Home made in cylinder transducer

Thinking back to when I built mine, both the transducer and the remains of the compression gauge kit were 1/4 NPT tapered thread. I just did the usual two wraps of PTFE plumber's tape that I do when fitting couplings to air-tools and it sealed up fine.

A lot are 1/4" Gas thread (more or the same as 1/4" BSP) as used on shop air compressors there is also a tapered version of this thread BSPT.
1/4" Gas looks very similar to 14mm spark plug thread but don't ever mix up the two types.

Also to clear up terminology a transducer is different from a sensor a sensor requires external power, a transducer dosen't require power it is two wire and generates its own voltage.

Aside from Brit and US pipe threads, which are different, there are also numerous other standard and metric threads Noahs transducers could be.

Andy.MacFadyen wrote: Also to clear up terminology a transducer is different from a sensor a sensor requires external power, a transducer dosen't require power it is two wire and generates its own voltage.

Three wire voltage output are transducers. 2 wire pressure transducers are usually 4-20 mA loop powered. I can't recall ever seeing one of those on a vehicle but they're the most common type for industrial process control.

www.omega.com/en-us/resources/pressure-t...cers-troubleshooting

The threads are small? Lol, not my bag. I never invested the time to learn threads...

I did find a brass coupler to marry it to my compression gauge but I think I'm abandoning the refrigerant pressure sensors.
The voltage output at rest is too low to use the pressure scale on the Verus. I ordered the same one (presumably) that Paul has had success with. The seller claims it to have a range of .5-5 volts.
All mine put out .012 at rest.
If faced with the prospect of spending several hundred dollars on a transducer set up, you better believe I'd just live with this setup on a 2v scale, measurement be damned. But for under $20, I'll give this a try.
Thanks for your help guys!

The 300psi sensor came in today. Hopefully there won't be too much work waiting for me Monday to try it out;)

The first testing with the new sensor is a bit disappointing. When compared to gauge pressure it is 5psi off (positive) around 5 psi and deviates proportionally as pressure increases. So 80psi gauge pressure is more than 100psi on the scope scale.

Looks like a proper 500psi & 100psi sensor is in order to properly use the pressure scale.

Is the sensor's update rate fast enough to deliver a good enough, not chopped waveform?
I got frustrated when playing around with these sensors because of the deficient resolution.

Could you upload a screenshot, please?

I never installed it in an engine after the bench test results were not favorable, but I should have something here at the shop I can get a waveform from and post it up.
It did seem to respond appropriately while changing the air pressure through my cylinder leak down tester, but obviously the changes taking place were not happening nearly as rapidly as inside a running engine.

For bench testing mine first I used a hand pump to confirm it would measure vacuum. Then threw together an airline quick connect Tee with a short hose from it to the transducer. Then hooked it up to a couple air hammers. The faster one is 4,500 BPM and the slower 2,500 BPM IIRC.

That's a pretty good idea to measure it's response, thanks Matt

I put it into my Ridgeline but unfortunately got occupied with visitors.

It did look like the sensor output at shorter time samples was choppy and not fluid, almost pixelated, but I was distracted. It could have been me...

After the clean captures from the salvaged refrigerant pressure sensors, I fully expected to see similar, nice, smooth transitions....

The sensor seems to have been damaged. It now outputs 1.5v at atmosphere and will not calibrate to use the voltage scale built into the Verus.

I do still have access to the Accord by the way. It's out in the yard with no tires, I just haven't had the ambition to go out there pull the head.

Noah wrote:
I do still have access to the Accord by the way. It's out in the yard with no tires, I just haven't had the ambition to go out there pull the head.

!!Go for it, Forest:) !!

Noah wrote: I do still have access to the Accord by the way. It's out in the yard with no tires, I just haven't had the ambition to go out there pull the head.

If it's past the point you can do any more running tests a cylinder leakdown test would probably be enough. That's if you can get compressed air out to it.

juergen.scholl wrote:
!!Go for it, Forest:) !!

Matt T wrote:
If it's past the point you can do any more running tests a cylinder leakdown test would probably be enough. That's if you can get compressed air out to it.

Yeah, I regret not doing the leak down test before she was put out to pasture.
It likely still runs but is quite far away from an air line now, lol.

I've really got to start from scratch now with the failure of the sensor I was counting on using. Very disappointing.
I think it's worth it to revisit the refrigerant pressure sensor and try to develop a repeatable test procedure as far as scope set up is concerned, to gather accurate, interpretable information

I pulled the valve cover off the Accord this week and turned the engine with a ratchet out in the yard didn't see anything right away up top. I'm not looking forward to the support bracket that goes from the intake to the block. That's really the only hard part of doing it out in the yard.

Noah wrote: Yeah, I regret not doing the leak down test before she was put out to pasture.
It likely still runs but is quite far away from an air line now, lol.

I just experimented with my 4 gallon 125 psi compressor. With a 100% leak it took me 5 seconds to crank the reg up then I got 15 seconds run time before the inlet gauge started dropping. A 60% leak I got 20 seconds run time but it would probably be useable for finding where the leak was for a minute total. So if you've got a decent sized portable air tank might be worth carrying it out there.

Noah wrote: I think it's worth it to revisit the refrigerant pressure sensor and try to develop a repeatable test procedure as far as scope set up is concerned, to gather accurate, interpretable information.

They looked really good other than the inconsistency at atmospheric pressure. I think it's worth playing around with power supplies and 'scope settings to see if you can get that repeatable.

Matt is going to love the newest addition to my scope


I got tired of losing my mouse or keyboard dongle to capture in cylinder or vacuum patterns.

I also caught a Camry with a restricted catalytic converter using one of my homemade transducers:
Before I realized the Amazon sensor was garbage a gave the transducers I had made to Tyler, so I rigged one up quick to diag a no power complaint that one of the other mechanics a previously looked at. He pretty much drove it with the o2 sensor out of the manifold (with no improvement) and bailed.
I've never had luck with that "test".
That mechanic has been there 20 years, so the boss doesn't believe me right away when I present him with conflicting diagnosis.
Since the o2 had already been removed, and since this was my first suspected exhaust restriction using the in cylinder technique, I backed up my data with a good old gauge.



2psi @ idle and maxed out on the pressure scale on a rev in neutral.

I'll upload a cleaner capture from the Verus today, but the pattern is very similar to what I got from the Accord with the "bad engine".

Noah wrote: Matt is going to love the newest addition to my scope

You can run transducers on all four channels now :lol:

Noticed the USB symbol on the back of that 'scope module. Didn't realize you could run it detached from the scan tool.

www.snapon.com/Diagnostics/US/KB/Using-t...4-Meter-Remotely.htm

Noah wrote: I also caught a Camry with a restricted catalytic converter using one of my homemade transducers:

SNIP

I'll upload a cleaner capture from the Verus today, but the pattern is very similar to what I got from the Accord with the "bad engine".

The trace definitely shows exhaust stroke pressure increasing with RPM. The pressure "spike" at the end of the exhaust stroke looks similar to the Accord. Is the Camry also an I4? Also what was the complaint on the Camry? Just low power or rough running?

Camry is a 2.5l I4 DOHC. 254,000 miles, no power but idles well. No codes.

Test drive revealed that o2s went rich under full throttle, load was high (EDIT: Calculated load was 100% for the duration of my wide open throttle pull.
Absolute load touched 100% at tip in, but quickly dropped to around, and remained near, 55%.), so I skipped fuel delivery and decided to revisit exhaust back pressure.

I've been pushing for the ability to run the scope module on my laptop with the stand alone Shop Stream software, but snap on has so far been unreceptive...