S3C Slight hesitation on part-throttle

[NaCl]

Half way through a long run out yesterday, the engine developed a slight hesitation at part-throttle.
It still felt normal under full acceleration, but just pootling around at 40 to 50 in 3rd or 4th, it was just noticeable.
I've checked the dizzy cap, leads and spark plugs - all good. Plug electrodes are all the same good colour. All breather hoses and induction hoses seem okay too. Coolant temp and oil pressures are fine.
Its a de-catted S3C with two years of excellent service up to now.
Any clues/help/advice would be appreciated.

[GreenV8S]

Maybe a worn throttle pot, if it tends to happen at around the same throttle opening?

[NaCl]

It seems to be most noticable around 2000 rpm.

By throttle 'pot', do you mean potentiometer?

I forgot to mention that the problem arose suddenly on a particularly bumpy mountain road. It first started as a proper misfire, leading me to believe we were about to break down in the middle of nowhere, but it quickly setted to this barely noticable hesitation. My first thought as I was thinking about phone signal was that an exhaust oxygen sensor had gone and the ECU had compensated (I don't know how to check them to test that theory) - then a bad engine earth - then a faulty injector - (etc, etc).

Edited by NaCl on Tuesday 26th April 07:38

[RayTVR]

Throttle potentiometer looks like this and is on the opposite side of the throttles from the cable. clicky

For diagnosing lambda sensors etc. there is a Ford fault code reader that can interrogate the ECU and identify such faults. Called a 'Star Tester' there are at least a couple withing the community, I have one and the very correctly spelled Phillpot also has one. Are you going to S Club?

Edited by RayTVR on Tuesday 26th April 11:14

[NaCl]

Thanks for the link Ray. I do hope to get to the Meet at Stoneleigh on Monday.

[phillpot]

RayTVR said:

I have one and the very correctly spelledspelt Phillpot also has one. Are you going to S Club?

I am indeed the "guardian" of a Star Tester kindly donated by an ex-S owner. Happy to bring it along to SCH, if your going?

[glenrobbo]

phillpot said:

I am indeed the "guardian" of a Star Tester kindly donated by an ex-S owner. Happy to bring it along to SCH, if youryou're going?

EFA


Sorry, I couldn't resist it. I dunno wot come over me.

Edited by glenrobbo on Tuesday 26th April 10:40

[RayTVR]

[glenrobbo]

Just checked:

Spelt: A hardy form of wheat grown mainly in Europe.

Spelled : What the witch did.

[phillpot]

glenrobbo said:

EFA


Sorry, I couldn't resist it. I dunno wot come over me.

It's a fair cop guvnor

[LawrieS]

Is this one of the fault readers you are referring to?

[phillpot]

LawrieS said:

Is this one of the fault readers you are referring to?

It does look like some sort of Fault Code reader

To the left of the book is the "official" Star Tester and a Draper version to the right....





I've never actually tried to user either, it's all to clever dicky for me ...

[NaCl]

Ray / Mike,

I'm going to the S Meet on Monday if either of you would't mind bringing your fault code reader along. I've no idea how to use it though, would one of you be able to oblige? Also, could you advise where it plugs in? I might have to do a little spaghetti re-arranging if it's under the passenger side dash behind the glove box if it is somewhere in there...

[TVRees]

NaCl said:

By throttle 'pot', do you mean potentiometer?

You can check the resistance of the TPS (throttle position sensor) with a standard multimeter, set on Ohms. The resistance change, as you open and close the throttle, should be nice and smooth.

NaCl said:

.... My first thought was that an exhaust oxygen sensor had gone ....

If the car is de-catted, do you still need the Oxygen sensors ? My non-cat S2 doesn't have these.

Edited by TVRees on Wednesday 27th April 22:07

[phillpot]

NaCl said:

Ray / Mike,

I'm going to the S Meet on Monday if either of you would't mind bringing your fault code reader along. I've no idea how to use it though, would one of you be able to oblige? .

Will glady bring it along, but....

phillpot said:

I've never actually tried to user either, it's all to clever dicky for me ...

Maybe someone who does know what they're doing could run a seminar?

[GreenV8S]

TVRees said:

If the car is de-catted, do you still need the Oxygen sensors ? My non-cat S2 doesn't have these.

It would depend on the ECU, but if the ECU think it's working with a cat then it will almost certainly be relying on lambda feedback and will then have to revert to a fallback mode if the lambda sensor input fails. Depending on the ECU and how it has been configured, that fallback mode might work just as well as the normal mode, or it might be terrible.

[RayTVR]

NaCl said:

Ray / Mike,

I'm going to the S Meet on Monday if either of you would't mind bringing your fault code reader along. I've no idea how to use it though, would one of you be able to oblige? Also, could you advise where it plugs in? I might have to do a little spaghetti re-arranging if it's under the passenger side dash behind the glove box if it is somewhere in there...

I'll bring mine along.

I have used mine in anger. It checked out fine on mine, and on a friends car it did diagnose the cause of rich running as a faulty coolant temperature sensor.

It's pretty easy to use, and is actually a prett clever piece of kit, running through cycles of controlling the engine at different revs etc. Mine is different to Phillpott's but is a proper Ford service tool.

Now where did I put it?

[AutoAndy]

Hi Andy, I will be at S club on Monday as well so will poke my nose into whats going on...I have a similar issue with my de-catted S3C so tended to solve by never driving slowly, but that doesn't really work on show grounds and in traffic etc...

I changed my throttle pot but no difference (it is easy to try though).

Had some improvement when I had the injectors cleaned, two were shown to be slightly blocked...apparently this happens after about 60-80k miles if you don't otherwise add cleaner every now and then

Edited by AutoAndy on Thursday 28th April 18:19

[NaCl]

Thanks for the messages chaps.

Its just a bit strange how the problem suddenly started while driving over a particulary bumpy section of Welsh tar.

Look forward to seeing the fault code reader (or readers) in action on Monday. Hopefully not too many codes appear during the seminar.

I'm hesitant to get a new TPS just yet and will try to test it with my meter as suggested. Don't suppose anyone has a known good spare TPS for a 2.9 they could bring along that I could try round the show ground to see if it is mine that's causing the problem?

I did actually add some injector cleaner the day before, not that it 100% prevents any problems...

Edited by NaCl on Thursday 28th April 16:33

[NaCl]

Sorted!

It was a broken wire to the water temperature sensor.

Thanks for your helpful comments and advice.

Thanks too to Ray and Mike for offering to assist with fault code reader test at SCH (which I couldn't get to in the end).

Andy