Hi all, i've recently bought a 2000 1.2 8v punto with 70k on the clocks, but i'm having a strange problem with it.
The car starts and runs lovely, but as soon as i try to rev over 4k, it misfires as though theres no fuel/spark. drop the revs and its perfect again.
I gave it a full service, still same. connected it to obd but that shows no faults. No management light on dash either. When running live data, at 4k it shows no signal to coil packs, so i replaced them both - still the same. I checked the timing and wasn't happy that the marks were dead on, so i replaced the belt. Lines up perfectly. Phonic wheel is bolted on in the correct place. Still the same!
Started to think the manicat may be blocked so i slackened the manifold bolts and pulled it half inch from head to let gases out. no different.
Has anybody else had this problem and solved it? I've read through the forums but no one seems to have posted a solution and what worked for them. Any help would be much appreciated.
Thanks.

No signal to coil packs would indicate to me that the coils themselves are OK and that the issue is "upstream" of them.

I'd suspect the coil drivers in the ECU.

On the other hand, it might be worthwhile checking the air gap to the TDC sensor and general cleanliness in that area, even swapping it out (cheaper than an ECU rebuild) just in case the sheilding is breaking down.

Sensors are clean, gaps fine. I was thinking either ecu or maybe the fuel pump on its way out, but there seems plenty of pressure on the rail. I should have mentioned that the no signal on live data occurs after engine stall (over 4k when it misfires).

Is it smokeing?

No smoke, runs and drives beautiful below 4k. As soon as you try to rev above 4k, engine stall/misfire.

i would have said fuel starvation but could be anything

I did try restricting the fuel return in order to increase the pressure, but that didn't seem to make any difference either.

My money (at the moment) is on TDC sensor or ECU.

FIAT (or anyone with the right kit) should be able to do a very quick pressure reading on the fuel rail.

Id think the crank sensor would effect runing all the time and not just above 4k, have you unpluged it and checked wires?

its not valve bouncing is it?

Aye, crank sensor wiring is fine, and the pulley looks fairly recent. I didn't want to blow 125 quid on an ecu if I wasn't 100% sure, but its looking more like I'm going to have to. Kinda hoping someone else on here had this problem and solved it.

I think someone did a DIY repair. A search may find.

Opening up the case and cutting into the sealed unit to look for a broken trace isn't the best plan, but looks like the cheapest option at the moment. At least if it runs right afterwards I know to order a replacement. Does anyone know if the ecu needs to be replaced with exactly the same model and hardware version? Or will any 1.2 8v punto one do?
IAW 59F.M3 HW 0002

Problem solved. It was the crank sensor. looks like someone had fitted the wrong one before i bought the car. the resistance across the pins was correct as per fiat spec, but it didn't have the rev sensor in, hence the problem. Changed it for the correct one, runs like a dream.
Moral of this: never trust the work done before you bought the car. all readings on the crank sensor were correct, just not the right one.