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mwebb Senior Member Offline Posts: 162 Gender:	Re: firstlook Reply #30 - Jun 9^th, 2007 at 7:39pm and zoomed in on the valve opening and closing events , that is not measured using FLS althiugh i believe the hi pressure FLS sensor can do this , i used a Fluke PV 350 .
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mwebb

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Re: firstlook
Reply #31 - Jun 14^th, 2007 at 9:16pm

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it is hard to find actual valve timing specifications , and
sometimes values provided are wrong .
so if you capture a running compression wave form with a
pressure transducer in place of a spark plug , you can use
the active cursor function in ANNOwave to measure exactly
when the valves open and close ,
to check for and confirm jumped timing components .

of course with out a known good reference it may not be
helpful.

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Rick Hill

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Re: firstlook
Reply #32 - Jun 15^th, 2007 at 12:10pm

That's good Michael. If I were looking for cam timing problems it could be very usable but I wouldn't bet on the the exact timing that shows I think I could work with the symmetry of it though in verifying cam timing with out any problem.
What kind of vehicle is that? What ever it is that cam is ground on pretty narrow lobe centers with a 100.5 degree displacement angle to be in a passenger car. I seldom see displacement angles this narrow on anything. Even though it's bottom timing would appear to be installed straight up it's actually installed 2.5 degrees retarded with the intake lobe center at 103 degrees after tdc and the exhaust lobe center at 98 degrees btc. With 224 degrees duration showing on the intake and 214 on the exhaust I would guess it was at least a 3.0 or larger engine. I wouldn't expect to see much change in the waveform until the valve was a ways off it's seat either.

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mwebb

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Re: firstlook
Reply #33 - Jun 16^th, 2007 at 7:58am

Rick Hill wrote on Jun 15^th, 2007 at 12:10pm:

That's good Michael. If I were looking for cam timing problems it could be very usable but I wouldn't bet on the the exact timing that shows I think I could work with the symmetry of it though in verifying cam timing with out any problem.
What kind of vehicle is that? What ever it is that cam is ground on pretty narrow lobe centers with a 100.5 degree displacement angle to be in a passenger car. I seldom see displacement angles this narrow on anything. Even though it's bottom timing would appear to be installed straight up it's actually installed 2.5 degrees retarded with the intake lobe center at 103 degrees after tdc and the exhaust lobe center at 98 degrees btc. With 224 degrees duration showing on the intake and 214 on the exhaust I would guess it was at least a 3.0 or larger engine. I wouldn't expect to see much change in the waveform until the valve was a ways off it's seat either.

that is a 1987 Porsche 944 ,2.5 liter 4 cylinder engine auto trans , red . basic version . 60k miles . no indications of any problems . AC repairs underway .

notice the descending value right after TDC ,    does that little dimple belong ? or is that an indication of a problem , leak . either way it is a minor change that is reflected in the waveform ,
   the piston is moving down, accelerating , all valves are closed .
      all the lines should be straight there . no abrupt change s . ????
   and yet there it is .

i think that that does show exact valve timing , i find that any change in pressure shows up right away [see above] in the waveforms , i was concerned that the engine speed might vary slightly and skew the the values and i cant say that didnt happen but at 2k rpm i think the effect is lessened.

since i selected every other TDC and set that space between to equal 720 degrees , if engine speed changed in the middle my measurements would be inaccurate . next time i need to add ckp to confirm .

pressure transducers do not usually line up with them selves , they all seem to have some small delay , but if there is only one transducer being used the delay is uniform across the waveform , not a factor .

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Rick Hill

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Re: firstlook
Reply #34 - Jun 16^th, 2007 at 11:57am

Quote:

that is a 1987 Porsche 944 ,2.5 liter 4 cylinder engine auto trans , red . basic version . 60k miles . no indications of any problems . AC repairs underway .

notice the descending value right after TDC , does that little dimple belong ? or is that an indication of a problem , leak . either way it is a minor change that is reflected in the waveform ,
the piston is moving down, accelerating , all valves are closed .
all the lines should be straight there . no abrupt change s . ????
and yet there it is .

i think that that does show exact valve timing , i find that any change in pressure shows up right away [see above] in the waveforms , i was concerned that the engine speed might vary slightly and skew the the values and i cant say that didnt happen but at 2k rpm i think the effect is lessened.

since i selected every other TDC and set that space between to equal 720 degrees , if engine speed changed in the middle my measurements would be inaccurate . next time i need to add ckp to confirm .

pressure transducers do not usually line up with them selves , they all seem to have some small delay , but if there is only one transducer being used the delay is uniform across the waveform , not a factor .

Hi Michael
I'm not sure what that dimple is either. Some kind of turbulence right near the plug or could there be some valve leakage? I thought at first it might have to do with piston transitioning from acceleration to deceleration bu it's too early. That would happen somewhere around 5 ms after tdc I think or somewhere between 60 and 80 degrees atc depending on rod length to stroke ratio if I'm right in assuming you have 9ms per division up there.

I agree that in looking at events with a pressure transducer the delay is not a factor as long as we're not trying to compare timing to electrical events or to another transducer and any events in the waveform itself are relevant. What I meant by not seeing much change in the wave form until the valve is a ways off it's seat is that there wouldn't be any effective flow until the valve is off it's seat a ways. In other words I would expect to see the change in the wave form on valve open events be a little delayed to actual seat timing and valve closing events to show up a little earlier than actual seat timing. I of course couldn't really know that with out actually checking that the old long way with a degree wheel and indicator.
What that wave form does show is that we can identify valve problems and we can identify cam to crank timing problems at least as long as there on the order of a tooth or so at the cam drive.
I really like your anno wave program and I'll have to put that on my list of things to get. I've also been limited to using my pv/500 (same as the pv350 just an earlier version but the exact same transducer and circuitry according to the fluke repair center) Mine has had a few failures along the way and has been to the repair center a couple of times. I've been thinking about upgrading to some different pressure transducers that would offer better resolution in their respective ranges such as the set that ATS offers. I just haven't been able to spend the money quit yet but I will eventually. Do you have any suggestions on transducers?

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Romain. Senior Member Picogroup Offline Deceased Posts: 212 Gender:	Re: firstlook Reply #35 - Jun 17^th, 2007 at 8:53am Hi Michael, I'm curious about that slight bump in the pressure waveform, have you made any comparison with the other cylinders to see if this is uniform throughout the engine or just a signature to that one cylinder only ?
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mwebb

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Re: firstlook
Reply #36 - Jun 17^th, 2007 at 11:57am

Quote:

Hi Michael,

I'm curious about that slight bump in the pressure waveform, have you made any comparison with the other cylinders to see if this is uniform throughout the engine or just a signature to that one cylinder only ?

i have seen an dimple in another car that did have a bad / leaking exhaust valve ,
the waveform is below, 1998 bmw 528 , i do not know what significance the dimple has , that cylinder did have a leaking exhaust valve BUT i cant say what if anything in the waveform may indicate that .

   i will stack up 3 cylinders from that car and see if there is a difference .

i did not record any other cylinders from that 944 . the dimple is not present at idle either , when recording relative compression waveforms , it seems like i should record idle then 2k rpm values with ckp ,

before i buy another pressure transducer i intend to explore various options , like this .
from Omega.    http://www.omega.com/ppt/pptsc.asp?ref=PX309-5V&Nav=preb03 ;
   these look very much like the Fluke PV 350 , but i can not say that that is where Fluke gets them from , i have no idea . but it looks like they should work - haveing said that i would NOT PURCHASE one until i found out how well they do with RFI and how well they do rejecting noise induced by vibration and or physical contact . the microphone effect.
the Fluke PV 350 has trouble with RFI and the FLS sensor has trouble with the microphone effect.

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Romain.

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Re: firstlook
Reply #37 - Jun 17^th, 2007 at 3:29pm

With this attachments, I would like to attempt a description of what I think the sudden momentary cylinder pressure drop is caused by,

since the area of the TDC compression is shown, there would have to be a brief pressure relief for the waveform to display the sudden pressure drop,

now since the cam lobes for that cylinder, at this point in time are pointing away from the cam followers, I submit that there is a bad spot / abrasion or irregularity on the base circle of one of the cams, so that the cam follower (Hydraulic) is transmitting it's movement on to the valve, and momentarily releasing pressure, allowing us to witness the resulting drop in the waveform.

in brackets I inserted Hydraulic, as a mechanical valve train would not be able to effect that same condition due to the valve clearance provided .

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Romain.

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Re: firstlook
Reply #38 - Jun 17^th, 2007 at 5:12pm

Hi again,

perhaps an other idea may well be a leaking exhaust valve ( usually due to that valve being stressed greater than the intake, except when carbon buildup is involved )

in the BMW wave, there was a fast pressure drop up to a point, where the lowered pressure made less of an impact on rate of drop,

so looking at the Porsche wave, we may be seeing the beginnings of a leaking valve.

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mwebb Senior Member Offline Posts: 162 Gender:	Re: firstlook Reply #39 - Jun 18^th, 2007 at 10:35am i can hardly wait until i get a car with a burned exhaust valve to see .
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Rick Hill LSD Guide Picogroup Offline Deceased Posts: 660 Gender:	Re: firstlook Reply #40 - Jun 18^th, 2007 at 2:50pm Michael just out of curiosity could you post the time in degrees from tdc to the change or dimple in the wave for both the porsche and the bmw running compression waves being discussed here. Thanks.
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mwebb

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Re: firstlook
Reply #41 - Jun 18^th, 2007 at 10:05pm

Quote:

Michael just out of curiosity could you post the time in degrees from tdc to the change or dimple in the wave for both the porsche and the bmw running compression waves being discussed here. Thanks.

the 944 has the dimple at 17 degrees after TDC at 2030 rpm .
i will check the BMW dimple location after i stack up the waveforms

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fisher

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Re: firstlook
Reply #42 - Jun 18^th, 2007 at 10:59pm

So, Ford's Thermactor system was an air pump that sent air to the exhaust stream to assist the catalyst ... but another systemFord used no air pump but, exhaust impulses and some sort of check valve to draw air into the exhaust stream; the exhaust pulses can induce a mild pumping effect at a particular load condition.
Intake manifolds have valves in them to change the direction of flow due to resonance issues.
Air stretches and compresses both and likewise does exhaust.

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mwebb

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Re: firstlook
Reply #43 - Jun 19^th, 2007 at 9:51am

fisher wrote on Jun 18^th, 2007 at 10:59pm:

So, Ford's Thermactor system was an air pump that sent air to the exhaust stream to assist the catalyst ... but another systemFord used no air pump but, exhaust impulses and some sort of check valve to draw air into the exhaust stream; the exhaust pulses can induce a mild pumping effect at a particular load condition.
Intake manifolds have valves in them to change the direction of flow due to resonance issues.
Air stretches and compresses both and likewise does exhaust.

i should have marked it off better sorry ,
the pressure transducer is in the spark plug thread.
at 17 degrees after TDC right there where the dimple is both of the valves are closed and the piston is heading down . the combustion chamber should be sealed , anything that happens in the exhaust or intake is isolated by the closed valves and not connected to the combustion chamber and so should not have any effect at all on the pressure inside of the combustion chamber .
assuming the valves have actually closed .
the exhaust valve opens at about 155 degrees at which point events in the exhaust will begin to have an effect on the combustion chamber pressure .

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fisher Super Nerd Picogroup Offline I love YaBB 1G - SP1! Posts: 2,734 Concord California USA Gender:	Re: firstlook Reply #44 - Jun 19^th, 2007 at 6:15pm I was befuddled... So, we are looking at a compression event but no firing event. I had an impression of resonance. I suppose the best way to see about that dimple is to take the motor apart. Sorry, I thought we were talking about FLS in an exhaust stream.
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