Tuning for emissions - High CO
Discussion
I've recently put my rather long term project car (1996 MK1 MX5) in for an MOT, the only thing it's failed on is emissions. It's last MOT was in 2011 and back then I was able to sit in the car with my laptop and tweak the VE table until it passed.
I now cannot remember what sort of tweaks are required to pass an emissions test, furthermore I'm no longer allowed to sit in the car whilst this occours so it's a bit of a crapshoot now for the retest!
For both idle and fast idle I'm targeting stoich for the fuel mixture and both those lambda tests passed fine, however at slow idle I failed marginally on CO and at fast idle CO was miles off.
I discovered on slow idle the ignition timing was quite low due to a mixture of realy hot manifold air temps and an idle timing strategy, in the end it was around 6deg. I have it idling nicely on my dirive at 14deg now so I suspect/hope I'll sneak the slow idle test.
However I'm not sure what to do with the fast idle, is there a strategy I can aim for, or are there any additives I could use to help?
the catalatyc converter is present and when fitted and eyeballed from both sides the matrix looked in decent condition. it hadn't broken down and you could just about see through it. Could it just be too old? I don't even know if a CAT affects CO emissions!
many thanks all
I now cannot remember what sort of tweaks are required to pass an emissions test, furthermore I'm no longer allowed to sit in the car whilst this occours so it's a bit of a crapshoot now for the retest!
For both idle and fast idle I'm targeting stoich for the fuel mixture and both those lambda tests passed fine, however at slow idle I failed marginally on CO and at fast idle CO was miles off.
I discovered on slow idle the ignition timing was quite low due to a mixture of realy hot manifold air temps and an idle timing strategy, in the end it was around 6deg. I have it idling nicely on my dirive at 14deg now so I suspect/hope I'll sneak the slow idle test.
However I'm not sure what to do with the fast idle, is there a strategy I can aim for, or are there any additives I could use to help?
the catalatyc converter is present and when fitted and eyeballed from both sides the matrix looked in decent condition. it hadn't broken down and you could just about see through it. Could it just be too old? I don't even know if a CAT affects CO emissions!
many thanks all
GreenV8S said:
Share the actual numbers you're getting.
In general, high CO levels indicates incomplete combustion, typically meaning you have excess fuel.
left the printout at home will get a copy and upload as soon as possible.In general, high CO levels indicates incomplete combustion, typically meaning you have excess fuel.
incomplete conbustion boggles my brain though, the car/engine is smooth and the AFR is 14.7:1 so that's the ideal combustion isn't it?
Richyvrlimited said:
left the printout at home will get a copy and upload as soon as possible.
incomplete conbustion boggles my brain though, the car/engine is smooth and the AFR is 14.7:1 so that's the ideal combustion isn't it?
Fast Idle: RPM:2741incomplete conbustion boggles my brain though, the car/engine is smooth and the AFR is 14.7:1 so that's the ideal combustion isn't it?
CO:1.196 - Fail
HC:100 - Pass
Lambda: 0.994 - Pass
Natural idle:
RPM: 933
CO 1.239
Passing marks are:
Fast Idle
CO: 0.300
HC: 200
Natural Idle
CO: 0.500
Richyvrlimited said:
left the printout at home will get a copy and upload as soon as possible.
incomplete conbustion boggles my brain though, the car/engine is smooth and the AFR is 14.7:1 so that's the ideal combustion isn't it?
Even with the ideal mixture, you can still end up with incomplete combustion due to flame quenching or poor fuel distribution.incomplete conbustion boggles my brain though, the car/engine is smooth and the AFR is 14.7:1 so that's the ideal combustion isn't it?
It can also happen due to cylinder-to-cylinder variation or cycle-to-cycle variation. Ideally the cat would take care of these, but we don't know how efficient your cat is. (Do you have upstream and downstream sensors?)
Don't assume your EGO measurements are accurate unless you know they are. I've had a couple of wideband sensor produce plausible readings which were wrong by about 1 AFR, and I've heard of other people seeing similar problems.
Given that the symptoms suggest it's running slightly rich, I'd be inclined to try leaning it out fractionally and see if that helped. Depending how well you get on with the people at your MOT test station, you may find they're willing to let you do some brief testing for a few beer tokens.
GreenV8S said:
Even with the ideal mixture, you can still end up with incomplete combustion due to flame quenching or poor fuel distribution.
It can also happen due to cylinder-to-cylinder variation or cycle-to-cycle variation. Ideally the cat would take care of these, but we don't know how efficient your cat is. (Do you have upstream and downstream sensors?)
Don't assume your EGO measurements are accurate unless you know they are. I've had a couple of wideband sensor produce plausible readings which were wrong by about 1 AFR, and I've heard of other people seeing similar problems.
Given that the symptoms suggest it's running slightly rich, I'd be inclined to try leaning it out fractionally and see if that helped. Depending how well you get on with the people at your MOT test station, you may find they're willing to let you do some brief testing for a few beer tokens.
Noted thank you. I did try leaning it out a tad, to 15:1 as indicated on the gauge.as soon as I got the car home, but the idle stability dropped off as soon as I did. I'll have a proper tweak this evening.It can also happen due to cylinder-to-cylinder variation or cycle-to-cycle variation. Ideally the cat would take care of these, but we don't know how efficient your cat is. (Do you have upstream and downstream sensors?)
Don't assume your EGO measurements are accurate unless you know they are. I've had a couple of wideband sensor produce plausible readings which were wrong by about 1 AFR, and I've heard of other people seeing similar problems.
Given that the symptoms suggest it's running slightly rich, I'd be inclined to try leaning it out fractionally and see if that helped. Depending how well you get on with the people at your MOT test station, you may find they're willing to let you do some brief testing for a few beer tokens.
I only have an upstream wiideband sensor unfortuantely.it's an AEM with integrated gauge, I send one of the spare outputs to the ECU.which is a Megasquirt3. There's no way of calibrating these, I used to have an Innovate LC-1 which allowed free air calibration, but it also ate sensors so I gave up and replaced with the AEM
The MOT station have been pretty helpful, but they're also permanently busy so not sure I'd get any time from them. They also cited insurance reasons for me not sitting in the building with my laptop so unfortunately I think thats not an option,
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