Cylinder balance test in Drive_ Valid?

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Cylinder balance test in Drive_ Valid?

Post by baldy » Wed Oct 30, 2019 12:46 pm

I have been unable to achieve a cylinder balance test result on my car with all electrical loads turned on.
The car is a 2004 VY Holden Commodore with 3.8 liter V6.
I don't think that it has smart charging.
However if I also load up the engine by putting the car into Drive at idle with the brakes on I can usually get the test to work properly. Of course the idle revs are then lower than normal.
Is there any reason why the resulting cylinder balance test figures should not be valid?
All cylinders happen to be between 96% & 100% which seems reasonable to me for this motor.

Steve Smith
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Re: Cylinder balance test in Drive_ Valid?

Post by Steve Smith » Mon Nov 04, 2019 1:55 pm

Hello and thank you for the post, sorry for the late reply.

This sounds like you are using the Cylinder Balance feature of Pico Diagnostics (PD)?

Unfortunately acquiring accurate cylinder balance data from alternator ripple frequency alone is challenging at best. (This is how the PD software displays cylinder balance/contribution)

What you have highlighted is a known limitation of this test based on the charging systems of today’s vehicles. Here is a similar discussion

SMART Charging systems, Cylinder “Cut” features, Hybrid vehicles, Smooth Charging, Long battery cable “runs” Remote generators/storage capacitors, and Multi-Cylinder engines (above 4 Cylinder) all have an adverse effect on the Cylinder balance result.

Throw into the mix an under-performing cylinder and we have a notoriously unstable signal on which to produce meaningful results (Often the software will not allow the test to complete if such an unstable signal is detected)

Rest assured the Cylinder Balance feature of PD will be improved using the crankshaft signal where available

We do have an alternative feature where you can monitor the AC ripple present across the battery when the vehicle is running and the alternator is charging under full load.

Using PicoScope click on the Automotive tab, select Charging Circuits, Alternator AC Ripple/Diode Test
Here you can monitor the exact same ripple monitored using the Cylinder Balance program of Pico Diagnostics.

If the ripple is sufficient and uniform you can then introduce an ignition or injection event to help identity the offending cylinder.

Alternatively (and far better) you can use a Crank math channel to highlight the frequency change in the crankshaft position sensor, therefore determine cylinder contribution.

Could you take a look here

I hope this information is of some help,

Take care…….Steve

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Mark Dalton
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Location: Melbourne

Re: Cylinder balance test in Drive_ Valid?

Post by Mark Dalton » Mon Nov 11, 2019 5:50 am

VY V6 Commodore definitely does not have smart charging.

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