Well it failed! Tester thinks it’s the MAF. Both CATs read the same so likely to be inlet side.

Is MAF adjustable/cleanable/ replicable

94 plus 8 3.9 Efi

All help gratefully received

Thanks

Speak to John Eales
J E Developments
01455 202 909

I do have a spare AMS/MAF which you are welcome to "borrow" if nothing else can be found. It is untested so there is some risk , but I purchased it as a spare a few years ago. However I am away from this weekend for a week , so won't be able to help much after tomorrow.

Years ago when living in California my 94 +8 failed the SMOG check, I cleaned the MAF with a sensor spray cleaner bought off the shelf from the local auto store. Worked a treat as it passed the next day and for ever more!!!!

Assume it is the Max Lambda. Just confirm they are using max allowed 1.05 as per Driver & Vehicle Standards Agency In service exhaust emission standards for road vehicles (eighteenth edition ?).
I have noted that most MOT stations use a max of 1.03 for my 4/4, but the above publication quotes 1.05, the same as the V8s.
If you note the same, you can download the publication from Gov Website. Sorry don't have the link, but that is where I got my copy. The copy always goes to the MOT station, just in case. On Monday my 4/4 passed but at 1.03, so OK.
Oh Lower is quoted as Min 0.9

I had a similar problem with the Roadster.
In the end I had to buy a new Ford air flow sensor, cleaning didn't help.
Once the new one had been fitted I had a close look at the old one. They work, I understand, by measuring the temperature drop across the heated wire caused by the air flow. The old one had what seemed to be almost glazed on gunge at the two ends which I think acted like an insulator.

The BMW V8 in the Plus 8, at the same age must use a different way of measuring air flow, the MOT results last year gave a Lambda of 1.006, the max limit shown is 1.03, as mentioned above.
So why don't they use 1.05 if that is in the D&VSA documents?
A perfect Lambda result is 1.000.

The CO was 0.03 %, limit is 0.2%
Hydrocarbons 12ppm, the limit is 200ppm.

So the engine seems to work as designed.

Thanks all for the above. I’m going to have a look tonight.

JE tried to help but were not too successful

There are some replacements available for Range Rover 3.9s for not too much money on eBay (£80), but they may or may not help

I understand it’s possible to adjust something with a screwdriver but without an emissions meter it’s not easy to know if that does anything or not.

Think I’ll clean it and see if that helps, my MOT guy is pretty good and ‘gets’ older cars

Get the Morgan vibes come in my way....—__—__—__

Thanks chaps

What’s it actually failed on?
Some numbers would help please

Here’s some photos hopefully.

One shows the fail sheet

Another is what I believe is the tiny Hotwire that can be cleaned

The third is some sort of adjustment screw. Chap at JE (not John) said turning his ‘might’ alter the emissions

There are specific emission levels for the 3.9 Plus 8 - Lambda is 0.9 to 1.05 , idle CO is 0.5 , fast idle CO is 0.3, HC is 200
These are listed in the 'In Service Exhaust Emission Standards for Road Vehicles'
For some reason the exhaust emission analysers don't seem to pull up this data

I appreciate that you are currently outside of these limits.

As there is no MIL light on the 3.9 there could be a diagnostic error that you don't know about, may be worth getting the codes checked

As well as the MAF it could be worth checking other common items, are the lambda sensor heaters working, is the engine temperature sensor working, and is the fuel pressure correct ?

Best wishes

Mike