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Oscilloscope graphs; This isn't mwebb stuff
Topic Started: Oct 22 2016, 11:20 AM (8,261 Views)
freegeo
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Recently I purchased a new oscilloscope and just checked out some general stuff to figure out some of the options. Thought I would share some of the graphs.

How long does the fuel pump initially run with the key in the on position. Most sources say approximately 2 seconds.

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Edited by freegeo, Jul 7 2017, 12:59 PM.
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t3ragtop
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Turbo3 and Twincam Tweaker

that pump on periodicity is measured for your car. actually, the time is set by several physical factors related to resistance, voltage, and current as seen by the ecu circuitry as well as the design and fixed time interval of the circuit itself.

2 seconds is a pretty good shot for a throttle body injector car but it can be as long as 3 seconds for another car. variants like the turbo3, twincam, and g13bb actually have a longer prime interval to bring up the fuel rail pressure.

the important thing to remember is that it runs its prime cycle for a short period to allow for the equilibration of fuel pressure at the initial key on operation. ;)

o'scopes are excellent diagnostic tools as long as you know what you are looking at. i have known quite a few people who could never get a handle on the concept of the scale of things with an o'scope. it takes a certain skill at translating the visual representation of an event to an actual concept of the length of the visual representation. since you adjust the scaling of the video screen you have to make the corresponding adjustment to your mental concept of the event.

i used to be an expert in high speed data acquisition and x-ray photography and routinely captured events that occurred during intervals as small as a couple milliseconds. the current assortment of pocket sized o'scopes are all nearly as good as the half million dollar burr brown high speed data acquisition equipment i used back in the space shuttle development era. ;)
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freegeo
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Where are you seeing 2 seconds for the injector signal. The graph I posted is just the fuel pump relay.
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t3ragtop
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Turbo3 and Twincam Tweaker

no, the only reference i made to an injector was to describe the difference between the throttle body injector cars and the others that use multiple injectors and fuel rails.

mpfi/ fuel rail cars have a fuel pump activation length that is longer than the prime interval for throttle body cars.

my main point is that the key on fuel pump interval isn't 2 seconds for every suzuki variant. 2 seconds is what your car runs. the prime interval for my twincam vert is 3 seconds. the prime interval for my turbo3 vert is 3 seconds. both cars have higher pressure, higher volume fuel pumps and both cars have multiple injectors and fuel rails.

also, the interval is generated by the ecu and can vary with factors like battery voltage, temperature, and wiring resistance differences. so, without a hard and fast specification for the fuel pump on interval it really isn't all that critical to actually time the event.
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davegran
Old Fart w/Wrenches

Perhaps he was looking for something to hook up his new scope to and that was an easy way to start. Hey freegeo, do you have the bits and pieces necessary to display ignition events? :popcorn
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freegeo
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davegran
Oct 22 2016, 08:53 PM
Perhaps he was looking for something to hook up his new scope to and that was an easy way to start. Hey freegeo, do you have the bits and pieces necessary to display ignition events? :popcorn
Yes I do Dave. You interested in seeing something. Only thing I bought I haven't used yet is a accessory for secondary spark.
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t3ragtop
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Turbo3 and Twincam Tweaker

your scope is really handy for checking timing events from the crank sensor, cam angle sensor, and injector triggers.

i find that monitoring certain sensors like the iat and clt that use a voltage/ time curve is a handy use of a scope although the time scaling is super long.

i guess that my first response and my second attempt were misunderstood. i don't have any issue with using the scope to look at the fuel pump voltage. i don't have any issue with the result. my point is that not every suzuki variant runs the fuel pump for 2 seconds as the key is switched on. that was all of it.

on the scope display in the op's signature line, see the crank sensor signal at the bottom? do you see that the trigger signal is very low and not fully developed for the first 2 or 3 pulses? that shows the crank sensor's hysteresis is low at slower engine speeds. the injector pulse on the top line gets triggered even at the low speed response of the cmp while the ignition trigger doesn't get tripped until the cmp signal is fully developed and the engine is running at idle.

the cmp is a variable reluctor. it generates a pulse when steel passes the core of the sensor. when the speed of the passing steel is slow, the signal is low. when the passing tooth's speed is faster, the output signal becomes fully developed.

the design flaw in a variable reluctance sensor is that as speed increases the sensor acts like a generator and the voltage increases as an envelope with the pulse riding the rising voltage. when i was setting up my megasquirt i ran into issues with this operation of the v/r type sensor. i would never have figured out what was overloading the signal conditioning section of the megasquirt without the use of my o'scope to ascertain that the crank trigger pulse was riding on a 70 volt signal.

so, there are conditions that come up where there's nothing like a scope for troubleshooting. nothing else will find the really odd things.

with regard to the fuel pump voltage vs time display posted, i was rather interested in the hash on the dc voltage and started thinking about what could be done to get rid of the noise. it was probably related to the pump motor's commutation. if the pump voltage had been measured with a volt meter you would never even notice the electrical noise. another case where the scope gives you more information. ;)
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freegeo
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Quote:
 
on the scope display in the op's signature line, see the crank sensor signal at the bottom?


No I don't (if you are talking about the yellow waveform at the bottom). That is not the crank position sensor signal that is the camshaft position sensor signal. The CMP signal on a obdii ( 1.0 L) car has a extra tooth on the # 2 cylinder. :smackface
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t3ragtop
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Turbo3 and Twincam Tweaker

yep, i confused cmp and ckp. still, the cam angle sensor is a v/r type and does the same thing. the faster the cam spins, the higher the steady state voltage goes. the metro's ecu has signal processing that can handle the higher voltage and still discriminate the pulse.

the v/r sensor's propensity to act as a generator really got my tit in a wringer with my megasquirt/ turbo3 project. the false ignition triggers and resets caused my buddy's turbo3 to blow a rod through the block. my scope allowed me to see the problem and correct it by going to hall effect devices to replace the v/r sensors.

you can see that at the beginning of the wave shapes that the signal is small and that after the engine starts and the revs come up that the cmp wave shape fully forms.

the ecu fires the injectors for 2 revolutions and then if the ecu doesn't see the ignition firing it shuts down injection after 3 revolutions.

and you can see the little tooth on the distributor shaft's lobes on the cmp signal every third pulse. so much more detail with a scope. ;)

so what type did you select? they are selling a dozen or so different "pocket" scopes on line and they have more that plug into a laptop and use the computer's screen as a display. from the graphic in your sig line yours is a multi-channel unit. 4 channel?
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freegeo
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Quote:
 
the ecu fires the injectors for 2 revolutions and then if the ecu doesn't see the ignition firing it shuts down injection after 3 revolutions.


Do you have a wave form that supports that statement, or factory documentation or is it something you just think it happens?
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nwgeo


Thanks for sharing these scope pics of injector and sensor signals. Very interesting to me.
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freegeo
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nwgeo
Oct 23 2016, 02:15 PM
Thanks for sharing these scope pics of injector and sensor signals. Very interesting to me.
You are welcome. That was the whole purpose of starting this thread. To share what i have seen so others might learn from it too. I plan to do more as I have time. I work 6 days a week and only have sunday to mess around with my car to try and learn how the system works as a whole.

Plan on doing some more today. Checking flood clear mode. Does my metro actually have it?
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t3ragtop
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Turbo3 and Twincam Tweaker

freegeo
Oct 23 2016, 12:06 PM
Quote:
 
the ecu fires the injectors for 2 revolutions and then if the ecu doesn't see the ignition firing it shuts down injection after 3 revolutions.


Do you have a wave form that supports that statement, or factory documentation or is it something you just think it happens?
read it in the fsm and have found it to be true while troubleshooting.

it is a protection against flooding the engine.

there's another function that almost never gets discussed and that is holding the throttle open at 70% of the tps range sets the ecu in "flood clear" mode. it holds off injection until the tps value is reduced below 20%. that allows the engine to blow raw gas clear of the cylinders.

and to be honest, since i don't play with the g10s as much as i used to, i get the twincam, g13bb, and g10t ecu functions stirred in with the g10 sometimes. :whistle
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freegeo
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Quote:
 
read it in the fsm and have found it to be true while troubleshooting.


Can you provide which year FSM and section you read it in? I have most of the metro FSM's and would like to see what it says.

Quote:
 
there's another function that almost never gets discussed and that is holding the throttle open at 70% of the tps range sets the ecu in "flood clear" mode. it holds off injection until the tps value is reduced below 20%. that allows the engine to blow raw gas clear of the cylinders.



It does get discussed from time to time on the forum. While flood clear mode is available on some vehicles the metro is not one of them. It is not mentioned in the FSM. When I got my 1st oscilloscope I tested it to see if my car had a flood clear mode. I will provide those graphs below. Today I already had plans to recheck for flood clear mode and check it in little different way. Below are the graphs.

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This graph is with the throttle closed

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This graph is with the throttle open. Notice that the injector pulse width did not get reduced but actually increased in width.

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Quote:
 
so what type did you select? they are selling a dozen or so different "pocket" scopes on line and they have more that plug into a laptop and use the computer's screen as a display. from the graphic in your sig line yours is a multi-channel unit. 4 channel?


I have a hantek 3064 scope.
Edited by freegeo, Jul 8 2017, 07:56 AM.
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freegeo
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Thought I would post a larger version of the graph that is in my signature. I did 25 start cycles and this is one of them. They are all similar. I will post another graph that shows it a little different and why. The same thing happens just in a different way due to the # 2 cylinder having the extra tooth on the distributor shaft. **This graph has been edited and updated from the original posting. I did take the starting enrichment mode info out. I want to collect more data on it and post it by itself.**

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Edited by freegeo, Jul 8 2017, 08:18 AM.
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