Today was the forth attempt at the dreaded MOT.

Car is sound mechanically, however it keeps failing on emissions and it's beginning to get on my wick......

Most recent test readout is below:



and the one prior to that:



Prior test was done with open-loop AFR. Most recent one was done with closed-loop turned on and a target AFR of 14.7:1. The Lambda 1.039 value equates to an AFR of ~15.3, so it looks like for some reason my wideband sensor is running with a +0.5 AFR offset, so I'm going to change the target AFR to 14.2:1 and see if that drags the lambda value down to what it should be.

What affects the CO at idle??? My car runs a "delta rpm" ignition map, where it works in conjunction with a damped response ISC valve to quickly vary timing to achieve the target RPM. The base value was 20° for the first test, and as can be seen changed to 10° for the second test:



However I don't know if that had the affect on the CO or the fact I'd turned closed-loop feedback on.

Any help gratefully received!

http://www.innovatemotorsports.com/reso ... ibrate.php
I also recall JP stocking the sensor in a pot of gas from the cooker but I can't recall what reading that was supposed to give
Half a point is within the calibration drift on a used sensor

I think lean burn might raise co levels so solving that might bring co into line

I guess you're running a cat from those numbers?

Ignition timing might also have a part to play if it's retarded at idle and not allowing a complete burn before the exhaust valves open. You'd see increased HC levels too but that isn't recorded

Generally high CO indicates lack of oxygen in the combustion which would indicate rich mixture, lambda seems to indicate otherwise.

Is CO one of the things that the CAT brings down, in which case could it be a b***d cat ? Otherwise, maybe ignition timing may have a bearing on the combustion causing inefficient burn or similar. The fact you're controlling idle with ignition timing would indicate you're not running at optimum ignition angle.

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I suppose ignition timing would be a good starting point then to get the CO under control. Has anybody got any suggestions for what are typical idle "good" ignition figures for a stock 3SGTE?

I think I'm about 15 degrees advance at idle from memory

Does that include the 10° of base advance on the dizzy?

we just lean the fuel out for the mot with mine and that seems to work to get it throw the MOT

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Louis, it's already running lean, hence the lambda reading greater than 1.0.

In the ECU settings it's being asked to run at a target AFR of 14.7:1, but it's actually running 15.2:1. So I'm going to instead ask it to run at 14.2:1 and hopefully that will then drag it down to the required 14.7:1.

The problem is the high carbon monoxide (CO) reading at idle which may be a result of the ignition timing rather than the fuelling. It may be that with the reduced AFR target value that the CO may also drop to the required figure of <0.3%.

Ah yes that would be a total of 25 degrees Dan.

15.2:1 is leaner than 14.7:1 i have mine at 16.1 for them mot

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Super, 25 degrees of advance at idle sounds like a good starting point then.



Hmm, do you have to pass the closed loop catalytic test in a Crate? Doubt 16:1 would get through TBH.

Test is different if its an earlier ST185

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GT4DC Events Co-ordinator
1996 ST205 UK

mine doesent need a cat test and 16.1 is lean

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Yeah but thats the point - lean is no good for a CAT test as the lambda reading has to be very close to 1.

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1996 ST205 UK

i see

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