Mercedes M120 Ignition Coil Testing
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MercTech20
- Newbie
- Posts: 3
- Joined: Sat May 13, 2023 6:20 am
Mercedes M120 Ignition Coil Testing
Hey picoscope newbie here, I would like to know how I can test this particular ignition coil design. It seems the ignition drivers are inside the ecu instead of on the COP. Any methods with the basic test leads, I unfortunately do not have the COP probes.
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Re: Mercedes M120 Ignition Coil Testing
Hi.
.
You need to connect one channel to a common power supply wire to measure current.
There are also two separate channels for the control wires.
If there is only one coil per cylinder, it is enough to connect two channels.
The first - is measuring the current on the coil power wire.
The second - is the measurement of the primary voltage on the coil control.
Here is the measurement of the signal on a dual coil with a diagnostic function :
.
.
You need to connect one channel to a common power supply wire to measure current.
There are also two separate channels for the control wires.
If there is only one coil per cylinder, it is enough to connect two channels.
The first - is measuring the current on the coil power wire.
The second - is the measurement of the primary voltage on the coil control.
Here is the measurement of the signal on a dual coil with a diagnostic function :
.
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MercTech20
- Newbie
- Posts: 3
- Joined: Sat May 13, 2023 6:20 am
Re: Mercedes M120 Ignition Coil Testing
Do i need an attenuator when connecting to the other 2 wires. One is secondary coil ground and the other is the primary signal circuit according to the diagram. So the primary coil signal is what i need to check really.vasek wrote: ↑Sat May 13, 2023 7:34 amHi.
.
You need to connect one channel to a common power supply wire to measure current.
There are also two separate channels for the control wires.
If there is only one coil per cylinder, it is enough to connect two channels.
The first - is measuring the current on the coil power wire.
The second - is the measurement of the primary voltage on the coil control.
Here is the measurement of the signal on a dual coil with a diagnostic function :
.
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ben.martins
- Pico Staff Member
- Posts: 502
- Joined: Tue May 16, 2017 1:02 pm
Re: Mercedes M120 Ignition Coil Testing
Hi there,
Apologies for the late reply.
As vasek has mentioned, current is the safest way to measure these COP styles if you're unsure. In my experience 3 wire COP units tend to have the primary winding in the COP unit so you will only have a supply, trigger and a feedback. Much the same as our guided test which can be seen here - https://www.picoauto.com/library/automo ... nt-3-wire/.
However, if you're ever unsure then it is best to use an attenuator regardless of what scope you have. Which scope do you have? If you can let us know we can provide the best solution to capture these signals.
Let us know.
Kind regards
Ben
Apologies for the late reply.
As vasek has mentioned, current is the safest way to measure these COP styles if you're unsure. In my experience 3 wire COP units tend to have the primary winding in the COP unit so you will only have a supply, trigger and a feedback. Much the same as our guided test which can be seen here - https://www.picoauto.com/library/automo ... nt-3-wire/.
However, if you're ever unsure then it is best to use an attenuator regardless of what scope you have. Which scope do you have? If you can let us know we can provide the best solution to capture these signals.
Let us know.
Kind regards
Ben
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MercTech20
- Newbie
- Posts: 3
- Joined: Sat May 13, 2023 6:20 am
Re: Mercedes M120 Ignition Coil Testing
Hey so I found a faulty ignition coil and got it replaced with a brand new one. Still there's slight misfire but after a scan it shows one whole bank misfiring. I was gonna try using a math channel on the crank signal and figure out which cylinders were actually misfiring, but unfortunately the belt tensioner broke and now it cannot be started until new parts arrive. Also the picoscope I use is the Xentry scope(4 channel picoscope) which is provided by Mercedes. There is also another ignition coil with the wrong part number but its new, I'll attach the file. The current ramp is different from the other ignition coils.
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- w140c2ignitionprimary.psdata
- (3.15 MiB) Downloaded 108 times
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- 20230519-0001.psdata
- (25.26 MiB) Downloaded 106 times
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- w140c7ignitionprimaryBAD.psdata
- (4.83 MiB) Downloaded 102 times
Re: Mercedes M120 Ignition Coil Testing
Put 2 wire inductive distributor pickup coils or 2 wire inductive ckp sensors on the COPs using double sided tape. Do 1200-1500 rpm brake torques to find lean injectors. The spark plug burn voltages will rise up when there is a lack of fuel molecules in the cylinder, which facilitates the spark to travel thru the plug's air gap to the plug's ground terminal.
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- Double sided tape to hold the pickup coils
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- 2 GM distributor 2 wire inductive pickup coils and a 2 wire inductive ckp sensor
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- Four 2 wire inductive pickup coils on 4 COPs