Fiesta RS turbo - running problem

[jac-in-a-box]

Need some advice as to what's going on guys if possible...

Low mileage 50K miles, doesn't burn oil, starts and idles from hot and cold perfectly. Plugs and leads fine. All electrical connections clean and free from corrosion. New fuel filter.
All air connections / hoses are sound

Runs fine off boost and will mostly run well on boost up to .7 bar...however, ocassionally it seems to "miss", but it's not like a regular misfire - more as though the electrical system shuts down for a fraction of a second. Ease off the pedal and it's fine - foot on the gas and it will start again.
Not sure if it's some sort of overboost protection that's kicking in (it won't consistently show the fault)
Just lately it's been happening intermittently at around .3 bar boost...I'm happy with the accuracy of the boost guage.

Suggestions from other sources have been the Map sensor or a weak wastegate?

Any advice on what to check - and how to, would be appreciated.

Cheers, Rhys (son of J-i-a-B)

[jac-in-a-box]

Thanks for your reply Sean

Pretty small and old fashioned engine in mine I'm afraid...1.6 CVH

Certainly been thinking along the lines you've suggested. It would seem that boost control is achieved through a device called an Amal valve. Controlled by the ECU it vents high pressure either back to the inlet side of the compressor or directs it to the wastegate (I think!)

Got to be worth a look at all the asssociated pipework; it's the intermitent nature of the problem that concerns me!

Thanks, Rhys

[jac-in-a-box]

nighthawk said:

Has the car been scanned for fault codes? If not, that should be the first thing to do. From what you've described it's a misfire under load at mid to high RPM, a fault on the map sensor or it's pipe work will cause incorrect fuelling until you back off enough to get a correct boost reading again. Again a leaking/weak wastegate actuator could bring the same symptoms. How are you reading off the .7bar of boost? There are other possibles, but you really need to have a look for trouble codes.

And thanks for your response nighthawk.

No, no fault scans yet - Ford dealer wil be able to do that I assume? Lack of local specialists where I am.

Boost readings being taken from an accurate boost guage (also checked by substution of another new guage - Blitz)

I hope I'm not mis-interpreting when I say "misfire" I've experienced a duff HT lead on another Ford although this feels loosely similar it isn't! A sudden loss of power / stumbling would perhaps be more accurate.
Since posting my rev counter has died, not sure if this is significant? I think it gets its signal from the ignition module...red herring?

Car is fine when not "loaded", travelled 20 miles with no problems with car off boost, it's when the engine is under load the problem seems to happen.

Thanks, Rhys

[jac-in-a-box]

I think an under bonnet ferret around is in order tomorrow, followed by a visit to the Ford dealer if I can't see anything obvious.

Thanks, Rhys