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M

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I've been looking into this for a while and have quite a lot of info on the Bosch Motronic AFM.

The main problem with them is the contact strip inside the meter becomes worn as the sliding mechanism wears away the electrical contact surface. This will give erratic voltages and affect the fuelling of the engine. The lambda probe will "iron" out this problem to a certain degree, but it doesn't do it instantly. During my testing, if I had the mixture too rich or too lean, the AFM voltage would take a few seconds to stabilise and sort out the mixture. Imagine the affect of this few seconds as the throttle postion is constantly moved during normal driving !!!!

Anyway here goes:

To test if the AFM contact strip is OK, connect a voltmeter between pin 2 and ground. With the engine idling, you should see a nice smooth reading. Gently open the throttle - the voltmeter should rise accordingly. If it's diving about, the flow meter needs attention.

If the contact strip is suspect, you can do a little modification as follows:

Carefully prise off the black cover on the bottom of the AFM. It's held in place with strong sealant. Inside you will see the contact strip and the wiper arm which is connected to the flap of the meter. Undo the screw that holds the wiper arm in place (note the position of the arm at rest so you can put it back in position afterwards). Undo the 4 screws that hold the rest of the black plastic housing in place. You will now have access to the plate with the contact strip. Remove the 3 screws and carefully remove the plate.
You will see the contact strip is scored by the wiper arm. The idea is to reposition the plate so the wiper has a fresh bit of track to run on. I used a small file and "ovaled" the screw holes so I could slide the plate up or down a bit so the wiper was on a fresh bit of track. Put it back together and check the wiper is on fresh track for the whole of it's movement.

OK, now you have to calibrate the AFM !!!!!


Put the AFM back on the car and connect the cable. Put the AFM on upside down so you can access it's internals. Run the engine until it's warm. Disconnect the signal plug for the lambda probe but the leave the heater wires (the white ones) connected. Measure the voltage of the lambda at idle. You want it to be between 0.35 and 0.65 volts (ideally 0.5 volts). The voltage may fluctuate a little (mine was between 0.4 and 0.5 volts at idle after adjustment). If the voltage is too high, it'll be rich, too low and it'll be lean. If you need to adjust this, loosen the screw that holds the wiper arm and move it gently up or down to adjust the voltage. Once the desired voltage is obtained, stop the engine and carefully tighten the screw up, making sure you don't move it or you'll have to do it again.

So that's the AFM set at idle. What about on the move ???

Start the engine and open the throttle by hand to say 3000rpm. You'll see the voltage from the lambda reach about 0.9 volts as the mixture richens for acceleration. Hold the revs at 3000 and the voltage will settle. Again, you are looking for about 0.5 volts, if not you will have to alter the spring tension. You do this by moving the big black platic wheel. Increase tension to bring the voltage down and decrease the tension to bring the voltage up. Do this with the engine off and only move it ONE cog at a time. After each adjustment, start the engine and check the voltage at your selected higher revs.

Once this is done, replace the cover and put it all back together properly....FINISHED !!!!

I've done over 140miles in the V6 since doing this and the biggest difference is how smooth the car is. Even changing gears is smoother as the revs don't drop away so quickly like they used to.

Like others, I'm not responsible for any damage/loss/death etc etc that occurs from these instructions.

Good Luck...................BOOOOOOOOOM !!!!!!
 

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Blinkin' flip! Marlon is the new "God of AFM".

I think mine's okay but I'm tempted to have a nose about in there ("If it ain't broke, fix it till it is!").

Good job, dude! :D :cool:

Ralf S.
 

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Fair dues Marlon. Great work.
Even my 309 GTI uses a Bosch flap, so I can repair the bistard now!
 

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Good write up Marlon...

Btw have you ever tried starting the engine and then watch the wiper arm when the engine is idling? Gosh; does it flap about or wot? Goes away as soon as the engine is above 2000 rpms.

When I did mine I just moved the "wiper arm" to make it travel on a unused piece of the track instead of moving the pcb. Just a thought :)

-- Hoygs
 
M

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Yeah it does go a bit mental when starting. Mine seemed to settle OK at idle though. It's interesting to watch as it demonstrates the engine air pulses really well.
Maybe it would be easier to try and move the wiper instead. I've got a spare AFM at home.....think I'll have a looky ;)

If anybody follows the above instructions, could you let me/us know how you get on please. Me being the author, is always gonna say it worked great etc etc. Just wonder how others find it ??

cheers
 

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Hi
Where has the 0.5 voltage come from. As I understand it lambda sensors are very carefully designed to read exactly 1 volt at lambda =1, they do this to make it easy for many manufacturers to easily incorporate the sensor without needing to correct the readings and calibrate them for the ecu to understand.

So based on that I would have thought in an unloaded situation on idle the lambda voltage should be 1volt or even leaner at 1.1volts. Even when the car is revved freely the lambda shouyld be around 1volt. Only when the engine is under load i.e. accelerating will the lambda richen up to 0.85 volt or so to give better acceleration. And when it reaches the terminal speed of that throttle setting it should settle once again at 1 or so, some cars even cruise lean at over 1 volt indicated to give better fuel economy. However reading the meter at full blast along the road would be awkward.

have you measured your average fuel consumption since these mods, have they got worse? :confused:
 

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Dom B said:
Hi
Where has the 0.5 voltage come from. As I understand it lambda sensors are very carefully designed to read exactly 1 volt at lambda =1, they do this to make it easy for many manufacturers to easily incorporate the sensor without needing to correct the readings and calibrate them for the ecu to understand.
Well, that's a pretty strange theory you've got there :confused:

The following is an excerpt from this page; http://www.wps.com/LPG/o2sensor.html, concerning the operation of a "normal" Lambda probe, not a wideband Lambdaprobe;

An Oxygen sensor is a chemical generator. It is constantly making
a comparison between the Oxygen inside the exhaust manifold and air
outside the engine. If this comparison shows little or no
Oxygen in the exhaust manifold, a voltage is generated. The
output of the sensor is usually between 0 and 1.1 volts. All
spark combustion engines need the proper air fuel ratio to
operate correctly. For gasoline this is 14.7 parts of air to one
part of fuel. When the engine has more fuel than needed, all
available Oxygen is consumed in the cylinder and gasses leaving
through the exhaust contain almost no Oxygen. This sends out a
voltage greater than 0.45 volts. If the engine is running lean,
all fuel is burned, and the extra Oxygen leaves the cylinder and
flows into the exhaust. In this case, the sensor voltage goes
lower than 0.45 volts. Usually the output range seen seen is
0.2 to 0.7 volts.

The sensor does not begin to generate it's full output until it
reaches about 600 degrees F. Prior to this time the sensor is
not conductive. It is as if the circuit between the sensor and
computer is not complete. The mid point is about 0.45 volts.
This is neither rich nor lean. A fully warm O2 sensor *will not
spend any time at 0.45 volts*. In many cars, the computer sends
out a bias voltage of 0.45 through the O2 sensor wire. If the
sensor is not warm, or if the circuit is not complete, the computer
picks up a steady 0.45 volts. Since the computer knows this is
an "illegal" value, it judges the sensor to not be ready. It
remains in open loop operation, and uses all sensors except the
O2 to determine fuel delivery. Any time an engine is operated
in open loop, it runs somewhat rich and makes more exhaust
emissions. This translates into lost power, poor fuel economy
and air pollution.

The O2 sensor is constantly in a state of transition between high
and low voltage. Manfucturers call this crossing of the 0.45
volt mark O2 cross counts. The higher the number of O2 cross
counts, the better the sensor and other parts of the computer
control system are working. It is important to remember that the
O2 sensor is comparing the amount of Oxygen inside and outside
the engine. If the outside of the sensor should become blocked,
or coated with oil, sound insulation, undercoating or antifreeze,
(among other things), this comparison is not possible.
 

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Hoygaard said:
Well, that's a pretty strange theory you've got there :confused:

.[/I]
No thats pretty fair, I just want to make sure i am setting the correct voltage based on published information, and i had just seen something about 1 volt written somewhere so wasn't sure.

I'll have a play measuring mine tomorrow.

While we are here talking about mixture and stuff, does anybody have emmisions figures from a V6(EC) from a recent mot printout to get and idea of other peoples emissions levels to compare to mine, that i will try and dig out?
 
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Discussion Starter #10
Here's mine from my last V6 MOT:

It's a good high speed razz to my MOT tester so the engine and cat are nice and hot when my cars are tested.

FAST IDLE TEST
CO level @ 2586rpm = 0.00%
HC level @ 2586rpm = 9ppm
Lambda @ 2586rpm = 1.01

NATURAL IDLE TEST
CO level @818rpm = 0.00%

The sensors etc were all new on the car just before the test along with new airfilter and plugs, oil etc etc.

I think Speedy gets results like these for his V6 too.
 

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My V6 seems a little different.

I dont know whaty is going on with the rpm on the test sheet but it says the test limits are between 2and 3000rpm but the actual recorded actual value was 65535!! so i dont quite know what that means unless i have installed a gas turbine under the bonnet lately.

But lets assume this was between the proper limits, and this was with a new lambda sensor about a week before.

CO % vol 0.10 @ 2-3000rpm
HC ppm Vol 19 @ same
Lambda 1.00 @ same

Natural idle test
CO % vol 0.02


So it would seem I am a bit rich.

The idle hunts at cold start up at the moment, and The idle motor has been out and checked to move very freely and is very clean, but it throbs on cold idle. After she has got hot(she is running a little cool too even with a new thermostat, about 85deg as opposed to 90deg dead on when I first got her) then if I clutch it, it idles at about 1200rpm then as the car stops and idles for a bit the revs slowly go down in steps, to the correct level, and for the most part is fine from then on.

This might tie in with when the lambda probe goes back into closed loop and starts correcting the mixture again.

I seems. When the car has got off of cold start and is allowed to idle with lambda in closed loop it eventually makes the mixture correction and then runs fine??Perhaps

So is my air meter the source of the problems?? I am going to do some voltage reading :(
 

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Sorry to drag this old dog up again :p

but when I try to get a reading from the lambda sensor it reads 0.8ish then you make the most minute change to the wiper arm and it drops off to 0.1 or just reads 0 and a minute flick the otherway it reads 0.8 again, I just can't get sensible readings from it.

The sensor is just a few months old and I gave the car a good clear out to make sure the sensor was clean, and I have checked the fuses for the heater coils and all seems fine. :confused: :confused: :rolleyes: :confused:
 

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It does seem to run a little rich yes. I assume these readings are open loop readings? Have you tried pulling the dipstick up? That way the engine sucks in a little fresh air and running leaner. Works on most cars, not sure about your vee-six. You could also try to pull the breather hose of and see if the reading drops.

Whats the reading when it's running closed loop?
 

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Hoygaard said:
It does seem to run a little rich yes. I assume these readings are open loop readings? Have you tried pulling the dipstick up? That way the engine sucks in a little fresh air and running leaner. Works on most cars, not sure about your vee-six. You could also try to pull the breather hose of and see if the reading drops.

Whats the reading when it's running closed loop?
A little rich, how does 100miles at half a tank sound!!!!!!. Yes the readings are open loop, I start the engine with the sensor disconnected instead of disconnecting it after is is running. I haven't tried the dipstick trick yet, but even if I manage to set the mixture with this trick it will be all undone when i plonk the dipstick back down unless I drive aorund with it up (saltwater).

I cannot check the readings closed loop as I need to make up a lead yet.
 
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Is you AFM ok ???
You say the sensor is pretty new. Is that the lambda sensor ???

Remember when this is disconnected, it won't alter the fuelling. My AFM did a similair thing to yours when I first had a looky. After I did the "mod" to run the wiper on a fresh bit of track, it was quite easy to adjust the readings, although minute movements were still needed.
 

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Of course you should not drive with the dipstick pulled out. You implied that the sensor was perhaps faulty, and one way of testing it is by leaning out the mixture by fidling a bit. Once tested the dipstick should of course be put back in properly. It was NOT MEANT AS A FIX :rolleyes: ;)
 

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I had another go after my mpg was at 14mpg. I then tried to lean it more, but then under load the injector light was coming on intermittently which I assume is the knock sensor doing its thing which is not good. I was out that day and I started the motor and it was ticking over roughly and any increase in thew throttle caused the engine to die. I read the fault code which was 1122 which I think means lambda sensor even though it is not on the list. I waggled all the plugs and tried again and all was back to normal if not still lean.

So I tried again, but I can edge up to 0.75 ish then after there ia a point where the lambda readings flick from 0.8 dropping to 0.2 then through 0.45 and back to 0.8, but this is such a micro move that was only possible with alterations to the spring tension too. (I think if I put a capacitor about about 1 micro farad across the test meter wires it should smooth out the fluctuations and give the reading of the average volts at any time.

I took the car out and it pulled well and felt good with no injector light under load. However I took a long motorway journey yesterday and measured the mpg which came out to be 18mpg, and normally I would expect 31 or 32 on a motorway trip, (25-27 on normal home driving with the odd blast) So it is still mega rich and any further tiny movement of the wiper arm makes the lambda reading go to 0.

And in the 15 manual in the electrical diagnostics section the lambda probe test says thet it should read around 0.7 volts?
 

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Sounds like a good bit of technical investigation. :cool:
I assume it's valid for all flappy AFM Alfa's? could be useful on my 164

Is there maybe an argument for a general technical section, for things like this where parts are common across several models?

Think I'll stick a little post in the request forum or whatever it's called.
 
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This'll work for all the flappy meters.

Dom....31 or 32mpg on a run and 25 to 27 normally !!!!
I get about 25-27 on a gentle motorway trip if I'm lucky and normally about 20mpg to and from work. I was getting about 16mpg before tinkering.

I didn't ever get over 30mpg with my 1.8litre 8v Silverstone !!!!
 

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These are genuine figures. When I first got the car i brought it from scotland and I filled it up to the brim at east kilbride and then drove all the way to oxford at 78mph being extra careful to not move the throttle too much ( I was skint having just bought a car.) and then got off the motorway and filled it up to the brim and calculated the milage and fuel and got 34mpg. :p

I always fill the car to the top and do the odometer so I can monitor the mpg, and I write the mpg on each receipt. When I first got the car normal country driving with the odd blast would always return 25mpg always always it never seemed to change, I have hundereds of receipts with mileages to prove it. Then last summer I spent a month with the induction system apart, and I removed all the steps and restrictions from the injector plates the choke tubes, including the rubber connectors that foul free flow quite a bit and the manifold. If you look at the manifols the holes to the tubes are not in the centre so I made a tool and marked the real concentric centres and opened them out and smoothed the internal casting marks. I also turned down the throttle spindle and made the butterfly a more aerodynamic shape, and fitted a green cotton filter in a specific cold air box isolated from the hot engine air.

............and after all this there was no performance increase, however it did increase the mpg to 27 :) all the time except major ragging, again I have loads of receipts to prove it.

Then the airmeter got dickie with the strange resistance and throbbing on start up high idle speed etc and 23mpg (rich) which is when I started to play with the airmeter, which had bad resistance readings (after new lambda sensor a few months previous) and here I am today trying to get the mixture adjusted but not too rich. :(
 
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