,

Dan :)

EDIT: Spelling, grammer and left bits out! Must be my old age.

Thanks to you both (Dan & BT Maldon) for your responses. Obviously, when you detect a problem you can't nail yourself immediately, you turn to others. Interesting that both of your replies contain the fuel filter solution, as that has been also mentioned by others that I have spoken to. I have always associated pinking with a "timing" / engine management issue, so my brain was heading more in that direction. You have both convinced me I should try the fuel filter option next, as i forgot to mention in original post that I had already tried the Redex injector cleaner trick, to virtually no noticeable difference.

The other cause I had considered (mainly with the lack of power) was the CAT. But Iv'e never had a car that's needed one so was not sure about the symptoms, however I guess if the cat had deterioroated, it would be a consistent power loss throughout the range.

thanks again blackcab 157