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**TraceZ** · 05-20-2005, 08:51 AM

Another question...

What wires should I buy? I have a wholesale account at my local dealer so the OEM ones would be easy to get. Should I just do that or is there an aftermarket product that is superior at similar cost?

**95TransAm** · 05-20-2005, 09:17 AM

Logically speaking....it would seem like your miss is derived from your wires if that was the only thing you were messing around with the other night. Knowing you and how you take care of your car, I'd safely assume that your Z wasn't missing before....so wires are probably your best start.

Did you put them on all the way? Did you rip any of the boots? Are they touching the manifolds in any way? Replacing the wires would probably be a good idea. I use taylor 8mm custom fit wires....heard nothing but good things thus far....no complaints from me either. I payed something like 80 or 90 bucks for them.

Also if you want, I've used this trick on a carbed sbc a couple times when trying to find a miss. I've never done it to my car (no reason to so far), but I can't imagine how this would hurt an LT1. Spray water on the boots when the car is running. The water increases resistance, and you should see the spark "arcing" if there is a problem with the wire. Do it in a fairly dim area though, it makes it a lot easier this way.

Good luck with everything, and just make sure to not drive her too long or it's bye bye Mr. Cat

**Crazy Canuk** · 05-20-2005, 09:19 AM

I went with Taylor 8mm wires, it seems that those are the wires of choice here. My mechanic complained that they were hard to get back into the original position because of the increase of there diameter but they seem to be ok. My AC Delco ones lasted 11 years and 100k kilometers so you wont be bad off going with stock but some will argue with performance gains I guess. Also just because the Opti looks ok on the outside dosn't mean that it is on the inside. Mine was taken off and replaced, the old unit was realy rusted yet the car would start no probs and run 'ok'

**95TransAm** · 05-20-2005, 09:27 AM

Hmmmm....I was just thinking and realized I'm not 100% sure about something and can probably get this answered from one of you guys.

Could a bad opti cause a miss? I've heard loss of power, sputtering, etc... in reference to a bad opti...but for the life of me cannot remember anyone saying their bad opti created a missfire. I would imagine a bad opti would create a weak spark which would explain sputtering and a loss of power, but I'm in the blue here if it can make you miss.

Anyone want to enlighten me on that one? If it can, then maybe you should take a look at your opti too TraceZ

**Injuneer** · 05-20-2005, 09:27 AM

The glowing cat can be a sign of raw fuel. The misfire dumps unburned fuel and air into the exhaust. The O2 sensor "sees" the air, and assumes its running lean, and dumps even more fuel into that bank to richen it up. Sort of snowballs out of control, so you end up with the original cylinder that was misfiring, plus the other three that are running too rich. Now the cat sees the unburned fuel and the unused air, and they burn on the converter substrate, releasing a lot of heat.

Check the plug and coil wire terminals on the Opti and on the wires for corrosion. Check the Opti harness connection for moisture and/or corrosion. If there's coolant in the harness connector, it could be a bad sign, because the seal in the harness wire tower it one of the weak points for moisture entering the Opti.

Let it idle in the dark, and look for sparks.

**Injuneer** · 05-20-2005, 09:31 AM

Originally posted by 95TransAm

Hmmmm....I was just thinking and realized I'm not 100% sure about something and can probably get this answered from one of you guys.

Could a bad opti cause a miss? I've heard loss of power, sputtering, etc... in reference to a bad opti...but for the life of me cannot remember anyone saying their bad opti created a missfire. I would imagine a bad opti would create a weak spark which would explain sputtering and a loss of power, but I'm in the blue here if it can make you miss.

Anyone want to enlighten me on that one? If it can, then maybe you should take a look at your opti too TraceZ

The Opti is the distributor. It can experience carbon tracking in the cap, damaged rotor, burned contacts, loss of dielectric strength, wobble from a bad bearing, etc.... just like a conventional distributor. If it has any of those problems, it causes misfires. Having moisture in the cap makes it worse. It can also put out a faulty pulse pattern and cause the timing to be off, firing plugs at the wrong time, having the same affect as a misfire.

**TraceZ** · 05-20-2005, 09:34 AM

I have no faith in these plug wires so I just ordered a set of the taylor spiro-pro ones from Summit along with a bag of black plastic conduit. When they arrive I will install them and inspect everything again. I think I just might fire it up tonight on jacks and turn off the lights while I'm under it to look for arking.

I have dielectric grease to put on all the boots. I should be all set once it gets here. Wish me luck, I hope it is not the opti, I guess I'll find out soon enough.

**95TransAm** · 05-20-2005, 09:35 AM

Originally posted by Injuneer

The Opti is the distributor. It can experience carbon tracking in the cap, damaged rotor, burned contacts, loss of dielectric strength, wobble from a bad bearing, etc.... just like a conventional distributor. If it has any of those problems, it causes misfires. Having moisture in the cap makes it worse. It can also pulse out a fualty pulse pattern and cause the timing to be off, firing plugs at the wrong time, having the same affect as a misfire.

It would make sense being the distributor that it would cause a miss...but I have the lack of experience going against me...I had no idea.

Moisture I know can always upset a distributor, but I also had no idea that it could create a faulty pulse pattern and screw up your timing. That's interesting and some good info to know.

Thanks a bunch...as always, you're the man Fred

**Injuneer** · 05-20-2005, 09:58 AM

The optical sensor in the Opti produces two pulse patterns.... low resolution and high. The low resolution pulse is actually 8 variable width "windows" in the rotating disc. By looking at the width of the windows (length of the light signal being received by the optical receptor) the PCM knows when to fire the sequential fuel injectors. Knowing exactly where the cam is at any point in time is critical.

The high resolution pulse is a series of 360 slots on the outer edge of the rotating, and that tells the PCM with extreme precision exactly when it needs to to fire each spark plug. The combination of the 8 pulses for cam position, and the 360 divisions in the high res signal allow the PCM to know EXACTLY where the engine is in the 4-stroke cycle at any point in time. Hence, you get very precise injector and spark timing. That is primarily of interest with respect to emissions, but it also helps performance.

All that said, if the optical wheel is dirty or wobbling, or the receptors in the sensor are plugged with rust (a common problem), the pulse patterns become inaccurate. I guess moisture could help "blind" the sensor, but its mainly the buildup of rust particles due to moisture, and (in the unvernted models) ozone.

The PCM is constantly comparing the high and low res pulses, to insure the number of pulses it is seeing is rational. If the pulse patterns are "off", it isn't even going to have an accurate measure of engine RPM. If it loses the low resolution pulse and can't determine exactly when to fire the injectors, it shuts down the fuel system and the engine won't run.

Sometimes, corrosion in the harness plug, or the presence of nearby pulsing high voltage signals, like a plug wire, can contaminate the pulse signals with "noise", and the engine will start to run rough.

The Opti is really a great idea.... they just put it in the wrong location. The concept didn't even originate with GM. Chrysler/Mitsubishi used it in a 3L V6 they put in a lot of cars in the late 1980's.... they just had the common sense to put the distributor in the "normal" location.

**Crazy Canuk** · 05-20-2005, 11:49 AM

I cant remember if I got the link here or found it on the net but if you want to know all about our opti's then here you go.
http://www.gmhightechperformance.com...htp_optispark/

I had a miss I did the small stuff and worked up, plugs wires, opti and then injectors, turns out 4 had to be rebuilt. Now the car seems to run so much smoother but sounds meaner. A random missfire is hard to knock down.

**95TransAm** · 05-20-2005, 03:24 PM

Injuneer....wow,
I had to read over your post a little bit slower a couple times over.....but for the first time I can actually say I know how my distributor works. It's simply amazing how an opti works....so complex...yet so precise. When explained like that, I now realize that the opti isn't as bad as everyone makes it out to seem; it's actually quite ingenious. It's a shame that the location for something so sensitive to moisture is right under the water pump

Then again though, if the distributor were in the "normal" position, it really would be one extremely tight fit.

Fred, thanks a lot for explaining everything so thoroughly....I appreciate it.

**Injuneer** · 05-21-2005, 12:02 AM

When you take the high voltage functions out of the Opti, and use it simply as a cam postition sensor, its a great piece. I've been running for almost 5 years now, feeding the Opti pulses to an aftermarket ECU, and driving 8 LS1-style coils in direct fire. The system performs faultlessly, providing precise cam position data that allows the engine to rev to 7,400rpm. With the data, the ECU can actually alter end-of-event injector timing, based on rpm and other inputs to pick up a little extra power.

Getting the high voltage function (cap/rotor) out of the system seems to eliminate a lot of the problems. I am running a "vented" Opti though. A friend of mine used the same system to make 1,125HP on a 383 LT1 with a Vortech S/C, running 22# of boost and turning 8,000rpm.

**TraceZ** · 05-21-2005, 12:59 AM

Good sign?

I think the opti is OK. I'm 99% sure the wires were the problem. I'm actually amazed it didnt have any problems until now. After removing the old wires I noticed they had electrical tape on two of them on the passenger side. The tape was old and stiff. Upon removing it I found the following. I'm pretty sure that wiggling the wires around caused these old repairs to fail and misfire. I cannot believe somebody would take wires as gashed as these and just tape them up?! They were not routed in the proper places either.

The new Taylor Spiro-pro wires are not here yet, so we'll see for sure if they fix it in a few days. I'm pretty optimistic.

**Joe 1320** · 05-21-2005, 05:10 AM

Nice.

There is a prime example of why I work on my own cars. I just posted a story about an experience on another thread.

At least you found it at a convenient time.

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