gruss
Part of things
Posts: 242
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Yeah been able to compare a good waveform with a bad one is useful. I've used one on some common rail diesel injectors and also a cam sensor. I'll have to get my manager to send me on some dedicated courses.  |
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Daihatsu Mira TR-XX
Suzuki Alto Works
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Common rail injectors really messed with my mind untill i worked out how they worked. I have a very interesting waveform from a sprinter somewhere that I'll try and find.
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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I have some more things that may be of interest. I bought a new current clamp today so had to have a little play with it. The first capture is an injector waveform at idle from my 850 T5.  The blue trace is the voltage measured between the injector and the ecu, the red trace is the current draw of the injector. We start of with battery voltage flowing through the injector. There is no current draw yet because the ECU hasnt completed the path to earth so up untill 0.0ms this is an open circuit. At 0.0ms the ECU switches the circuit to earth and the current begins to rise. The injector opens and fuel flows into the manifold. At about 2.5ms the ECU cuts the path to earth, the magnetic field in the injector collapses and the resulting EMF causes the huge voltage spike, around 75 volts. Now lets see what happens when we rev the engine.  The engine demands more fuel so the ECU increases the injector duration. Theres actually a couple of things worth pointing out in this waveform. First of all, notice how the current ramp flattens off just after 2.0ms, this is due to the current limiting circuit in the ECU, without it, according to Faradays law, the circuit would continue to increase its current draw and in very little time would burn out the injectors. The second thing of intrest is the small hump in the current ramp about two thirds of the way up. This is the point that the EMF overcomes the resistance of the spring and lifts the needle off its seat. In other words, this is when the injector actually opens. If you look at the voltage trace you can see a similar bump at around 7ms, this is the needle falling through the magnetic field as it closes. So from this waveform we can not only confirm that the injector is recieving a signal and reacting to it but it is actually opening and closing. Suddenly sticking injectors became so much easier to diagnose. Also we can use this to calculate exact injector duration should we need it. Our pulse width is 6.92ms, opening time is 1.53ms, duration is 5.62ms and closing time is 830 microseconds. Anyone who's needed to map a megasquirt will know how usefull that info can be. The last one is just a quicky. A current trace from an electric fuel pump.  This is with the ignition being cycled on and off, we can see the pump draws almost 15 amps when first powered up the it settles dow to around 6. This is normal and quite uninteresting. What is useful though is the ability to zoom in 32 times.  Each one of those little peaks represents a sector on the commutator. We can see by looking at the waveform that the pump is slightly worn but has plenty of life left in it. If there was a gap in that pattern it would mean part of the commutator was worn away and should the pump stop in the wrong posistion it wont start up again. Ever had a pump that wouldnt work unless it was hit with a hammer? Thats why. |
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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scruff
Part of things
Posts: 621
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Awesome Dear Santa.... |
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1994 Lotus Esprit - Fragile red turbo with pop up lights.
1980 Porsche 924 - Fragile red turbo with pop up lights.
I spy a trend...
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rob0r
East of England
Posts: 2,743
Club RR Member Number: 104
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Electrickery and stuffrob0r
@rob0r
Club Retro Rides Member 104
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A very interesting thread! Thanks for sharing.
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E30 320i 3.5 - E23 730 - E3 3.0si - E21 316 M42 - E32 750i
ETC
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Another couple of interesting captures i took today that demonstrate the kind of versatility of a modern digital scope. I had a Honda S2000 in with the engine management light on. Fault memory showed missfires on all cylinders, after clearing the fault codes and starting the engine No2 cylinder was still showing a missfire. The engine was actually running very well with only the slightest ocasional stumble. This is where i started to go wrong and make assumptions. I was convinced i was looking for a faulty coil or injector and wasted a good couple of hours testing things that were working fine. Eventually i decieded to go back to basics and used the scope to carry out a basic compression test by measuring the current draw from the starter motor.  Each peak on the waveform represents a compression stroke. Because the engine is harder to turn on the compression stroke the starter draws more current. Looking at this waveform we can see that one cylinder takes less effort to compress than the other three. If this is number two cylinder then it looks like we've found our missfire fault. I used another channel on the scope to measure the trigger signal for No2 coil to give me a reference point.  Looks like we've found the problem. The cylinder with low compression is definatley No2. While this technique wont tell you exact cylinder pressures its good enough for showing up a fault and justifying the time to strip down the engine and carry out a normal leak down test. |
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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Just renamed this thread as its started going off on tangents.
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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Very useful tangents Rev! I've got a golf in at the moment, just failed the Mot (10% CO and 800ppm HC) and reading a code of P0302 (which is cylinder 2 misfire as it happens...) So I'm going to have a play around with a scope tomorrow and see what I can find out before stripping it - It's the one with the inlet manifold over the top of the engine so you can't get the plugs or injectors without removing it....
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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Nice. If your anything like me then you'll get so involved in the playing around you'll forget what your actually looking for.
It can do wonders for your credibility with a customer when you show them a print out and actually explain what it means then show them the 'after' shot with everything working as it should. Not enough garages are using this technology yet. I was on a course at Mercs the other weeks and out of a classroom of 12 diagnostic techs i was the only one who had ever used a scope.
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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I did a stint as a TV engineer in the '90s so scoping cars is pretty easy. I discovered the other day that our MoT emmission tester has a 2 channel scope built in (never been used) so I've been experimenting with it.
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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scruff
Part of things
Posts: 621
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Keep it coming - awesome stuff.
I understand the theory but it had never occurred to me that a scope would be so useful.
Starter motor current draw to measure compression - genius!
How do you measure high currents - what kit do you use to connect to the scope?
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1994 Lotus Esprit - Fragile red turbo with pop up lights.
1980 Porsche 924 - Fragile red turbo with pop up lights.
I spy a trend...
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I have a couple of inductive current clamps that just clamp around the wire to be tested. One is for low currents up to 60amps and one that goes up to 600 amps for starters and alternators.
Once you get into buying all the toys things can get a bit expensive but no worse than a serious tool habit and these things make me money on a daily basis.
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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Yeah, I just went on the pico tech website and scared myself silly with the prices! I'm looking instead at second hand stuff on ebay. unfortunatly, the scope on the gas analyzer needs paying for before it will work outside of demo mode  connect an input up and it wants a product key. This means that all I did with the golf was run a live data test drive - I'm going to look at the results and see what's going on. Probably in a new thread though. |
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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Nov 11, 2011 12:16:26 GMT
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 ;D ;D ;D although, the software is windows only so I've been forced to use win7 (I feel dirty now) |
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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Nov 11, 2011 22:11:33 GMT
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Excellent. Did you get a complete kit? I'm already on the lookout for a replacement for mine. I've realised that two channels are good, four are better  |
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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Nov 11, 2011 22:25:16 GMT
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Pretty much. I'm missing the 20:1 attenuator for inductive loads but other than that it's all there. Been playing with it all evening!
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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Nov 11, 2011 22:33:42 GMT
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Those attenuators are well handy. I broke one of mine a few weeks ago. They're 50 something quid from pico but you can get them off ebay for about a tenner.
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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Nov 12, 2011 13:37:10 GMT
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Found (on ebay) and bought. £50 is a bit steep for what is basically 2 resistors and a couple of BNC connectors  |
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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gruss
Part of things
Posts: 242
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After spending the last couple of months researching scopes and watching lots of videos, I've come back and reread this thread and it actully makes sense..! When I first read it I thought god that looks complicated! But once you get your head around it.... Just waiting for my new scope now then I can get playing with my car. I personally suspect that the O2 sensor is lazy as mpg has gone down.. Anymore waveforms rev? |
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Daihatsu Mira TR-XX
Suzuki Alto Works
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connect an input up and it wants a product key.
