Testing the ignition ground 3.2 and 3.0T

[pgill]

MVS readers,

This was discussed on a different thread but I wanted to create a thread just for this.

Without getting too deep into the Electrical Engineering lets just agree that if the ground connection for the coils has too high a resistance then the voltage at the coil will be lower and the coil is essentially a voltage amplifier.

Lets also assume that the voltage for the system is 13 Volts.

If the Voltage drop from the coil connection to the wiring harness on the negative side is high then the coil isn't getting the voltage it needs.

Also lets assume that each group of three coils consume 5 amps (I would need to measure it to be sure)

I measured the 2010 S80 3.2 and here is what I found

50 millivolts = 0.050 Volts

If you go back to your physics text book you will see V = I * R --> R = V / I

0.05 Volts / 5 amps = 0.01 Ohms


This is a very low resistance.

If you make this measurement (and you should) a bigger number for the voltage drop is bad


Engine running at Idle

Here is where to make the measurement

GND_2.jpg (169.08 KiB) Viewed 593 times

Place one of the leads for your Volt meter on the terminal attached to the wire and the other lead on the Battery Negative post.

GND_1.jpg (181.03 KiB) Viewed 593 times

You should be measuring something like 50 millivolts if you measure a few volts then the ground connection is very poor and it should be fixed.

If you make the measurement and you find several volts then reply to this thread and I will offer further advice.

Good luck

Paul

[abscate]

These are very small measured values and I dont think most VOMs we can afford will reliably report 10 mOhm resistance. You cant make this measurement easily while running as the current in the ground loop isnt going to ground but to the ECU

You cant even measure the coil primary easily on COP cars, as the ground is isolated through a trigger Q

[pgill]

ABSCATE,

You are making a good point.

- a good ground connection will show a very low voltage and it may not show any voltage on the meter

- a poor connection should show a high enough voltage that even a very inexpensive meter should read it correctly

Here is the wiring diagram from Land Rover

COIL_1.jpg (40.57 KiB) Viewed 555 times

Without getting too deep in the electrical engineering here is my understanding of the circuit

If the connection at G1E123-1 is poor then a voltage will be present at the terminal

The higher the voltage the larger the resistance

Because the coils are constantly switching the output current is not really a direct current

However the three coils connected to a capacitor should behave close enough to a DC circuit that we can measure as described


Fundamentally the measurement is using Voltage Drop to calculate resistance.

Ideally the resistance should be very low and in my case it is.


Here is the way I am thinking about this. If the ground connection to the cylinder head is very poor then when the coil turns on it will see the battery + voltage level but it won't be able to complete the connection so that the voltage will not drop to zero.

If the connection is good then the ground will see battery + when the coil is switched on and it will very quickly drop to zero (This will be much faster than my Volt meter can see)



Here is the diagram for the other three coils

COIL_2.jpg (44.31 KiB) Viewed 555 times

Hopefully this helps

Paul