Middle is just the high res signal. Otherwise, correct.

As in, I measured one at a time.

 

Yes…. My typo on MIDDLE.

 

I could be very stupid, but it appears my Opti is good since it matches up fairly well.

 

Clarify what is shown in the middle video. All I see is a blank screen, the bottom of which suddenly turns to opaque green. That's what you got on the high res circuit?

The engine can start and run with only the low res signal. It uses the high res signal, if it is present, to time the spark more precisely. GM did that timing tweek to reduce spark scatter, reducing emissions, and allowing for more aggressive ignition timing. If you don’t have a high res signal the Opti is OK to run the engine, but part of the cam position sensor circuitry is not working.

I'm going back to correct my error in post #75, and your quote of that post.

 

Yes, the base line seems to rise up, and fills in below that. I might have the scale wrong, but there was some sort of signal coming out there. I basically hooked it up and shot the video not knowing how to tweak the axes to have more clarity.

I may do it again tomorrow with different display settings. I should also consider longer clips, or figure out how to get a screen grab.

 

At this point, the low res pulse is present. No need to solve the problem of the high res display. Could be a matter of horizontal scale. There are 8 variable width low res slots in the shutter wheel, and 360 high res slots.

You have the signal required to start the engine. The signal appears to be reaching the PCM, since it appears to be sending the pulses telling the ICM to fire the coil. You have visual on the spark and visual on an intermittent problem with the injector grounds from the PCM. Just keep following the steps in post #63. And your “capability” seems more than adequate.

One other thought…. the Opti drive shaft may not have been indexed correctly to the cam sprocket. That would mess up the spark timing. Given the fact you appear to have fuel and spark, I would expect a few pops and backfires even if the timing was off. But I don’t recall seeing any mention of that happening…. or I saw it way early in the process and my senior citizen memory forgot it.

 

I’m running out of ideas here, but would a low coolant sensor prevent startup?

Opti is telling plugs to fire, and injectors to flow. I put on a new ICM and coil, and am no further along. The only other thing that would make sense to me right now is if the engine couldn’t make compression.

You mentioned earlier about timing. When I put the Opti on there was no forcing whatsoever, I lined the indexes up. It is said that TDC doesn’t matter, but what else to check along those lines?

 

No, low coolant sensor does nothing but turn on the dash light. Unplug the sensor and the light will go out.

Correct, splined shaft only goes in one way, in theory. Unfortunately about 10% of the installs don’t get it aligned correctly.

http://shbox.com/1/93-94_opti.jpg

 

Yeah, I marked the spline on both the Opti side and block side. Smooth as butter, no resistance at all to get it mated right up to the block. No effort required to bolt it up. I did the resistor on VATS tonight, just to take that out of the equation. After a bit the light went off (was not ever blinking). I still can only get the spark plug tester on #4 to show around 20k volts with a consistent spark. Anything further, it wants to ground somewhere else.

Spark, fuel, air, compression.

Getting spark to the plugs, may or may not be enough.
Fuel rail is pressurized, at least during cranking. Injectors at least somewhat firing. Fuel getting to plugs. Didn't seem wet, but smelled.
Air I can't readily verify.
Compression is also still the unknown.
Timing seems like the easy answer, but also possibly the most improbable. It all does seem like it might be off, but not by a little.

Since I don't know the history of the car, I suppose I can't rule out a bad cam install, a replacement PCM that is for a wrong make. What about no vacuum? I noticed I cannot change the HVAC routing, and that's vacuum. I have never seen the oil pressure gauge move, but my expectation was that it wouldn't until it actually fired up. Neutral safety switch seems to be doing the job, no crank at all outside of park or neutral.

Trying to think of anything I've noticed to this point. I've come a long way in a short amount of time, but it is still very frustrating to not put a finger on what is going on. If the cable doesn't show anything on Thursday, I don't know where to go. Maybe I should pump some fuel out and see if it lights.

Also parking this here if I need to come back to it: https://www.pro-touring.com/threads/...-timing-issues

The only other thing about the Opti - I was able to rotate it without opening up the cap. I don't know if that means anything.

 

Don't worry about the vacuum connections that aren’t required to run the engine. Put vacuum caps on things like the HVAC, EVAP on the TB, EGR. Check the vacuum connection for the brake booster to make sure that’s not a vacuum leak. Make sure the FPR vacuum is connected, and the PCV components. Shoebox's picture of the driver side of the intake manifold vacuum connections is for a 95. 93/94 are different. The EGR vacuum connection is the same, but there is no Opti vent line. The PCV valve doesn’t get vacuum from the front of the manifold, it has a very short “U” shaped hose that turns backward to the nearby vacuum connection where 95 shows the Opti vent.

http://shbox.com/1/opti_vacuum_conn.jpg

One thing that affects starting is the coolant temperature sensor in the water pump housing. It has to tell the PCM the engine is cold, so the PCM can richen the A/F ratio for cold start. If the sensor is shorted, or the 5 VDC reference circuit from the PCM is shorted, resistance on the circuit is near 0, and that tells the PCM that the engine is hot, and it doesn’t richen the A/F ratio at col start (just like the choke would do on a carbed engine).

 

Also, make sure the rubber 90° elbow between the MAF sensor and the throttle body is soundly connected on both ends, has no tears, the plastic silencer tube that runs down in front of the engine is there, the inlet air temp (IAT) sensor is plugged into the elbow and the harness connected, and the bottom edge of the elbow hasn’t slipped off the bottom of the throttle body flange.

 

You may be very stupid but in this case you are correct! Wait..I mean about the latter not the former ;-)

 

Normal. He would have to reduce the repetition rate of the "scope" rep time to get a clearer view.

 

Images are perfect for a good Opti.

 

Yes, usually that means the engine starts but does not stay running for more than a few seconds. The test is to apply a bit of the accelerator pedal to keep it running until a little warm.