Hello All,

Sorry for my first post being a problem, but I've been searching for weeks and I've often ended up on passion ford via google with similar, but not identical problems and have been impressed with the users knowledge.

My girlfriend has the 1.3 Duratec (2003+) Ford KA that has a strange missing / hesitation problem.

This problem only occurs when the engine has warmed up (so is running closed loop I think), only at low rpm (I'd say under 3000rpm, but no RPM gauge to see for sure) and feels like the engine is missing once or twice as it accelerates under load.

So far I have tried changing:
Front Lambda (o2 / HEGO)
Plugs
Leads
Coilpack
Oil / filter
fuel filter
Air filter

I have also tried:
Cleaning TPS / TB
Cleaning all engine earths
Unplugged rear lambda sensor and went for a drive, still did it so plugged it back in

As it's ONLY at low rpm and ONLY when the engine is warm I have to assume the ECU is using sensors that are only used at that part of the engine map, but I don't know what. I thought it would be a lambda sensor for sure, but it wasn't.

I'm starting to lose the plot on this one, engine experts please provide a hint! I couldn't tell you if the engine is missing or pinking, there's a definite loss of power like a miss fire and a slight popping sound from the exhaust.

Thanks in advanced.

 

Get the fault codes read and then check sensor readings.
This might be a leak somewhere either in the inlet manifold or exhaust manifold.
But a defective maf-sensor (if it has one) can't be ruled out.

Rear lambda has NO effect on engine fueling, so that's not the problem.

 

Ah yes, I meant to say there are no fault codes

The duratec doesn't have a MAF, though I think it has a MAP somewhere. I guess I'll find it and replace it.

 

We had one like this some time ago , and it turned out to be badly seating valves , have you checked the compressions ... we did the same as you swapping bits and still no joy , so went right back to basics , the compressions all lower than expected i then did a cylinder leakage test and the exhaust valves where not good , took head off and reground seats and fitted valves and it sorted it .

 

Maybe a clogged/defective cat?

Martin

 

JonathanJ, thanks for the suggestions, I think I've a compression tester somewhere, I'll just have to try and work out how to use it

Marty, the cat is something else I've considered, but like with Jonathans suggestion why would it only do it at a) low rpm and b) when it's hot?

I'd have thought something like badly seating valves or a blocked cat would be WORSE at high rpm, but the engine is sweet as to the red line.

 

Well I have had reason recently to suggest that even bent valves work better at higher revs , a customer brought a 1.6 focus black top to me with a low speed misfire , it had suffered a broken cam belt at idle it even struggled to run , but as soon as you lifted the speed up to above 2000 rpm it ran on all 4 .

The same thing was happening on the ka , at higher speed the combustion gases cannot escape fast enough through the valves but at low speeds it caused low compression .

Just my 2 pence worth lol .

 

Interesting Jonathan, thanks. I'll do some tests and report back

 

Update: Emissions were spot on and we can't find any cracks in the inlet or exhaust side.

Compression test is next. I might throw another new set of plugs in there just in case.

 

Have you tried the coolant temperature sensor?

 

Interesting you suggest that, can I ask why?

My gut tells me it's running hot, but without a temperature I can't be sure. the fans come on as they should (ie if the car is sitting in traffic)

 

Well the coolant temp sensor gives a reading to the ECU for cold start etc. It would make sense that this sensor could be giving a cold reading all the time so it works ok when the engine is cold but when it warms up it is still giving a cold reading, thus making the ecu control the fuelling all wrong.

There should be two on your engine, one which gives a reading to the warning light on the dash and one that gives a reading to the ecu. Could be worth a try!

 

Interesting theory, though if the car was running in cold start mode all the time I think I'd have seen a really poor MPG, when it's running fine (at around 45 mpg), also the emissions might have been poor, when they were perfect.

It's something I'll add to the list, after new plugs and a compression test!

 

have you made sure you took the plastic seels of from inside the ht leeds thats wt i foughtot so it caused it to miss