Zetec issues

[Aidan Flack]

Hi all, hoping there's someone who can possibly shed some light on my engine problems. I have a zetec in the car running standard ford ECU and wiring.
A few days ago it suddenly dropped onto 2 cylinders on the way home, I found that it was fine once I was above about 3k rpm and accelerating. Ease off and it was straight back to 2.
Since then I have changed the coil pack and TPS (fault code in ECU). The engine had new leads and plugs 3 months ago.
I have tried unplugging the cam sensor, maf, idle valve, TPS. All seem to be working as expected.
There is continuity between ECU and all sensors. It runs on cylinders 2+3 with everything connected. I disconnected leads 2+3 from the coil and the engine ran on 1+4 instead. Disconnected 1+4 and it ran on 2+3. Connected all back up and I'm back to 2+3 only.
The strange thing is that the tachometer wavers (driven straight from the ECU), if I gently blip the throttle the needle momentarily drops and then recovers to 800rpm. Rev it for longer and the needle doesn't match engine speed going to about 1500rpm, occasionally twitching up to the expected level.
Its got me stumped but hoping there's an expert with another idea?

[Aidan Flack]

Thanks both, I've got a new ECU on the way. I was suspicious of it but didn't want to accept the reality!
I think the vibrations might be killing them as it's the second one that's given up (probably)
It has threatened to do it before, but always cleared up within about 1/2 a mile.
Time to crack the current one open and see if there's anything obvious, corroded components is a distinct possibility, what with being a year round Dutton!
I'll update once the new one is in.

[Big Vern]

Does it have an external EDIS module? The coil pack is actually two coils in one and the edis controls the coils so if one is dropping the fault could well be with the edis. The external type is easy in so far as you can swap it for another to see if the fault goes away. Internal edis and you will have to send the ecu for checking/repair.

The rev counter behaviour does seem to suggest internal issues as the clean tacho output comes from the ECU and is not related to the coils.

[James Doulton]

I'm no expert. The rev counter is a strange one as that suggests that either the crank sensor or the ECU. Alternatively it could be a whole bunch of wiring problems but apart from a connector coming lose or getting water everywhere, then that is unlikely.

On the 'only running one 2+3': could it be that it is missing all of the cylinders every other cycle - a bit like running on 2 cylinders but a different pair every cycle. So if you take any two leads off then it still runs but it never runs properly.

Did the problem develop when you were actually driving or was it apparent as soon as you started it (as it would be if someone had tampered with it).