Re:APT-100 Pressure Transducer

I finally got around to ordering one of these transducer sets off AliExpress after Juergen gave it his endorsement:

www.aliexpress.us/item/3256801110009701.html



In case you don't speak AliExpress-ese, APT-100 translates as, "Pico WPS-500 photocopy." Look, I'd love to have the real deal, but the WPS *starts* at $900. This thing is $300 shipped! I see a lot of value in having an in-cylinder transducer around, but it's not a tool that gets used every day. Love my PV-350, but it's getting on eight years old now, and it quit zeroing correctly awhile ago.

There's been several excellent YouTube reviews if you're curious:

Ben wrote:

But did you get around to taking some captures with it?

Nah, I don't have it yet. Made this thread mostly so Juergen would have a place to post his captures.

It arrived! Finally got time to play with it a bit today. Didn't have time for comparisons with the PV350 or a pulse sensor. That'll come later. Some in-cylinder shots:





I'm a bit confused at the readings. In 1st gear (or what the WPS-500 would call Range 1), the conversion is something like this:



I took that cranking capture off my '13 Sentra. Soooooo by that capture, my engine only making 118 PSI cranking? I don't know what spec is, but that sounds low. Am I missing something here? Just for giggles, I tried converting 1180 kPa (1.18 V) into PSI and got 170-ish. Maybe the adapter was leaking...

I also tried out the WPS equivalent of Range 3 and got some entirely decent looking intake pulses:



It's a win so far. I'll compare it back and forth later. I'll also take the opportunity to make a custom probe on the Ultra, since I've never had reason to play with that before.

Got to play with the new APT-100 a bit more. After the last post, I had a few concerns about the in-cylinder captures. So for a direct comparison, I hooked up the APT-100 to the #1 cylinder (red) and the good ol' Fluke PV350 to #4 (green). The conversion values are a different between the two transducers - The APT-100 is set for 1V/100 PSI (or 10mV/PSI), while the PV350 is set for 1mV/PSI. That's why there's a difference in scales. Cranking compression first:



APT is showing right at 116 PSI. Again. But the PV350 says otherwise:



Flukie says 166 PSI, which I find to be much more reasonable. Interestingly, if you take 1.16V, change that to 1160 mV and figure 1mV/kPa, you get to 168 PSI. Not sure if that's a coincidence or not.

Anyway, I tried some running compression waveforms as well. Turned the scales down for more detail.



#1 definitely doesn't look right. Leaning compression towers, decompression pocket doesn't reach full vacuum, and the exhaust plateau is missing detail compared to the PV350 (which has a filter applied).

So maybe there's leakage in the hose or adapter, right? Nope, I got it to hold vacuum with a hand pump. Maybe that cylinder really is leaking? Moved the PV350 to #1 and got good waveforms. What the hell.

Tried the same setup on my '15 Equinox and the problem got even worse:



You don't have to be an expert to know something's wrong here. Aside from the transducer itself, the only thing I can figure is there's something wrong with the provided compression hose. The APT-100 uses a different style (Foster? Honestly don't know) connection than most compression testers (Milton M-style). That means I can't use any of my existing compression hoses, or swap hoses between transducers for test purposes.

Maybe the included hose just sucks? Juergen had mentioned the APT-100 benefitting from a stiffer hose. As always, any thoughts you have are welcome!

when I got my APT 100 the passage within the brass portion of provided hose was bad/clogged and caused erratic results. After drilling it out it performed much better.

Interesting. I'll have a look at mine tomorrow.

Nevertheless I changed the interface/coupler on the transducer itself so I can work now with any standard compression hose.

Definitely going to do that. Do you happen to have a link to the coupler you're using? While I'm at it, I'll probably buy a sacrificial compression hose to use for intake pulse testing.

Regards the kPa looking peak pressures see what the thing reads with a known shop air pressure. Then you'll know whether you've got a kPa unit or not.

Another excellent idea.

Ended up stealing the hose coupler off the PV350 and an adapter out of my OTC oil pressure test set. Now we're free to use normal compression hoses.



Back in #1 on the Sentra, the cranking compression is closer to what I was seeing with the PV350:



My whole kPa scale idea is out - 1,550 kPa converts to 224 PSI. 155 PSI is much closer to the 166 the PV350 was reporting. The running compression still isn't perfect...



I'd do another direct comparison capture, but I scavenged the coupler off the PV350 to make the APT work. I'll get another coupler and follow up later.