Well originally I was going to post the images I captured from my UScope but they didn't save correctly so that is out.

Anyway, here is what I learned from using the scope on my 93 that other may find useful.

Background: When the car is started below approx. 40 degrees and warms up to operating temperature the car develops a misfire/popping in the exhaust/sometimes the idle surges. Can be hard to restart if you shut it down and restart when it is doing this. If you let the car cool a bit and then restart it fires right up and can warm back up and have NO issues at idle or running. If you start the car in warmer cold start conditions say above 45 degrees you have ZERO issues with it running or idling.

I hunted this problem before but came up with nothing the car passed all the tests so nothing conclusive.

Given I don't drive the car when its cold outside and it runs fine otherwise I never really worried about it. I had some time to finally put my Uscope on it to run some patterns.

Opti-Spark High Resolution: 5V Square wave signal. High frequency, very fast. No drop out when car was missing.

Low Resolution: Also 5v square wave signal. The squares vary in on time because the slots are different sizes.

PCM signal to Ignition Control Module (ICM) is also a 5v square wave that is pulsed on/off.

All of these signals increase in frequency when engine RPM goes up.

ICM coil output control is a typical primary ignition waveform.

I also tested my secondary ignition and found NO issues with the waveforms and no drops in plug firing even with snap throttle testing.

Here is a good video I found that shows GOOD scope patterns for a Opti-spark. Exactly what I had but without his delay issue.



Long story short my issue is NOT the Opti-Spark nor any other component of the ignition system.

I want to run some injector scope patterns and watch the ramping rates from injector to injector. I have ohm'ed the injectors hot and cold all within spec. However, Ohm test is a **** poor one as the component is NOT loaded. Amperage ramping is a WAY better way to test an injector. Fuel pressure was good previously and like I said I have NO issues with the car at WOT or at cruise, etc...

So if you suspect a bad opti-spark I recommend finding a GOOD automotive digital storage oscilloscope and doing some testing. I spent maybe 10 minutes doing this after the car was warmed up and once it started to misfire and pop. How long do you want to mess around with spark checking and all that crap when you can easily check the entire ignition system in minutes?

The FSM is a good resource but testing methods and technician knowledge have moved on. I'm sold on using oscilloscopes for many things automotive its faster, easier, and more accurate.

I will post my ignition images once I get another chance to redo them and my injector current ramping images and any results I find.

BTW, this scope kit will do 90% of stuff you need to scope without the cost of a 2 or 4 channel "big boy" scope like a PICO scope or similar.

http://www.aeswave.com/uScope-Master...ope-p9273.html

 

If it were my car, I would get the car to misfire and wait a few minutes of running the engine before I shut it off. Now the important part to this is that you have to shut it off while the problem is still persistent. If it clears up, it's likely too late and you'll have to start over. After you shut it off, pull the plugs and look for the odd one out. I imagine it's going to be either rich or misfire fouled. Check ohms of the ignition wires and compare all of them to that effected cylinder. I would then place an ammeter on a graphing meter on each injector when you can get the engine to act up again and look for the odd one out. Those are the places that I would start for now.

 

when my 93 opti was bad, i had mis fires if you were lugging in too high of a gear (esp when hot) or under load (going up a hill).

one example is wind resistance. with a bad opti, the car just wouldnt go over 106 mph or something like that.

then id get occasional hiccups at the dragstrip in low gear, unimpeded acceleration - it would misfire and then pull hard again.

never once had an issue with any other part of the car (fuel system, fuel pump, injectors, ignition control module, coil, plugs, wires, ecm)

the optispark was the only thing that ever gave me problems and that was because seals had shrunk/cracked allowing water inside

 

Thats some good info and thx for your efforts Rubie. That sent me on a PC oscilliscope shopping binge. Im sure the aeswave scope is a quite a tool but it seems a bit much for the entry level equipment for those that just want to look at wave forms so i like the SainSmart DDS120 for that: http://www.sainsmart.com/sainsmart-d...pe-silver.html. Its only 60 bucks and has less features to confuse a beginner. But if u need all that diagnostic stuff the aeswave package would be the ticket though it will cost 6X more.

Anyways i think owners would spend a lot less money in parts/repairs and effort troubleshooting if they learned what the opti and ICM outputs should look like.

 

You might find this site of interest:

http://autolabscopediagnostics.com/signals.html

I've made a few oscilloscope traces myself (for my '86 L98):

http://home.earthlink.net/~cliff_har...waveforms.html

 

my issue with using an oscilloscope to diagnose the problem is thAt optispark issues tend to be intermittent.

you would have to have an oscilloscope trace the exact moment on the exact cylinder the misfire (or bad optical signal) occurred.

my 93 optispark would work fine until it warmed up, then would give the issues

 

Well thats kinda a bit of unluck for those that get an very infrequent problem. The next step for that would a data acquisition setup but u would need the time to review all the traces also. And really any electronic device can develop an intermediate problem. Just some bad turn of luck but at least the o'scope gives u chance to look at any hard problems.
Im kinda surprised all the devices they have base line signals to diagnose with like Cliff posted. Myself i would rather look at signal traces than have to swap out parts.

Good point though as intermittent problems occur plenty enough it seems.

 

Did you test the injector power feed thru the fuse box using an inductive amp pickup synching the number one inj signal as the trigger...or did you tap into the injector harnesses directly somehow?

 

good to check those too, but the 92 and up lt1 cars got a more reliable injector (multecs? i cant remember the name of them). they dont give issues like the earlier injector designs did

 

you just reminded me that the early LT1's were still batch-fire and it would be hard to isolate using my suggested method.

 

When I have time I plan on hunting the issue some more. As it stands now the Opti-Spark is NOT the issue. Car runs fine, this condition is ONLY present when the car is started below 40 degrees and at idle.

I suspect some sort of injector issue, scoping the injectors with a inductive amp clamp is one thing to explore. I plan on spending time looking at my fuel trim numbers and 02 readings.

 

And yes Mike, 92 and 93 LT1 is batch fire injection.

 

Ok did a redo on the Opti-Spark patterns of both the high signal and low signal. Here they are.





I found my issue but I am opening another thread so this one can remain dedicated to Opti-Spark scope patterns.

 

Also performing some signal captures in order to determine why i am not getting confirmation of low-res by the ECU on my 93 LT1.

My thoughts are that these look ok, but i am seeking a second opinion before moving on to ECU replacement.
https://www.dropbox.com/s/gofdi2lp3s...21.03.jpg?dl=0

captured this low res using a hand drill.

 

Looks ok to me. Good 5v signal and clean. I can see that you are rotating the wrong way (cw) with that drill, but that doesn't really matter.

Here's a scope (DSO201) you can put in your pocket. Costs about $50 with one 10x probe.

You can actually buy a circuit board kit (DSO138) that works about as well as this one without a case for $14 from China. Lots of assembly required.

 

I bought 20 years ago a 7k+ HP scope with logic analyzer as doing embedded systems design at the time as well. S opted for a phase module and RS 232 module to spool traces to a PC. Best money I ever spent though in the EFI biz so a tax deduction as well. I have found more bad parts that tested good and god parts that tested bad. All mysteries solved quickly. Nw low cost ones all I can say is buy the best you can possibly afford as the longer you own it the more uses you find.

 

Was your idle speed around 740 when these patterns were made? Where did you make the connections to the Opti-Spark signals?

 

I recently gave away an Iwatsu DS6121 Digital Storage scope made in 1989 that originally sold for $6k. They go for maybe $200 used now. It worked fine while it was in use, but nowadays the cheaper ones do way, way more and weight much, much less. It weighed 75 lbs. Imagine trying to stick that under the hood somewhere. Time marches on.

 

Yes, idle. I made them at the distributor test connector on the passenger side of the intake manifold with the injector covers off. Its easier and I don't get burnt on the hot hoses.

 

Hi,
Does anyone have a scope trace that shows both low and high resolution signals together? I want to see the relationship of the edges. I am making an opti-simulator for bench test. Many of the pictures that were here got old/deleted.

Thanks