So this is the typical opti thread with a bit more info.

I purchased an autozone opti in May w/ lifetime warante. I replaced it a total of 5 times and finally gave up and ordred a new gm one for JC. Now I have about 2k miles on this one and more problems. Everytime I replace it, she runs fine for a while. Then bad again.

The miss is at the top end, the odd thing is the tach jumps up when it does. While scanning the logs show the same, an instant, usually only 1-2 frames on the scanner the readings jump from 4k to 5.6k, then back down again.

No cam, so it shouldnt be a dowel issue. Vacume hoses are hooked up. Everything was buttoned up pretty tight.

I have a nitrous kit coming tomorrow and now this crap again.

 

does it act like its bouncing off the rev limiter? Or before the rev limiter?

Sounds like its delteq time for you dude.

Mike

 

I'm pretty sure the tach on our cars gets its readings from the coil. Have you replaced your coil recently? When I first got my car it was acting in the way you're describing and I thought it was the Opti, but a new coil+wire cured it.

 

The tach gets it's signal from the PCM which inturn gets it's signal from the optical encoders inside the opti. The first thing to check is the 4 pin connector at the opti and the others about 2 foot from that and finally at the PCM.

By the way, you won't get much of a response without some particulars in your signature regarding your vehicle. If we knew you had a vented opti, we might ask you if the vent lines have the restrictor in place and are routed properly.

You should ask yourself "why am I going through so many optis?". And ask, Am I masking something else when I replace them or am I doing something wrong? Could you have some type of mod that is creating a problem? See where I'm going with this?

 

Sorry, most forums I have a good list

95 m6 z28
No cat
flowmaster 80
cai
air pump and hoses removed
throttle body bypass
thats really about it for mods

I have not changed the coil, but never thought it could affect the tach. First opti (110k on it) did the low end stumble. All since have been high end that start as barely noticable then get violent.

I changed the fuel filter and 1/2 the plugs tonight. Will finish the plugs and test tomorrow. I did find a cracked plug in #2 which would have been there since I changed the plugs back in March-April. Could a bad/damaged plug come back and damage the opti in any way? Or could a bad plug cause the tach signal to jump? Wires have about a year on them and the ones I checked tonight all looked good.

The 2 vacuume lines are hooked up, not 100% sure they are in the right order though. I don't think that would matter too much would it?

This drove me crazy and I finally thought the GM opti was the anser. There is only a voltage, ground, and singal wire going into the opti, then that signal wire going back to the pcm are the only things that I would think could affect the tach, all look to be good.

Yes if the tach spike high enough it feels like hitting the rev limiter. But its jerks a little even if it doesnt go all the way up

 

If the pin was off a spot from the cam I would have had problems long before.

If something was so unballlanced that it was ripping the internals apart, again I think this would be noticable.

No smoke, runs great (well when it runs right)

The vin for the pcm matches the dash, and the one I changed first was vented, so Im assuming I am putting the right opti on.

Another odd thing, when I have taken the bad ones apart in the past there has never been any oil/coolant/rust or any other kind of buildup on them. Pop on a new one however and it runs fine for a while.

Thanks for reading though everything. If my title wasnt tied up on my motorcyle loan Id be giving up and going ls1...

 

By restrictor you mean the little round thing between the opti and intake manifold? Yes its there.

 

Had a similar problem, would definitely go with the coil, msd coil is less than 50 bucks i believe

 

I just had a Dash, injectors, ignition event after I installed my msd6a two days ago.

I tapped into the switched power feed for the fuses that feed ignition, injectors and cruise control. since it was switched I figured it was perfect for the MSD6A box. It ran fine till I got stuck in traffic... as the engine got hotter the misfiring got worse and worse. My dash power was fluctating ... voltage gage was dancing at the same rithm as the voltage and fuel presure was down to zero... when my check dash gages light came on... I put my hands by the ingnition switch at the steering wheel and it was too warm....not hot just way too warm..

It was the MSD6a sucking too much juice from that power feed... I fixed the problem with a 30amp Automotive Relay from Radio Shack, 10 gage wire and some free time. I drove to work and back today.. in traffic again and everything was back to normal...


Could your problem have a similar origin?? is the power feeding your system fluctuating??/ My power at the Battery and Alternator was fine... but that switched power line could not hold my MSD6A... This time I only used to it to turn on the Relay. My gages are working fine now... so far and the misfiring is gone.

I will have to drive her a few more days to make sure though..

Marvin