Fiesta RS Turbo

[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.

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)

Any advice on what to check would be appreciated.

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

[jimmyfish]

Hate ts say it but my frst did this just before the bottom broke up
But still could be electrical fault or a spark plug they
post in the ford forum aswell speak to knighthawk he is a very clever chap

[stp007]

I have a SVO mustang and not too long ago had the same problem. The vacuum line that ran from my boost controller to my intake came loose. I just put the hose back and it ran fine after that. I'd check your vacuum lines. Hope this helps, or at least steers you in the right direction.

-Sean

[Dyno-W]

Sounds very much like your hitting overboost cut, which is around .7 bar for standard ECU. Lower boost slightly by adjusting actuator and you should be OK.

[beedub]

Dyno-W said:

Sounds very much like your hitting overboost cut, which is around .7 bar for standard ECU. Lower boost slightly by adjusting actuator and you should be OK.

exactly what i was thinking BUT... it would be a very large jolt you would feel as it nota progressive cut out

[rs lover]

I've had two similar problems wi my escort rs, i know the engines slighty differ but the principles r the same.problem one i tuned the engine, cams etc, but didnt have the chip to fuel it alln that caused a misfire which also had the jolt when it misfired, solved that wi a chip. problem 2 when boosting up car jus died, like an electrical fault n when i let revs off cured, but when applied again it repeted. my replacement hoses were not fit right n had a tiny air leak where it joined to the crossove pipe and took me months to find it, when i finally had i 'd stripped the car!

[Matt_FP]

Are you sure the plugs are fine? Have you checked the gaps?

Most misfires on force inducted engines are due to ignition breaking down under boost. Plugs (gap too large), lead shorting out (have you check them properly?) or coil failing (is it EDIS Coil Pack on RST?).

Matt