Injuneer

Using data logs from Scan9495 and TTS DataMaster, I've identified several MSD Opti's with optical modules producing erratic pulse signals from the high resolution pickup. That resulted in huge RPM surges, when the PCM reacted to erratic RPM signals AT IDLE as high as 7,000 RPM, and jacked up the IAC counts, producing idle surges to 2,500+ RPM. Are you experiencing anything like that?

I sent two of the data logs to MSD Engineering, thru one of their tech support people I met on another site. MSD then requested one of the owners to return his Opti. Last indication they said they found the problem, and returned it to the owner so he could try it. That was the last I heard, no insight to the problem, etc.

Point is, this problem was endemic to MSD units produced over the last year or two. Something faulty, maybe a change in supplier of the optical module, or some design change.

DTC 36 sets on loss of the high resolution pulse signal. The engine will continue to run OK on loss of that signal, with a very small loss of accuracy in ignition timing and injector timing, and increase in spark scatter. But you wouldn't notice the difference. Seems total loss of the high res signal, possibly due to heat soak, has less impact than erratic signals, which don't set DTC 36, but cause surge and rough engine.

marlar98

I'm not seeing erratic rpm surges or anything. Even after the DTC 36 code the idle seems normal but the engine runs a little rougher.

I'm going to check the wires as I mentioned before but I'm betting it's the opti.

94Z28LS1toLT1

hey marla98,i had the same exact issue u have now,i tried everything u can think of,
spark plugs,spark plug wires,Icm, coil,fuel pump,fuel filter,charcoal canister,fuel hoses/lines,cleaned throttle body,my opti was only 6 months old so I assumed it was ok.

but I remember when I installed the opti after these mechanics did a head work on my car bcuz they said " i had a bad valve thats why the car was misfiring and rough" towed back to my place bcuz they said they don't know why it's not starting.So i took the opti off n examined it, when I was spinning it,it kept getting stuck.

as I mentioned in the thread about the all black gm original,i had that one in the box brand new,n I spun that one n it really smooth. So I swapped optis n stomped the gas pedal and hit high rpms n no more misfiring n rough at high rpm.

marlar98

And the plot gets even weirder....

Drove yesterday, no problems whatsoever no matter driving style. Drive to work this morning in stop and go traffic, no problem. Drove home today and after 15 minutes of driving got the DTC 36 and 16. Car stayed running. Made it home. Cleared the codes and now driving fine again. Only thing I can think of is whatever is causing the problem it has to be heat related. Yesterday was rather cool. This morning was cool but this afternoon it was low 90's.

I'm just gonna change out the opti and be done with it. How long should it take me to do it? Thanks for your help guys.

Injuneer

Never did one with engine in the car. Converted my 94 to vented when we built the stroker, but that was on an engine stand.

marlar98

It doesn't seem too bad of a job. Drain antifreeze, undo hoses, remove fan, remove water pump, balancer, disconnect spark plug wires, coil wire and electric connector, pull the opti. I mean there are a few more details but that's pretty much it right?

Chimera96

You should go buy a Haynes service book for your car year/model. Most auto part stores carry them. Amazon, etc.

If you have some "wrench" skills you can do it

The FelPro Timing Cover gasket & seal kit for around $12 at most auto part stores has all, and more, the gaskets you need for the job. Often people replace the WP drive and Opti seals when they do a Opti replacement. Those are included in the FelPro kit. If you see oil leaking from the WP drive seal and/or your opti is covered in oil...you need to fix the cause of that leak if you have it

Use blue loc-tite on the rotor screws. Don't buy a store brand Opti. Get a reman AC Delco or new Delphi if you can find one.

If your opti was exposed to oil r coolant leak...pull the cap, rotor and the metal wheel with the slots around the perimeter...if oil or crud in opti carefully clean with Q tips. That may be the only problem with the Opti. Cap & rotor are wear items just like any regular distributor so replace if needed. MSD does make a good cap & rotor...not whole opti though

marlar98

Thanks Chimera96. I'll grab a Haynes. Looks fairly easy. I've turned a few wrenches. Even set up my own gears in my 8.8.

Injuneer

Or.... free download of the factory service manual, for your year vehicle:

https://www.mediafire.com/?40mfgeoe4ctti

marlar98

And another twist, lol. This is getting comical. I bought this car about 18 months ago so I'm still learning it since I don't drive it much. Get this, so before I go through the trouble of changing the opti I decided to swap the wiring harness since I have a brand new one. Easy enough, right? WRONG!!! The wiring harness I got was for a non vented opti since that's what I THOUGHT I had. Pulled the harness that's on the car and what do you know... it's for the VENTED opti! My car is a 94 so I didn't think it had a vented opti. Either it's been converted or the intake isn't original. The intake even has the port for the vacuum hose that runs to the opti but Doesn't have the vacuum hose running to it from the intake. It's just plugged with a vacuum plug. Wow!

Anywho, The connectors were corroded so I cleaned them with crc electric cleaner and plugged it back in the opti. Went for a drive and everything is fine, but I'd like to connect the vacuum line to the opti. Good news is I have a spare original vented opti that came with the car when I bought it. Just need the vacuum hose that goes to it. This has been an adventure lol.

marlar98

Oh, I love free, lol! Thanks Injuneer

marlar98

Just confirmed the vacuum diagram on the radiator support is indeed the 94 style, but the intake has the vacuum ports for 95 & up. PCV valve line runs under the throttle body and doesn't have the u shaped vacuum line.

marlar98

Just a quick update. After cleaning the connectors I haven't had any issues the last couple of days. Just got back from a spirited drive and so far so good. No codes. Just need to purchase the opti vacuum hose and connect it now that I know I have a vented opti.

Thanks for all your help.

Chimera96

This may help. Courtesy of Shbox.com

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

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

marlar98

Thanks again. I've become very familiar with shbox's website, lol. It's helped me numerous times without having to ask questions. Excellent and invaluable resource! He should be nominated for LT1 sainthood, lol.