Robert Thomas

'93 LT1, auto, no mods, replaced Opti last year.

Symptoms: Runs fine for about 15-20 minutes then misfires. Misfire clears after a few minutes and engines runs okay. Terrible gas mileage according to instrument panel (down to around 15 mpg or less indicated, normally 27 on freeway).

DTC codes 32, 36, 45, 65.

I replaced the EGR valve and O2 sensors, cleaned the opti wire connectors (didn't see problems) did the FSM diagnostic checks. The black/pink wire had 4.6 volts all the way to the distributor. I wiggled the wires while checking continuity and didn't see any indication of intermittent opens. I have cleaned and reworked the grounds on the engine block.

The engine stills misfires after 15 minutes then starts running fine and shows only DTC 36 now.

Although the FSM says the engine will run without the high res signal, will the loss of that signal cause the engine to run poorly?

The book solution is to replace the distributor. Does anyone have other ideas?

bassackwards

Mine needed a distributor. See posts for my struggle

93Rubie

Sure sounds like a bad one. What brand is on the car?

They typically are heat sensitive.

Robert Thomas

I don't know what brand it is. I bought from someone, not a dealer. I has a yellow/orange cap. I'm mystified by the engine stumbling then running fairly well. I'm going to try to learn how to datalog to see if I can better understand what's happening this but from what I've been reading, to me it's PFM.

93Rubie

What is amazing is that the Opti-Spark is actually quite simple not HEI simple but simple.

A stainless steel disc with 360 slits in it on the outside diameter and 4 slits on the inner part of the outer slits.

Two optical LED lights and a reader for each LED on the other side of them. The disk spins of the camshaft and the light is picked up by the reader as the slits pass over them. This signal is called a high resolution (360) and a low resolution signal. Both of which are sent to the ECM.

On a scan tool data readout the high res. signal starts at 0 and counts up. Into the 250+ range or so. I don't remember exactly how high it does go.
The low res. signal is read as events per msec. A typical reading might be 22 m/sec. for example.

The Opti-Spark has a power and ground for the LED/Encoder and that is all there is.

The signals are used by the ECM along with other sensor data to compute outputs to ICM, Fuel Injectors, etc...

The ICM just fires the coil based on what it gets from the computation from the ECM, that is its sole job.

Obviously, the cap and rotor do what a cap and rotor do. Distribute spark, nothing new there.

Now what happens inside the ECM during its computations is PFM. You'd need to be an electronics engineer or computer engineer to understand all that detailed stuff. I understand how the basics work. The 1's and 0's and so forth but, writing the program, logic, and making it work. Yeah not so much.

Data logging and programming engine parameters is NOT as advanced as actually writing the programs the ECM operates on. Useful tuning tools for sure.

Heat and moisture can really f-up electronics. Lots of both on the front side of an engine. Not to mention sub par grade Opti-Sparks. Personally, I think the 95-96 OEM Opti-Sparks as long as they are kept dry are VERY reliable. The vent system helps with the heat. Notice I said OEM, seems like everything else even the AcDelco ones (made in china) are suspect at best anymore. We should demand a quality unit and get it. I'd be willing to pay for it, as long as it is a QUALITY unit.

93LT1

Robert
I'm experiencing that same 36 code. Since I have 140K miles on this 93 Lt1, I've decided to try to eliminate the front area oil leaks which I think contributes to the demise of these Opti's. I'm in the process of incorporating the OEM vented system and I'm replacing all the front seals and gaskets. Checking the Timing chain, sprockets and shafts that touch the seals. I'm also replacing the Pwr steering pump and O-rings and anything else that looks defective, like the idler/tensioner pulleys.

I was able to purchase a new Delphi Opti. I opened it up and confirmed it does contain a new Mitsubishi Optical element. I've applied the thread lock and modified the case to support the vacuum lines. I also purchased the 96 cap and will be RTV sealing it once it arrives. This 96 cap has the built in vacuum nipple.

I'm hoping this darn Opti will actually last as long as my original (70K).

Once this project is complete, only time will tell of it's benefits.
Hank

93Rubie

Don't forget the LT1 intake leaks.

I'm glad to hear the Delphi Opti contains the Mitsubishi unit. I've been wondering about this.

I'd like to see pics of your modified Opti Vents on the 93 case. If possible.

Good info, thanks.

93LT1

Oh yea! thanks for the reminder..Will be doing this too... I'll take some pic's.

Robert Thomas

I'm gathering the parts to change the opti one more time. I took an old one apart and I don't see anything that could fail except for the sensor. I guess the short from the rotor center tab to the rotor mounting screws could cause a misfire but that's not what mine's doing.

It misses severely for a few minutes, produces an SES light, then runs fine.

I sealed the replacement opti so noting could get in it except through the bottom vent holes - admittedly not perfect.

Bah

93LT1

So no opti mechanical issues? Was the Opti an OEM?

Are the fans running? The reason I'm asking is because my fans stay on when the car finally starts. Seems as if the ECM is in monitoring mode. I'm not sure why it's doing this. Hmmm I don't think the ECM ever went into closed-loop