Wolf95

I recently picked up a 93 Trans AM, and it ran fine for about a week after I got it, however I noticed one day the engine lost power, and then would pick back up after I let off the gas, the CEL was lit for a second but then shut back off. It was fine for several more day and then it started dying anywhere below 2k RPM. Engine did not run too well through high RPMs either. I pulled the code and got code 16, the harness tested out fine, so I swapped the optispark for a new MSD Billet vented optispark unit.

Now, it drives fine until the engine reaches full operating temperature for about 6-7 minutes and then it has a loss of power and code 36 came on. I had my laptop on with TTS Datamaster connected while I did the initial test drive, and it showed Code 16 was set from the get go, and 36 was set after it was warm for 6-7 minutes. I checked the voltage on the ignition test connector coming from the PCM and I had 4.7V on both. However that reading was done when the engine was cold. Do I need yet another optispark to replace this one? Or is there more I should check before replacing the MSD unit?

Injuneer

If you had DTC 16 and the engine was running, it is a stored code. When DTC 16 is active, the PCM shuts down the fuel system = no start/no run. DTC 16 does not turn on the SES light. It isn't unusual to see DTC 16 stored. Seems like the PCM just saw a delay in the low resolution pulses appearing.

DTC 36 on the other hand does turn on the SES light. The engine will run with that code active. In theory it will not noticeably affect engine operation, causing a slight loss of ignition/injector timing accuracy. However, an erratic high resolution signal seems to be capable of causing surging, strange tach movement, and roughness in the engine.

I have diagnosed several MSD's with high resolution pulse problems. One of them had just been returned from MSD service after a "rebuild". Sounds like yours may have a heat soak problem. Personally, I would never consider the MSD unit.

When you tested the ignition test connector, which wires did you get 4.7V on? When slowly turning the Opti, you should get a switched DC volts on the red/black and purple/white wires, switching between 0 V and 5 V. Basically, a 5 V square wave.

Wolf95

The 4.7 Volts is what came from terminals A & B. I'll test the red/black wires and purple/white wires recommended tomorrow. What unit would you consider best to drop in? I contacted my dealership for a Optispark and they wanted 980$ for one.

moparman

Check out Rock Auto for a Delphi opti.

Injuneer

+1 for the Delphi, or an AC Delco.

NEVER buy a part at list price from a local dealer. They are available online from discount GM dealers, and from reliable online parts stores for way less than list.

GaryDoug

That would be close to normal if the engine was not cranking. Although the 4.7 seems a bit low if that was measured with the connector unplugged. Normally it should be 5.0v. Perhaps the meter is in error.

LT5

So whats really wrong with the MSD opti?

Injuneer

Costs more.

Has problems w/ optical module

Has a somewhat useless "timing adjustment". OK of you are advancing or retarding the cam, but not a smart way to adjust timing. The is no marked "0" point for the adjusting screw. You have to count turns and guess.

Over the years has been bugged by problems with sealing (appears they fixed ths), rotor falls off (common problem to most brands), the optical module, which can produce erratic high resolution pulse pattern, even right out of the box after a "rebuild". Probably a few others I've forgotten over the many years they have been trying to get it right. Maybe they've solved the optical problem, but about two years ago problems seemed frequent.

Definitely better than the store brands and others that are probably cheap Chinese rip-offs. The vent system on the replacement for the 93/94 unvented unit is good, but you can get that just buying an MSD cap, or DIY it using a guide on one of the Corvette forums.

LT5

Yeah cause im in the market in the next month for an entire new ignition system and i really wanted to try the msd opti. There are a few articles where they have said it was superior and "smoothed out" the power band but ive heard just as much bad as good. Ive replaced stockers before and they never last. Ive gone through 2 so far. I heard the delphi is really good to.

Injuneer

Did you read what was posted in above responses?

Are you having a problem with your current Opti - misfires, erratic idle, DTC's, hard starting?

LT5

Yeah im not sure if its the opti though i need to do more testing.....tested all my fuses and relays (i have a relay buddy) and even the fuel pump relay. Everything came back good.....sometimes the car just does not want to start....just cranks and cranks lol. But when it does start it runs really good. There is a service light that comes on but then goes away....when it comes on the car loses idle rpm and runs really rough....when it goes off the car runs normal. It has a line lock which i am going to take off...and all of the egr stuff has been taken off...although the air pump and egr soiloniod are still on i would like to get all that stuff off to....don't want any smog stuff on it as i can get a special smog anytime

Injuneer

Since it sounds like the SES light is coming on, have you scanned it for codes? That's why the light comes on.

LT5

Think that will be my next step.....never understood why it comes on and then goes off though lol thats kinda odd.

Wolf95

Well MSD called today, they said that they soaked it at 200F in attempt to get it to fail, it was still producing the proper signals. Then they said that they replaced the optic sensor and cap just as a precaution as at that temp it can be destructive to it. Is there anything else I should be checking or swapping out? Being so intermittent I'm thinking of pulling back the sheathing on the harness for inspection?

Do you think having 4.7 volts vs 5 could play a factor in this? I'll look into borrowing a different meter, but so far that meter has been accurate, at least up to this point.

Wolf95

Threw the MSD back on, and now it seems like it is missing a cylinder or two. I tore it all apart, inspected it, it appeared it was 1 tooth off, so I reassembled it again. Now it's all back together for the third time and I am still having issues. Inspected spark plug wires, replaced plugs. (Wires are 10mm wires that are a month old). Is there anything else I should be checking?) No check engine code, but then again, I don't drive it for more than a block as it does not like to move and constantly backfires. The idle is fairly smooth, but then as soon as it's in gear, the whole car rocks side to side.