Emissions problems!

[Bonce]

My car (S1 111S) failed it's MOT on Friday on emissions. The garage reckoned it was the lambda sensor so they replaced it yesterday which cured the emissions on idle, but fast idle is way over the limit even when the car is well warmed up.

Any ideas what could be causing it? I'm worried that

a) the garage are lying to me and trying to fleece me (and succeeding!)
b) it's going to take hours to never really get to the bottom of the problem.

The car has recently had head work after gasket failure, could that be related to the problem? I was also wondering if the Trophy 160 throttle body could cause it to run slightly lean.

Any ideas? What can I do to get it to pass?

[tonykart]

Just being nieve but I don't suppose you've tried swapping out the CAT for a newer one? Do you have any other mods on it like Emerald ECU etc? Could the mixture be too rich?

[Bonce]

They've just called and told me that they now know what's causing it but not why.

The injectors are staying open too long

What could cause that?

[Bonce]

Oh, and in answer to your questions, the ECU is unmodified and the Cat should be fine because it's only been used once before... at it's last MOT!

[Captain Muppet]

Could it be over-fueling due to a faulty temperature sensor - ie thinks it's cold?

Or the trottle position sensor needs adjusting?

Dunno - just guessing.

[fergusd]

Throttle pos sensor is not used to determine fuelling in a steady state, it's only used to deal with transient throttle movement IIRC.

Fd

[Bonce]

OK, it's still giving me trouble! Well to be precise it's giving the guy at the garage a headache and my wallet trouble.

Here are the emissions readings:

Slow Idle:
HC: 0
CO: 0
CO2: 13.9
O2: 1.7
Lambda: 1.09
Air/Fuel Ratio: 15.7

Fast Idle:
HC: 90
CO: 1.8
CO2: 13.5
O2: 0.4
Lambda: .97
Air/Fuel Ratio: 14

Any ideas?

[alunr]

Daft question to an old hand like you bonce but did you reset the ECU when you put the CAT back on?

[fergusd]

So, high CO and HC's tends, to me, to suggest the cat is fecked . . .

Fd

[Bonce]

Alunr: the ECU has been reset by unplugging the battery for 2 hours - is that sufficient?

Fergus, the problem is before the cat so we don't think changing the cat will solve the matter.

The lambda sensor doesn't seem to be doing it's thing. At idle, it's fine, the voltage switches perfectly but at fast idle it doesn't switch at all - the voltage is a flat line, so the ECU is overfuelling the engine.

Could it be a faulty lambda sensor (bearing in mind that it's brand new)?
Any other ideas what could be causing this or what to try?

I'm getting really fed up with this now.

[Bonce]

Update, just spoken with mechanic again and asked him if it's possible the new lambda is faulty. He says that it's working perfectly because it switches correctly when the gasses are ok, but at fast idle the engine is running rich and the lambda is sending out a constant "too rich" signal (+.5v).

So the next thing he's gonna try is looking at the fuel recycling system by disconnecting the charcoal cannister fuel recycling system. Fingers crossed.

[fergusd]

ok you didn't mention the lambda was behaving like this . . . I concur with you in that case ;-)

only other things that have an impact are the map sensor off the plenum and the temp sender to the ECU . . .

Fd

[fergusd]

And I assume the ECU/lambda connection is fine . . .

Fd

[Bonce]

Good suggestions, cheers.
According to mechanic man the Rover/Lotus check tool is showing normal readings from all sensors and no errors.

[Bonce]

Turns out it was caused by high resistance on the wire between the lambda and ECU. He replaced a pin on the plug and voila, it passed.

So £475 for a fecking MOT

On the plus side, it means I can have my car back now!

[fergusd]

Was wondering how you'd gotten on . . . ah well, as you say at least it's back on the road . . .

A rule I live by ever since working for GEC on trains (millions of electrical connections) is, check the connections first . . .

ah well . . .