Crank No Start In Cylinder Pressure
In cylinder pressure cylinders 1 and 4 tested. Builds compression on exhaust so I would think no exh valve opening. I am looking for good cam crank pattern.
Also any ideas or input appreciated I am new to Incylinder testing, breather off so I can see the both cams are moving intake and exhaust valves cylinder #4
I'm not the greatest with cam and crank wave forms yet, but what I do if I have a theory like yours I will sync my two ignition events. Example if i think #1 exhaust is not opening and my firing order 1324. I will sync my ignition event on #1 & #3 and look at my in cylinder compression waveform just to make sure that the extra hump isn't actually a TDC compression. hope that makes sense
In the second picture , CYL#1 has the ignition primary signal every other pressure rise.. crank does have the 58 pulses then missing so that should be 1 pressure rise per revolution ? I am just plain confused ATM....
Brain you are correct. I apologize. Because you are getting dam near 172 PSI in compression I would pull that valve cover off and inspect that exhaust valve. You said what are you confused. Tell me what you are confused so I can try and clear it up for you.
any updates ?? findings
As of evening 3/22/19 waiting for customer approval for upper timing cover removal. Customer already has $450 at one shop.. and 2 tows into this vehicle , plus current diag 1 hr...
The things standing out to me are the varying pressure peaks, about 8 PSI differential, the leaning tower (rapid drop in pressure on the expansion stroke compared to compression) Still working on reading these waveforms but that is my gut reaction. I don't have a cam-crank capture for one of these unfortunately so i'm not sure as to the timing either.
You took an in-cylinder on 1&4, but what about 2&3? You can save yourself a lot of time by putting your WPS in cylinder 1, trigger your scope from the ignition command for cylinder 1 & hook a current probe around a negative battery cable and get a relative compression. That compression looks very low for cranking, and with the equal pressure pulse at 360 degrees from the
Good point. I assumed (which is a my bad on my part) that he already did a relative compression.
I did a relative compression test with the scopes software as first step. I am a newer scope user So I do not know if this way of testing ( the pico automotive test with just voltage measured across battery vs just a scope with amp clamp) was a valid test.
Yes, excellent advise - look at the current waveform cranking (relative compression); you should see twice the current demand on the companion cylinder'scompression due to the exhaust not opening on the bad cylinder.
Hi Brian, I just started looking at these myself so I am by no means an expert. A few things stood out was the uneven compression. That could be due to cranking speeds. I'm seeing about a 12 PSI difference (not seen in the upload I put up. That's about 8 PSI) I also noticed that the ramp is not even from where compression builds up to TDC and then the piston starts traveling down. There is no
Setting 0-720 cursors using the pressure humps is not working here. Try using the ignition pulse or CAM's second short pulse to reveal what really happens.
Thanks Dmitriy, I pulled up the 2nd Pico file, didn't have the ignition sync and I got tunnel vision. Pretty obvious once you pointed it out. Much appreciated.
Same here. Thanks Dmitriy!
Brian, couple of things to look at. First of all your middle pressure pulse does not begin to build pressure until approximately 50 degree's ABDC to me if the exhaust valve was not opening you should be building pressure right after BDC at the 180 mark. Also even though this is a cranking waveform there is usually a small amount of measurable vacuum in the exhaust pocket. This doesn't seem to
Thanks everyone for all the feed back!! diag.net/file/f578h0etc… in this picture ( Cylinder #1 ) I synced the 720 ruler with the ignition on signal.. I am still learning pressure testing with scope. this is my 2nd go at it just got my transducer on Friday.. below are from a jeep that the lifter / valve stuck and rocker fell off that one was so easy LOL .. So to day on the VW when I had seen
I believe what is happening is that the exhaust valve is opening 90 deg early. There is no vacuum pocket because the exhaust valve was already open while the piston was moving down. Then it closes 90 deg early which is why pressure is built on the exhaust stroke. It would be great to see a intake vacuum waveform at the same time. I think you could then verify exactly what's happening.
I was doing a in shop training session, and this VW is what they started on the day before, a tow in from another shop that hung cam and crank sensors.. When I first got a look at the vehicle I scoped cam and crank, have not found a good pattern to compare. Then I put the in cylinder tester and knew something was wrong!. I agree no exhaust pocket and looking closer I do believe the pressure is
If you have a vacuum transducer add that to your in cylinder test along with ignition sync.
you have exhaust restrictions to flow exhale air , exhaust valve not opening , we are going to say you have 6 cylinder engine and you have that wave form in 1 bank 3 cyl, you will go first for ccatalyst converted , but second scenario in the same bank . if it only happen on this cylinder you have problems with the specific cylinder . to me that capture where you have the ignition triggers tell
Joel. I would have to disagree with the "exhaust valve not opening " A valve not opening typically causes a very smooth and rounded pocket. I'll post a capture later but once you see one, its unmistakable. That abrupt 90deg change at the bottom of the expansion stroke wouldn't happen with closed valves. Edit: Here is an example from Bernie's website
one of the down side of the in cylinder pressure transducer are variables, over time I have had found several variables in testing , find attached to this the capture of 2009 Toyota corolla with even low compression, where the finding was blown head gasket compression leaking from one cylinder to another all 4 , I requested help for that here and I have a video on you tube too of diagnostic. My
Yes there are many variables for sure, however, there are some universal rules of thumb. If the towers are leaning, you have compression loss, if there is a deep exhaust pocket on a cranking waveform, you have compression loss, if the valve pockets are smooth and rounded, the valve didn't open (or there is some major blockage) Things like that.
stay with the rules of thumbs for sure but believe me on the back of my head are the variables when doing this test. how is normal wave form i am thinking than start analyzing when we find the wave form on vehicle is not working correctly , you can have deep exhaust pocket for other reason for intake restriction too, when I have crank no start and I already found spark and injection pulse and
you are right I was not clear with my statement if he exhaust valve does not open will leave that presure as what he show on that capture
Anatomy of the Compression Waveform Go to "automobile test solutions" and read this article, it has an excellent breakdown for in cylinder pressure testing