Won't rev past 3000rpm

[Leslie Graham]

Ok, not my car. Haven't worked on it.
It's a friend I'm meeting at track with a Ph2 172. Recently had engine out and box changed. Apparently after refit will not rev past 3000rpm.
Any ideas or suggestions or places to start would be much appreciated as this should be out in 3 hours...

 

[MarkX]

Ok, not my car. Haven't worked on it.
It's a friend I'm meeting at track with a Ph2 172. Recently had engine out and box changed. Apparently after refit will not rev past 3000rpm.
Any ideas or suggestions or places to start would be much appreciated as this should be out in 3 hours...

Crank sensor? Could be just corrosion, two 10mm bolts and give it a clean up

 

[Leslie Graham]

She wouldn't start if crank was off. Had that myself. It's Brendans car, had engine out after blown box last time. I've a ball of sensors I'm bringing up for him. He seems to think throttle potentiometer. A lot to be said for Ph1 cable!

 

[MarkX]

She wouldn't start if crank was off. Had that myself. It's Brendans car, had engine out after blown box last time. I've a ball of sensors I'm bringing up for him. He seems to think throttle potentiometer. A lot to be said for Ph1 cable!

Yes it would! Mine had a similar problem, only revving to 4K along with a misfire, crank sensor cured it. Easy swap anyway to eliminate it, throttle pot would seem to be common on here, so far not suffered that one

 

[Leslie Graham]

Ah ok, mine had same but wouldn't fire. Just leaving now. See you up there bud

 

[GrahamS]

She wouldn't start if crank was off. Had that myself. It's Brendans car, had engine out after blown box last time. I've a ball of sensors I'm bringing up for him. He seems to think throttle potentiometer. A lot to be said for Ph1 cable!

I saw a car with this the other day, the car is in limp mode and probably has the coil type light on the dash. The FBW throttle has two tracks which do the same thing but act as a fail safe, you need to know which track is not working and then go from there.

Hopefully this should help. Check for continuity at every point of the circuit, starting with 5v on pins 4 and 5 of the pedal plug.