7MGTE Voltage Drop on AFM Circuit_Help!

**hks7mgt** · 01-12-2006, 05:01 PM

Hi,

Can someone please confirm for me the following conditions on their MA70/7MGTE (later loom model)?

Check that the voltage across KS and E1 is 5V when the ignition is switched on ONLY and when the car is running, that the voltage drops below 4V?

I have an issue with my AFM circuitry and me thinks it's an earthing issue, not the AFM, but i need to rule out the AFM completely first.

Any assistance is muchly appreciated. Thanks!

**ViPeR_NiPPleX** · 01-12-2006, 05:16 PM

do you mean VS and E2? This will be the output of the airflow meter. The karman vortex maf outputs a frequency varying 5v squarewave, or some kind of wave form. So with your multimeter, it's probably not updating fast enough to show the voltage going up and down.

If you have access to an oscilloscope or even could try an led with the correct resistor in series, you might be able to see the output pulsing.

**hks7mgt** · 01-12-2006, 05:22 PM

Nah, Specifically KS and E1. VC and E2 is the main power and signal earth wires.

I need to be sure that on a working car, the voltage actually drops to a consistant voltage once the engine is running (not pulsing).

I see what you're saying, but the Hz signal fires over the voltage without interferernce. and from what i can see, i'm not sure why the voltage should drop according to the circuitry provided by the workshop manuals.

**ViPeR_NiPPleX** · 01-12-2006, 05:22 PM

actually i was looking at the 7mge wiring diagram when i checked that, so it's more likely KS in your case, but i'd still assume E2 for sensors ground.

**ViPeR_NiPPleX** · 01-12-2006, 05:24 PM

hmm, well I dunno

I don't have a 7mgte on me to confirm the situation unfortunately.

**hks7mgt** · 01-12-2006, 05:33 PM

DOH! Thanks for assisting thou. I'm hoping a fellow Toyo driver might be willing to throw a multimeter on there and test it out for me.

Just for reference, the two earths E1 and E2 are different. E1 is an engine earth (true earth) where as E2 is a signal earth to assist with controlling the environment on the sensors themselves. If all sensors were plugged into E1 (or directly to Chassis Earth), all the fluctuation in electrical interference or engine loads, etc, would show on the signal inputs into the ECU.

**RA35GT** · 02-12-2006, 01:03 AM

G'Day mate,

I've taken some photos of relevant pages of the engine manual to help you mate.

Rudi

**Mos** · 02-12-2006, 05:13 AM

The KS signal is a squarewave of variable frequency depending on the air flow.
The duty cycle of the squarewave will determine what the average voltage should be (your multimeter will measure average and not peak voltage, hence the lower voltage).
I have no idea what this duty cycle should be, but if it was 50% your multimeter would read half of the supply voltage.

The "Hz signal", as you put it, is not "on top" of the voltage, it *IS* the voltage - ie the repeated presence and absence of the voltage. The duty cycle is the ratio of the presence to absence of the voltage, usually expressed as a percentage of the complete cycle occupied by the presence of the voltage. Hence if the voltage is present for half of the time of the cycle, the duty cycle is 50%.
The frequency of the signal is the rate of repetition of this presence and absence of the voltage.

Mos.

**hks7mgt** · 02-12-2006, 01:13 PM

Brilliant! Thanks Heaps Mos for the description of the workings of the AFM Signal output (KS).

It's now pointed me in the right direction, to the phone calling up for second-hand AFM's.

Thanks 7MGTE MX73. It was those readings that initially confused me.