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Discussion Starter #1
I'm having random misfire code and the engine has a little shake to it. So it's got a miss. Since everything is new from the opti ( with mitsubishi sensor ) to the plugs, I'm pretty sure it's none of that. I already found a dead injector and replaced that, now all 8 are working properly ( used a tester ).

So I got this air gap tester and tested directly from the coil. Most info I can find online for generic testing with these is to set it to 30 and look for a nice blue spark. I did it at 20 ( smaller gap ) and I get a mostly orange spark. Since every make of car is different, does this confirm that I have a bad spark? It's jumping the gap every single time, just mostly orange with the occasional blue flash in it. Would this be a weak spark that causes misfires? Or would it still run fine even like it is and I should keep looking for a different problem?
 

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Try testing at 30, then 40. 20 would be a setting for an old points type ignition system. Electronic ignition likes a wider gap. Consult service manual for plug gap and try that size gap with spark tester.

So to recap, start with 30 and go progressively wider. See if you get a good blue spark. The orange spark is weak.

And don't count your opti out as a suspect. The Chinese love to make counterfeit parts that look like the original. Even have the company logo on them. But they are crap.

Please heed the warning to only use GM, Delco, or Delphi opti. But in the meantime, if you really want to confirm that optical section of opti is good, buy a $70 PC based oscilloscope. You can get it on Ebay, Amazon, etc.

Your opti low & high resolution signals should be a nice square wave with no drop outs or funky waveform changes. Bad optical sensor, or wonky discs can cause all sorts of running disorders.
 

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Discussion Starter #3
When I say I have a mitsubishi sensor, I mean I pulled an oem from a junkyard and swapped it into the aftermarket opti. So it is a mitsubishi sensor.

I'm not sure what you mean about using the spark plug gap in the air gap tester. It only goes up to to 40 kilovolts. The spark plug gap according to the manual is 55mm. At 20 kilovolts, it's already way bigger than the spark plug gap. Are you saying that making the gap wider could actually give a stronger spark on the electronic ignition? I assumed the opposite. I'll test it at 30 and 40 this afternoon.
 

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Electronic ignitions need a wider gap for the higher voltage to jump across. By using the spark plug gap, I'm saying to see what the gap is. Then use that amount of gap to do your testing. I don't have measurement memorized, but I'm pretty sure it's over 0.040"

When you put used oem sensor into opti, did you test the low & high resolution signals with an oscilloscope to see if all was well?

And since you had to pull the timing wheels out of new opti to change sensor, could they have become damaged do to handling?
 

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Discussion Starter #5
It sounds like we're not on the same page for the gap tester. When you set it to 40, it's a gap large enough that it takes 40 kilovolts to jump it. It's not the same as a plug gap of 0.04". It's closer to an inch and a half. The idea is that if the spark is strong, you'll get a blue spark over that large gap. If the spark is weak, it either won't jump, or it'll be a smaller lighter colored spark. At the 20 kv setting, it was jumping consistently, but it was orange. I didn't get to test the other settings yet. But I want to before I buy a new coil.

I do not yet have an oscilloscope to test it. I know I'm not getting the codes for the hi signal to be bad. Unless I'm misunderstanding the shoebox site, the low signal failure either won't let it run, or runs like crap but doesn't throw a code. Since I'm getting a misfire code, I figured that wasn't it.

The timing wheels looked perfect to me, unless the excess heat from the very short overheat caused them to warp. The misfire code didn't start until it got hot at the end of that 2 mile trip. That was also the first time the car had been driven since putting this motor in and solving all the other issues. Another reason I'm thinking coil is that being under load the first time stressed the coil too much. I've heard excessive spark plug gaps can burn up a coil, so if it's already weak, I could see that damaging it further.

I need to test that spark at the coil again with the air gap tester opened up. I need to see if it turns blue with a larger gap or won't jump at all.

This is the video that shows the tester I'm using, though it doesn't mention the color. I honestly don't remember where I read that part.

 

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Yes, I was misunderstanding how the air gap tester works. But spark should not be a orange or yellow-orange color.

Funny thing about the dtc 16 & 36 codes, they don't set if the waveform is the wrong shape, or it drops out for 1 or 2 firing events. So don't rely on the codes setting for intermittent problems.

I've been telling members for years that all lt1 owners, and all modern car owners as well, need an oscilloscope for troubleshooting.
 

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As an example, my 90 camaro with 3.1 v6 would not run. I tested it every way I knew. Could find nothing wrong. I tested 30 hertz fuel enable signal with my multimeter, which can test frequency. It showed 30 hertz signal was present. But fuel injectors would not open.

I finally hooked up my scope, and low and behold, the signal being sent out by the theft deterrent module was not the square wave it should have been. It looked like the teeth of an alligator. Yet no code set because there was a signal present.

Changed the TDM, car started right up.
 

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Discussion Starter #8
Okay, I opened up the air gap tester to 30, and then to 40. Weird that the spark was orange at the low gap, but was nice and blue on the bigger gaps. It was jumping every time, so now I don't think it's my coil.

I'm buying an oscilloscope before I go any further. I'm not pulling the opti unless I can confirm the signal isn't good. If I can find a good one on amazon that'll be here before Saturday, I'll test that first. IF it tests good, then I'm going to start pulling plugs. Give them a look over. If they all look good, then I'll start the compression tests per cylinder.

The fact the misfire didn't start until it got hot makes me worry a bit about that part. As much of a pain as it is to pull the opti, head gaskets are worse. I'd hate to think it blew one that quick though. They're brand new with brand new bolts and the engine has run less than an hour and it was shut off pretty quick when it got hot. But I don't see how the opti would be affected by the engine heat. I'd think the temperature threshold for damage to a sensor or reluctor wheel would be much higher than that.
 

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Discussion Starter #9
Funny thing about the dtc 16 & 36 codes, they don't set if the waveform is the wrong shape, or it drops out for 1 or 2 firing events. So don't rely on the codes setting for intermittent problems.

I've been telling members for years that all lt1 owners, and all modern car owners as well, need an oscilloscope for troubleshooting.
I know I can't count on the 16 and 36 codes ( I'm assuming those are OBD1 codes ), or the low resolution code ( for OBDII ) as you stated. But I AM getting code P0300. Will the intermittent problem throw code 0300? Because if it doesn't throw that code, then that's probably not my problem either.

Also, will that misshapen wave form cause a consistent miss? I can feel the miss this time better than I could when cylinder 2 wasn't getting fuel and it doesn't seem to come and go. It's consistent shaking. Very light shaking, but consistent.
 

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Discussion Starter #10
Here is a quick video of my car's spark at the 30 kilovolt setting of the air-gap tester. Looks good and blue to me. I see some occasional orange. Does that mean it could still be my coil? If it occasionally throws a weaker spark, that'd cause a misfire as whichever cylinder was firing at that moment would fire weaker.

 

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Discussion Starter #11
86601655_10218354309062125_3115863911274905600_o.jpg
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Okay, so this is the waveform I'm getting at the white wire going into the coil from the PCM. Are these square enough or would those little jagged lines be enough to cause a misfire? The opti is either causing my misfire or it isn't and I'd love to know before I tear this thing down again or waste time looking elsewhere for the problem.

It did get worse. Cylinder 2 has gone down again. It was a dead injector before. So far, I've confirmed the new injector is still clicking. I'll have to start on it again on Saturday, I'd just like to know if I should start with the opti or look at the plugs and wires first.
 

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Those little tiny variances are not enough to cause a problem. But opti low & hi hes signal needs to be checked at opti pigtail. If you have a dual channel scope, you can check both at same time. If single channel scope, check one at a time. These are the most import indication of optical section health.
 

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Discussion Starter #13
Those little tiny variances are not enough to cause a problem. But opti low & hi hes signal needs to be checked at opti pigtail. If you have a dual channel scope, you can check both at same time. If single channel scope, check one at a time. These are the most import indication of optical section health.
My scope is single channel. I checked both and they looked as good as the signal I measured at the coil. If it's cool there, it's cool all around.

I found my problem. When I put the a/c compressor in, the lines pushed the #2 plug wire up against the exhaust manifold. It burned through the insulation. Several tight rounds of 3m electrical tape seemed to have fixed the problem. She's running good now.
 

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Discussion Starter #15
I'd still get a replacement plug wire.
Oh, absolutely. I just don't have one on me and the tape was to get me on the road until the new ones come in the mail. I did reposition the plug wire so it's not against the manifold anymore. I positioned it correct originally, but I think it was the A/C lines attached to the compressor that pushed it up when I was putting the compressor back in.
 
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