Question about RC Test
Hi guys. I am pretty new at the Pico and I was wondering if someone can explain what I’m seeing in this RC test. This van sat for 10 years. Customer got it running and drove it in with a dead miss. Scan tools would not communicate so I did RC test. You can hear the obvious sound of a dead cylinder. At first look, it looks to me like cylinder 6 is the problem. Manual gauge showed 125psi. Pulled the intake and found cylinder 5 port way cleaner than the rest. Camera shows 5 intake valve not opening. Question is can someone explain why it looks like 6 to me on the RC test? My Trace is cylinder 2 injector. I understand that a bad cylinder can affect the next in line. Just looking for a better explanation. Sorry for the long post. Thanks!
An injector event does not happen at the end of the compression stroke for that cylinder (talking about this case, not all engines!), so the labeling is off. To match things up, you need to add a 4-stroke overlay like here: diag.net/file/f663krew9…
As the others have said injection timing isn’t based on TDC, you need ignition to determine cylinder.
Not direct injected engines typically inject fuel at the end of the exhaust/beginning of the intake stroke. In your picture #5 cylinder appears to be injecting (companion of #2), hence #3 seems to be the offending one without compression. You could take samples of spark and injector of the same cylinder on a working vehicle to get an idea of their relationship. In general it's a good thing tu…
I agree completely with your analysis. Since it is only to ID which cylinder is in trouble there isn’t a need for precise timing measurements. An intake valve not opening will not cause a total loss of compression, there is still air in the cylinder , at atmospheric, to compress. The pressure should be near normal. Disabling the injectors is good theory but I don’t think that cylinder washdown…
Stephen, regarding whether an intake valve not opening causes compression loss... - Let‘s rewind back to the 360 deg. mark. The exhaust valve has just closed or is closing, the intake valve is always closed, pressure is atmospheric, the piston is at TDC and is about to go down. What would happen by the end of the induction stroke (540 deg.)? - Once you had enough fun with question 1, here is…
Well,,Here’s another fine mess that I’ve gotten myself into. I haven’t found it in the case study yet but I now see where my thinking went wrong. Thanks for letting me know, again.
You are welcome, glad that my leading question was helpful.
I studied the link that you provided. It verified and enhanced my thought experiment answer to your question. I am sorry to have given information to others that is incorrect.
Geez I didnt even think about and thats why I asked the question. Honestly I’m not sure why I grabbed the injector instead of the plug wire. Rookie I guess. I have done mostly cop systems as we don’t get to many plug wires anymore around here. That’s why you guys are here right?! Lol.
Put your sync on #1 ignition.
The injector will fire before tdc.
Reference off of ignition and you will see your problem I believe. Think about when the injector fires in the cycle.
...Best guess...it stuck a valve and bent a push rod or broke a rocker...get on with looking under the valve cover and fix what ya find...try to free up that valve...bad/varnished gas is what did this...Dan H. ...South Texas...
Shift your identifiers one hump right, the injector fires for the cylinder hump that follows it. -Kyle W._ South Philly
Thanks guys. May have been a stupid question cause it was a light bulb when y’all answered. Wasn’t thinking straight but that’s why I asked. Gotta learn somehow right? I’m gonna re run the test just for my sake and records. As I said I know for sure the vale is stuck. Just trying to get some learning in while I can.
Using the injector as a reference is fine just remember the sequence of operation. —Kyle W.- South Philly
It's easy to go cross-eyed when you're learning this stuff, I know because I'm still learning it too. Don't be worried about asking "stupid" questions, be worried when you stop asking.
It wasn't a stupid question at all. Ive done it in the past and was confused for the same reason,as Im sure others have. Now you know better.
Chris, You are doing great! Keep taking samples and asking questions. You will be giving great advice to others in no time!!! This day and age the fuel timing strategy can be all over the place and will not time with the combustion or compression event. Here is the rule, sync with power (Ignition). It is a good foundation for the cam timing and the combustion event. It will help to pinpoint…
Totally agree with Rick. -Kyle W.- South Philly
Just for a follow up, I did rerun my test while hooked to cylinder 1 plug wire just for fun. I can clearly see the correct cylinder now. Unfortunately For the customer cylinder 5 intake pushrod is bent. Valve contacted the piston, is bent and will not seal. Thanks again for the learning lesson on using injector for a trace! I’m enjoyed learning this stuff.
...Just as I suspected...although the valve to piston contact was unfortunate...the bad fuel caused it to stick ,most likely. ...Dan H.