How the Opti Works

[popo8]

EXCELLENT WRITE UP BY :



Oklahoma Corvette and Performance Specialist
Opti-Spark. Sounds like something from the new transformers movie, eh? If you have had one fail, you may think it was out of a horror movie. Well the truth behind the opti has been told a few times here and there. It basically boils down to a great idea and bad follow through. I am sure we have all been guilty of this before, but we don't manufacture cars, so we get spared of our mistakes. So lets get that out there first...

Why does everyone run screaming from an opti-spark? Why is it a POS?
Well GM engineers fathomed up this brilliant idea for a low maintenance distributor that was very accurate, and for the most part they did a damn good job. The problem lies in the rest of the design that caused the failures.
1. Ya see, a water pump has these seals on the spinning shaft. When the seals fail, coolant is bypassed though the seal housing and out of a weep hole in the bottom of the water pump. This is on virtually every water pump out there. GM kinda didn't realize that the weep hole was above the opti-spark, or they overlooked it, or just said screw it... no one knows for sure.
2. After 1994 all of the opti-sparks became vented. Why? Ozone. Ozone is a gas that is created when there is a spark of electricity. Inside of this tiny arc that occurs from the tip of the rotor and on to the distributor cap there is basically a lightening bolt that cooks the air around it. When you “cook” the air, you produce the gas ozone. Also, if there is moisture in the air (look up to see where the water is coming from) you create steam. Ozone and steam do not play well with optical sensors, because they are “looking” at each other. If you fog up your buddies glasses, he cant see you any more...
3. Sealing the cap and the bearings... The pre 95 had an unsealed distributor cap and the bearings were subject to letting fluids past. This did not help the dripping water pump.
4. Heat kills.... And in this case, heat weakens the electronics that are inside of the 'optical' side of the house, causing heat related failures which often mimic a failing ICM or Fuel Pump.
5. Printed distributor cap... Uhhh yeah, electronic conductive ink was used to print the pattern on the inside of the distributor cap. This unique design prevented cross-fire of cylinders and allowed for a great layout to get even and odd plugs to their corresponding side of the block. But you guessed it, when it gets old or overloaded, electricity will always find the shortest path to ground... That may be the next fancy line of conductive ink- which leads to the next cylinder. Try diagnosing that misfire.
So you can see, there were some flaws. So what? Its not like you have to pull apart the front half of the engine to get to it once it got wet... Oh, right, you do. And this is why people hate the optispark. Even if you only have to change it once every 120,000 miles, it still looks like a worthless chunk of crap once you have dissected your engine to get to it. Because of this, “opti-spark sucks” is the common chant.

Well if its such a hunk of crap, why don't they come up with a fix?
GM tried in 95-97 by venting the cap and using incoming filtered engine air to supply and a one way check valve on the intake manifold to pull vacuum on the inside of the distributor. They also made other changes to the drive mechanism. The end result? Its pretty water proof if maintained... meaning as long as you dont take your LT-x through the next big flood, you should be good to go. Well so long as the foam seal thats around the distributor doesnt rot away...
Bailey Engineering created the LTCC to eliminate the high voltage side of the optispark. You can google it.
Deltec made a solution too.... again google
And to follow a few others (including myself) have designed ways around the Opti. We wont discuss that here, but just know that if you have had enough, then you can source your own solution.

Many of you out there are not ready to make that great leap ($$$$) for a different approach. I don't blame you. I think the Opti is an amazing design! And to convey that message, I will explain how the Optispark works...

PART 2:

Oklahoma Corvette and Performance Specialist


How the Opti-Spark works...

First off, lets look at what it does-
It provides a signal to the computer (ECM/PCM) about where the engine is rotationally in respect to where it has been. Basically, what degree of rotation is the engine at, and what is coming next as far as firing events are concerned.
Well thats easy, eh?? Not exactly...
So lets break it down some. You should know that your engine crank will spin 720* for a complete rotation. The camshaft is driven at half the speed of the crank, so it will go 360* per full event cycle. The Opti is driven by the camshaft. So it has to spin once and give enough information to complete 720* worth of events.
How does it do that?
The Opti has a shutter wheel inside of it. The wheel is about 2.5” in diameter and thinner than a credit card. The wheel has 360 holes cut into it on the outer most “ring” and the inner ring has 8 holes of varying size cut into it. (more about these holes later) This is mounted on the center shaft which is supported by some bearings that are pressed onto the shaft and then into the metal housing of the Opti. The camshaft has a dowel pin pressed into it, and it sticks out of the cam a certain amount, which varies depending on year. This dowel pin slides into a slot on the Opti. Supposedly only one way, but actually it will go about ¾ down the wrong hole and she screams. (!) The opti wont completely bolt on if you have it in the wrong slot, which is slightly frustrating. Anyway, when the cam turns, it spins the shaft in the opti, which in turn spins the shutter wheel and the rotor. The holes that are in the shutter wheel are the vital pieces of info here. To read this vital information the Opti has OPTICAL sensors (that moment when they say the name of the movie in a movie...) These optical sensors are actually a matched pair of LED transmitter/receivers. One transmits infrared light at a certain wavelength. The other sees only that same wavelength of light that the other is transmitting. And there are TWO pairs of these LEDs. One reads the outer ring with the high number of holes, the other reads the one with low number of holes. When the infrared light from one transmitter is seen by its receiver through one of the holes, it essentially becomes a switch and allows current to flow through it. As this current passes through the LED it is then sent though a transistor and amplified to a high enough voltage so that it can be sent to the computer. When the wheel moves, the space between the holes does not allow the infrared light to pass through, so the LED turns off, which turns off the transistor and the signal is zero. While the wheel spins and the holes pass quickly in front of the LEDs the signal turns off and on quickly. It creates what is called a square wave pattern, because it goes from high to low instantly and is held high or low for the amount of time it takes for it to move to the next hole or not. If you were to draw that represented by a line it would make a wave that is squared off...
This square wave is taken by the computer and it means shit.
What does it all mean!?
I am glad you asked, cause this is where the accuracy of the optispark comes into play. I wont go into how other ignition systems work, but lets just say they suck in comparison. Because what the opti provides for information is 90 times better than what existed at the time, and still better than what the LSX uses.
These holes on the outer ring... there are 360 holes. So that means there are 360 filled areas. So it can go low to high (two different states of logic) 360 times each, or 720 times. Wait a sec, there are 720* in a full engine cycle... so if the wheel turns once, that means the cam turned once, which means the crank turned twice.... by golly they found a way to tell the computer where the engine is DEGREE BY DEGREE. Holy crap, thats accurate. They call this bit of information the HIGH RESOLUTION SIGNAL. Sound familiar?
Onto the 8 slots on the inner part of the shutter wheel... There are 8 slots which have a unique design. Their function is to tell WHICH cylinder is passing. The way they did this was kind of ingenuous if you ask me. They made the holes different sizes, but only 5 sizes. Wait a sec, whaaa? If there are 8 cylinders and only 5 different sizes... WTF bro? Welcome to the computer age, we can do a lot with a little. The signals are provided by the length of the hole. 4 of the holes are the same length, between these holes are 4 different sized holes. I hope you understand when I describe the holes' length by degrees... The holes correspond to a cylinder. They go in the firing order according to rotation of the engine. Since its a small block, you should have this memorized, 1 8 4 3 6 5 7 2. Since every other hole is the same size, cylinders 1, 4, 6, 7 all have a 2* long slot. Cylinder 8 has a 7* long hole, 3 has a 12* hole, 5 has a 17* hole and 2 has a 22* long hole. (I will post pics) These signals are all, of course, 45* apart.
What does this do? Well depending on how long the computer sees the LOW RESOLUTION signal determines which cylinder it is on. This is also used for the sequential injection. Now the engine knows exactly what cylinder its on. The low resolution signal tells the computer which cylinder its on, and the high resolution tells the computer how many degrees are passing while it is on which ever cylinder. Woah. If you crunch some numbers, you can see that this is an amazing amount of information. I know it takes me a few mins to find out which cylinder is at top dead center, and if its on its firing stroke or exhaust stroke... this puppy can tell you in 1/100th of a second. And its always right. Thats accurate.

Well thats all fine and dandy. What good it knowing when and where the engine is? For starters, I can tell you that the computer is smart enough to know that on cylinder 1 it should take 2* to get its signal and should see 90 total high and lows for that cylinders firing event, and if it sees too many or not enough it knows that something has happened. It compares this with a multitude of other info and it can reason that there was some knock. Oh yeah, its smart. Ever wonder why the LTX was so sensitive to knock retard and why there was an updated LT4 knock module? There is your answer! This is only a small reason for the fancy opti... the biggest reason was cold starts and emissions. With the computer now able to know exactly when and where the engine was, it was able to start from a dead stop much faster. This enabled the use of less fuel on startup, which decreased initial cold start emissions to the point it was hailed in the engineering community. Ill be damned, the opti was a good idea for something.

This is just what the shutter wheel does... the high voltage side of the opti is, well basically a distributor. The computer takes all the info from the shutter wheel, makes its decision when to fire the next plug, and sends a signal to the ICM (ignition control module). The ICM takes that info, amplifies it to 12v, calculates dwell time, applies 12v to the coil, removes the 12v and a large inductive spike occurs in the coil and magically 30,000-50,000 volts are blasted out of the coil and sent down to the optispark. It comes in and touches the center of the rotor and is distributed to which ever cylinder the rotor is pointing towards. Then down the fancy conductive ink, to the plug wire, into the plug where It bridges the gap to the electrode ground and SPARK!

THANK YOU TO: https://www.facebook.com/OklahomaCor...anceSpecialist

[meissen]

Awesome article.

[popo8]

I didnt even realize he was a member till I posted a link to this thread giving him props (SEAN's excellent idea)...

According to his page... he has other opti write ups to come!!!


Larry (Popo8) Co-owner
LTXtech.com

[zooguy]

dude knows his shit

[zooguy]

EXCELLENT WRITE UP BY :

What does it all mean!?
I am glad you asked, cause this is where the accuracy of the optispark comes into play. I wont go into how other ignition systems work, but lets just say they suck in comparison. Because what the opti provides for information is 90 times better than what existed at the time, and still better than what the LSX uses.

THANK YOU TO: https://www.facebook.com/OklahomaCor...anceSpecialist

can we make this guy a moderator in the tech section?

[GreenZ96]

Wow, that's a lot to read. Wish it were in a video.

[ThoR294]

better than coil over plug? :O

[ginoz28]

So if someone can seal off the opti side from the spark side the opti will be perfect.

Sent from my PC36100 using Tapatalk

[Merlot566jka]

Hey Guys! I have the finished "Testing the Opti-Spark" article posted on my Facebook page:
https://www.facebook.com/OklahomaCor...53648071469146



If anyone has any questions or requests, find me here: https://www.facebook.com/OklahomaCor...anceSpecialist

Testing your OPTI-SPARK By Jonathan Anderson

You stalled out on the side of the road, and got a code for high resolution and or low resolution?
You have a very strange misfire?
You have an odd misfire at idle?
So you have a misfire at high RPM?
Your car wont start?

First off lets remember, this is a distributor. So before you get overloaded, STOP AND THINK. It's as easy as your old 350 distributor... just with a fancy computer and pickup. So if you are having random cylinder misfires, or a couple plugs not firing, check your plug wires and cap. Yes, these are like any other distributor, the cap and wires need to be maintained. I know its a pain in the ass to get to, and they arent all the cheapest parts ever. But hey, you pay to play.
In the case of the actual codes for high resolution and low resolution loss, well youre going to have to test it.

Here is how I test it:

1) Verify Ground on ALL ignition related components.
2) Verify all fuses related to the situation are good.
3) Verify Correct voltage at battery and all components involved.

These are the first three steps I take in almost any situation. I would go as far as checking the connections on the rear of the ECM, unlikely, but hey, its easy to check.

Next is where I would take it a step further.

1) Test for spark on #1. While cranking the engine...

A.) If no spark go to step 2.
B.) If spark is present, the ICM and coil are working, for the most part. Trouble lies in the high voltage side of opti for the other cylinders or else where.

2) Test for spark on coil to opti ignition high voltage wire (the short plug wire from coil to opti) First test on the side that connects to the opti. Then test on the coil itself. This is done to ensure the wire itself is good.

A.) if no spark go to 3.
B.) if spark is present, go to step 4

3) Disconnect the ICM connector. Verify +10v DC (should be battery voltage, but sometimes its lower because of crappy old wire) from PIN A to ground and PIN D to ground on the ICM connector. This tests the coil, and wiring all the way back to the ignition fuse. (key on engine off)

A.) If no voltage, check fuse and wiring.
B.) if correct voltage is present the secondary wiring of the coil could still be bad, but we'll assume its good because they rarely die completely like that. Continue to step 4

4) Verify Pulse signal at PIN B of ICM. Connector plugged in, you will have to pierce the jacket of the wire or push into the connectors seal. This is done with a DMM or o-scope. It should be a pulse (AC Voltage) that varies between 1-4v. On a scope, it will look like a square wave, Each pulse corresponds to a cylinder firing. (you're cranking the engine to get the pulse) This will produce 8 pulses every rotation, while cranking this could be 800-2400 pulses per min. (if you dont know how to use your meter, get on youtube and look for a video to teach you how) **** read at the end for more on how this test can be useful...

A.) if no pulse, go to 5
B.) if pulse is present, ICM is faulted. Replace, and return to step 4.

5) Verify pulse signal at ECM connector to ICM. PIN B5 (dont have the book in front of me, might want to check that pin location).

A.) if no pulse, go to 6
B.) if pulse is present, the wire or connection to ICM is faulty. Check continuity, check short to ground. Replace wire, connector, or repair.

6) The signal to the ECM for the ignition comes from the opti. This is where an o-scope would be handy. Test at both the opti, and the extension cable!!
6.1) Pin A on the opti is Low resolution signal. It will be different for each pulse, but only 5 variations. So you will see every other pulse get progressively longer after each other. Crank the engine and watch the scope. The low resolution signal comes from the big long slots on the wheel. It will cycle through twice per rotation of the crank.

A) if no signal, optical sensors in the opti are bad, clouded, or the shutter wheel is fudged up. Replace opti.
B) if there is signal continue to step 6.2.

6.2) PIN B on the opti is the high resolution, it is the 360 small slots in the optispark trigger wheel. it will pulse 720 times per crankshaft revolution. Use the scope and look for this signal. It may be hard to dial in, but a signal is what you are looking for regardless of how perfect you can get it. You might want to use a scope with the capture feature and auto trigger.

A) if no signal present, the optical sensors aren’t reading. Replace optispark.
B) if there is signal, go to step 6.3

6.3) PIN C should be 12v. check to ground.

A) if no voltage, check wiring, fuses and PCM
B) If voltage is present, go to step 6.4

6.4) PIN D is Ground. Check continuity on wire.

A) if no ground continuity, inspect wire and PCM, replace damaged area.
B) if ground is good, Opti is faulty.



After all of this, you have tested the opti, coil, the ICM, the ECM input and output, Voltage on all components and you are left with only one thing that could be wrong...Cap and Rotor.

So let me sailor proof this...

1. Verify power and grounds
2. Verify signals from opti
3. Verify signal to ICM from PCM
4. Verify pulse to coil from ICM
5. Verify spark at coil
6. Verify spark through coil lead (look for arcing by the thermostat)
7. Verify spark at plugs
8. Re-test until you're 100% sure you found the problem

Now I know some of you are out there thinking “Who has an o-scope? Who even knows how to use one?” I realize most of you dont have this, and wont be able to just go down to the local parts store and pick one up. So in that case, I want you to use a low voltage logic test light for the optical sensor signals (steps 6.1 and 6.2). If the logic LED test light flashes high to low, on and off or red to green, then you know that it is pulsing. May not be the right pulses, but if its pulsing that means that the shutter wheel is spinning and the optical sensors are reading. And in that case, you can assume that it is working. Now if there was some coolant clogging up some of the holes on the shutter wheel, it could blank out some areas on the wheel and you would not get the correct pulses... unfortunately with out the proper equipment, this will not be easy to tell with a test light.

A little trick...
Your Opti-Spark uses optical sensors... So next time you get a loss of low resolution or high resolution, just open it up and look for coolant, oil, dust, rust etc. Lightly blow out the contaminate with DRY air under low pressure (keyboard dust-off stuff). Then clean it out gently with rubbing alcohol. Use a lint free cloth or glasses wipes, and wipe off the optical sender and receiver. If you cant imagine where they are or see them, then just clean it the best you can and be careful. Make sure you have cleaned out all of the holes in the optical pickup disc. Dont be a monkey and beat things up in there, be easy on it!Let it all dry. Pop your cap back on, connect the needed things to fire the engine. (If you know what your doing, you can run the engine for a few seconds with no water pump on. This speeds up the testing time!) It should only take 30 seconds or so to realize if its working or not. This is how you fix a wet opti for free.

****About test 4... If you have an oscilloscope, put channel A on this wire. Now take channel b (C and D if you have them) and connect them in firing order to the plug wires (clamp and 10x probe). Use Channel A as your reference, and place the other 3 channels superimposed over channel A. As the engine cranks, channel A is going to get 8 pulses, adjust your time to get at least 8 on the screen. Adjust your ref v to like 5 or 10v to get a nice tall pulse. On the other channels you will see them pop up as the distributor swings around and fires that plug. Adjust your voltage to get it down on the same scale as channel A. adjust your time so its on the same as channel A. Now you can see in order, every pulse from the ICM and when its getting to the plug...
How is that useful? Well I am glad you asked... cause you can now see every time a pulse goes to the distributor, and where that pulse is going... this is how you find if your conductive ink has found a new trace. I spoke about this in one of my articles earlier this year. What will happen, for example, is the conductive ink will bleed through and spark for cylinder 1 may be showing up on cylinder 6... thats because its arcing out of its path to the closest ground. This will cause 2 cylinders to basically fire at the same time, and only one of them is supposed to. By looking at which one is supposed to fire, you can determine which one is bleeding through... or you can say screw it and just replace the cap, cause thats not supposed to happen.

If you guys have any questions about how to test or what to test on your optispark, just give me a shout. I know this may be a bit much to handle for someone who hasn't messed with electronics. This is pretty much right out of the factory service manual.

[popo8]

So glad to see ur still on it. So much to read...but wow... I love to learn so ssoooooo well worth it.

LTXtech.com is my drug.