Testing a COP with Oscilloscope
05-05-2010, 10:39 AM
#1
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Testing a COP with Oscilloscope
Can somebody tell me what settings to put the oscilloscope on and what to do in general to test a COP with one? I think i'm having a very slight misfire on my driver's side bank. I'm pretty familiar with observing and adjusting signals on an O-scope.
Recently I accidentally raced an 08 GT/CS with a 93 octane tune while running 87 octane and I heard a very clear ping on my driver's side. I noticed that after tuning back to 87 what I had always just kind of wrote off as an "airy" sound was actually what sounded to me like a very feint pinging. The reason I think this sound is pinging now is because i'm now very familiar with the sound after running the wrong tune but its about 90% quieter than when I had the 93 octane tune on. The sound is most evident at 1500-2000 RPMs in Over-Drive but is there throughout most of the powerband if not all. I guess it might some loud injector clatter but something doesn't seem right. I'm trying to put a blower on in a month and I want to make sure its not missing.
How safe is it to unplug injectors/COPs while the engine is running? Wont the engine continue to supply fuel if you just unplug the cop? And vise versa? Not that it would help me much because I doubt this sound is recognizable @ idle at all.
Edit: This sound is more noticable going up a hill
Recently I accidentally raced an 08 GT/CS with a 93 octane tune while running 87 octane and I heard a very clear ping on my driver's side. I noticed that after tuning back to 87 what I had always just kind of wrote off as an "airy" sound was actually what sounded to me like a very feint pinging. The reason I think this sound is pinging now is because i'm now very familiar with the sound after running the wrong tune but its about 90% quieter than when I had the 93 octane tune on. The sound is most evident at 1500-2000 RPMs in Over-Drive but is there throughout most of the powerband if not all. I guess it might some loud injector clatter but something doesn't seem right. I'm trying to put a blower on in a month and I want to make sure its not missing.
How safe is it to unplug injectors/COPs while the engine is running? Wont the engine continue to supply fuel if you just unplug the cop? And vise versa? Not that it would help me much because I doubt this sound is recognizable @ idle at all.
Edit: This sound is more noticable going up a hill
Last edited by Hangwire; 05-05-2010 at 11:06 AM.
05-05-2010, 12:03 PM
#2
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should be fine to unplug them for a second to test, but it could destroy your cats if you have any.
you can try just using a DMM first though and ohm them out. if one is significantly lower or higher resistance than the others, its probably the bad one.
also have you done the easiest thing first and checked for any cracks in the rubber boots?
you can try just using a DMM first though and ohm them out. if one is significantly lower or higher resistance than the others, its probably the bad one.
also have you done the easiest thing first and checked for any cracks in the rubber boots?
Last edited by MU71L4710N; 05-05-2010 at 12:07 PM.
05-05-2010, 12:23 PM
#3
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I just pulled all four drivers side COPs. Ohmed them out and all are between .5 and .8. But from what i've read you can only really tell if the cop is totally shot using a multimeter.
Here are pics of the COPS. Boots looked just fine to me.
I will post a video of me driving tonight or tomorrow. Though the noise is so feint I dont think a camera will even pick it up.
Here are pics of the COPS. Boots looked just fine to me.
I will post a video of me driving tonight or tomorrow. Though the noise is so feint I dont think a camera will even pick it up.
Last edited by Hangwire; 05-05-2010 at 01:08 PM.
05-05-2010, 01:11 PM
#4
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This was taken across the primary of cylinder #5, the probe's ground connected to the light green/yellow wire, the probe to the red wire. I used a 10X probe, the conventional negative going signal was inverted to make the trace more intutitive:
The vertical axis is 10V/div, the timebase is set to 1mS/div, the HF rejection filter on the trigger was set.
This is an OEM COP.
Of some note is the "triple-strike" spark, at idle and lower rpm operation the PCM fires each COP three times in succession, in 3mS or so. The inital dwell is 1.8mS or so, the subsequent dwell times are about 1.0mS.
The spark duration curves are interesting. In the first strike it is intially smooth and then "spikey", in the center quite smooth, and in the last strike there is quite a bit of spiking toward the end. I suspect this reflects the propogation of the flame front and pressure variations as the piston rises and falls and combustion proceeds.
I would not unplug a COP with the engine running, although the control electronics are quite robust there is the possibility that some damage to the drivers could result.
The OEM COP primary resistance will measure between 0.5Ω and 0.8Ω as others have indicated, the secondary between 5.0kΩ and 8.0kΩ maybe a bit higher. However the low voltage used by typical multimeters when measuring resistance is not near enough to properly test the secondary windings, a high voltage instrument commonly known as a "megger" is needed to properly test the secondary's electrical characteristics.
The good news is that using a 'scope on an operating COP works better than all of the above!
The vertical axis is 10V/div, the timebase is set to 1mS/div, the HF rejection filter on the trigger was set.
This is an OEM COP.
Of some note is the "triple-strike" spark, at idle and lower rpm operation the PCM fires each COP three times in succession, in 3mS or so. The inital dwell is 1.8mS or so, the subsequent dwell times are about 1.0mS.
The spark duration curves are interesting. In the first strike it is intially smooth and then "spikey", in the center quite smooth, and in the last strike there is quite a bit of spiking toward the end. I suspect this reflects the propogation of the flame front and pressure variations as the piston rises and falls and combustion proceeds.
I would not unplug a COP with the engine running, although the control electronics are quite robust there is the possibility that some damage to the drivers could result.
The OEM COP primary resistance will measure between 0.5Ω and 0.8Ω as others have indicated, the secondary between 5.0kΩ and 8.0kΩ maybe a bit higher. However the low voltage used by typical multimeters when measuring resistance is not near enough to properly test the secondary windings, a high voltage instrument commonly known as a "megger" is needed to properly test the secondary's electrical characteristics.
The good news is that using a 'scope on an operating COP works better than all of the above!
05-05-2010, 01:45 PM
#5
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What is an indication of a COP malfunction on the 'scope screen? I dont believe I have software to view the data in the manner you have posted it.
How practical is it to have a missfire so feint that you would have to turn the radio down and lean over the dash to hear it? I dont even thinking driving with a camera in my hand will expose this sound, am I just damn crazy? I know I hear something.....LOL. I dont imagine my connecting rods, pistons, or piston rings will be ok with any miss whatsoever with 9 PSI through a KB being pumped in.
How practical is it to have a missfire so feint that you would have to turn the radio down and lean over the dash to hear it? I dont even thinking driving with a camera in my hand will expose this sound, am I just damn crazy? I know I hear something.....LOL. I dont imagine my connecting rods, pistons, or piston rings will be ok with any miss whatsoever with 9 PSI through a KB being pumped in.
Last edited by Hangwire; 05-05-2010 at 02:50 PM.
05-05-2010, 03:52 PM
#6
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Can somebody tell me what settings to put the oscilloscope on and what to do in general to test a COP with one? I think i'm having a very slight misfire on my driver's side bank. I'm pretty familiar with observing and adjusting signals on an O-scope.
Recently I accidentally raced an 08 GT/CS with a 93 octane tune while running 87 octane and I heard a very clear ping on my driver's side. I noticed that after tuning back to 87 what I had always just kind of wrote off as an "airy" sound was actually what sounded to me like a very feint pinging. The reason I think this sound is pinging now is because i'm now very familiar with the sound after running the wrong tune but its about 90% quieter than when I had the 93 octane tune on. The sound is most evident at 1500-2000 RPMs in Over-Drive but is there throughout most of the powerband if not all. I guess it might some loud injector clatter but something doesn't seem right. I'm trying to put a blower on in a month and I want to make sure its not missing.
How safe is it to unplug injectors/COPs while the engine is running? Wont the engine continue to supply fuel if you just unplug the cop? And vise versa? Not that it would help me much because I doubt this sound is recognizable @ idle at all.
Edit: This sound is more noticable going up a hill
Recently I accidentally raced an 08 GT/CS with a 93 octane tune while running 87 octane and I heard a very clear ping on my driver's side. I noticed that after tuning back to 87 what I had always just kind of wrote off as an "airy" sound was actually what sounded to me like a very feint pinging. The reason I think this sound is pinging now is because i'm now very familiar with the sound after running the wrong tune but its about 90% quieter than when I had the 93 octane tune on. The sound is most evident at 1500-2000 RPMs in Over-Drive but is there throughout most of the powerband if not all. I guess it might some loud injector clatter but something doesn't seem right. I'm trying to put a blower on in a month and I want to make sure its not missing.
How safe is it to unplug injectors/COPs while the engine is running? Wont the engine continue to supply fuel if you just unplug the cop? And vise versa? Not that it would help me much because I doubt this sound is recognizable @ idle at all.
Edit: This sound is more noticable going up a hill
would checking the plugs them self be any use?
05-05-2010, 04:20 PM
#7
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Wont these signals be flying across the screen real fast if they fire that fast? What is an indication of a COP malfunction on the 'scope screen? I dont believe I have software to view the data in the manner you have posted it.
How practical is it to have a missfire so feint that you would have to turn the radio down and lean over the dash? I dont even thinking driving with a camera in my hand will expose this sound, am I just damn crazy? I know I hear something.....LOL.
How practical is it to have a missfire so feint that you would have to turn the radio down and lean over the dash? I dont even thinking driving with a camera in my hand will expose this sound, am I just damn crazy? I know I hear something.....LOL.
What 'scope (make/model) do you have?
With a digital scope, using a triggered single sweep, you can capture just a single sweep as I did with my Lecroy WaveJet 322.
With an analog scope and triggered sweep you will get repetitive and overlapping traces every 160mS or so at idle --there will be some flickering and blurring from the overlapped traces but the pattern will be recognizable.
Typically a weak coil will show up as a half-hearted attempt to ionise the gap, the initial spike will build slowly and/or be rather short; also the spark duration will be short, with no "ringing"--dissipation of residual energy after the spark ends--because there is none left after firing the plug.
You can also use the 'scope trace to diagnose misfires. As basics a lean mix will cause the spark duration voltage to be high and erratic, a fouled plug will show a shorter than normal ionisation voltage and spark duration, and a bad COP boot or other "out-of-cylinder" discharge will have a very low voltage initial spike and a very long duration downward tapering "spark" with little to no ringing...
05-05-2010, 05:43 PM
#8
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What 'scope (make/model) do you have?
With a digital scope, using a triggered single sweep, you can capture just a single sweep as I did with my Lecroy WaveJet 322.
With an analog scope and triggered sweep you will get repetitive and overlapping traces every 160mS or so at idle --there will be some flickering and blurring from the overlapped traces but the pattern will be recognizable.
Typically a weak coil will show up as a half-hearted attempt to ionise the gap, the initial spike will build slowly and/or be rather short; also the spark duration will be short, with no "ringing"--dissipation of residual energy after the spark ends--because there is none left after firing the plug.
You can also use the 'scope trace to diagnose misfires. As basics a lean mix will cause the spark duration voltage to be high and erratic, a fouled plug will show a shorter than normal ionisation voltage and spark duration, and a bad COP boot or other "out-of-cylinder" discharge will have a very low voltage initial spike and a very long duration downward tapering "spark" with little to no ringing...
With a digital scope, using a triggered single sweep, you can capture just a single sweep as I did with my Lecroy WaveJet 322.
With an analog scope and triggered sweep you will get repetitive and overlapping traces every 160mS or so at idle --there will be some flickering and blurring from the overlapped traces but the pattern will be recognizable.
Typically a weak coil will show up as a half-hearted attempt to ionise the gap, the initial spike will build slowly and/or be rather short; also the spark duration will be short, with no "ringing"--dissipation of residual energy after the spark ends--because there is none left after firing the plug.
You can also use the 'scope trace to diagnose misfires. As basics a lean mix will cause the spark duration voltage to be high and erratic, a fouled plug will show a shorter than normal ionisation voltage and spark duration, and a bad COP boot or other "out-of-cylinder" discharge will have a very low voltage initial spike and a very long duration downward tapering "spark" with little to no ringing...
I'll record myself checking the cops so you can see if i'm hooking things up right and so you can see exactly what I see on the 'scope.
05-05-2010, 06:13 PM
#9
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A set of these makes life a lot easier when probing wires on a an engine:
They are spring-loaded insulation piercing clips that work like a hypodermic needle, and make just the tiniest little hole in the insulation--that can be sealed with a dab of RTV sealant, or even dielectric grease on something you monitor a lot.
The probe part is 5-1/2" long, the needle is stainless, and they have a V-shaped end that make 'em easy to get onto bundled wires. They're only $16 + shipping from SL Discount Tools (good people!).
Pomona makes some nice piercing clips too, but they are kind of pricey ($38/pr for the short ones shown below) and a bit more difficult to handle with greasy hands:
They are spring-loaded insulation piercing clips that work like a hypodermic needle, and make just the tiniest little hole in the insulation--that can be sealed with a dab of RTV sealant, or even dielectric grease on something you monitor a lot.
The probe part is 5-1/2" long, the needle is stainless, and they have a V-shaped end that make 'em easy to get onto bundled wires. They're only $16 + shipping from SL Discount Tools (good people!).
Pomona makes some nice piercing clips too, but they are kind of pricey ($38/pr for the short ones shown below) and a bit more difficult to handle with greasy hands:
05-05-2010, 06:59 PM
#10
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Yeahhhh I think i'm just gonna do it the ghetto way but I was wondering today if I would have to pierce some insulation. I'll just bring a little RTV out there with me. Thanks for the help. I'll probably end up not finding anything at all. I'll change my injectors and spark plugs when I put the KB on anyways. That will only leave 2 options on the table. Bad COP or mechanical issue causing pinging/missfire. I'll make sure to tell my tuner to give it a thorough lookover for slight pinging. Though chances are i'll know if theres an issue before I get there because i'll be limping it over there on their baseline tune.
Will probably swap COPs around this weekend depending on what I see on the 'scope.
Will probably swap COPs around this weekend depending on what I see on the 'scope.
