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Discussion Starter #1
When you adjust the mixture screw on a Lucas AMM (or any AMM) does it only alter the idle mixture or does it govern the whole output - ie can the mixture be tunned leaner or richer throuhghout the whole range. Turning the screw alters the resistance but is this resistance in series with the voltage output to the ECU? On my 91T16 with a Lambda feedback system the Saab workshop manual says the AMM adjustment is ignored but the output from the AMM must be used when the sytem goes outside closed loop?
 

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I don't know much about this but something that might help. The system goes 'open-loop' at full throttle (IIRC) - so if the manual says it's only relevant at closed-loop time then this might give you a clue (if I'm right)
 

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The mixture screw on the Lucas Amm only changes mixture (across range) if you have an early car without Lamda sensor. Later cars its not connected. Same AMM, just a wire missing from loom and different ECU.
 

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Discussion Starter #5
AFAIK the adjustment on the AMM only adjusts the idle mixture - there is a seperate idle input from the AMM to the ECU. If you want to change the fueling you have to get the EPROM rechipped in the ECU - the standard fuel map is a good compromise between power and economy- if you are having problems with poor performance or poor economy you should look at other things first.
 

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trackside said:
AFAIK the adjustment on the AMM only adjusts the idle mixture - there is a seperate idle input from the AMM to the ECU. If you want to change the fueling you have to get the EPROM rechipped in the ECU - the standard fuel map is a good compromise between power and economy- if you are having problems with poor performance or poor economy you should look at other things first.
Just curious Trackside. Why are you looking at changing the fueling?:)
 

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Discussion Starter #7
I'm not now - I was curious a while back as to why I was getting variable MPG and to see if there was any way to improve it. It averages 31mpg now which is about as good as I can expect for a 15year old car with 190k on the clock.
 

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Fred said:
The mixture screw on the Lucas Amm only changes mixture (across range) if you have an early car without Lamda sensor. Later cars its not connected. Same AMM, just a wire missing from loom and different ECU.
I have an early 1990 Non CAT T16, so my AMM adjust the mixture across the whole range?

I am only getting 23Mpg and you say your getting 31Mpg Trackside:eek:

How lean are you running your engine?
 

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trackside said:
I'm not now - I was curious a while back as to why I was getting variable MPG and to see if there was any way to improve it. It averages 31mpg now which is about as good as I can expect for a 15year old car with 190k on the clock.
WOW! :eek: What have you done to your car to get 31mpg? Serious question, as I have an '89 8v 900i Auto that is currently achieving low mpg, and I would like to know what fixes I can attempt.

My car has been tuned and the fuel mixture toned down more towards the lean side (it would have failed the emission tests, so I was told ;)), but I'm getting it fully serviced, with new bougicords, plugs, dizzy cap & rotor arm, oil/air filters, all done IAW the 24,000 mile service schedule (or 10,000 mile schedule according to Haynes). Hopefully that will solve the issue and bump my mpg up so that the car doesn't use a tank of petrol every 250 miles (notwithstanding the reserve of course).
However, do you have any additional pointers?
 

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Discussion Starter #10
Even on the Non Lambda car the adjuster only sets the idle mixture AFAIK - are you getting different MPG when you adjust yours?. Running lean does not get you more mpg - the correct mixture produces the most efficiency. My setup is stock apart from; ignition timming 22deg idle and 11 on boost, no CAT, heat wraped downpipe, cone filter direct on AMM. I get about 36mpg on a 70mph M-way run - a bit more in the summer. Never goes below 25mpg when going round town even in the winter. I've run T8's and early T16's with similar MPG so I'm always suprised when people say 25mpg is all they can get - maybe they are more 'enthusiastic' drivers. Keeping off the boost is the No1 fuel saver - tweaking the timing, and wraping the downpipe after the cat removal improves low end power quite a lot so you don't need to be heavy footed to drive around.
 

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trackside said:
Even on the Non Lambda car the adjuster only sets the idle mixture AFAIK - are you getting different MPG when you adjust yours?. Running lean does not get you more mpg - the correct mixture produces the most efficiency. My setup is stock apart from; ignition timming 22deg idle and 11 on boost, no CAT, heat wraped downpipe, cone filter direct on AMM. I get about 36mpg on a 70mph M-way run - a bit more in the summer. Never goes below 25mpg when going round town even in the winter. I've run T8's and early T16's with similar MPG so I'm always suprised when people say 25mpg is all they can get - maybe they are more 'enthusiastic' drivers. Keeping off the boost is the No1 fuel saver - tweaking the timing, and wraping the downpipe after the cat removal improves low end power quite a lot so you don't need to be heavy footed to drive around.
Surely that adjuster alters the signal coming out of the amm all the time? So one would have to wonder what use the amm is at all, if its signal is being ignored. Or maybe the amm has multiple outputs?
trackside: I get about 33mpg on long runs. I've just removed the cat, we'll see what effect that has. Will wrapping the downpipe improve mpg as well as low end power? Did you just bend the arm on the distributor to set that advance? Sorry for all the questions :cool:
 

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Discussion Starter #12
The AMM does indeed have 2 outputs - 1 for idle and one for all other running. When you remove the cat the exhaust gets cooler just down from the turbo and this slows the gasflow - wrapping it keeps the heat in and restores low down pull. It just makes it nicer to drive as without the flatspot you don't need to put your foot down as much to try and compensate - I guess this helps economy?. I drilled out the stop tab on the vacuum cap and fitted a bolt head in it's place - th head was ground into a cam shape so when you turn it from the outside it changes the gap and hence the amount of retard - this makes adjustment so much easier. I've said this before but....according to the manual the Lucas 14CUx takes a reading of exhaust gases from the Lambda sensor at idle and then computes the fuel maps for the rest of the engine range therefore adjusting the idle mixture may well have some influence. However I have also observed that the ECU uses the lambda signal nearly all the rest of the time to trim the mixture as it goes along and presumably it learns what is right and wrong to account for any variations in the performance of individual sensors and changes in engine efficiency over time. So if you did adjust the AMM it may well behave diferently for a whie but will gradualy return to what it was before.
 

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Cheers for the reply. Did you remove the front box from the new downpipe or retain it? The pipe narrows as it enters and leaves it, was wonder if it would be worth replacing it, though it could be noisy then :)
 

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I don't have the answer but for reference: my AMM was set at a ridiculously high 1204 ohms. I adjusted it down to below the factory setting to 250 ohms as I am trying to increase fuel economy and so thought I would be leaning the mix. The effect was a drop from 24 mpg to 18mpg, not as expected! Could the lambda have 'over ruled' the AMM and made the mix extra rich to compensate???
I'm going to adjust it to 350 now and see what happens - let u know...
 
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