In Cylinder Pressure Analysis

Edwin Technician Utah Posted   Latest   Edited  
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Driveability
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2001 Isuzu Rodeo LS 3.2L (W 6VD1) 4-spd (4L30-E) — 4S2DM58WX14344431
In Cylinder Practice

I have been trying to build my library of known goods. Had this Rodeo in for a starter & had some time on my hands so I captured this in cylinder pressure waveform with a ignition event on the same cylinder. This is a home made pressure transducer ($200 ish total cost) however I have quite a few other wave forms using this transducer that look normal. With this transducer 1 volt is 0 PSI & 5 Volts is 300 PSI. It reads negative pressure but have not accurately calculated yet. Guessing 13.1 InHg per 100 millivolt. Below 1 volt. Looks like my transducer only reads down to 25 InHg. I am at 4500 feet altitude. So the 25 InHg seems unlikely. I should have put a mechanical gauge on it but I didn't.

In this waveform the towers are not symmetrical & the negative pressure is bottoming out or flat lining low. In all my other in cylinder wave forms I do not see this.

I would love to hear some input on what is going on with this waveform. 

I attached 2 PICO files. 1 is of the Isuzu that looks weird & the other is a Tribute that looks normal using same transducer

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Dmitriy Analyst
Ontario
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It looks like internal calibration of the transducer has drifted downward. Possibly due to heat. You will have to figure out whether this is permanent or intermittent. The lowest value the working transducer should give is 1 -14.7*(5-1)/300 = 0.8 V, so it is not surprising the output gets clipped at that level.

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Edwin Technician
Utah
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Appreciate the feedback. I will start paying close attention to where I am setting the transducer.

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