Mpg going south - dodgy afm?

[asd2001]

Got a standard 4L and noticed mpg been worse recently (more than heavier right foot might suggest!). Otherwise running well.
Hooked up rovergauge and noticed long term trim at 100%, although short term cycling ok. Tested afm and shoots up over 1v before settling down with ignition on, then c1.9v at tickover.
Does this mean my afm is past it?
Also checked faults on rovergauge last weekend and had a low fuel pressure fault - cleared it and have done around 100 miles since without it reappearing- could it be related. Will change fuel filter to rule that out.
Anyone got a good afm surplus to requirements that I could try?
Cheers
Andrew

Edited by asd2001 on Friday 15th September 22:21

[asd2001]

Any ideas for sources of decent replacements without tvr tax?

[Belle427]

The tests on this page may help, mark will be along soon to offer his expert advice!
http://www.g33.co.uk/pages/technical_fuel_injectio...

[blitzracing]

Which way was the trim? Adding or removing fuel? A low fuel pressure fault would say it was lean, (so adding fuel) and faulty AFMs tend to make it over fuel. Whats the idle AFM reading in direct at idle in percent- it should be between 32 and 35 % (3.9 to 5ltr).? A misfire will give high levels of adding fuel trim, as un burnt mixture looks like a lean mixture to a lambda probe.

[asd2001]

Will check % when I get home. Green bar on the long term trim was 100% to the left (thought it was? ).
Fuel error was historic and didn't reappear after 4 or 5 decent trips. H also shown a lambda sensor error (1 side) but also cleared and hasn't reappeared.

[asd2001]

So after being out for a decent run this morning, the MAF is showing 32/33% and the long term trim moved to -28%(left) +16% (right), then after ticking over for a few mins -32%,+4%.

From what I've read these sound more sensible and the car runs fine - maybe the rich running is in my mind and I've just been more heavy on the right foot more recently ;-). I've not got any fault codes.

Does this sound ok and should I be concerned at all about the AFM voltage readings?

Thanks for your help.
Cheers

[blitzracing]

All sounds OK- I only got about 22 mpg on a 3.9 running the TVR catalyst map.

[asd2001]

Thanks Mark - must be heavy right foot!

[QBee]

My 4 litre was around 26-27 mpg
4.6 turbo driven on the road is 22-23 mpg
5 litre was 19-20 mpg.

Not something they tell you when you are buying.....