MOT Fail on CO emissions

[ben9040]

Hey guys had a quick search on this but nothing definitive has come up. Took my 1990 325i for its mot on Saturday and was fine other than the CO. It has been off the road over the winter (as usual) but was warmed up for a while before testing.

the reading was around 3.8 for CO (max is 3.5) although this did rise up to around 5.0 on idle. Last year it passed on 3.3.

The garage reckon they can adjust airflow slightly to change the CO, is this the best approach or should I look to do some other checks first? Any help appreciated.

[Sanchez]

Shouldn't really be adjusting the afm screw. When was the last service? Do the plugs look good?

[jonny323i]

Don't touch the Afm ever!!!!!

Mine did the same as it had been stood for some time try a good full tunk of new fuel first and a good high rev run

[ben9040]

Had a service last summer including new plugs. The fuel had been in there for a few months so could be that. Battery had been disconnected but I think the ECU had time to get back up and running properly.

[bss325i]

This whole "dont ever touch the AFM" is wrong BUT is it the last thing that should be touched.

[ben9040]

Ok, what else should be touched first so I can rule them out?

[Brianmoooore]

For anyone that needs to ask the question, "don't touch the AFM screw" is correct.
It should only be touched when everything else relevant is known to be working properly, and with a CO meter connected.

[bss325i]

For anyone that needs to ask the question, "don't touch the AFM screw" is correct.
It should only be touched when everything else relevant is known to be working properly, and with a CO meter connected.

This. But to say "don't touch ever" is wrong.

[ben9040]

Thanks guys, the garage suggested they would adjust the screw with the co meter in to adjust the reading but as mentioned I would rather look into everything else first. What should I check first and in what order? I have read about possible inlet air leaks, topping up with fresh fuel and possibly looking at the cat?

[bss325i]

Valve clearances
Check for air leaks
Check blue temp sensor is working correctly
An injector refurb ideally if never been done and not low mileage

Also, being a 1990 car it may have a cat along with an oxygen sensor. If the sensor is fooked, that can ramp up the CO.

Then adjust the AFM if needed and as said, only when connected to a gas analyser.

What were the HC readings?

[bss325i]

There is plenty of info on tuning motronic on the web.

[ben9040]

Thanks, injectors most probably have never been refurbed, it's on 112k so I guess they could do with a look at!
May be worth mentioning it has a speed touch mild chip rather than standard. Going back over the history, the year before the chip was fitted the co was very low about 0.2 at the mot, the following year with the chip it rose to 2.8, think this would affect it?

[bss325i]

I have found that some chip upgrades just richen it up at the top end of the rev range but i have no experience of a speed touch chip.

[broadie]

I had this quite a bit as I used to buy a lot of salvage back in the days before Vic check's.
If you think it's running OK get it hot and give it a good work out up in the revs for about 5 miles. Normally does the trick.

[ben9040]

apreciate the help here, I will give a few things a go and try and get it through. At the worst, could get the AFM adjusted to get a pass then put it back to the way it was (if I mark the adjustment screw up) and spend a bit longer getting everything sorted, don't want a quick fix but could do with it getting through the MOT!

[ben9040]

Update

So I replaced the chip with the standard version and gave it a drive around for 30 minutes. I then took it straight to the centre for the restest.

With the modified chip CO = 3.97 HC = 306

With the OEM chip put back in CO = 0.06, HC = 111

Clearly a pass so thanks for the help. Car feels slightly less smooth with the old chip (barely noticeable most of the time) but clearly the modified chip is causing emsissions to spike

[Brianmoooore]

Going by those figures, and what you say, I'd suggest that your car is now running a little too lean.
Next thing to do is to invest £66 with 'injectortune' (see our traders' section) and send off your injectors to be rebuilt. If your car is like 90% of the E30s around, they will be unbalanced and flowing far less fuel than they should, costing you in both MPG and BHP.
While you're waiting for them to be returned, take the rocker cover off and check/adjust the tappet clearances, as Barry suggested.
Only after that consider adjusting the AFM screw, and set it to around 1% CO.

[ben9040]

Thanks Brian. Tappets and spark plugs were done last summer. I have had her 6 years now and never had the injectors done. Before that there was a couple of "careful lady owners" so my guess is the injectors are 24 years old without having had a clean. It's on the to do list!