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Discussion Starter #1
The 96 LT1 has a crank sensor. This gives a 96 owner a advantage to check the OPTI.



Ok well baiscally a GOOD Driveability tech who is knowledgable about the Optispark and can use an Oscilloscope can check it. Your car has to be a 96 with a crank sensor though.You see your cam spins at half the speed of the crank. You can compare the signals to see if they are in sync or if they are off a little. It is kind of a flat rate mechanic shortcut.
RamAirImpala


https://www.impalassforum.com/vBulletin/34-engine-problems-maintenance/1156177-symptoms-timing-chain-slop-2.html


I have been working on a problem that i though was significant enough to warrant some investigation. I have tune several cars in our area with some success and have many of those running very well. Some of them have fairly large cams. So as not to give too much away, one of the cars is running a 503 cam that has a significant amount of overlap and an exhaust closing point that is much later. This will be our "example" car.

Using a 2 channel scope, I have played with settings from the "spark reference table", which i have figured out is an electronic method for adjusting the mechanical "slop" between the commanded timing and actual timing of the engine.

Further testing on that has led me to find as much as 21 degrees variance on at least 1 car that had 100,000 miles and that car had stumbling and stalling even after a tune-up, MAF cleaning, new exhaust, and new fuel injectors. A new timing set brought this car back to life and restored fuel economy. On my own 91,000 mile ss i measured 12 degrees. For now, I use this as a diagnostic step after other methods fail to reveal the cause of odd drivability symptoms.
Chris Rocko350


https://www.impalassforum.com/vBulletin/35-pcm-programming-engine-management/268536-injector-timing.html


I am wondering if any of the people who keep swapping the OPTI have checked to see if it is sending the proper voltage signal to the PCM?


If the signal is good does it match the crank sensor timing?


When they get a P0336 do they scope the crank sensor to ensure the PCM is getting the correct voltage signal?


Optical sensors are used in industrial setting day in day out. Fewer are used at the temperatures experienced by the OPTI but making a dependable optical sensor is not hard.


I am wondering how many OPTI swapers have scoped or pay to scope the OPTI before replacong it?


The OPTI assembly is a wear component but if it does not correct a problem do OPTI owners check wiring and mechanical timing?
 

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The CPS on a 96 Impala is only used to see that the distributor is properly working on alignment... no need for a scope because the PCM will throw this code in .5sec....


IMO I use a timing light to check for the opti miss firing .. coil/ICM/plug wires/ headers whacking the plug wires/opti connector corroded/venting /cap leaks distortions / rotor wobble etc etc etc....


timing light works for me if I think the ignition is not working properly..


expensive to have a scope that is able to observe the wave form and duration / amplitude ..
 

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Discussion Starter #3
I use a timing light to check for the opti miss firing .. coil/ICM/plug wires/ headers whacking the plug wires/opti connector corroded/venting /cap leaks distortions / rotor wobble etc etc etc....

This is a good start and checks out the ignition from the PCM to the plugs and proves the low resolution signal is present.



If I understand correctly people are getting no spark while cranking but the PCM does not throw a code for OPTI high or low resolution signal loss.


What I am wondering is what the OPTI high/low signal looks like when this happens? Is it a bad signal or no signal(dead)?


I am wondering if the PCM will run without the high resolution signal for a time without triggering a error code?


expensive to have a scope that is able to observe the wave form and duration / amplitude ..

I agree but if one keeps replacing the OPTI instead of OPTI wiring or the PCM it is expensive and frustrating.


There is nothing worse than chasing a intermittent problem but most of the forum is sure the optical sensor quits when hot. Can we see this by unplugging the fans and taking the temp up to max?
 

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possible the optical sensor will operate erratically when it gets hot.. timing light should show that.



resolution signals I believe are switching signals from high to low so when the switch is made at the wrong time the PCM on a 96 will throw the code..I went threw that .. opti new setup up wrong at factory...


I did use expensive O scopes years ago but not on cars... checked out radars ,submarine signal testing antennas,and waveforms on a high power laser ... speed sensor signals on transportation vehicles..scopes are very good for a very short drop out , timing light probably will not show it..
 

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Discussion Starter #5
To throw in my to bits here about the opti clocking,,

The distributor turns at half crank speed , so 1 rotation is 720 crank degrees.
Obviously if you can see the rotor is not the same position , it is way out .
What about the ones that are "only" out a few degrees???

While a 96 might pick it up and blow a code because it has a crank sensor, the 94-95 will have no way of detecting it.
Retarded, a guy might be chasing heat and lack of power, advanced detonation .

Any hot rod LT1s I have done I put a timing mark on the engine so I could compare PCM commanded timing to actual.

Where am I going with this??

If I had a running LT1 with an original Optispark, I would find a way to put a reference point on the flywheel or damper so I could point a timing light at it.
Then you check before and after opti change to make sure it was the same, or close enough you could fudge the tables in the PCM.

I remember taking apart an old Optispark , thinking I would change the bearing.
The fact there was no way to positively re index the top plate to shaft , had me shelve the idea.
Judging by what guys are running into now days, seems the "professional" rebuilders can't get it right either!!!
95wagon


https://www.impalassforum.com/vBulletin/34-engine-problems-maintenance/1313370-changing-optispark-do-i-have-everything-4.html



If people did live data scanning before and after a OPTI change under the same conditions they might find a OPTI clocking problem. Data logging a familiar drive would be another way.

I was thinking that if one marked top dead center on the crank then scanned live data for the spark advance and marked that point as well one could compare a new OPTI's spark advance number to the physical point on the crank with a timing light.


I have a cheap timing light that has a "degree adjust" knob. It is great for cranks that do not have timing advance markings. I can mark TDC then run the engine and adjust the timing knob to get TDC. I can then get a rough number of the advance from the marking on the timing gun's knob.


While a 96 might pick it up and blow a code because it has a crank sensor, the 94-95 will have no way of detecting it.
Retarded, a guy might be chasing heat and lack of power, advanced detonation .
95wagon


If the person did some scanning or data logging this would show up as spark advance numbers "hitting the wall" of the PCM's max or min number. One would see the advance number "stuck"


The question is how much adjust is programed into the PCM to compensate for things like a slack chain or a OPTI that is "not clocked correctly"
 
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