So, was going to drive the '77 GTB to work today but it was running very rough and backfiring. Setup is stock carbs, Pertronix Ignitor II setup with modules in front distributor and Flamethrower II coils. NGK Iridium plugs. Taylor Hemi resistor plug wires (no plug extenders needed). So far, I have checked the ohms on both coils and they look good. Both are getting full voltage with ignition on (ballast resistors not used with this setup). Pulled plugs and #5 looked a little cleaner than the rest (gasoline washed maybe?). Checked compression and good across all cylinders. I called Pertronix and they said they only way to check the Ignitor II modules would be to remove them and send them back to Pertronix. Rather not do that. I am taking a break for now, but next step will be to pull the distributor caps and check caps and wires. Any other thoughts or ideas?
I'll do that after I check the caps and rotors. However, witness marks on the distributor have not moved.
Plugs are showing rich with a slight whiff of gas so I will say yes, LOL. Car was running rich and back firing so only possible carb issue may have been a stuck float, but only one plug looked like it had an issue and I would expect two adjacent plugs to be gas washed if it was a float issue. Right now, I am leaning towards #5 not getting spark for some reason (or a reduced spark). Like a friend once told me (and I have verified), "99% of "carb" problems are really ignition issues."
Hi Steve, This may be too basic and you may have already tried, but here goes in case it helps somebody else: One of the more difficult problems for me in identifying a misfire is to figure out which cylinder(s) are not firing. On a 308, with the engine shut down, I pull the plug wires/extenders off at the plug end, and lightly set them back in place, without pushing them all the way on to the plug terminal. The spark will still jump to the end of the plug. Then I crank up the engine. Now I use a pair of pliers with rubber coated handles to gently pull each plug wire away from each plug in turn so the spark can no longer reach the plug. The rpm will drop on the good cylinders. There will be no rpm drop on the "dead" cylinder. Another technique that can be used on something like an old motorcycle is to start up the motor when it is fairly cool. Run it for a minute or so. Then carefully touch the exhaust headpipe for each cylinder. A good cylinder will be hot, a dead one will be cold. I apologize if this is too basic, but it has helped me over the years to focus on the cylinder that is causing problems. Good luck, Jeff
Take a look at your Spark Plug Connectors. The Red ones that go on to the plugs at the Cover. My car, (28,000 miles), 2 of the push on Connectors were shorting through to the cylinder head down in the spark plug hole. Replacing these fixed my intermittent missing problem. Worth taking a look at them, you will see a small dis-coloring if they are faulty.
Update: Pulled distributor caps and the rear cap was full of brass shavings. Also, when I pulled that cap, the center carbon contact and spring fell out. Spring was stretched out and will not fit back in its hole. Carbon contact fell down into the engine compartment. Heard it, can't find it. So, looks like new caps are on the menu. Also, no extenders to worry about since I am using the Hemi plug wires.
