Okay guys, first off pardon my long-winded nature but I'm very detail-oriented. I'll start off with a little background on myself as I am new to this forum. I'm a master technician at a local Chevy dealer and have about 11 years with GM now with experience at all 6 of the original major brands. My mainline experience would be with Chevy and Cadillac focused on light-body and major engine repair. I have been tuning for about 5 years now, but primarily on near-stock vehicles and "converting" them to run on E85. I found out on my current project just how little I know about ecm tuning (I am quite adept with a carb and HEI for a person my age). The swap was rushed and I was not properly prepared, but my L03 was quickly fading and I had 3 easily repairable L31's sitting in crates.

The vehicle and hardware;
It's a 1989 Firebird Formula originally equipped with an L03 and manual trans. The car has 217k miles on it and it is my daily driver that sees 100 miles a day for my commute to and from work. Sometime before I bought it, the manual trans had been ditched for a 700r4 and performed the swap fairly decently except for the tcc wiring and changing to the proper PROM. I chipped the ecu and wired in the trans harness shortly after buying the car. In anticipation of a future port injection upgrade and also as an uprgade for E85 I installed a walbro 255lph high volume AND high pressure fuel pump not knowing that the passages in the TBI unit itself couldn't handle that kind of fuel flow. After discovering my mistake and that the fuel pressure was sitting at over 20psi with no mods to the stock FPR, I replaced it with a billet adjustable unit plumbed to manifold vacuum making it a VAFPR. I set the pressure to 30 psi base with about 22psi at idle. And that brings us to the present setup. I replaced the tired L03 with a used 117k mile L31 bottom end paired with some 96k mile heads. The bottom end was fine and one of the original heads had a crack. The heads came off of a bottom end that had wiped out the bearings due to an intake gasket failure. I used an Edelbrock Performer RPM 4bbl intake with a Holley TBI to carb adapter plate. I reused all of the EFI hardware from the car along with the flexplate and exhaust manifolds and just replaced the distributor gear and used new coolant temp and knock sensors. I installed a GM parformance parts heavy duty single roller timing chain, melling m55hv oil pump and 7 quart oil pan with matching bolt-on pickup tube, and an O.E. style timing cover without the crank sensor hole drilled. I reused the stock L31 balancer and crank sensor reluctor behind it for proper fit. Due to clearance issues with the oil pan I fabricated the front section of the exhaust out of 2 1/4" pipe and bends from the parts store and ditched the y-pipe. The passenger side follows the route of the y-pipe and necks up into the 3" intermediate pipe at the stock location. The drivers side runs straight back until just past the tranny crossmember and makes a shallow bend over to the intermediate pipe attaching right where it bends to follow the driveshaft tunnel. From there it is 3" back to a flowmaster muffler and dual 2 1/2 outlets. The cap and rotor are tan Accel units, the plug wires are Accel super stock spiral-core, the coil is a MSD streetfire, and the plugs are Delco O.E. iridium replacements. The EGR and AIR injection hardware are all gone and disabled in the ECM along with the pins backed out of the connectors at the ECM. The base timing is set at 0 degrees and the thermostat is a high-flow 160 degree unit.

The problem;
The car fired right up and idled fine with a blind tune and ran fine driving in and out of the shop until I fabbed up the exhaust. The initial driveability seemed decent, but when cruising at very light throttle and no load the engine had a random intermittent misfire. The stumble felt like it was either cutting fuel or ignition so the first thing I did was disable the DFCOIt also seemed soggy at WOT in the higher RPM range. After 54+ tunes moving the fuel and timing all over, the engine is running ok and has decent power but it is gradually getting rougher and the roughness is moving into other areas of operation. I pulled the plugs yesterday and they showed signs of either detonation or overly lean mixtures as the insulators showed signs of blistering. I pulled more timing and added more fuel, but to no avail.

Update;
I finally figured out that that a 305 and 350 require matched and specific knock sensors and ESC modules. I will upload a bin image and datalog as soon as I get a chance. Thanks in advance,

Phil