Crazy Secondary Spike - not possible???

Alex Diagnostician Australia Posted   Latest   Edited  
Resolved
Driveability
P0303 — Cylinder 3 Misfire Detected
P0353 — Ignition Coil "C" Primary Control Circuit/Open
P0301 — Cylinder 1 Misfire Detected
Misfires

Observed some curious crazy sec ignition measurements today on a Coil on Plug Volvo V70 5cyl engine. Sometimes defaulted to a ridiculous 150kV peak firing line. I'm thinking Impossible!! No coil can produce that even open circuit even once??? Or can they? Im thinking the scope is not doing the math of X10,000 probe properly from the Inductive probe (I'm using a good HT wire extention between COP and plug) ... I try the alternative Pico just for comparison ... get a good wavefore 9kV-12kV at idle, good burn line etc, scope correctly set to X10,000 attenuation ... then suddenly on one coil I get the same phenomena. Huge firing line, apparently, and massive lean nose at end of burn line ... I'm pushing the plug connection down to ensure connection, I'm pushing the coil boot connection in to ensure connection, but it continues. Reconnect from the top later, and it's a good waveform again. Also saw same deal on at least one other coil. I have new Bosch plugs as per spec in the car. Have changed out two coils (OEMs replaced) in a few weeks, now on to 3rd dead coil (blown secondary, primary working fine). Just pausing before I change out 3rd coil. Only old coils dying so far. Am I crazy? Any thoughts on what's going on?? I've selected a good and a crazy waveform posted here for reference.

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Missing Vehicle
Spiro Service Manager
New York
Spiro
   

Can you see or feel misfire? What are the fuel trims? Is the car drivable? Any Power?

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Ray Diagnostician
Ontario
Ray
 

Measure all COP ground wire voltage drops, the B+ to the COPs and measure all COP primary coil winding current draws. This capture is from an 08 Volvo XC90 4.4 with some COP misfires due to high COP ground wire voltage drops. CH C is the COP B+ at 14.5v CH D are the COP primary coil winding current draws at the fuse. CH A is the COP 6 with a 3.5v ground voltage drop in the ground wire to the…

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Alex Diagnostician
Australia
Alex Update
 

Spiro, car originally drove in with a dead miss, but running and driveable … it was easily nailed down to cyl 3 and OEM coil fixed it immediately. Two weeks later, a dead miss again, Cyl 1. Customer declined full diagnositc on the presumption that it's just old coils (ie 320,000kms on original coils). OEM Coil fixed it again. One week later, dead miss again on cyl 3, (but NOT the new coil (had…

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Ray Diagnostician
Ontario
Ray
   

Some Nissans have melting COPs due to ground voltage drops between the block/transmission to the battery negative battery post. Measure the block/transmission ground voltage drops with the engine cranking. To scope the COP secondary, try any old distributor 2 wire inductive pickup coil and put it on the COPs. The first photo is two GM distributor 2 wire inductive pickup coils on a paint…

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Interesting
Doug Owner/Technician
California
Doug
 

Greetings Ray, two questions one is the first capture it looks like it has a lean condition high spike and why the double strike on the second waveform? Hope you're doing well, Doug

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Ray Diagnostician
Ontario
Ray
   

The first capture looks like it has a lean condition high spike because the secondary coil winding has to create more voltage to force the spark to arc across the spark plug's air gap to the plug's ground terminal with the high cylinder compression and the turbulence in the cylinder during the 1500 rpm brake torque. That's why you should always scope the misfiring cylinder along with a non…

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Doug Owner/Technician
California
Doug
 

Thank you for that Ray. So I'm thinking that without a higher sampling rate, the lean cylinder won't be as visible as you mention? I've been wondering before what changing the sampling rate in a capture would do to make it more apparent on what is happening. I've tried changing sampling rates to see any differences in a waveform but haven't as of yet. Here's one example of which would show that…

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Ray Diagnostician
Ontario
Ray
 

If your scope is set at 2 or 10 ms/div and you're using 1 or 2 channels, the higher sampling rate won't make much difference. But if the misfire is intermittent and you're using 4 channels, you'll need to put more time on the screen and the sample rate will need to be higher in order to catch the glitch. Set your scope to 500 ms/div or 1 sec/div and the sampling rate to 6 MS for ALL of your…

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Ray Diagnostician
Ontario
Ray
 

Good example of a secondary waveform with the scope set to a low sampling rate.

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Alex Diagnostician
Australia
Alex Update
 

Ray I love these home-built rigs … I really have rig up some of this myself! Appreciate your generosity in sharing knowledge. On my issue, i was thrown for a loop by the just incredibly high voltage in the secondary … I think the highest spike I saw was nudging 200kV … Honestly, I thought my scope was stuffed and just not doing the math properly. Learning 1: I now know that an open COP…

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Ray Diagnostician
Ontario
Ray
 

When using an adjustable kv output spark tester, the highest kv that you will measure from a COP will be near 35-40KV, or about a 1" long spark. You can get this COP extension lead set thru Autonerdz and connect them on a known good non misfiring engine to see what known good secondary waveform captures looks like. The insides on the spark plug boots must be lubricated and I use a 3/8" crows…

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Doug Owner/Technician
California
Doug
 

Thank you for that Ray, I was wondering about those! And what is it that you see by using those much better than just with the cop pickup on top of the coil? I can probably know but I thought I'd get your input on that.

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Ray Diagnostician
Ontario
Ray
 

The first capture is from a COP with an extension spark plug wire and the secondary scope lead is on the plug wire. The injector is connected and I'm doing a brake torque, known good. You will not be able to accurately measure the kv output of the pickup coil on the COP, whereas the secondary probe on the spark plug wire will be more accurate, if the scope's sample rate is fast enough. Again…

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Thanks
Eric Owner/Technician
Wisconsin
Eric
 

Alex, I'm not sure where you got the idea that a standard issue COP coil can produce nearly 200kv output. I believe your oversized ignition capture is a fault of your scope, probe, or attenuation device. If the rest of your pattern was normal sized and the firing line voltage was near the 150kv or greater output I would agree that the coil was actually producing the voltage the scope is…

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Alex Diagnostician
Australia
Alex
 

Eric thanks, yes that was my initial thought and still at the back of my mind. It's possible that these coils, at 320,000kms were just dying … I've replaced all coils and new OEM plugs and I have not anomalies on the scope pattern and a normal running engine using the same probe. Fair point on the scope, thought I've never seen a similar issue and really has behaved pretty well for me. Oddly, I…

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Eric Owner/Technician
Wisconsin
Eric
 

Alex, a failing coil is going to short or open circuit, both will reduce the possible output, not increase it.

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Alex Diagnostician
Australia
Alex
 

Hi Eric, great to have your knowledge and input. Yes I can see that on a short. Not clear why an open wire, plug or coil with a bigger than plug spec gap wld reduce sec V output? Main issue at moment for me is that although the car has eaten 3 coils and has now for 100kms run perfectly with new coils and OEM plugs, with no scope anomalies showing up, I still can’t answer definitively answer…

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Eric Owner/Technician
Wisconsin
Eric
 

It is important to look at each part individually. Lumping a plug wire in with an ignition coil will change cause and effect as well as changing the test results. In my reply I was only talking about an open or short circuit in the ignition coil windings themselves, not an open in the spark plug wire.

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Alex Diagnostician
Australia
Alex Resolution
 

Thanks all for the assistance. I've just been waiting to hear whether any further issues have emerged after the fix. This was a bit odd for me, and I believe the super spikes were are artefact but the coils were definitely being killed one by one By default, the conclusion is one of two: a. The Bosch plugs that were installed a year and 20,000kms ago were killing the coils; b. the coils were…

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