High RPM Miss I've had for years that I can't figure out
05-02-2012, 06:11 AM
#21
I have a friend that swears by extra grounds for any phantom problem like this. It is cheap and easy to try.
Might consider trying a autolite 103 just to further rule out detonation.
Far as the ICM I thought like you did they worked or were dead sometimes temperature sensitive and only died hot, BUT then I tried helping a guy diagnose a car that was just soft under hard throttle, drove perfect normally but pedal to the floor just felt soft, eventually he kind of threw his hands up in the air and started putting old parts back on the car. Well when he did heads/cam he had replaced the ICM and coil just because they were off. Swapping in the original ICM fixed it. The aftermarket replacement was just "soft" and it is the only case like that I know of.
Might consider trying a autolite 103 just to further rule out detonation.
Far as the ICM I thought like you did they worked or were dead sometimes temperature sensitive and only died hot, BUT then I tried helping a guy diagnose a car that was just soft under hard throttle, drove perfect normally but pedal to the floor just felt soft, eventually he kind of threw his hands up in the air and started putting old parts back on the car. Well when he did heads/cam he had replaced the ICM and coil just because they were off. Swapping in the original ICM fixed it. The aftermarket replacement was just "soft" and it is the only case like that I know of.
05-02-2012, 10:54 AM
#24
i had emi issues like you couldn't even immagine with the msd's.....when the motor got under a big load....it was reaking havoc in the car.....blue screen of deathing my lap top.....screwing with cam signals......all sorts of stuff....i swapped to Moroso Ultra 40's and have never looked back.......and the issue occoured every single time at 6050rpm......which just happens to be my peak torque point (biggest load on ignition)......id start there...because it seems as though the issue is more prominent in your peak torque area when the ignitoin gets under a load........not saying thats it but its somthing to think about.........my issue got really bad after i swapped to the msd 7al2 box......like their own plug wires couldn't handle their own power on an EFI car.....90% of people dont see the issue because they are either carb'd or an LS with 6" plug wires or just dont have the spark demand to cause the issue
05-02-2012, 11:52 AM
#25
I'm going to go ahead and be the first to blame your opti 
Have your tried replacing it during the time the issue has been happening? My old motor had a constant miss at 5200 RPM no matter what wires/ICM/coil was on it forever....new MSD opti and it's gone 
Have your tried replacing it during the time the issue has been happening? My old motor had a constant miss at 5200 RPM no matter what wires/ICM/coil was on it forever....new MSD opti and it's gone
05-02-2012, 12:01 PM
#26
No matter what the problem is with your 93-97 LT1, if it wont start, misses, down on power, has bad brakes, pulls to the right, window wont roll up, t-tops leak, girlfriend left you... its the opti spark. Just change it. If it dosent fix it, youve got a dud. Change it again until you get a good one. Sometimes it takes a few, but eventually you should get one that will at least last 6 months.
I don't know why people have such 10 bolt issues...I've never broken mine or personally seen one broken so it must NEVER happen.... 
05-02-2012, 12:54 PM
#29
not what im saying....... your comparison is rediclious...........what I am saying is ive replaced many opti's on customer cars and never once had one come back with an issue........i ran a STOCK opti on my 355 with a MSD cap for 4 years and never once had an issue........so my pattern says yes 90% of these opti failures are due to neglect upon install or just poorly chosen product in the first place......dont compare apples to oranges....
05-02-2012, 01:04 PM
#30
not what im saying....... your comparison is rediclious...........what I am saying is ive replaced many opti's on customer cars and never once had one come back with an issue........i ran a STOCK opti on my 355 with a MSD cap for 4 years and never once had an issue........so my pattern says yes 90% of these opti failures are due to neglect upon install or just poorly chosen product in the first place......dont compare apples to oranges....
) opti resolved the miss.
05-02-2012, 01:15 PM
#31
I'm not taking about opti failures...I'm just bringing up a valid point that a "bad" opti/cap rotor CAN cause a high RPM miss; just because it hasn't happened to you does not mean it's impossible....my 3rd opti never actually failed; the MSD (#4 lifetime total over 14 years) opti resolved the miss.
) opti resolved the miss.
05-02-2012, 01:16 PM
#32
What about your rockers, valve springs and retainers? My buddy had the similar deal and chased it for years. It would miss in 2nd-4th on pass then only 3rd-4th another. Turned out to be the rockers would rub the retainers at a high rpm load. He had the Blue GM roller rockers and they were worn silver in areas from rubbing.
05-02-2012, 01:35 PM
#34
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When I had my vette, I remember people having this problem with the 96-97 ODB2 ECM's on the Corvette Forum. Converted back to ODB1 94-95 ECM and the problem went away. When I built the 383 in my 96 LT4 vette I did the ODB1 PCM swap and never had a problem.
I could have sworn I put in a new set of wires in the last couple of years. Do you know if moroso makes a cut to fit set for LT1's? 