1.3 duratec low rpm misfire when warm (KA)

[jon-]

As I'm totally stumped, and have done a bit of googling without much success i'm putting it to the PH collective genius!

My girlfriend drives the 1.3 duratec version of the Ford KA. About 6 months ago it developed a miss at low RPMs. This miss only happens when the engine is really warm (been sitting in traffic etc) and you apply too much throttle at a low RPM (guessing between 1000rpm and 2500rpm but this version of the KA doesn't have a rev gauge.) It doesn't do it every time and only hesitates once or twice.

The miss got progressively worse (but you could drive around it by avoiding high throttle at low RPM) until one wet night it started running on 3. It was overdue a bit of a service anyway so I replaced the plugs, leads and coilpack along with the oil and filter.

This seemed to cure the problem for a short time, but it's started to creep back after about 1000 miles. Other than a funky ECU i can't think what it could be, but as it only happens when really warm i can't see how it could be the ECU.

Any thoughts would be welcome.

[Spleeble]

Lambda, cat or crank sensor.

[The Wookie]

Might be a stupid question, but you said coil pack, does it only have one? If so, does it have a distributor? It sounds very much like weak spark

[lescombes]

Spleeble said:

Lambda, cat or crank sensor.

If you have done the coil pack........ then +1 start with the Lamda

[jon-]

The Wookie said:

Might be a stupid question, but you said coil pack, does it only have one? If so, does it have a distributor? It sounds very much like weak spark

Might be a stupid question, but I don't actually know the answer! I'm pretty sure it only has the one and no distributor though.

lescombes said:

Spleeble said:

Lambda, cat or crank sensor.

If you have done the coil pack........ then +1 start with the Lamda

I'll try the lambda next, thanks

[jon-]

Just to confirm before I order, it would more likely be the PRE cat sensor that's causing the miss, rather than the POST cat sensor?

They're only £40, but I'd rather buy the one that's most likely causing the miss.

Thanks

[jon-]

Right, I changed the pre cat lambda and no change. Gutted.

Next step will be to test the post cat, but has anyone got any other ideas?

[HellDiver]

Crank sensor? Might be going a bit funny when heating up? Might be worth removing and cleaning before replacing.

[jon-]

Just to update this thread (it's number 1 in google for "ford ka low rpm misfire") I threw another set of plugs and leads at it and it now runs beautifully.

[jon-]

Thought I'd updated this thread, as it still features on google.

Car runs ok for the first 1000 miles after a service then this weird miss fire slowly starts to creep back in when warm.

No idea what it is still, but now the car is approaching 120,000 miles it's safe to say it's not going to break the engine.