Overfuelling problem - a question for the brains trust

[Uncle Arthur]

The car has a developed a small problem which I am seeking the assistance of the brains trust to solve.....

Basically - it's over fuelling. Not all the time - just occasionally.

Cold starts are perfect. Warm starts are also perfect. the car idles up nicely and normal driving brings it up to run temperature. Then at around the 80-90 oC oil temp mark, on a nice cruise throttle level - you know - just rolling along at 60 in 4th, she starts over fuelling. I can see it on the stoich meter - no boost, all green (rich). I can smell the excess fuel in the car. Any application of throttle and she coughs and splutters like she's drowning. If I happen to catch being stopped at the lights, she'll idle at around 2k, which says to me it's not the spark dropping out. If I can get a few really hard boost accelerations, it seems to burn the extra fuel away, but the problem does repeat itself.

It is as though the "choke" is activating. Now I have one possible culprit, and will be hanging the O2 sensor out in case it's a bit dicky. I'm also wondering if the bypass valve on the throttle body might be sticking causing the car to dump fuel in like its cold.

Does anyone else have any other suggestions? It doesn't appear remotely related to the turbo or plug in ECU as the car runs beautifully right up to and right after each little episode - the intermittent nature of the problem suggests to me a dodgy sensor somewhere - just where is the question.....

Can the brains trust be of assistance?

[JBT]

I'd start with the O2 sensor first. After that it will be a process of elimination I guess. Could be the fuel pressure regulator but sounds more like an electrical thing.

[Uncle Arthur]

My research tonight has also indicated the engine water temp sensor could be an issue.

Lucky mine is now located on the front of the engine (coolant re-route) which provides easy access for changing it.

[JBT]

Wasn't the water temp sensor replaced a couple of years ago?

[Uncle Arthur]

Not replaced - just relocated.

[JBT]

Sounds like a better place to start then.

[Uncle Arthur]

$40 - new sensor - installed tonight so I'll try it out tomorrow.

[jules]

Keep us posted!

Jules

[Uncle Arthur]

A problem no longer.......

and somewhere on Brisbane's southside, a guy pulled into his garage pondering a visit to Mercedes because his $100K V6 Kompressor couldn't out run a $20K MX5 with a bolt on hairdryer and clutch spin - in the wet!!!