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I few years back I stated to get into in-cylinder pressure testing, other projects came up and it kind of got pushed to the side. I recently took a WorldPac class and the instructor was very big into this kind of testing. He is the one who told me about the overlay software that I had posted about a few days ago. Searching previous posts and PMing with some members here I see there are others with interest in pressure/vacuum sensor testing.If anyone would like to post screenshots, test procedures, tools they are using, different uses etc that would be great. It would be nice to get a library going of different patterns. It will take me a little bit to get going as I am waiting for an adapter to come in for my Modis, I have the adapter for my first gen Verus but it has just gotten to slow. My current tooling will be a Modis Ultra, Snapon 100 and 500psi transducers and a SenX first look sensor. Anyone else?
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I think unlike a normal compression gauge hose, shouldn't a pressure transducer adapter for use in in cylinder pressure testing ideally have a super narrow inner diameter no larger than a 3/16" brake line, be kept short and stiff as possible , Solid metal preferably to prevent any damping of the signal from occurring due to hose expansion, and naturally not have a schrader valve tthat traps and hold pressure like a regular compression gauge
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Pressure and vacuum transducer testing
I’ve captured some useful compression waveforms using a compression gauge hose with the schrader valve removed, but a while ago my Snap on guy had a set of compression test adapters made of steel tubing to be used in place of the hose,sounds like a better way to go if access allows.Comment
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JamesI think unlike a normal compression gauge hose, shouldn't a pressure transducer adapter for use in in cylinder pressure testing ideally have a super narrow inner diameter no larger than a 3/16" brake line, be kept short and stiff as possible , Solid metal preferably to prevent any damping of the signal from occurring due to hose expansion, and naturally not have a schrader valve tthat traps and hold pressure like a regular compression gauge
See the below picture the added length is only about 8 1/2 inches. Back when I first started with this I purchased a Video class from AVI given by John Thorton. He discussed this and my setup is pretty much how he set his up. I don't know about "solid metal" as some of the vehicles I work on its hard enough to get a flexible adapter in there. I also don't know about the 3/16 measurement you gave and NO I'm not cutting open one of my adapters to measure the orifice! Everyone's patterns will be slightly different due to the tools they are using. Also you could have two of the exact same vehicles both with say burnt exhaust valves and the patterns will be different as the amount of leakage from the damaged valve will never be exactly the same.
Also this post is not just for in-cylinder pressure testing. I would like to see any kind of testing members here are doing with pressure/vacuum transducers, first look sensors and so on. The more members post the more we can all learn.
IMG_1748.JPGLast edited by Steve6911; 11-15-2018, 09:28 AM.Comment
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When you crank over an engine with a regular compression gauge with a 3/8" inside diameter of over 12"inches long it takes 3 or more cranks with the schrader valve in place before the gauge displays what the true cranking pressure obtains in the cylinder. Remember wet dry compression testing ? Not always a good idea. If you reduce the inside diameter of the hose and collector area inside the gauge it would likely reach full pressure within 2 cranks, but the down side of this reduced area is any trapped fluid like gasoline or oil is not very forgiving in a near hydrolock situation with no where to go except out and will trash your compression gauge or expensive pressure transducer in short order, so if you got a leaking fuel injector, oil or coolant ingestion , say bye bye to your pressure transducer. Maybe reduced inside diameter adapter hose incorporating with some sort of relief valve with an hose (so it don't vent in someone's face )or on a hot manifold.
I have to do a 3 hour job to change out plugs on a 2007 Nissan Quest with a Missfire on #3 where the upper plenum and EGR tube need to come off beforehand to access. I think if I had a Verus or Modis with a DLC Line SPI to spend a few minutes to take a couple clear flood WOT cranking voltage checks with scope ( not even bothering with #1 trigger) to just see that all the Humps appear the same height. That is time well spent before taking anything apart and then taking compression check on suspect cylinder after the fact.
Maybe check fuel trims and doing a relative fuel injector flow test would be wise to do to if the scantool offers the option before taking something like this apart. Fuel trims on the high end? Maybe smoke that intake too.Last edited by Witsend; 03-25-2018, 08:23 AM.Comment
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JamesWhen you crank over an engine with a regular compression gauge with a 3/8" inside diameter of over 12"inches long it takes 3 or more cranks with the schrader valve in place before the gauge displays what the true cranking pressure obtains in the cylinder. Remember wet dry compression testing ? Not always a good idea. If you reduce the inside diameter of the hose and collector area inside the gauge it would likely reach full pressure within 2 cranks, but the down side of this reduced area is any trapped fluid like gasoline or oil is not very forgiving in a near hydrolock situation with no where to go except out and will trash your compression gauge or expensive pressure transducer in short order, so if you got a leaking fuel injector, oil or coolant ingestion , say bye bye to your pressure transducer. Maybe reduced inside diameter adapter hose incorporating with some sort of relief valve with an hose (so it don't vent in someone's face )or on a hot manifold.
I have to do a 3 hour job to change out plugs on a 2007 Nissan Quest with a Missfire on #3 where the upper plenum and EGR tube need to come off beforehand to access. I think if I had a Verus or Modis with a DLC Line SPI to spend a few minutes to take a couple clear flood WOT cranking voltage checks with scope ( not even bothering with #1 trigger) to just see that all the Humps appear the same height. That is time well spent before taking anything apart and then taking compression check on suspect cylinder after the fact.
Maybe check fuel trims and doing a relative fuel injector flow test would be wise to do to if the scantool offers the option before taking something like this apart. Fuel trims on the high end? Maybe smoke that intake too.
As far as using the hoses go, see the below pictures, I took these from the workbook that came with the AVI video. John Thorton is much smarter then me and knows much more on this topic then me so, if its good enough for him its good enough for me. And yes the cores are removed for this testing. As for the rest of your post, in my diagnostic routine this is not a first in test, (in-cylinder pressure testing) weather with a pressure transducer or a conventional compression gauge. Other testing is needed to determine that there is a mechanical issue before starting with this. And as I also stated this is only one test set, I would like to see everything that members are going with these sensors.
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IMG_1751.JPGLast edited by Steve6911; 03-25-2018, 01:10 PM.Comment
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2005 Mercury Mountaineer 5.0L 277,000 miles. Lack of power, worse hot. Good fuel pressure, Bad VE, but due to fuel trims I felt it had a breathing issue not a bad MAF. Vacuum gauge would drop on no load cruise speeds, upstream oxygen sensors frozen into exhaust and hard to get at so a backpressure test would have been difficult. All the In-cylinder testing was done with the engine cold.
Started off with a Cranking compression test, which looked good.
33107004.BMP
Next is a Running Compression test at Idle, appears to be ok.
33107005.BMP
Next is a Running Compression test at 3,000 RPM, note with the cursors I have 5.1 psi in the highlighted area. Again this is with the engine cold, pressure increased with Engine temperature.
Backpressure.JPG
This is the VE test when the engine was at full operating temperature.
BAd VE.JPG
The problem was clogged Catalytic Converters. The customer didn't tell us he had changed the Spark plugs recently due to oil fouling and mis-fire codes.
Just a quick edit, The vehicle is a 1997 Mountaineer, not a 2005. That will not change any of the readingsLast edited by Steve6911; 04-02-2018, 07:48 AM.Comment
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What is bad VE? Vacuum Exhaust?, Velocity Exhaust ? , Venturi Effect?, Valve Exhaust?, A clinical achronym for how far she's dialated ?2005 Mercury Mountaineer 5.0L 277,000 miles. Lack of power, worse hot. Good fuel pressure, Bad VE, but due to fuel trims I felt it had a breathing issue not a bad MAF. Vacuum gauge would drop on no load cruise speeds, upstream oxygen sensors frozen into exhaust and hard to get at so a backpressure test would have been difficult. All the In-cylinder testing was done with the engine cold.
Started off with a Cranking compression test, which looked good.
Looks like a noise hiccup on one cylinder to me. I think 277k be all she's gonna write, and that it's just a waste and going to trash any new cats within 12 months. Can you see any improvement taking out the downstream O2s before the midship cat?The problem was clogged Catalytic Converters. The customer didn't tell us he had changed the Spark plugs recently due to oil fouling and mis-fire codes.
Last edited by Witsend; 04-02-2018, 07:53 AM.Comment
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Volumetric Efficiency, probably.Comment
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Yes VE is Volumetric Efficiency, air in air out. But what are you using to test VE? Ford tool?Comment
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As Brian said VE is Volumetric Efficiency, I use it on almost every Driveablity issue, helps rule out a lot of things. First time I am using this one, I mis-labled the vehicle (2005 when its a 1997) but the reason it has no effect on the readings is that entering the vehicle is just a records keeping thing. As long as the "inputs" are correct which they were the tool will give the correct reading. I matched it up against the calculator I have been using and they are very close. This is from the same guy as the overlay program and its free.
Last edited by Steve6911; 04-02-2018, 10:09 AM.Comment
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Very cool programs , but Since it is a Ford Explorer/ Mercury Mountainer with a DPFE sensor couldn't you also have just plug the EGR valve vaccum tube, Pull the hoses off the DPFE sensor and feel the one that has the best back pressure puttering out the hoses and connect your pressure transducer directly to that hose and pinch off the other one to confirm you do indeed have 5psi exhaust back pressure? If relative compression check looked good, is pulling a sparkplug and going in cylinder testing easier than popping the hoses off a DPFE sensor ? A lot of times those newer Plastic DPFE sensors are already going into melt down mode when Ford's start to let you know you got an exhaust restriction issue too, still could be possible the pre cats could be more restricted for the cylinders on the opposite bank though
Last edited by Witsend; 04-03-2018, 08:56 PM.Comment
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Scanner Danner Exhaust Back pressure testing a Ford from the DPFE feed tube with a old school vacuum/ pressure gauge.
I'm not sure what the range of pressure difference from one hose to the other hose that a DPFE sensor is capable of measuring before it change from 1volt base same pressure on each hose (no EGR flow) to reaching nearly 5 volts (VREF)? if you disconnect and plug the smaller DPFE hose and leave the small hose port of the sensor open to atmosphere and the larger hose still attached to the sensor then the sensor should show the voltage increase that is the difference between 1 volt at atmospheric pressure and the higher voltage in proportion to the higher exhaust pressure. Figure out what voltage the DPFE sensor reads at 2psi with a hand pump , and any voltage higher than that running with the smaller DPFE hose off the sensor and plugged (and the egr valve vacuum plugged) and you have an idea. If your over that voltage you got applying 2psi to the sensor with hand pump, you have over 2psi back pressure.
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Overlay?
How can I get the overlay ?Will it go on my zues? I have a engine in diagnosis i printed and drew lines with a ruler. How crazy lol pay 30k for my zues if I just do my payment and the laptop scopes are kicking its ***.there no possible way to diagnos s a cylinder pressure pattern on the verus,zue s without a proper layout.Sorry I goal was to find a way today hopefully you can guide meComment
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