I did a relative compression test on my 1997 Dodge Ram 2500 5.9L Cummins it has some blow by. On the test it showed good compression but after every 6 compression spikes there was a down dip that I didn’t understand any help would be greatly appreciated.
Mike T wrote: I did a relative compression test on my 1997 Dodge Ram 2500 5.9L Cummins it has some blow by. On the test it showed good compression but after every 6 compression spikes there was a down dip that I didn’t understand any help would be greatly appreciated.
Is that waveform current or voltage? It looks inverted which'd make your dip the top of the best cylinder's compression stroke....
I can check it again tomorrow if I have time but I’m almost positive. And is there anyway to mark a cylinder on a diesel like this? Like you would with spark on gas?
Mike T wrote: It’s on voltage. I’m pretty sure it’s not inverted. The old truck runs good and strong.
I guess I could have worded my earlier reply betterer. It looks like a cranking voltage waveform that hasn't been inverted. That makes it upside down, compared to a cranking current waveform, with the compression peaks at the bottom of the trace instead of at the top.
It was set at 2v coupling AC and I used my low amp clamp on 60v is that right or should I have inverted it? I’m not positive on if my clamp was on right or not
Yes your waveform is upside down. When the truck first starts cranking is when it will draw maximum current, but in your picture it is going negative. Hit the invert button on your scope.
Also if you notice on the original waveform picture, it looks like (because it is inverted) every single has the exact same amount of compression, and while they should all be very close, I don't usually seem them in a perfect line like that.
There is but I am not 100% certain how.
I *think*:
On those 5.9's there are those connectors by for the valve cover gasket/ injector wiring. I believe if you probed the command wire for a know injector this would allow you to sync TDC of that cylinder with your compression test. But some engines run pre and/or post injections so it you would have to figure out which one is the primary injection. That is the best I have.