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help. how to probe conventional ignition?

posted Jun 04, 2016 05:15:36 by Matthew Conner
Hey guys I have an 02 chevy 1500 with conventional ignition (coil, distribitor, wires, and plugs. I have been unable to get a secondary waveform with my dso nano and compasitive probe. I had no issue at all getting a good waveform on my sons 01 chevy malibu but it is a DIS ignition. any help would be great. thanks
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13 replies
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Tyler said Jun 04, 2016 13:43:57
Hey Matthew!

No luck with using the probe on the individual plug wires? If you're not getting a waveform there, then I'd suggest clipping onto the coil wire itself. Since the coil wire is before the distributor, the patterns you get from it are stronger and more detailed. You won't be able to distinguish individual cylinders, but it would be a step in the right direction.

If you're still not seeing a pattern at the coil wire, then I'd have to wonder about the scope settings. Not sure if the Nano has an 'invert' feature, but worth checking. I'd also suggest turning off any triggering if you haven't already.
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IsshmanGarcia said Jun 04, 2016 19:15:34
Im not familiar with your scope but from whst I here, its like a uScope-which I do have. I dont know why you aren't picking anything up on the scope. I suggest you turn the scope off then on (not connected to the car).CHECK TO MAKE SURE YOU HAVE A GOOD GROUND before you connect to the vehicle. If that checks out go ahead and hook up to the car and pkace your probe/pickup to the sparkplug wire. At that time you need to set your voltage. Try setting a 1 or 2v scale first. (I dont know if your scope goes by divisions or how many division you have) also dont know the attenuation on your probe! Basically what im getting at is that you might be in a situation where your scope isnt setup to see the amount of voltage being produced, thus not picking anything up on the scope.If you were scoping a 12v source but your scope was setup to view 8v,you have a problem.I hope this helps a little. Let me know.
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IsshmanGarcia said Jun 04, 2016 19:18:26
Also, for a trigger try putting it on AUTO. That should stabilize any waveform if there is one somewhere in there.
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AndyMacFadyen said Jun 07, 2016 04:08:15
Try the following:
Trigger: Auto and downward slope
Voltage VD Y setting 50mv/div
Time TD X setting 1ms/div

You will need move the trigger level up and down until you find a good setting also try triggering on the upward slope.
[Last edited Jun 08, 2016 19:07:08]
"Rust never sleeps"
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AndyMacFadyen said Jun 08, 2016 19:03:12
Hope this helps Sorry about the quality of this image but it shows a capture of an ignition primary voltage on a DSO210 Nano using a Hantek Capatictive probe. It is actually a wasted spark. Same settings should work any type of ignition with plug wires.


[Last edited Jun 08, 2016 19:04:29]
"Rust never sleeps"
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Matthew Conner said Jun 10, 2016 05:10:01
Here is an image I took with my Hantek Capatictive probe hooked up to the wire from my coil to distriburator, but when I move the probe to a spark plug wire I don't get anything. any ideas?

Sorry my scope doesn't have an invert option.
[Last edited Jun 10, 2016 05:13:29]
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AndyMacFadyen said Jun 10, 2016 07:46:18
Try moving the trigger level setting up closer to the base 0v volt line.
Also turn the volts/div up one notch

At the plug wire the KV will be lower because in a distributer ignition system the spark will have already jumped one air gap between the rotor arm and the cap.
"Rust never sleeps"
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alandk said Jun 10, 2016 13:16:48

Do the roter arm have a build in resistor 5 Kohm, it can fail?

http://www.da7c.co.uk/technical_torque_articles/bosch_distributors-ROTOR%20ARMS.htm
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AndyMacFadyen said Jun 11, 2016 05:18:50
Check the rotor arm resistance with a multimeter, I don't know the setup on your vehicle but I used to see so many Lucas and Bosch rotor arm resistors causing problems on Ford CVH and Rover engines back in the 1980s and 1990s that we started changing them as a service item.
"Rust never sleeps"
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Matthew Conner said Jun 11, 2016 18:46:13
I should have said this in the first post but I am trying to find the cause of a cylinder 4 misfire. If it was the rotor wouldn't it cause a random mis? I guess it could be build up on the number 4 contact. Any thoughts?
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AndyMacFadyen said Jun 11, 2016 20:45:39
You have to look at the the things that will only cause a single cylinder misfire.
I take it you have tried switching the plug and wire on to a different cylinder.

Paul has a couple of excellent video on how to test plug lead insulation using test light (with a tungsten bulb) to and multimeter to check for breaks in the conductor. The official NGK method and specs for checking spark plug lead continuity is here https://www.ngk.de/en/technology-in-detail/ignition-cables/diagnosis/testing-of-ignition-cables/

It could be the distributer cap, rather than just replace it straight off remove it and examine inside and some cracking or trace of arcing or burned contact might be visible.
You can stress test the coil cap and plug lead by making the spark jump a very wide gap in air and comparing it with other cylinders, you can jury rig a setup for this or you can buy low cost adjustable spark tester. The spark should be able to jump about 20+ mm in air.

As you are able capture the secondary waveform on the coil to plug lead then reduce the time per division and capture a parade of sparks. You are looking for a repeating of a spark that looks different from the others. A low or high plug voltage on one cylinder is a major clue.

The other suspects for dead miss are an injector related problem, or a compression related problem such as a closed up valve clearance or a burnt exhaust valve.

"Rust never sleeps"
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Matthew Conner said Jul 05, 2016 02:41:03
Hey guys here is some freeze frame data for my cylinder 4 misfire. Anything look off?

Vehicle Manufacturer: Chevrolet
Vehicle Calibration ID: 12212156
09358545
0935

Freeze frame information:
------------------
Fuel Status = 0 byte
Engine Load = 7.059 %
Engine Coolant Temperature = 49 °C
Fuel Trim Bank 1 Short Term = -9.375 %
Fuel Trim Bank 1 Long Term = 10.938 %
Fuel Trim Bank 2 Short Term = -3.125 %
Fuel Trim Bank 2 Long Term = 11.719 %
Intake Manifold Pressure = 4.061 psi
Engine RPM = 1,597.25 rpm
Speed (OBD) = 46 km/h
Mass Air Flow Rate = 12.03 g/s
Throttle Position(Manifold) = 0 %

End of report.
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Noah said Jul 05, 2016 03:21:32
So, have you verified spark on the missing cylinder? Is it a dead miss, or something that comes and goes, and flagged a p0304?
Are you able to pick up a secondary trace on any other cylinders?
No sense reinventing the wheel if you aren't getting spark out of the cap on #4cylinder only.
[Last edited Jul 05, 2016 03:24:06]
Massachusetts, USA
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