The V8 Owners Forum -

Is there a set of diagnostic procedures that you can use to test the 2AM AFM? I'm pretty sure that mine is knackered after a couple of LPG induced backfires and the fact that it is running rich (on petrol), whilst everything else checks out ok?

Can they be repaired (my dad used to be an electronics engineer, now retired..)?

Cheers, Martin

The EFi diagnostics manual gives advice on checking them - they have fuel pump contacts, and air flow meter and an air temp meter which all need to work.

But repair is not really possible - they have a thick film laser trimmed potentiometer surface with two wipers, not something that can be fixed easily.

If you've had a backfire, just open it up and see if it looks OK. It may be mechanical damage to the actual flapper which makes it scrap.

Most people don't do up the big jubilee clips so a backfire just blows the pipe off. Have you got a flap opener? they are supposed to stop a backfire doing any damage?

Chris.

Cheers for the info, I'll have a butchers later, I'm not overly concerned as it runs mostly on LPG anyway and more importantly it passed it's MOT today! Woohoo!

Martin

I've had 2 go on backfires but like you I run mainly on LPG. However, when it came to MOT time I couldn't get the petrol emissions to pass! Not surprising really as it's timed for better LPG performance, and to reduce the risk of backfire! I just stuck it through on LPG and adjusted the emissions to pass... It runs much better now!!

mr_s wrote:Is there a set of diagnostic procedures that you can use to test the 2AM AFM?

It doesn't sound like you have a big problem..more like your flapper spring has lost it's tension and is telling the ECU to provide too much fuel.

First, test the unit. Remove the plug and take the following ohm readings
between Pin 6 and 8: 360 ohms
between Pin 6 and 9: 560 ohms
between Pin 8 and 9: 200 ohms
There are other checks..but that is enough for now if these figures (or close) are the ones you find.

Now you need an C02 tester. If you don't have one, Gunson sells a decent digtial unit for 70 GBP available at any Halfords.

Pry off the cover of the AFM. You do this by running a razor blade between the plastic and the metal and then prying gently upwards between the plug and the top.

Then follow the instructions at http://www.gomog.com/articles/EFIflap.html In your case you can lean it out to as low as 1%.

Can they be repaired (my dad used to be an electronics engineer, now retired..)? Cheers, Martin

Sure. There are places that will bead blast them and refurbish them to new of you want to do that. Cheapest place on the planet is probably Fuel Injection Corp in the US http://www.fuelinjectioncorp.com/ They charge 85 GBP. There are also places in Germany and the UK..(it is a Bosch part) but they are double. Actually, just buy a few for 10 GBPs each off ebay..most will be ok.

If you are going that route..think of getting unit from a mid-80s Jag 4.2. It flows 35% more and uses the same plug. More air, more fuel, more power...appr. 20 bhp on a 3.5

racer

Fantastic information, thanks racer!

I know what I'll be tinkering with later

Cheers, Martin