David94TA

On the 95+ optis that are dowel pin driven, while it is possible to install them incorrectly, they will not fit completely flush against the mating surface unless you have the dowel in the correct slot. Correct? I changed out my opti and now it won't start. Car was running with the old opti. Everything is hooked up and the new opti is the only thing that has changed. New opti is AC Delco remanufactured from Rock Auto. Supposedly tested. I haven't put everything back together, but with the opti hooked up to the wiring harness and the MAF on the car hooked up, car should crank.

Injuneer

Is there spark at the plugs, at the coil? Do you have the required AC voltage on the white wire at the ICM connector? Do you have the required voltage at the gray Opti test connector? Does the tach needle move up to 300-400 RPM while the engine is cranking? Are there pops and/or backfires that tell you something is igniting the fuel, or complete silence?

4th Gen LT1 F-body Tech Articles

That tells you if the Opti is working and the harness connection is good.

Yes, it's possible to mis-index without a lot of force being applied to seat the Opti, particularly if the dowel pin is on the short side, or has been pushed into the cam nose. Had one case where the dowel pin ended up in one of the cam bolt reliefs. Car started and ran OK. Owner swore he installed it correctly and applied no excessive force. But in this case (OBD-2 1997) the misalignment caused a CKP sensor “out of range” code, because the Opti signals were more than 15° off from the CKP signals. Only mention this to confirm misalignment is possible. Also saw a photo recently of a dowel pin with only about 1/16” sticking out of the cam.... not sure how that happened.

David94TA

I installed it first and it wouldn't crank so I took it back off and installed it again being especially careful to make sure the mating surfaces were flat with no pressure needed to make them match up. Still wouldn't fire. No pop or misfire, just silence. Dowel pin on cam looks right and before last install, I felt it to see if it would move. Seemed solid.

I have Bailey's LTCC so I don't have the ICM or stock coil anymore, but will check those circuits. I just installed a new wiring harness and the car cranked right up and ran, but it didn't solve my problem. I decided to replace the Opti on the suspicion that perhaps the optical sensor was going bad. So, like I mentioned, that has been the only change. I must be missing something somewhere. Maybe just still don't have it lined up correctly.

At least I didn't put it all back together this time.

I'll check the items you mentioned. Many thanks for the info.

Chimera96

If you have not "put it all back together" (read WP is still off) and the old Opti was working than put it back on and see if car starts. That would immediately indicate the reman AC Delco is the problem. People do "test start" their cars without WP on for Opti swaps/service to confirm it works and or installed correctly before putting everything back on

Otherwise follow the steps noted by Injumeer as his advice is excellent

David94TA

Unfortunately I already sent the old opti back for the core refund. I guess that's a good lesson for all reading this post. I just would have never thought that there might be a problem with the "new" opti, especially since they claim to have tested it. I did take it apart and loc tite'd the rotor screws, but I doubt that I would have messed anything up since it only goes back together one way. Thanks.

Chimera96

well than do as Injuneer suggests to try and pinpoint the "why". the shbox site he noted has great 411 on it

Not heard of a AC Delco reman being bad out of box like offshore cheap optis often are but it is possible.

Really confirm your connections are good, especially at the coil/ICM ground terminal on PS head

you are going to need to do the tests Injuneer points out without having a known good opti to swap in

Injuneer

Doesn’t the LTCC box have LED's that flash proprietary trouble codes? And the white wire from the PCM that went to pin
B on the ICM now goes to pin F on the LTCC box.


You can still check for spark at the plugs.

You still need to make sure the high and low resolution pulses are reaching the LTCC box. You should still see the tach move up slightly when the starter is cranking the engine. When checking the high and low res signal wires, if you turn the key on and slowly rotate the engine, you should see DC volts switching back and forth between 0 V and 5 V, particularly on the low res wire, where there are only 4 variable length pulses per crank revolution. High res gets trickier, because there are 180 pulses (actually 180 1-degree switches between 0 V and 5 V and back to 0 V = 360 events) each crank revolution.

David94TA

Very good. I'm going to work on it this weekend. Thanks for the input.

David94TA

OK, so here is what I have so far:
1. Tach needle does not move when cranking
2. Checking the opti harness as Shoebox suggests shows proper voltage coming from PCM: A--5vdc, B--5vdc, C--12vdc (with key ON) D--0-0.2 ohms with key OFF
3. Cranking and watching LTCC module lights--4 blinks meaning "EST signal from PCM=Missed Pulse. Check connection to White wire" (originally to ICM). I soldered this connection when installing the new harness and splicing in and I know I got the correct wire because car cranked and ran with old opti.

Injuneer

Sounds like the Opti low res pulse is not being received by the PCM. Check the pins on the Opti harness connector(s) for damage or corrosion.

From your initial post, sounds like you didn’t put things back together - water pump? damper? If not, pull the Opti, leave the harness connected, turn key to “run” (not “start”). Rotate the splined shaft manually, while checking the red/black wire (pin A) for a 0-5 volt switching signal (square wave), using the pink/black wire (pin D) as the ground. If you turn the splined shaft one full turn, you should see 8 switches between 0 to 5 volts. Some pulses will last longer than others. The variable pulse width is how the PCM knows which cylinder is approaching top dead center on the combustion stroke.

David94TA

Got my new opti from Petris, put it in and car cranked right up. So either (a) my remanufactured AC Delco was defective or (b) perhaps I messed something up when I dissembled it to put locktite on the rotor screws. I don't see how that could happen but maybe I did something. I've done the locktite preventive fix before with no problems.

Hopefully get the car put back together and running today.

On a side note, I put a small drop of white paint on the end of the dowel and a drop marking the position of the slot on the opti and that seemed to help lining it up.