I did the 7747-7427 swap in my '91 1/2 ton while the old worn out 305 was still in it and got it dialed in pretty good. Unfortunately tuning a motor with almost 300,000 miles on it pretty much finished it off. OK, it was a 305 so maybe not so unfortunate!
I pulled the 355 out of my crusty '78 ElCamino and dropped it in with new Vortec port aluminum heads and reused my Edelbrock dual plane air gap manifold. It's also running a 10120702 Lunati Voodoo FT cam with 1.6 roller tips. CR is 10.2:1 I'm running a 454 TB with the factory spreadbore adapter and 80 lb/hr injectors running at 14-20 psi with a VRFPR and long tube headers. That motor only has about 15,000 on it as of now.
The main issue I've had with it is idle and low part throttle surge in closed loop because the AFR swings to lean then back to stoich. I'm pretty sure it's a PID issue causing the NBO2 to swing too far from lean to rich. I've been studying threads on the subject and am still in the weeds as to what parameters in $0D are used to control NB oscillation. The thing runs fine in open loop but I would like to incorporate lean cruise, DE and DFCO because 91 octane at damn near $4 a gallon and 12 MPG is killing my wallet. This truck is my DD, not just a weekend toy. In the ElCamino this engine with 9:1 CR, a mechanical/vacuum dist., long tubes and a Q-jet I was getting 17-19 MPG.
Another issue that just showed it ugly head is getting stuck in PE with PE turned off and I'm thinking that's a sync/async issue. I will be running along at pretty close to stoich and mash the pedal to the floor and when I back off my AFR's will be down in the 11's and 12's Get back to the house and play the log back and sure enough it went into PE when a stomped it and stayed there after I let off. I have the PE set to come on at max temp and max speed which should keep it from coming on at all. DFCO is off, DE is off and carbon canister hose is disconnected. AE is on but at factory settings. I can tell by the logs it could use a little more AE but it's not stumbling or popping back through the intake. I'll deal with that once I figure out this closed loop issue.
TIA!!!

 

I don't know anything about the tuning part of this.

The coolant heated Q-jet to TBI adapter has horrible AF mixture distribution and the earlier 454 TBI unit doesn't have that great of an IAC system. The IAC system was greatly improved on the later 454 TBI unit.

 

You don't know anything about tuning but you know that the adapter and TB are junk? Have you ever run one or are you just repeating what you've heard elsewhere?

I worked the inside of the TB adapter and according to my spark plugs my fuel distribution is fine. The adapter as it comes from GM has big fins inside to direct air/fuel more towards the front cylinders and shrouds air from the center cly's. I smoothed those down but didn't completely grind them away. I ground them in a manner to create low pressure regions on the undersides to help curl the air towards the center four. If I had a WB in every primary tube I may see differences in distribution but the plugs are happy and so am I. I also have no issues with IAC works just like it's supposed to.

 

I'm not a guru but I've been dealing with surging idle too. I have a 7427 pcm controlling a 350 Vortec 9.3:1 with an LT1 cam, and older style 454 TBI throttle body with 61# injectors at 20psi on a TransDapt plate on an Edelbrock dualplane spreadbore intake.. With idle target of 650 rpm (manual) it would start off steady, then start to fluctuate. The oscillation would get worse eventually drop to 400rpm, nearly stall, then recover and jump up to 900 and repeat. If I stabbed the gas it would stabilize for a few seconds. No manual 7427 bins exist for a 5.7 so I started with the bin file from a 95 Tahoe, but switched to bin BJYL from a 1995 1500. I added a heated O2 sensor and bumped the rich/lean tables up about 50mv. Lowering "Proportional Gain if Rich (Stable) and increasing "Proportional Duration Dead Band" seemed to help. I also dropped my closed throttle idle timing to 20 degrees so the idle spark control would have more authority. Idle will still occasionally fluctuate +/- 100 rpm after coming to a stop, but stabilizes after a few swings. I doubled my MAP AE values and +50% on TPS AE. I can stomp on it without bogging as long as I'm above 1500 rpm. I also copied over the Spark Latency Correction table for my small cap distributor. I too noticed that PE kind of ignores the temp parameters. My workaround was to max the "TPS for (Fast) PE vs. RPM" values in both tables to temporarily disable PE.

I think the 454 TBI unit just wants more airflow. Bumping the idle target to 900rpm solved idle surge, but I know I'm wasting gas at that speed.

 

Thanks for the reply.
I found the my motor idled best at 28deg and made the best vacuum at 800 RPM's. My surging wasn't as bad as yours, it oscillated about 150 RPM at idle and just off idle. The problem was only in CL because the NBO2 was leaning out the mixture. I messed with PID's, O2 thresholds etc. It got better but still had the annoying surge at idle and low speed cruise. For awhile it set it up to run in OL for idle and up to 6% TPS and drove it that way but it bugged me that I couldn't get it right so I pulled the TBI and bolted one of my Q-jets on it, made a bypass regulator to run the intank pump and installed the TPS on the carb for TCC control. I discovered that 647 CFM 454TB was holding my motor back. I'm running the 7427 for spark and TCC control and using my WBO2 and TunerPro to datalog the carb and got the fuel mixture almost perfect. I'm running 13.9-14.3 AFR at idle, 14.9-15.5 at cruise and 12.9-13.9 with the primaries at WFO. I'm waiting for a couple sets of main jets so I can pull the fuel down to 16-16.5 at cruise and primary WFO to about 14.0 I haven't messed with the secondaries too much yet other than to get the air flap opening rate right. Secondary AFR is around 14.9-13.9 which is too lean but there is no need to mess with it now till I get the primary side right. I've got needles and hangers out the wazoo so it won't take long to get that dialed in. Even with it not perfectly tuned it runs circles around the TBI.