RoverGauge and Lucas afm

[SMB]

Car was seemingly running ok but I finally got round to using RoverGauge on my 500 as part of a general check over. I don’t tend to check mpg.

The long term lambda trim on both banks is +100%, short term much closer to zero. so having got my multimeter out I checked the probes and they seem to have the right resistance and correct voltages, so then moved onto the afm. Following blitz’s advice I checked the voltage at the afm and it started at 0.5 and never seemingly drops below 0.46.v, so I’m guessing I need a new afm asi think it should be 0.3-0.34v. RoverGauge reports 32% direct measurement at idle.

Can anyone confirm my assumption here is correct?

If I need a new one, does anyone have a known good Lucas part to save me risking the Brit part / all makes type aftermarket.
Thanks

[blitzracing]

A good check is to get your test meter on the output and then turn on the ignition- you will get a spike, but it should last only about 1/2 a second as the hot wire warms up. If it takes longer to stabilise you have a problem. This trace is a working one on a 3.9.

[SMB]

blitzracing said:

A good check is to get your test meter on the output and then turn on the ignition- you will get a spike, but it should last only about 1/2 a second as the hot wire warms up. If it takes longer to stabilise you have a problem. This trace is a working one on a 3.9.

I can’t see any real spike registered on the meter, but it seems to stabilise quickly at 0.46 ish volts. JUst sounds high vs the normal figures but the RoverGauge direct measure shows 32% which seems in range but perhaps a little low for a 500, I’ll try again but maybe I need a better meter.

[blitzracing]

The problem is the AFM is very sensitive to low at volumes so so can also be air leaks or low idle. Personally Id get a second hand unit of a Range Rover as they dont get cooked like on the TVR. Chinese ones are a mixed bag to say the least. I personally dont know a supply of new lucas ones. It was a pity APT electronics where doing referb's but last I heard that had now stopped. Might be worth getting a handful of old AFMs together to see if they could do some more if they can get the required components. They are not complex.

[SMB]

Thanks for the suggestions, I can’t see or hear any obvious air leaks, I managed to get another reading on the meter, it spikes to 0.7-0.8v initially and takes 8-10 seconds to get down to 0.34v. , so sounds like afm then?

[blitzracing]

Yep, its knackered then.

[Dalamar]

Sounds similar to the problem I had with my AFM earlier this year. See my notes here and where I sourced my second hand unit which sorted my problem.

https://www.pistonheads.com/gassing/topic.asp?h=0&...