Strange opti spark problem
Thread Starter
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Strange opti spark problem
Here is a good one for you guys. I got a street rod in the shop with a LT1 engine. It has no spark, with a tech2 checking the PCM I see NO Low or High RES signals. first guess would be bad OPTI. I plug in a brand new MSD OPTI, spin it by hand BINGO! I got the required signals, spark blasting out of the coil wire and the fuel pump runs and I hear the injectors clicking. Fixed right??? HELL NO! 
I remove the old opti, connect it up hold it in my hands and spin the wheel, same thing, coil fires, fuel pump runs, got good signals at the TECH2, put the damn thing back in the engine, remove the cap so I can see if the rotor turns and it does upon engine crank but still no signals. OK WTF! Plug in a brand new MSD into the engine crank her over and SAME DAMN ISSUE! Now its WTF *&^!@*@&#@!!
So I remove the PCM plugs check all power and grounds and continuity of the opti signal and power wires to the PCM plugs, all grounds check out to <.5 ohms to the battery cable, power is fine at all points, there are NO DTCs in the PCM.
So anytime the opti is installed there are no signals from the opti during crank and no start, the thing spins with the engine so its not anything mechanical binding it up, take the POS out of the engine spin it by hand and its fine, anyone come across something similar? I gotta spare PCM at home that I will try tomorrow.......
I remove the old opti, connect it up hold it in my hands and spin the wheel, same thing, coil fires, fuel pump runs, got good signals at the TECH2, put the damn thing back in the engine, remove the cap so I can see if the rotor turns and it does upon engine crank but still no signals. OK WTF! Plug in a brand new MSD into the engine crank her over and SAME DAMN ISSUE! Now its WTF *&^!@*@&#@!!
So I remove the PCM plugs check all power and grounds and continuity of the opti signal and power wires to the PCM plugs, all grounds check out to <.5 ohms to the battery cable, power is fine at all points, there are NO DTCs in the PCM.
So anytime the opti is installed there are no signals from the opti during crank and no start, the thing spins with the engine so its not anything mechanical binding it up, take the POS out of the engine spin it by hand and its fine, anyone come across something similar? I gotta spare PCM at home that I will try tomorrow.......
Last edited by tjwong; Jun 13, 2007 at 08:43 PM.
Melting Slicks
Joined: Jul 2003
Posts: 2,140
Likes: 0
From: Cincinnati Ohio
One morning my 92 would not fire up.... I damn near killed the battery cranking... had fp... I had spark also though...Hmm I wonderd
I screwed the MSD timing screw all the way in and it fired right up.....
I dont know if youve tried that or not....worth a shot anyway...
... at least I still had spark..
I didnt/dont have a tech2 to check for signal.
Good luck
I screwed the MSD timing screw all the way in and it fired right up.....
I dont know if youve tried that or not....worth a shot anyway...
... at least I still had spark..
I didnt/dont have a tech2 to check for signal.
Good luck
Thread Starter
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Found the problem, I had a bad distributor low reference connection to the PCM. One of the grounds was faulty due to the painted surface of the frame and engine. One of the major issues in these street rod builds is that everything is finished and painted, which makes for a **** poor ground 
