Used my scope tonight for the first time!

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Used my scope tonight for the first time!

Postby GRUSS » Tue Jan 24, 2012 10:12 pm

Had a couple of hours tonight in the garage with my new picoscope and my car, its a 1990 daihatsu 3 cylinder 660CC turbo petrol! I worked my way through the pico diagnostics looking which was great.
I then looked at the map sensor which looked ok. Then i looked at number 1 injector..had a go with the measuring rulers

Next i looked at the oxygen sensor, on this engine its just got a single wire mixture control sensor. I tried various time scales but couldnt get it to display a decent waveform. I was using the battery negative as a earth.

Any help or guidance would be great.
Attachments
660cc injector one voltage.psdata
(219.45 KiB) Downloaded 227 times
o2 sensor.psdata
Thsi looks like i'm doing something wrong, please help.
(549.28 KiB) Downloaded 241 times
660cc injector one voltage.psdata
(219.45 KiB) Downloaded 223 times
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Re: Used my scope tonight for the first time!

Postby taho » Thu Jan 26, 2012 12:37 am

Activate the filter of high frequencies to improve an image kind, be convinced that the car engine is heated-up to working temperature (the sensor of oxygen with one wire gets warm by exhaust gases, sometimes long), search for the reason: it is a lot of variants including a faulty sensor of oxygen.
It was quite good to check up structure of exhaust gases 4 componental gas analyzer...
22 years age of a sensor control of oxygen - the extreme old age, oxygen gauges have a resource.
If the sensor is good, it is necessary to search for the reason poor mix fuel-air.
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Activate Filtering.jpg
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Re: Used my scope tonight for the first time!

Postby Alan » Thu Jan 26, 2012 5:07 am

Hi,

A few things here. Taho is right about the filter, it cleans up the lambda signal quite a lot but you still seem to have interference - perhaps ignition. It may be possible to reduce this by changing where you probe / moving wires away but sometimes you have to accept that the interference is actually there & is due to the design of the wiring in the vehicle.

The low amplitude is a bit odd unless you were perhaps using an oscilloscope probe on the 10:1 setting? If not then was the engine fully warmed up, as its a single wire sensor there is no heater circuit so it would rely on exhaust gas to heat up the sensor.

Let the engine warm up & give it some revs, we are expecting something switching up towards 1V.
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Re: Used my scope tonight for the first time!

Postby GRUSS » Thu Jan 26, 2012 10:20 am

Please bear with me as I'm very new to this. I selected the lambda sensor preset and connected the earth to the battery. Have I got the screen settings correct? I read afterwards about the low pass filter etc which I will try. The engine had been idling for 30 mins as I carried out other tests before.I will have another go at the weekend. If someone could advise the best suitable settings that would be great!
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Re: Used my scope tonight for the first time!

Postby Wally » Thu Jan 26, 2012 11:04 am

Hi Gruss, Try opening up your saved capture then at the top left of the screen click on the "A" where it shows chanel A,B,C etc. Tick the Low Pass Filter option and change the setting to see what happens to the waveform. Just have a play to see the changes. Try 3kHz for a resonable clear waveform without loosing to much data. I would think that the result is possibly ignition interferance but may be wrong. ( You said the car was a three cyl and at idle, Count the peaks on the scope trace, roughly 21 per second, 21 x 60 seconds = 1260 per minute, One cylinder fires every other revolution, if idle is 850rpm then it will spark 425 times per minute per cylinder, 425 x 3 cylinders = 1275. Very close to the amount of peaks.)

Good luck with your learning
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Re: Used my scope tonight for the first time!

Postby GRUSS » Thu Jan 26, 2012 12:52 pm

Thanks for that wally
I wish I knew what you know! I'm getting to grips with the time scale and sample rate.THe oxygen sensor is very close to cylinder 3 COP so that could be one of the main problems. Is using the negative on the battery the best place to use in this case?
Thanks
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Re: Used my scope tonight for the first time!

Postby GRUSS » Thu Jan 26, 2012 7:17 pm

I've just got in and loaded the 02 waveform up on the laptop and tried the low pass filtering.. what a difference!
Whats the difference between the resolution enhancement and the filter, i presume the filter is the favoured choice as any more than 14 bit (12 bit default) then the vertical lines start to slope. i read this was a side effect of using the resoultion feature.
I will have to connect the pico back upto to the engine and carry out some more tests on the o2 sensor now i'm armed with this new info!
I have a wideband innovative LC-1 sensor and controller on the exhaust as well,its a standalone unit not connected to the ecu. I have a fuel controller which works on the map signal wire so i can adjust the AFR's etc. During normal cruising i'm getting a steady 14.7:1 so the o2 sensor must be doing something, i just suspected it was a little lazy when the engine was cold as it has no heating element..

When i attach files can you guys load them up in pico and make changes or can i only do this?

Does my injector waveform look ok then?

Thanks
Attachments
02 sensor with filter.psdata
(549.44 KiB) Downloaded 246 times
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Re: Used my scope tonight for the first time!

Postby taho » Fri Jan 27, 2012 1:00 am

GRUSS wrote:.... During normal cruising i'm getting a steady 14.7:1 so the o2 sensor must be doing something, i just suspected it was a little lazy when the engine was cold as it has no heating element..


I believe that the sensor control is faulty, first of all the form of a wave of a sensor of oxygen should not be less than 0 (basically).
The best decision will instal a universal oxygen sensor instead of yours and to look at result. (I am not assured that at such indications oxygen a probe you actually will have a parity 14,7:1)
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Re: Used my scope tonight for the first time!

Postby Wally » Fri Jan 27, 2012 10:15 am

Hi Gruss, Just working backwards on your last post, Injector waveform Ok, Yes when you post the psdata we can all view it in Pico software. This is one of the real benefits of this system.

A fairly simple explanation follows.

I also use a LC1 on a regular basis. I assume you know that the standard O2 sensor will osccilate between rich and weak as the Ecu changes the fueling from slightly too rich to slightly too weak on purpose, as it can not tell how rich or how weak the mixture is once the sensor has switched from one extreme to the other. This will result in the waveform you are expecting to see, It will not oscillate if the mixture is perfectly constant. The differance between switching too rich and too weak is a very fine line kept somewhere near by long and short term fuel trims.

The LC1 is a wideband sensor with digital output (which can be set if required to output an imitation the standard sensor) so this will give a steady reading of say 14.7 or 14.3 etc without the oscillations. (Althought it is actually quick enough to show mixture changes on an individual cylinder if required)

Now you say you have an Lc1 connected to a fuel controller which works on the map signal so you can adjust the AFR's -
What do you think the standard sensor will output if the mixture is slightly weak or slightly rich ?
If you then ask yourself how sure are you of the 14.7 that the Lc1 is reading, being absolutely spot on ?
What would the standard sensor show if the mixture is constant at 14.7 ?

Enjoy scratching your head :twisted:

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Re: Used my scope tonight for the first time!

Postby GRUSS » Fri Jan 27, 2012 7:14 pm

Wally
My head hurts!

The LC-1 is totally on it's own, I know about the outputs that can be connected up to a standalone ECU or data logger but I fitted it purely because I'm interested in tuning the car mildly and learning.
The fuel controller is an apexi SAFC which just alters what voltage the map sensor is feeding back to the ECU, a fairly crude method but it works well.
I've calibrated the LC-1 a couple of times, where you remove the sensor and do a free air calibration ( as you probably know this)
So I am assuming that what the digital gauge of the LC-1 is true.

Forgot to add that the SAFC only takes 'control' under hard acceleration or full throttle as it's linked to the tps so normal driving, of which is 95% plus is do e by the ECU.

What would the standard sensor read in volts with a 14.7:1 AFR? .... 0 volts lean and 1 volt been rich then I would say a middle figure of 0.4? :?

I'll get the pico back on tomorrow afternoon and have another go but apply some revs and te and keep away from the ignition...

Thanks for the reply

Ps what do you run the LC-1 on?
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