TBI. The 2.8V6 came with two different ECMs depending on the year. 1985.5-1987 got the 1227429 ECM, which as far as I've found is unique to the 2.8V6 TBI. It has not been fully hacked, though partial hacks exist. True DIY tuners that don't want to finish the hack should probably ditch this ECM in favor of the 1228062 ECM. 1988-1993 2.8 V6 TBI trucks used the 1228062 ECM. This ECM was also used in some 4.3V6 TBI S-series. It has been more-or-less hacked. Buy a copy of TunerCat, and EPROM burner and eraser, and some 2732s, and you're ready to start tuning. I don't have any association to TunerCat except that it's one of the few readily available DIY tuning packages.
I have a pinout for the 1228062 ECM and the 1227429 ECM but I haven't bothered to go pin-by-pin to see what changes are needed. My gut says that converting to the newer ECM won't take much work. If you're going to do DIY tuning, I'd make the swap.
If you're swapping to a V8 from a 2.8 TBI truck, the existing harness can be used. Not much changed between the 1227429 ECM and the 1227747 ECM (used on V8 TBI apps in the late 80s). I'm using a 1227747 ECM harness on my 2.8V6 TBI truck right now. New ECM, some *minor* wiring changes, and you're good to go.
TBI is a good system. It's not as cool looking as port injection but it does work. Off-roaders like it better than a carubretor because there's no issues with steep angles like there is with a carburetor.
The TBI ECM controls three major functions: fuel control, spark control, and the automatic transmission's lock-up torque converter. Fuel control is speed-density, where the ECM calculates the amount of air entering the engine, reads the engine's VE from a table, and calculates the amount of fuel needed. Lots of knobs to turn here, including idle and part-throttle fueling as well as WOT. Also tables for acceleration enrichment (pump shot), engine temperature compensation (choke simulation), fuel adjustments for starting the engine, and so on. The ECM also has a lot of controls to adjust idle speed, based on engine temperature and vehicle speed.
One person found that the in the 1227429 chip he was hacking (ASA if memory serves), the VE table for >4000 RPM was all 0, meaning that GM didn't bother to tune the upper RPM tables. The ECM uses the VE entries from the last row in the lower RPM table for the rest of the range. Those wanting to push their 2.8 into the high RPM range should probably consider some custom chip tuning. I don't know if the 1228062 chip is the same or not.
The ECM has several load cells in it, which are the BLM numbers that you see on a scan tool. This data is used as a correction factor to adjust the fuel calculation. The oxygen sensor provides crude feedback to the ECM, which it uses to adjust the integrator (short-term fuel trim). Over time, the integrator's adjustment is fed into the BLM cell for that RPM/MAP range. This is the mechanism that the ECM uses to "learn". For those that are into controls theory, the ECM uses a PI controller for fueling, and the BLM is an adjustment to the integral term. It does NOT learn about WOT conditions, and the corrections it can make aren't all that large. It was designed to adjust to an engine as it wears over time. The ECM can compensate for the owner that doesn't do regular tune-ups, but it can't completely compensate for that lumpy cam and high-dollar head porting job. Big changes mean some chip tuning. This is normal -- nobody expects that their stock carburetor will work on a modified engine without jetting, new metering rods, etc. and the same is true of your EFI system. The EFI system is just more forgiving.
The other really big system the ECM controls is engine spark. A traditional distributor adjusts spark based on RPM (mechanical advance) and MAP (vacuum advance). The distributor is constrained to using a linear curve for both. The TBI ECM has much more flexibility. It adjusts based on RPM and MAP, as well as engine temperature, with correction factors for starting, and WOT. The adjustments don't have to be linear, either. This really helps when running a hotter cam and an automatic transmission. Tuning spark timing can really make an automatic transmission more streetable with a hot cam. Hotter cams tend to be really touchy about spark and fuel control at low RPMs, and the ECM's good spark and fuel control help tune for that.
The knock sensor is a special beast. The ECM listens for knock using a knock sensor, which is just a piezoelectric element that is fed to the ECM through a knock filter. The ECM pulls out timing based on a table that determines how much spark to remove for a knock event. The ECM gradually adds timing back into the system until it gets back to its normal value for that RPM/MAP value.
The knock sensor and the knock sensor filter module are specific to the engine, or more specifically the engine's bore size. 3.4 owners probably don't have cause for concern, but going to a V8 or 4.3V6 means a new, matching knock sensor and module.
Note that the ECM does NOT learn about spark control. The tables are what they are, and the ECM does no long-term learning or correction. The knock sensor just does immediate corrections that are decayed out over time. The knock sensor is crude, too, in that it can hear false knock (valvetrain noise, rattling clutch damping springs, etc.), and it can miss some really subtle knock. It probably can't reliably hear knock from too much timing under boost, or under a nitrous shot, since those ?sound? different.
A tuning note: ALWAYS run the minimum amount of timing consistent with maximum performance. More timing than you need doesn't improve performance. It does strain the starter, forces you to run higher quality fuel than you need, and makes the engine "peaky". It also does a good job of pounding those nice, round rod ends and bearings into ovals. Not good. Running super-high static timing or adding tons of spark into the spark tables is not a good idea.
The ECM also controls the automatic transmission's torque converter clutch (TCC). The ECM receives data on RPM, vehicle speed, and TPS, as well as information on whether the transmission is in overdrive. The ECM uses tables to determine if the TCC should be locked or unlocked. Some calibrations tend to make the TCC ?hunt?, and this can be tuned out. You can make the TCC less aggressive about unlocking for smoothness, or it can unlock quickly for more power with less throttle opening.
