Compression Waveform

Darren Mechanic West Allis, Wisconsin Posted   Latest   Edited  
Discussion
Driveability
2008 Saturn Astra XE 1.8L (1 2H0) 4-spd (AF17)
P0101 — Mass or Volume Air Flow Sensor "A" Circuit Range/Performance

maf is fine, engine has breathing problem, any thoughts on compression waveform, suspect valve timing, I may decide to do cam / crank waveform if needed.

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Dean Owner
Albany, New York
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I am chasing the same code on the same car. Does your car run ok? Does it set lean codes or rich codes? Can you provide more info?

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Darren Mechanic
West Allis, Wisconsin
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Runs lean . No fuel mix codes yet. Runs super lean at idle.

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Stuart Owner/Technician
Prestonpans, United Kingdom
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Looks like the inlet is late in opening and there is quite a bit of turbulence on the exhaust closing and inlet opening periods as well. Valve timing is defo worth a check and are all cylinders the same ? Does it have an EGR Valve?..

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Darren Mechanic
West Allis, Wisconsin
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No egr

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John Instructor
Beaver, Pennsylvania
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Agree Stuart. The intake cam timing is retarded, the first thought from there is where does the PCM want it to be at that point in time?

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Jeff Diagnostician
Cathedral City, California
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Can you upload the raw pico file ?

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Bob Owner/Technician
East Longmeadow, Massachusetts
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Darren, We could better help you out if you could post some more test data such as fuel trims at idle, cruise and under load. Also, the freeze frame data would be helpful to see under what operating conditions is the code setting. A VE test would be helpful also. This code can set for many reasons. Vacuum leaks, heavy deposits in the throttle body, intake restrictions, sensors out of spec etc…

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Keith Diagnostician
Fayetteville, North Carolina
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Looks like possible exhaust event closing early. There is a noticeable rise in exhaust pressure at end of event. Cam crank correlation would be a good choice.

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Nicholas Diagnostician
Brooklyn, New York
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Hi, did you check exhaust back pressure?

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Justin Mobile Technician
Herriman, Utah
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I don’t see any backpressure issues in the capture.

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Keith Diagnostician
Fayetteville, North Carolina
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Doesn’t appear to have a exhaust back pressure issue. Hovers around 0psi on evo. Just sudden rise at the end of exhaust timing. Makes me wonder about valve timing.

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Eri Technician
Larchmont, New York
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As stated by Stuart intake valve seems be a bit late possibly

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John Instructor
Beaver, Pennsylvania
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The intake cam timing is late in this capture, that is evident by both the pressure rise at the end of the exhaust stroke which needs all of the valves closed to occur and how long it takes the cylinder to go into a vacuum after TDC (E-I). Grabbing a CMP/CKP capture before teardown would be a good idea. Overlap the compression waveform with the CKP and the CMP captures.

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Bob Owner/Technician
East Longmeadow, Massachusetts
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John, I would agree with your assessment of the pressure waveform capture, I'm just a little curious how we got from a P0101 to an in cylinder test. It may turn out to be a mechanical issue but it would be nice to see the data that supported going to an in cylinder pressure test in the first place.

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John Instructor
Beaver, Pennsylvania
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Isn't the engines ability to pump air part of "the basics"? A P0101 is easily divided into two categories, low calculated engine load with fuel trim correction and low calculated engine load without fuel trim correction. From there it's all fundamentals, it's just the way that we measure them today that appears exotic.

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Justin Mobile Technician
Herriman, Utah
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I just posted a basic example tonight.

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Bob Owner/Technician
East Longmeadow, Massachusetts
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Sure it is, but wouldn't you be looking at some scan data before diving into in cylinder testing? Don't get me wrong, I love my pressure transducers but I usually have gathered some other data that will lead me to using the transducer. It's not the first test I'm going to do. I was just hoping the OP could post some supporting data for going in cylinder.

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John Instructor
Beaver, Pennsylvania
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He didn't post data but he started off with "maf is fine, engine has breathing problem" which while he didn't specifically share the data strongly suggests that he had already investigated that angle.

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Richard Technician
Virginia Beach, Virginia
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You don’t have any data posted so I will give you results I just had on a 08 Saturn 3.5. I was asked to go to another shop and program a new ECU . After I was done, the car had a number of drive ability issues. Later , I was asked for some assistance in diagnosing it. I found voltage drops on ground wires for the MAF , TCM , ECM and the trans range selector​.​It ended up being a

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Keith Diagnostician
Fayetteville, North Carolina
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He has a performance problem at MAF. My suspicion is that it’s extremely out of range. It looks like the cam timing is off. No real way to know that without a little more info (known good waveform, cam crank correlation). This would certainly cause this issue. Should be able to see it with absolute load as well. In fact I’m sure he would. Any way hope he resolves it soon.

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Eric Owner/Technician
Edgerton, Wisconsin
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I would really like to see the actual Pico file if you could upload it please.

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Darren Mechanic
West Allis, Wisconsin
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I will try.

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Simon Diagnostician
Auckland, New Zealand
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As stated by some of the replies above, the original PSDATA file would be needed to analyze the data efficiently. However, if the in-cylinder trace is taken at idle, the compression pressure is high, I usually see about 70-90 psi at idle. Also, the compression cone is uneven, note the intake side (vacuum) is higher than the exhaust side. But, as I said, I would need the PSDATA file to be

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Caleb Technician
Mishawaka, Indiana
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Looks a like very retarded intake cam timing. What is the manifold vaccum at idle with VVT solenoids unplugged assuming it has VVT?

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Orlando Technician
Toronto, Ontario
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Any updates?

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Darren Mechanic
West Allis, Wisconsin
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Customer took vehicle.

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