For starts.....

"Arisa" AmsOil air filter, Throttle Body Bypass, LT1edit, Hotcam, Ported heads, LT's, Mezere EWP, Custom exhaust w/Random Metal Matrix Cats, & MagnaFlow Mufflers, Fidanza Flywheel, Stage III Clutch

New knock sensors
MSD 8.5mm plug wires
NKG Iridium plugs
Opti has 20K or so on it and 8 or so years

Plugs and wires have maybe 300 miles on them

That should cover the important stuff.

Now to the problem.

When I start off from a stop or roll gently into the throttle the engine bucks and misfires like hell. It violently shakes the car bad. I can hammer it off the line and she runs mean as even and I can drop a gear or two to get the rpms up before rolling in and she is fine. Up until the problem started I could cruise fine in 6th at 60mph and roll in to it to pass without issue. Now she is pissed at 60 in 6th.

I've looked the plugs and they look good and I've ohm'ed the wires and they seem in spec to. No burns or cuts or cracks on/in them.

The car has had maybe 30 miles put on it with this problem.

Thoughts? Suggestions? Prayers? lol

As a side note...not sure it is related but more info always helps....When I bring up the OBD on the dash I don't get the options of 4.0, 4.1, or 4.7 (PCM related functions)

Any idle problems?

Aftermarket throttle body?

Who did the tune? How does the scan look when it stumbles?

Matthew

I'd check the TPS voltage.

And I'd pot an ODB-II scanner on it to cee if you're getting DTC 21 or 22.

Sounds like it could be an intake gasket leak. Any recent history on pulling the intake manifold?

Take it to a parts store for a FREE scan. I would be curious why the paperclip method isn't giving you the codes.

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Yea especially if modules 1. 7, and 9 are coming up.

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Excellent suggestion (parts store).
It's an OBD II, so paperclip doesn't work.

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Doing some research, that looks like it's true.

I even saw where someone said the other modules will come up not not mod 4.

You can't even start this diagnosis without pulling the codes.

Lets see if I catch everyone.....

No idle problems.
Factory Throttle body
MY tune. Spent over six months getting it where I wanted it. She has ran this tune for 11 or so years (damn I've had this car a while. lol) Bogus can tell you how well tuned it was. :-)

Will check the TPS voltage tonight.
Yea I had AutoTap before I move but I'll be damned if I can find it now. Of course I found my Ford version with no problem... $&%*#^$*)@*@)$&%^*%^

Engine hasn't been broken open in years (at least 7)

Oh I use to always grab a quick code with the paperclip. One thing I really like about our displays.

Oh and the fuel filter has been changed right after this started. forgot that last night

When did this start? After any changes/upgrades/repairs?

I still recommend a computer scan so you can see what the sensors/computer is doing while this happens.

Matthew

Started while out on a drive one day. Had driven her several times before in the week before. NOT ONE single change, mod, oil change, nothing. Okay I may have wiped the dust off her with a car mop (or whatever they are called).

Trust me I agree. I need my damn AutoTap. Trying not to break down and go buy another right now cause I don't have the jingle.

Try one free check. Start it up in a dark space and look for any sparks from shorting out plug wires, including the one from the coil to the opti.

Then ohm check the injectors.

Both free basic checks.

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What's the brand on the opti? GM? One from an internet seller?

After seeing all of this laid out, I have had some more time to think.

I checked the 1996 FSM, and interestingly enough, you CAN get to PCM codes via the CCM/IP; they are just cropped, so they are of little good.

By your inability to reach these codes makes me think the PCM is bad or failing.

This does not sound like a communications problem as much as a functional failure of the PCM.

Do you see the message "ERR" in the speed area? If so, this means that the CCM and PCM are not talking. I am thinking they are, but not constructively.

If there was a problem with the CCM or PCM communications ports, you have have a no-start condition. And that doesn't seem to be the problem.

GM Opti

No ERR in the speed area that I remember but will recheck.

Oh she starts just fine.

The PCM failing crossed my mind.... and I had to stop thinking down that road. :-(

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What do you mean by "cropped", Andy? Curious.

Double checked the DTC's through the CCM. No ERR. It just doesn't appear. According to the service manuals ERR will only show up if NO communication.... which leads me to this... (unrelated issue) could the CCM be flaking out and just not be looking for the PCM ?

TPS voltage ..... .6 closed and ramps up linearly to 4.5 at WOT.

All injectors ohm at 12.1 to 12.5 ohms.

IT's the PCM... the way they communicate requires that the CCM send a handshake to the PCM to allow the fuel to start flowing.

There is a separate control from the CCM that instructs the starter to fire.

This means the PCM is talking to the CCM at some level. If you are not getting the codes out, then that means the PCM has lost that ability, and now I wonder what else?

Bill - Cropped = truncated = cut off. If the code is P1003, you may only see 003.

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thanks

Can GM check the PCM ?

yes. the Tech II can sort it out...

Also, 96 PCMs are not that expensive.

Bigger question.... If it has to be replaced can they put the VIN back in the new one so the LT1 Edit software will still work? It is VIN locked ya know.

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See Andy's (95Vette) post - #21 on who to talk to about this.

http://www.corvetteguruforum.com/modu ... hp?topic_id=16595&forum=1

Any word, Neal?