slick1hunting

So I haven't been on the forum for several years. Hopefully my info is current on my signature. Anyway car had sit for couple years as clutch was out and time to go twin disc. Once I got the clutch in it started having engine issues. Started with sticky injectors, then fuel pump went out. Once I had that sorted it was running good except a slight hesitation off idle. Then it just shut down in the middle of an intersection as I was getting ready to make a turn. It had no fuel pulses at the injectors and no spark. I figured that it lost the optical sensor in the optispark so ordered a reman ac delco.

Once I got the Opti I opened it up to see if it had the mitsubishi sensor inside and it did not. I locktighted the rotor screws and installed it. Put it back in and still no spark or fuel injector pulse. That's when I started looking for troubleshooting an opti with a ltcc setup. I really didn't find much to help on the icm and coil side testing with ltcc box and tried an email to Bob about my findings. I haven't heard back and may not but this is what I have done or where I am at.

On the ltcc box I get the 5volts on the high resolution side and I do not get the 5 volts on the low resolution side, nor do I get any pulses on the white wire on the ac scale. I do get 5 volts on the low resolution side if I unhook the connector going to the Opti. I feel like the new remanufactured optispark is likely a dud as I haven't found any bad wires or connectors. The one thing I haven't done is check continuity on the wire(or wires) going to the pcm as I feel it's the Opti, the pcm, or wiring between. Anyway I knew there where some very knowledgeable people on here as I was building the car and hoping someone could point me in the right direction to proceed as I may need to send the Opti back. Car is a 96 firebird , 383 with custom cam ,le heads,forged internals etc. Anyway thanks for any help or suggestions you might have.

Injuneer

Any flashes from the red LED on the LTCC?

slick1hunting

I get the initial flash green , then red at key on but with extended cranking(20-30 seconds)I get no red or green flashes(ltcc trouble codes or low res signal)

Injuneer

If you've been gone for a while, you need to be aware that there are very few people who are active on this site, Not like the old days. Sad.

I have never used/worked on an LTCC setup. So I'm just looking at the install instructions, and making some observations.

It appears the green LED should stay lighted, but in your description sounds like you only get an initial flash, then it goes off. It appears from the instructions it would stay green as soon as the LTCC has decoded the Opti signals and is controlling the engine. The fact you have no AC volts on the white wire would seem to indicate the PCM is not receiving or maybe not sending the required pulses.

When the engine is cranking, does the tach needle move upwards a couple hundred RPM, which would indicate the PCM is receiving the low res pulses?

Have you checked for corrosion in the gray Opti harness connector on the bracket on the passenger side of the intake manifold? Ditto with the harness connector at the Opti, if it is not the newer style with the short harness permanently connected to the Opti.

slick1hunting

Yes, I am just getting the initial flash at key on. Then it's my understanding the green will flash if it is getting the low res signal or red will indicate a code on the ltcc. I also have not gotten any ses codes from pcm. I have not watched tach during cranking and will do so next chance I get. Every connector looks great with no bad pins or no corrosion etc.
Sad to hear not much activity any more but very happy to see you are still on the site as you have always been very helpful and about as knowledgeable as anyone I've seen. I'm pretty sure it's the Opti or pcm but have not looked at wire going and coming from the pcm, all the other wires I have followed out and no damage or change from when all was good.
Do you think the fact I get the 5 volts at the low resolution pin in the ltcc box only after I disconnect the Opti harness might indicate opti over pcm as I'm not quite sure of how the voltage flow is setup or any way to further isolate pcm working or not working. Thanks for the help and tip with the tach and any other suggestions I definitely appreciate it. I have to be out of my shop in about a week as it sold so if need to pull the Opti would like to do it while I still have my shop.

Injuneer

I don’t know the details of the LTCC as to where the Opti gets the 5 volt reference voltage from. Normally without the LTCC, when disconnecting the black-to-gray Opti harness connector on the passenger side of the intake manifold, you need to check there for the 5 volt reference for both the high and low resolution pulses. Shoebox (who fortunately still helps out here) has the terminal data: I would try checking, since the PCM still needs the pulses for the tach and the sequential fuel injection.

4th Gen LT1 F-body Tech Articles

Scroll down to “Optispark Harness”.

Injuneer

With regard to the PCM code for the low res pulse, it does turn on the SES light in OBD-2, but can’t set until the PCM counts a certain number of high res pulses without seeing a low res pulse. That seems to require more continuous cranking time than one would normally do.

slick1hunting

Thank you Fred, I did not get any movement on tach when cranking and I do get the 5 volts on both low and high side on the connector with key on and connector apart or disconnected. If I have key on and disconnect the connector it runs the fuel pump prime(don't know if that's normal or not). I have also tried plugging in my original opti and the one I replaced checking the voltage at ltcc box and get the same= no 5 volts on the low side until I disconnect the harness connector from Opti or the next connector towards rear of intake manifold(both of which I get the 5 volts when checked disconnected) should I be checking that connector connected(backprobe) as I do not get 5 volts when connected as I probed the wire with it connected where it splices into the ltcc harness.

Injuneer

I can’t tell you how to test the LTCC connector because I don't know how it is wired. I don't know if it picks up the 5 volts from the PCM (likely), or somehow produces its own reference voltage (unlikely???).

The PCM supplies the 5 volt reference for both the high res and low res functions of the optical module in the Opti. When the module light source can’t pass through a solid portion of the slotted disc, it pulls the voltage at the harness connector down to 0 volts. When the light can pass through a slot, the voltage returns to 5 volts. In effect the pulse signal is a 0 to 5 volt square wave.

Two foolproof methods to verify the Opti is functioning correctly (key on):

- put an oscilloscope across the correct signal and ground wires in the connector on the intake manifold, and see if you get a 5 volt square wave. The high res pulse is a rapid, equally spaced on/off wave, 180 switches per crank revolution. The low res signal is four equally spaced, but variable width pulses per crank rev. The width of the pulse identifies the cylinder #.

- with Opti off the timing cover, fully wired and grounded, put a DC volt meter across the reference voltage wire and ground at the connector, and slowly rotate the drive of the Opti, watching for the signal to switch between 0 and 5 volts - rapidly for high resolution, slower for low resolution.

slick1hunting

Thanks again for solid advice. I didn't really have any time to check voltage but I did hook the Opti I just replaced(the assumed bad one) up and grounded it and when spinning it I get fuel injector pulses confirmed with sound and noid light. So I guess it points more to the pcm or wiring or the Opti is not spinning(broken cam). Will hopefully have more time soon to check a little deeper.

95LT4Z28

go on the ltcc site and email bob bailey. i had a problem when i first did the ltcc conversion and it turned out that the coil harnesses i bought on ebay were pinned wrong. he was extremely helpful. he should be able to give you a good idea whats up