MOT emissions fail

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: 2000 W reg 1.6 NB
  2. I’m based near: __West Sussex
  3. I’m looking for technical help or recommendations on: __
    MOT emissions advice please for my 2000 1.6 Mk2 NB, 143,000 miles.

Failed last week with 2 year old BM cat so fitted a new BM one today. Helped with Lamda readings but CO still double! Any advice? Tank fuel or Momentum, blast to get the car hot. Serviced, oil, fuel filter, new plugs leads. No exhaust leaks…

First pic first fail and second photo after new BM cat fitted.

Maf?
Injectors out and cleaned?
Lambda sensor?
Second hand gen cat?

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2

I’d look at the lambda sensor.

3

Thanks for reply.

Even tho Lanmda readings ok?

4

Ah yes, I see that it got through on the 4th fast idle test. For it to be so inconsistent I’d still be checking it.

5

Genuine best one to buy isn’t it?

£170 from The Mx5 restorer or mx5 parts

6

Check the coolent lines that go to the air valve on the intake plenum. If they become blocked, the choke will be fully open all the time. Apparently this can cause a high CO reading. I checked mine a few days ago and one of the lines was half blocked!

7

Thanks Jacob, the small lines that go underneath?

8

Here’s a diagram of the lines I’m talking about.

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9

Thanks will take a look

10

These pipes?

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11

I have a mk1 1.6 so it may be different.

12

Went through all that on my 96; plugs, changed the MAS, new lambda sensor, fuel injectors pulled and reconditioned. The aftermarket cats are junk. The car showed near perfect emissions when a 25 year old genuine cat was fitted.

4 Likes
13

Yes have heard the same about aftermarket cats

14

My previous NC had a similar emission fail. Taking advice on this site, I was told to put a full bottle of Cataclean in the near empty tank, and take the car for an “Italian tune-up”. On the retest it passed with flying colours. As this was the cheapest option, the advice was perfect. Just a thought…

15

Might be a stupid question but out of interest how did you check them?
If you just pull the pipes off doesn’t coolant come poring out?
Also you say yours were half blocked. How did you clean them and the air valve out?
Thanks.
D

16

Yes tried that but no joy

17

The good news about getting the fuel injectors cleaned (properly cleaned) is now the car literally starts on the button.

Looks like the going rate, from a reliable supplier, for a Mk2 factory cat is £500.

But see if you can get the overall engine health to be assessed, eg a compression check.

18

My engine is out and having a rebuild with forged pistons. So it was easy for me to check them. I just scraped the gunk out of the metal parts, then used a drill (slowly and carefully) to pull out any debris. Then replaced the rubber lines.

19

Might try getting the injectors cleaned next

Also I have done the charcoal canister delete, potentially an issue?

20

Ah ok, not an in situ job then.
I’ve just been looking at my 1.8 and it doesn’t seem to have an air valve.
Would be nice to have the equivalent diagram for the 1.8.
Anyone know of one?
Emissions, and particularly high O2 readings, seem to be becoming more and more of a problem as these cars get older. It would be lovely to have a diagnostic flow chart to follow, but as there are so many variables interacting I guess that’s never going to happen, and if it did would probably involve throwing parts at it.
Ah well, may our exhausts be forever clean.
Dave.