Guys,
I'm about to my wits end trying to figure out this issue and now I'm looking for a fresh set of ideas.
Here's a list of things that have been done to the car, which never displayed this behavior before the changes:
1) Installation of FAST EZ-EFI system to replace Edelbrock 1406 carb. This includes fuel tank and fuel pump out of a later model Fox and vacuum actuated fuel pressure regulator set at 43 psi per manufacturers spec.
2) New pickup coil to replace factory unit that had the insulation coming off the wiring. Tested new pickup coil before install and it OHM'd within factory specs. Cleaned and lubed distributor shaft upon install as the old coil was seized onto the shaft effectively making it not advance.
3) Replaced all vacuum lines and block off caps. Replaced these one at a time to ensure that I did not get them crossed up.
4) Checked distributor for play and slop. It appeared fairly tight.
5) Closed the mechanical advance window on arm, as it was noted that the current arm had way to much advance if it actually advanced that far. Reused springs that were in the distributor.
6) Checked vacuum advance operation to the best of my available tools. It actuated upon application of vacuum and held until release of vacuum.
7) Rewired certain portions of the engine bay due to insulation wiring falling off. Eliminated wiring that was no longer used.
8 ) Fixed all exhaust leaks on car. Needed to happen with the application of the O2 sensor I now need.
I have worked a lot with the A/F ratios and accel shot values with the EFI system and I have made the driveability much better, but I still get the bucking during light roll on throttle at cruise. Engine load doesn't seem to make much difference as it does it going up hills, down hills and on flat land. During the bucking, if I hop of the throttle and roll back in, sometimes it goes away and sometimes it comes back. If I stab the throttle hard, it might cough once and then takes off like a rocket.
I pulled the plugs yesterday to replace them with new Motorcraft plugs and the plugs looked ok for the most part. They weren't white like they were burning too lean, but they weren't really tan like I'm used to. They also weren't oily or wet.
I set the timing awhile back and I don't have my notes with me, but I believe it is around 12 degrees initial.
I have not changed the plug wires, which were new as of last year, Ford Racing wires. I also have not changed cap and rotor which look decent not have I changed the replaced in the past aftermarket ignition module.
One thing to note is this car has in the past went through a smog delete so there is no air pump, canister purge or egr system. It ran ok with the carb though.
I know this is a fairly vague description, but I'm hoping to get a fresh direction on which way to go, I have looked at this issue so much that I'm beginning to think I have overlooked something obvious.
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