Discussion
My limited understanding of AFM's is that they measure temperature and airflow and relay this information to the ECU.
I have a couple of questions:
Why are there 2 and is there a difference between them?
What would happen if I swapped the leads over?
I need to test that mine are working properly. I am in the lucky position of having a couple of spares that I can use by substitution to find whether I have a fault in my existing ones.
Is there anything that I should or shouldn't do in swapping them over?
Any other advice?
Cheers
Tim
I have a couple of questions:
Why are there 2 and is there a difference between them?
What would happen if I swapped the leads over?
I need to test that mine are working properly. I am in the lucky position of having a couple of spares that I can use by substitution to find whether I have a fault in my existing ones.
Is there anything that I should or shouldn't do in swapping them over?
Any other advice?
Cheers
Tim
I switched the plugs around on mine the other day in my ever lasting quest to find my emission/running issues. Switching them round seems to make no difference on my car although if you remove the top plug on its own, the engine becomes asmatic. This happens whether you have switched the plugs or not. Removing the bottom one seems to have no effect.
This may mean that the top AFM is dominant over the bottom one.
Of course the other thing could be that my car is completely broken, in which case disregard everything I've said
This may mean that the top AFM is dominant over the bottom one.
Of course the other thing could be that my car is completely broken, in which case disregard everything I've said
Gerald-TVR said:
One does temperature and the other airflow but I dont know which is which
My guess would be that the top AFM is air flow and the bottom one temperature, judging by the effects that removing the plugs has on my engine. I imagine disconnecting the air flow sensor probably has a massive effect on engine running and mine started choking when I removed the top plug.Once again this could be crap
OK I'm going to go off on a bit of a tangent here.
The way the AFM works for airflow with these is it moves a flap which moves a variable resistor which sends a variable voltage to the ECU.
The problem with some of the airflow meters (and I don't know if it applies to the Ford ones or not but I think it does) is that it moves a contact on a carbon track - the carbon track eventually wears and contact becomes unreliable.
What then happens is that as airflow increases you don't get a steady increasing voltage - you get an increasing voltage with spurious voltage spikes on it and as this gets worse the ECU can no longer cope with the electrical noise.
The same principle also applies to the throttle pot.
OK, SO:
The best way to look at these voltages visually is with an oscilloscope.
It just so happens that I have one.
I could be persuaded to bring it to S Club, but what I would really need to make it work easily are some airflow meter leads and connectors - so we don't have to hack around with any car wiring.
(so the bit of loom that connects to the airflow meter and an old airflow meter that we can open up and use the connector from).
This would allow us to connect the scope between the airflow meter and the plug on the car without having to mess with the car wiring. Ideally we'd have 2 sets then we can connect both airflow meters at the same time (my scope is dual beam so you can have 2 traces at once).
Similarly if anyone has a bit of loom and an old throttle pot I could make up leads to connect to that too.
I am likely to be busy on S Club day but if anyone else whats to run this (I'm happy to make the leads etc) then we could have a nice little side show
.
It really needs someone with a bit of electrical knowledge and better still if you can work an oscilloscope but its really not that hard.
The other thing we would be likely to need is a small briefcase generator.
The way the AFM works for airflow with these is it moves a flap which moves a variable resistor which sends a variable voltage to the ECU.
The problem with some of the airflow meters (and I don't know if it applies to the Ford ones or not but I think it does) is that it moves a contact on a carbon track - the carbon track eventually wears and contact becomes unreliable.
What then happens is that as airflow increases you don't get a steady increasing voltage - you get an increasing voltage with spurious voltage spikes on it and as this gets worse the ECU can no longer cope with the electrical noise.
The same principle also applies to the throttle pot.
OK, SO:
The best way to look at these voltages visually is with an oscilloscope.
It just so happens that I have one.
I could be persuaded to bring it to S Club, but what I would really need to make it work easily are some airflow meter leads and connectors - so we don't have to hack around with any car wiring.
(so the bit of loom that connects to the airflow meter and an old airflow meter that we can open up and use the connector from).
This would allow us to connect the scope between the airflow meter and the plug on the car without having to mess with the car wiring. Ideally we'd have 2 sets then we can connect both airflow meters at the same time (my scope is dual beam so you can have 2 traces at once).
Similarly if anyone has a bit of loom and an old throttle pot I could make up leads to connect to that too.
I am likely to be busy on S Club day but if anyone else whats to run this (I'm happy to make the leads etc) then we could have a nice little side show
.It really needs someone with a bit of electrical knowledge and better still if you can work an oscilloscope but its really not that hard.
The other thing we would be likely to need is a small briefcase generator.
the use of an oscilliscope to test would be a hugh advantage, barkychoc i'm jealous!
the best i can manage is a heathrobinson approach of an old pc power supply to gain almost 5.0volts.
as i understand it, both afm's are used by the ecu to gauge/measure airflow, and one used to measure air temperature. the plug with four wires is the one being used to measure temperature and airflow, the plug with three wires just airflow. both afm's have a temperature sensor in, so swapping the plugs over shouldn't have a difference if both sets are working correctly.
if you unplug the unit you can view the terminals, and if you look above the terminals on the plastic plate that attaches the meter you'll see the terminals are numbered from right to left 22,7,9,6.
the afm is terminals 7,9,6
the ats is terminals 6,22
9 is supply voltage 5.0v
6 is sensor return
7 is singal voltage
22 is signal voltage temp dependant
using an ohmmeter to test resistance;
resistance between 7 & 6 flap closed 25-120 ohms; flap fully open below 2100 ohms
resistance between 7 & 9 flap closed 250-600 ohms; flap fully open below 2100 ohms
resistance values approximate, its more important that the flap opens and closes smoothly and resistance increases and decreases smoothly.
resistance between 22 & 6 at 0degC 5k-6k ohms; 10degC 3.5k-4.5k ohms; 20degC 2k-3k ohms
hope that lot makes sense.
bil
the best i can manage is a heathrobinson approach of an old pc power supply to gain almost 5.0volts.
as i understand it, both afm's are used by the ecu to gauge/measure airflow, and one used to measure air temperature. the plug with four wires is the one being used to measure temperature and airflow, the plug with three wires just airflow. both afm's have a temperature sensor in, so swapping the plugs over shouldn't have a difference if both sets are working correctly.
if you unplug the unit you can view the terminals, and if you look above the terminals on the plastic plate that attaches the meter you'll see the terminals are numbered from right to left 22,7,9,6.
the afm is terminals 7,9,6
the ats is terminals 6,22
9 is supply voltage 5.0v
6 is sensor return
7 is singal voltage
22 is signal voltage temp dependant
using an ohmmeter to test resistance;
resistance between 7 & 6 flap closed 25-120 ohms; flap fully open below 2100 ohms
resistance between 7 & 9 flap closed 250-600 ohms; flap fully open below 2100 ohms
resistance values approximate, its more important that the flap opens and closes smoothly and resistance increases and decreases smoothly.
resistance between 22 & 6 at 0degC 5k-6k ohms; 10degC 3.5k-4.5k ohms; 20degC 2k-3k ohms
hope that lot makes sense.
bil
Thats great info and should make it to the FAQ's for future reference...
can anyone say, if everything else on the car is good what the effect of an AFM would feel like?
i.e. if the temp sensor failed...
if the flow sensor failed in one or both AFM's
if a flap became stuck or just stiff
K
can anyone say, if everything else on the car is good what the effect of an AFM would feel like?
i.e. if the temp sensor failed...
if the flow sensor failed in one or both AFM's
if a flap became stuck or just stiff
K
Gassing Station | S Series | Top of Page | What's New | My Stuff