Hi guys. I'm trying to get a dual capture on my scope. Channel 1 I'm doing a current ramp on the number 1 injector (diesel) and on channel 2 I'm trying to do a relative compression test. I'm trying to do a single capture for comparison in the hope I can pinpoint on a specific bad cylinder compression. Problem I have is - low compression on one cylinder (as shown on a relative compression test I did) and I'm trying to identify which cylinder it is. However, the problem I get is when I attempt the dual capture, it doesn't work out. The time base I have set gives me a clear capture of the injector ramp but poor capture for the relative compression. Relative compression needs its own specific time base to give a clear capture and the current ramp also needs its own specific time base to provide a good capture. Is it possible to set two different time bases on a scope? Or is there a way around this? Thanks
Typically labscopes apply one time base for all measurements to all the active inputs. There is only one scope I have heard of featuring two different time base, it is the e-scope elite. I have not worked with this piece of equipment though. Some links to it:
You will not need two time bases for what you want to capture. The injector signal purpose is to identify a specific cylinder so you can apply the firing order and id every cylinder individually in relation with the compression humps. You don't need to get an injector waveform with many details that short time base would provide. You just need an identifiable sync signal, nothing more.
You also can take the glow plug of one cylinder. The affected cylinder will have no compression during the RC test. This also allows to identify specific cylinders.
What scope you're actually working with?
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Thanks for that info. Scope I'm using is just a low/mid range model that doesn't offer the capacity the Pico brand is known for. Glow plug removal on this truck is near impossible. Too much involved to get to it. Like you mentioned, I dont really need a waveform with that many details, I just need an identifiable sync to relate the RC to firing order thus pin pointing the bad cylinder. Also found out earlier today there was an issue with the scope PC software. Got corrupted somehow. I had to download the software again. I'll play around a little with the settings tomorrow. But I think it had to do with the software. See how I go. Thanks.
If you already have identified at least one of the cylinders has low compression scandata on a lot of common rail disels will show you RPM contributed by each cylinder at idle for example on my own Rover dailly runnner with Bosch CRD1 injection I know cylinder no3 is contributing slighlty less than the other three at idle.
In my case not enough to be significant but I keep an eyen on it.
RPM #1 780
RPM #2 780
RPM#3 774
RPM #4 780
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