Home made in cylinder transducer

Could just be carbon buildup on the intake side of valves due to the backpressure pushing back into intake with the plugged cat. Time for some seafoam or pop intake off and clean intake runners and valve ports with some cleaner.

juergen.scholl wrote: Is it possible that the air filter was/is coming apart and restricting the airflow?
I once experienced this on a Ford F150 where the plastic cone came off the filter. The car would bog down on heavy accelerating/WOT as the cone was sucked into and blocking off the air.

The air filter looks to be brand new-ish.
There was this bit of under britches integrated into the lid of the filter housing assembly.


And there were some leaves in the bottom of the box, pre filter, but I don't think either one explains the change in symptoms.
It still barely ran with all of that off the car until I gave the throttle a right boot work out.

I returned said under britches to it's place in the filter box and it still runs just the same.

Weycraze wrote: Atta boy Noah, awesome diag. Looks like you were up against a couple of issues and came out ahead. Tell your Boss to put the old Cat in and take her for a ride!! He'll come back and thank you!

Nice Work,

Paul

Thank you Paul, it still doesn't feel like a win though.
Many unanswered questions...

As for the boss, I'm not interested in convincing anyone at the shop. I find that when I'm doubted, the universe has a way of eventually delivering my vindication.

Noah wrote: Many unanswered questions...

One quick thing you could do is have a look for camshaft position PIDs. Might tell us whether the cam timing is screwed up or something the PCM is doing.

Another would be to put a transducer in the O2 sensor bung to see if there are any pressure pulses which could be affecting the in cylinder waveform. Best to do this with another transducer in cylinder but if you don't have two of them an ignition sync would be good enough.

So you connected both power and ground from the USB cable and then connected the scope to the ground at the sensor to monitor the signal? I've been building my own pick ups and sensors so I have to try this. Can you draw up a little diagram, if not too much trouble.

The EVO is advanced, but it's closing almost on time. This to me can be an indicator of valves out of adjustment. A tailpipe waveform tailpipe waveform along with the in-cylinder could confirm this. But the opening early with the spike does look like an advanced cam. Pretty nice capture with that sensor.

al514 wrote: So you connected both power and ground from the USB cable and then connected the scope to the ground at the sensor to monitor the signal? I've been building my own pick ups and sensors so I have to try this. Can you draw up a little diagram, if not too much trouble.

If you've got a 3 wire transducer you give it 5v power and 0v from the USB and scope the signal wire. There's some discussion on whether or not to also tie the USB 0v to scope ground earlier in the thread.

al514 wrote: So you connected both power and ground from the USB cable and then connected the scope to the ground at the sensor to monitor the signal? I've been building my own pick ups and sensors so I have to try this. Can you draw up a little diagram, if not too much trouble.

It's very simple. The sensor is 3 wires. It wants 5v and ground to operate, the USB port is capable of delivering this power and ground.
(Matt T is wise to be apprehensive about sourcing this power and from the scope. I haven't hurt anything yet and don't think I will, but the possibility can't be over looked!)
The third wire on the sensor goes to channel one on the scope. Done.
I don't even hook up a ground lead to the scope every time, but when I do it's to the car, not the sensor ground. I honestly haven't tried using the sensor ground.

John Curtis wrote: The EVO is advanced, but it's closing almost on time. This to me can be an indicator of valves out of adjustment. A tailpipe waveform tailpipe waveform along with the in-cylinder could confirm this. But the opening early with the spike does look like an advanced cam. Pretty nice capture with that sensor.

Thank you for your insight! Now that the power has been restored, I haven't been afforded the opportunity for much follow up testing. I do have some test drive scan data that isn't very revealing (vvt PIDs don't respond, I'm told that's a common snap on thing with toyota).
I'm very pleased with the waveform that sensor produces. I bought 3 sensors on Amazon thinking they would be better but the resolution doesn't even come close.

I am powering my home made transducer from a 5v USB portable charger from a battery pack. Use it on a SO Vantage pro. It does work well with the transducer voltage signal plugged into the selected channel be it #1 or # 2. So far only use one channel at a time. Would I be able to input an additional signal (like an ignition event for example) through the other scope channel ?. Will the scope react nasty to this setup due to the feed/grounds being source separate. One from the USB the other from the vehicle battery?. I have done the setup with two separate DVOM both sharing a common ground with no apparent issue. But the DVOM's have higher impedance than the VP. Please if any opinion. itwill be apreciated Thanks

You should have no trouble using the second channel for an ignition synch or just about anything else for that matter.
I frequently use mine with more than one channel.

So I've made a couple of diy pressure transducers with a 5volt ref box to power it and a bnc to the scope. I've found the linear equation to set up a custom probe that another tech had figured out. It works really well, except that at 0psi I'm reading about 1.6psi. I'm wondering what methods others are using for the custom probe set up. Obviously I need to change the equation alittle to get it to read 0. Using a look up table wouldn't go into a vacuum if I remember correctly when doing incylinder testing.

With the Snap On scope there is no custom probe set up and the transducer presets don't work well with the refrigerant pressure sensor I use.
I bench tested mine with a vacuum hand pump and a cylinder leak down tester, and just wrote down the voltage to pressure correlation.
It's pretty linear from what I recall. Most of the time when I do use the transducer, I'm less worried about the actual pressure and more interested in the shape of the waveform.

Oh I'm using a pico scope, guess I should have mentioned that. I'm wondering if I change the linear equation alittle I can get my pressure reading to zero. I'm only bringing it up because on an incylinder test I want to be able to see the condition of the cat. I know a really bad cat will give a huge spike 180° in, but I'd like to see more accurately than being 1.5-2° off.

Hi....A GM tank sensor likely works superior for deplete beats. On the off chance that you supplant GM fuel pumps it is beautiful simple to choose one up since the modern pumps more often than not have a modern sensor. If they are troublesome to come by I have a part and may send you a couple. A Outline sesnsor will work for vacuum either will require either employing a 9V batt or setting up a 5v supply.

www.7pcb.com/

The setup I have works really well, it's a 300psi transducer, and measures vacuum if the correct calculation is put into pico custom probe settings. I just need to figure out how to lower the setting by 2 psi. That's all

wrote:

The setup I have works really well, it's a 300psi transducer, and measures vacuum if the correct calculation is put into pico custom probe settings. I just need to figure out how to lower the setting by 2 psi. That's all
 

Try using a lookup table. Numbers I threw in are guesses for a 300 PSIA 0-5 V transducer. You'll have to adjust the voltages in the table to match your transducer. Also bear in mind that if you do have an absolute transducer the PSIG zero will drift around a bit due to changes in barometric pressure.

 

  This is the Linear equation I used for the 300psi transducer so I could use it for incylinder. That way I can see the vacuum pockets, it's just about 1.8psi off. I just need it to read zero at atmosphere. I can see incylinder waveforms with this equation great. I watched a video about setting the custom probes using a look up table with a 5 volt sensor, and it instructed to want to set your 0 psi at 0.5v and your max psi at 4.5v. Here's the video about that. I set my 80psi transducer by this and it compensates for atmospheric pressure I guess is the reasoning behind it

I'm still playing with these, just wanted to share an update for anyone interested.
Really my only complaint using salvaged pressure sensors is the lack of accurate voltage to psi scaling.
I recently discovered that the oil pressure sensor on Chrysler 3.6l V6 engines is just about a perfect 1-1 scale using the 100psi transducer setting on Snap-On scopes.
When bench tested against a trusted gauge I never saw more than a 3psi variance up to 100psi on the Verus Edge and Vantage Pro scope.
And, bonus, since I can use the transducer preset, now I can power the sensor with the appropriate AUX connector on the scope and not the USB port. (The aux power source is only switched "on" when selecting a preset that requires it, so on voltage scale the transducers need a different 5v power source)

I have changed a handful of the oil filter housings on these engines under the intake manifold (mostly Grand Cherokees and Chrysler 300s) and decided to harvest the pressure sensors.
It's a pretty common issue so chances are if you're in an independent repair shop, you'll have a chance to score one no charge.

Thank you Noah for this interesting update. Two questions here:

- Did you take a scope capture of both the pressure reading and the signal voltage as such at the same time?

- Do you happen to know the range/ max. pressure this sensor is capable; does it work with snap throttle acceleration reaching the 300 psi region?