cylinder contribution test

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Jul 5, 2015 | 07:02 PM

jp127761

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From: pa

cylinder contribution test

What are good readings from a cylinder contribution test?

Jul 7, 2015 | 03:22 AM

Steve-l

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From: Germany

How much more vague can your question be? What are you calling a contribution test? If you are referring to an infra-red temp check at the exhaust manifold, then no variation from port to port is correct, any deviation is a fault.

Jul 7, 2015 | 10:06 PM

Beer Barrel

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Cylinder contribution test means only one thing - how much each cylinder contributes to maintaining a specific RPM. This is done by a sensor watching the acceleration induced from each cylinder's power stroke. If you have a poorly performing injector, you may see a cylinder provide less input and the next to fire more input to make up for the loss in crankshaft speed.

Good readings are equal contributions from all cylinders.

Jul 31, 2015 | 03:09 AM

Steve-l

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Beer Barrel,
I'm confused. I understand your English, but you state the obvious. I asked what the OP is calling a contribution test. You responded with a sensor......what sensor? Please describe the test and with what instrument or tool is used. I ask this as a very experienced engineer and other than using EGT, I am unaware of any other sensor. Please elaborate.

Jul 31, 2015 | 02:48 PM

Beer Barrel

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My understanding of the contribution test is that there is a crankshaft speed sensor that can be read by the contribution test tool to show how much each cylinder causes the crankshaft to speed up to maintaining a specific RPM. So, a poorly performing cylinder will cause the crankshaft to speed up less causing the next cylinder to produce more input to bring the RPM to the same speed.

Like this simple thing:

start
1 = good, 750 rpm maintained.
2 = good, 750 rpm maintained.
3 = bad, lets RPM drop to 730. contribution is 97%
4 = good, brings back RPM to 750. contribution is 103%
5 = good, 750 rpm maintained.
6 = good, 750 rpm maintained.
back to 1.
1 = good, 750 rpm maintained.
2 = good, 750 rpm maintained.
3 = bad, ECU provides a little more fuel, 750 RPM maintained. contribution is 103%
4 = good, still 750 RPM. contribution drops to 100%
5 = good, 750 rpm maintained.
6 = good, 750 rpm maintained.
back to 1

I could be wrong, but that's my understanding of it.