Emissions for MOT - idle CO high

[daveo2002]

Hello,

I'm desperate to get this baby through the MOT but bless it there are a few issues going on Can anyone shed light on emissions for a 1995 turbo model please?

According to the MOT sheet from last year, it scraped through last year with an advisory about high CO at idle. The previous owner reckoned it might need a new cat.

I tested it this weekend on my basic gunson and warmed up I'm getting an idle reading of 0.7% CO (plus or minus 0.2 - not the most accurate device). I think this exceeds the allowable level so I'm expecting an MOT fail. Slightly more troubling is the fast idle (1400rpm) which gives a reading of 1.1% - surely CO should go down not up at higher revs?

I tested the lambda probe today and that seems to be working okayish - returning voltages oscillating between 0.2 and 0.8V at roughly 2Hz. I think that's slightly sluggish but it might be that my digital voltmeter cannot keep up.

My gut instinct from the way she drives is that she's running rich. So what's the verdict - is it worth getting hold of a replacement cat and lambda for the MOT man or is it likely to be something else. Incidentally as well - does the engine temp sensor (the one which determines mixture) also inform the infocentre or is it a separate job? Infocentre temps read fine, ironically enough!

Thanks,

Dave

[glasgowjim]

info centre uses a different temp sensor .

[volviz]

info centre uses a different temp sensor .

where is this bastard located - mine died

[Iroll480]

Hello,

I'm desperate to get this baby through the MOT but bless it there are a few issues going on Can anyone shed light on emissions for a 1995 turbo model please?

According to the MOT sheet from last year, it scraped through last year with an advisory about high CO at idle. The previous owner reckoned it might need a new cat.

I tested it this weekend on my basic gunson and warmed up I'm getting an idle reading of 0.7% CO (plus or minus 0.2 - not the most accurate device). I think this exceeds the allowable level so I'm expecting an MOT fail. Slightly more troubling is the fast idle (1400rpm) which gives a reading of 1.1% - surely CO should go down not up at higher revs?

I tested the lambda probe today and that seems to be working okayish - returning voltages oscillating between 0.2 and 0.8V at roughly 2Hz. I think that's slightly sluggish but it might be that my digital voltmeter cannot keep up.

My gut instinct from the way she drives is that she's running rich. So what's the verdict - is it worth getting hold of a replacement cat and lambda for the MOT man or is it likely to be something else. Incidentally as well - does the engine temp sensor (the one which determines mixture) also inform the infocentre or is it a separate job? Infocentre temps read fine, ironically enough!

Thanks,

Dave

I

I don't think it's the cat. The cat does't do much with the CO. The cat only reduces the SOx, NOx and HC gasses, hence 3way cat. The CO is controlled by the lambda. If the CO is too high for the lambda to control it could run too rich by a bad or maladjusted MAF sensor. Have a look at this topic

[daveo2002]

Thanks Iroll. Luckily I am picking up a known good MAF on Saturday so I'll try that first and post an update.

[daveo2002]

Quick update: Measured the resistance of my MAF tonight, that was 863ohm which seems on the high side.

I wound it back down to 443ohm to see if it helped the emissions. It didn't but darkness descended before I had time to set the MAF properly. Tomorrow I will set it again with the LED lead. Should the engine run signicantly rougher with the MAF disconnected? I'm sure my 960 grumbles when I pull the lead. Not so the 480, slight stumble when the lead is first pulled, then business as usual... I'm thinking it's a duff MAF.

Thanks again for the pointers.

[daveo2002]

I do hate emissions gremlins!

Well the new MAF made a difference but a fix it was not. CO is now down to 0.6% on idle, consistent over several tests. Curiously with the new MAF the lambda behaves very differently, now oscillating between 0.2v and 0.5v sporadically. I guess that's the next suspect and its replacement arrived today. Booked an MOT at the garage tomorrow morning to have the O2 sensor fitted and tested so fingers crossed.

Plugs are new and I've replaced the idle air valve with a known good, though I don't think the old one had failed (so a useful spare).

If that fails goodness knows, engine coolant temp sensor, fuel ECU, leaky injectors, burning oil... where would you start?

Dave

[Iroll480]

It's normal that the lambda reacts differently with the good MAF. It doesn't have to adjust the fuelmixture as much as with the duf one. If the lambda has to be replaced, do this only with an original Bosch lambda. Other brands can/will give problems.

[bkf_uk]

High idle + bad emmisions = duff lambda from my experiance with the 440. nice to see that parts of the 440 have been put to good use!
I must adnit i ran the 440 with a universal cheapo lambda from the autofactors and it run perfectly with it.

Also check for any air leaks AFTER the MAF as this will make it run badly as well.

When you do get it running right be prepared for a rotton egg smell from the cat for a couple of miles

[daveo2002]

Well yesterday was nothing if not entertaining. The electrics to the entire rear light clusters went out halfway through the MOT, even took out the rear number plate lights. Fortunately a few digs with a screwdriver brought them back. That'll teach me to leave her parked outside the night before the MOT - grrr! Think I just added cleaning connectors and hunting dodgy earths to my list of fun things to do on a weekend.

But she saved her real move for the emissions test, declaring her feelings on being unceremoniously revved hard for 10 minutes by weeing on the floor and filling the workshop with steam. Cue hurried kettles of water to top her up and emergency resuscitation to her fan motor. Amidst all the confusion she somehow registered a pass on the emissions machine, not sure it could be repeated but there's now a year to work on that so I wasn't going to complain!

From the diagnostic side it was interesting to see her maintain 0.18-0.25% CO for several minutes before radomly going high to 1.2% with the lambda going high as well. All whilst idling at 800rpm. I'm inclined to rule out mechanical skullduggery at this point because I think if she were burning oil or had leaky injectors the rich running would happen more consistently. Guess that leaves lambda sensor, temp sensor and fuel ECU as the suspects.

Hey Bryan - yes those were parts were very timely, thanks again. I haven't fitted the ECU yet but that's on the cards as soon as I've got a cambelt and fluids changed.

[volviz]

2 dave - no other car is capable doing that sort of things except 480