Home made in cylinder transducer

I took an AC pressure transducer from a 2010 Altima, connected the power and ground to a USB phone charging cord I cut the end off of, connected the the cord to the USB port on Verus and clamped it in a compression gauge hose :huh:

Very nice capture.

One interesting thing about the trace is that the voltage is going negative. Looks like the phone charger 0V is floating. Did you use a wall wart or a 12V charger? If it's a wall wart I'm not surprised but I wouldn't expect a vehicle charger to be floating.

Thank you.
The Verus has 2 USB ports on the side.
I used the top one.
I edited the original post to make it more clear.

I just went to double check, the negative portion of the wave form is only when using AC coupling

Noah wrote: The Verus has 2 USB ports on the side.
I used the top one.

You're a lot braver than me. I made a USB to 4mm cord for 5V but I'm not plugging it into anything that costs real money.

Lol, I understand your apprehension. Maybe I'll make a longer cord to power the transducer elsewhere, but I think it will be ok.

Like my dad used to say "God hates a coward".

Noah wrote: I just went to double check, the negative portion of the wave form is only when using AC coupling

So the sensor will only show vacuum while AC coupling? Or will it show vacuum on a normal voltage scale?

It will show vacuum no matter what, it just won't be reflected as negative voltage unless I'm using ac coupling.

I tried it on the preset 100psi transducer scope setting, but the calibration fails and the scales end up being greatly skewed negative.

The first thing I did with it on my tool box after I powered it on was pop it into the Mighty Vac hand pump to see if it would show 20"hg.
The voltage range in relation to the change in vacuum compared to atmosphere is not very large.
I slowly applied vacuum to the transducer while watching the trace on the scope, and voltage does indeed decrease until just after 25"hg. After about that pressure, the sensor reaches it's minimum output potential.

Next I hooked it up to my cylinder leak down tester to get an idea of it's maximum measurable pressure. (That's actually the hose I used to capture the running compression waveform on my Ridgeline, I still need to rig it to an actual compression gauge hose).
All Data, if I'm remembering correctly, said that this sensor is a 100psi.
The gauge on my tool goes to 100psi and I was able to gradually increase the pressure on the sensor until needle was way beyond 100psi and the sensor signal continued to climb without appearing to have maxed out.
The crusty antique gauge on my crusty antique compressor reports 140psi when the motor cuts off, so I thinks it's reasonable to assume that it will continue to produce a waveform into that range but whether it's accuracy is diminished, I don't know.

So far I'm happy with the waveform. I've never used an in cylinder transducer and have only used this one on my truck, so we'll see.
If I really start getting into it and this isn't enough, I'll feel more comfortable making the investment in a good one having had some experience.

Noah wrote: Lol, I understand your apprehension. Maybe I'll make a longer cord to power the transducer elsewhere, but I think it will be ok.

Like my dad used to say "God hates a coward".

Since you've already done it I guess it is OK. If you make anything else probably best to at least test it with a wall wart before hooking it up to the $$$$cope.

And it's Murphy you gotta watch out for doing stuff like this :lol:

BTW 100 psi doesn't sound right for an AC transducer. Low side would probably be able to go to 200 for measuring static pressure and a high side probably 400 or more.

You are correct Matt.
All Data provides the voltage reference chart for the sensor. It appears to max out at 4.16v and 398psi.

A really nice capture, one thing to watch out is the internat liner of the hose collapsing when doing running compressions as many fail with repeated rapid pressure vacuum cycles.

Noah wrote: So far I'm happy with the waveform. I've never used an in cylinder transducer and have only used this one on my truck, so we'll see.
If I really start getting into it and this isn't enough, I'll feel more comfortable making the investment in a good one having had some experience.

The frustrating part is that the signal looks cleaner than what my PV350 produces. Damn you and your junkyard engineering!

I'll mail you one. (And the .vsm files if you want to poke around)

Trying one from a Focus today that has a slightly higher voltage at atmospheric, so I'm hoping for more definition in the vacuum area of the waveform. Also snagged a FTP sensor out of the gas tank pile for intake pulses.

Any suggestions for an overlay?

The focus one works just as well.
This is from a 2005 Taurus OHV 3.0l
@ idle:

[quote="Noah" post=40969
Any suggestions for an overlay?[/quote]


1drv.ms/u/s!AilHGEYrlbUTcr8AKqChD3Qb_Js?e=ufKgs5

If you were to work on a computer with W10 you can get it here for free from the microsoft store:

www.microsoft.com/en-us/p/pressure-wavef...ab=pivot:overviewtab

Now you just need some broken cars to play with.

Actually, what you need is two of the same transducer. That way, you can put one on each side of a V-engine.

Tyler wrote: Now you just need some broken cars to play with

[EDIT: fixed the labeling of the captures in this post to reflect the actual cylinders the captures were taken from. Sorry for the confusion]

I've got one of those. 2001 Honda Accord Vtec 4 cylinder manual.

Customer claims to have been beating on it on the highway, hearing a pop and then heavy misfiring.
He did install a timing belt, because who knows, and then sent it to the shop!

Another tech diagnosed low compression in two cylinders. #'s 2&3.
A leak down test was not performed and the customer decided to junk it.

So here's the data I was able to get after work tonight.
Cylinder 3 with the Focus transducer
Cylinder 2 with the Focus transducer

Now unfortunately, I didn't zoom in enough on the Taurus capture with the Focus transducer to make a good side by side of a single 720°
So I made a side by side using the Ridgeline capture, but it's using the Altima transducer. I'll include it anyway since I took the time to make it.

This should be a more accurate comparison, both captures were taken with the Focus transducer

The most obvious difference I see is there is considerably lower compression, although the towers appear to be even.
The second thing is the exhaust event.
It looks like it takes longer for the exhaust valve to open than on the Taurus, but that could be a normal difference between the two cars I suppose.
The pressure builds and kind of ramps up at the end of the exhaust stroke but the duration seems roughly the same as that of the Taurus known good capture. Then the cylinder goes into an unequal vacuum compared to what was in the cylinder at the end of the expansion stroke making for uneven pockets.
I wanted to get a known good from cylinder 1 or 4 of the Accord that's broke for an apples to apples comparison, but it won't run on one cylinder, lol.

Any of the experts care to reflect on the waveform and share there their interpretation of what that actually means is happening in the cylinder?

Noah wrote: Any of the experts care to reflect on the waveform and share there their interpretation of what that actually means is happening in the cylinder?

I'm no exspurt by any means but it looks like positive pressure building on the exhaust stroke. I checked to confirm 2 & 3 are both TDC at the same time so I suspect that exhaust stroke pressure build is the adjacent cylinders compression leaking across a blown head gasket.