2011 Mazda CX-7 in cylinder waveform

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OwhangoAE
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2011 Mazda CX-7 in cylinder waveform

Post by OwhangoAE »

Start and stop fault. No fault codes. Still learning how to interpret these wave forms. Can anybody help shed some light on what may be happening in this waveform. Zoomed in on while engine was actually running for a few seconds. Could this be a lifter problem, or are we looking at a possible exhaust cam timing issue. There is VVT on intake but not on the exhaust. Any help please.
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Mazda_CX-7_2011_20210908-0003.png

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Grant_Baker
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Re: 2011 Mazda CX-7 in cylinder waveform

Post by Grant_Baker »

The compression peaks are clearly leaning. Please retake capture with an ignition reference and CKP sensor if you have enough channels, then upload at least one buffer of the .psdata file so we can take some measurements. Also state what pressure transducer you are using.

OwhangoAE
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Re: 2011 Mazda CX-7 in cylinder waveform

Post by OwhangoAE »

Yes I have learned that leaning towers point to a mechanical issue.
I did take a capture with cam sensor and ignition. Unfortunately the ignition was shut down to cylinder under test while capturing cam signal. I have included two psdata files. The one with ignition trigger was crank no start. The other file has running event and stall. The transducer is not pico. I have checked pressures against a known good gauge and it seems to be quite accurate. If any more captures are required I will need to return to vehicle. This was a quick five minute capture to see if i could help garage with a real problem vehicle. Thanks in advance for any help.
Attachments
Mazda_CX-7_2011_20210908-0006.psdata
(6 MiB) Downloaded 47 times
Mazda_CX-7_2011_20210908-0002.psdata
(10.06 MiB) Downloaded 44 times

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Grant_Baker
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Re: 2011 Mazda CX-7 in cylinder waveform

Post by Grant_Baker »

OwhangoAE wrote:
Fri Sep 10, 2021 11:48 pm
I did take a capture with cam sensor and ignition. Unfortunately the ignition was shut down to cylinder under test while capturing cam signal. I have included two psdata files. The one with ignition trigger was crank no start.
File "0002": the ignition timing signal is not pulling to ground. See my attached screen shot. Where did you place CHB input and CHB ground leads?
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IGTiming_and_InCylinder_IGT_high_ground.jpg

OwhangoAE
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Re: 2011 Mazda CX-7 in cylinder waveform

Post by OwhangoAE »

3 wire ignition coil disconnected and CHB + on trigger signal CHB - on engine earth. I do also believe there may be an engine earth problem and have asked garage to check all these. But if there is a mechanical problem, it would be nice to identify areas of interest.

Steve Smith
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Re: 2011 Mazda CX-7 in cylinder waveform

Post by Steve Smith »

Thank you for the posts and psdata files

This is a tough call to make based on the pressure waveforms alone

My main concern is "measurement error" based on either the style of transducer, couplings used and possible leakages within the measurement equipment

Whilst peak pressure may be comparable with a gauge we have so many other items to consider with a transducer which include response time, accuracy and the ability to handle negative pressure

With capture "Mazda_CX-7_2011_20210908-0002" I can see the formation of an expansion pocket followed by no expansion pocket (Is this the transducer or a realistic cylinder event?)

I can also see an increase in cylinder pressure around 360 degrees crankshaft rotation.

The increase in cylinder pressure around 360 degrees is not unusual and often attributed to clever VVT operation during post crank period

The leaning towers may or may not be relevant and this comes down to our physical connections, can we be assured of no leaks and what we have captured is a true "in-cylinder" event? (Any doubt here must be removed to continue our diagnosis)

The Waveform Library may have a number of pointers from such a Mazda?

The vehicle history will be helpful too (i.e. fuel used, gas converted, previous mechanical repairs etc.)

How is the transducer performance when used on a similar vehicle with no fault condition?

I hope this helps, take care.....Steve

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