1985
All Firebird models underwent redevelopment to boost sales as a number of power train improvements were introduced. The LB9 Tuned Port Injection (TPI) 305 was released, replacing the 305 H.O. as the high-output engine: using a tuned runner design, the LB9 produced 215 hp, which brought it suitable attention from buyers despite being unavailable with a manual transmission. The carbureted V6 was replaced with a new, multi-port fuel-injected 2.8L V6 making 135 hp. A Borg-Warner 9-bolt differential was made available for the first time, and the new positive traction rear end was said to be stronger than the Dana 44.
The interior evolved with the addition of new, Recaro-styled seats; a new dash with redesigned gauges that used an embossed graph patterned background; new door panels; a new T-handle shifter for automatics; a new, more ergonomic console; an updated stereo; a dash-mounted map pocket; and a new, more ergonomic steering wheel. Further attempts to put the Trans Am into higher regard included a new digital dash and a new overhead console. The console included two manually adjusted reminder wheels, a positionable map light, a removable "Firebird" flashlight, and a small pocket for a garage door opener or sunglasses. The T-tops were also redesigned to use a pin-mounting arrangement rather than the earlier latch-based setup.
The Trans Am drag coefficient was measured at 0.32 but was as low as 0.29 with the standard Aero wheels instead of the High-Tech turbo aluminum rims. At the time, it was the most aerodynamically-efficient car GM ever produced.
The Firebird received a restyled nose with wrap-around inserts known as "bumperettes" to replace the old grille/solid inserts; wrap-around "bumperettes" were also added to the rear bumper. The Trans Am "Turbo Bulge" hood was discontinued in favor of a new flat hood with twin louvered "nostrils" that were non-functional. Trans Am also received a restyled nose with integral fog lights and newly redesigned ground effects now standard, and its new "low density" taillight lenses have a grid-style pattern rather than the now-familiar "slit" or "louvered" pattern. A new, optional rubber/vinyl wrap-around rear spoiler was introduced on Trans Am (available only in black; as they aged, these and subsequent model-year spoilers would suffer from cracking and splitting problems). The Trans Am now received the 15th Anniversary WS6 suspension as standard, which had been upgraded with the new, larger sway bars, and aluminum 16-inch, 20-slot wheels were made available on all Trans Ams. The Recaro option package was no longer available, but Recaro seats still were.
1986
All Firebirds received center, high-mounted stop lamps to comply with Federal legislation; these were placed on top of the back hatch window. New tail light lenses were now introduced on the base Firebird, completing the replacement of the "slit" or "louvered" taillight lenses that had been a Firebird signature since 1967. The 2.5L 4-cylinder engine was dropped, replaced by the multi-port fuel-injected 2.8L V6 as the standard engine. The Firebird S/E model was discontinued. The previously optional rubber/vinyl wrap-around rear spoiler was the standard spoiler for 1986 Trans Ams and the pedastal spoiler became optional. Mid year, Pontiac introduced a new light-weight, cross-lace wheel rim, available for the Trans Am.
Only 26 Trans Ams with the 305 H.O L69 were built in 1986; it was discontinued because of fuel boiling problems. The 305 TPI engine output was decreased from 215 hp to 190 hp, however, the L98 TPI 350, rated at 225 hp, made its mid-year appearance in the Trans Am. Paint RPO's were changed to reflect the new base-coat/clear-coat paint process. American Sunroof (ASC), licensed by Chevrolet to build the 1987 Camaro convertible, also built 3 1986 Trans Am convertibles as a "design exercise."
1987
The Firebird body remained basically unchanged. All center, high-mounted stop lamps were relocated to a new position between the spoilers and the rear deck lid, and the large Firebird hood emblem disappeared forever. All V8's now received factory roller camshafts, and faced with consumer demands for more power, GM officially released the new 5.7L with tuned port fuel injection. Available only with an automatic transmission, it produced 225 hp and takes the top performance seat from the 5.0L TPI. L69 production is stopped, leaving the LG4 as the only remaining carbureted V8 used in the F-body. Trans Am GTA (Gran Turismo Americano) was introduced, available with the LB9 305 TPI engine (which was returned to 215 hp) or the L98 350 TPI. Gold 16-inch, flat-mesh, diamond-spoke wheels were standard on GTA, with 16-inch, 20-slot wheels standard on Trans Am. Firebird Formula was re-introduced, available with a choice of V8's (LG4, LB9 305 TPI, or L98 350 TPI), 16-inch convex wheels, and the earlier Trans Am "Turbo Bulge" hood. The wrap-around spoiler was updated and now standard on Trans Am and Formula; the regular, flat-wing spoiler from earlier Trans Am models was now made standard on Firebird. Trans Am and Formula were also offered with an optional 140 mph speedometer.
The Trans Am GTA was Pontiac's pride and joy with a standard 5.7L 350 Tuned Port Injection (TPI). The engine itself was pulled directly out of the C4 Corvette, which itself began using the engine in 1985, and gave the GTA performance numbers comparable to GM's flagship performance platform from whence it came. The GTA came with a standard TH-700R4 (4L60) automatic transmission, A/C, new seats with inflatable lumbar and side bolsters, special door panels, epoxy-filled emblems, body-colored ground effects, a special GTA horn button, and the legendary WS6 performance handling package. All of these options were packaged into the Trans Am under the RPO code Y84, and the model was produced until the end of Third Generation F-body production in 1992.
Finally, Pontiac offered a Firebird/Trans Am convertible, built after-market by ASC (of ASC McLaren fame) along-side the new Camaro convertible.
1988
The Firebird remained basically unchanged. The 170 hp LG4 carbureted 5.0L V8 was dropped in favor of the new 170 hp L03 5.0L V8 with throttle body injection. All V8's engines received serpentine belt systems and the A/C compressors were moved to the passenger's side of the engine, de-cluttering the engine compartment. The Firebird Formula received new high tech 16×8" aluminum wheels with distinctive silver "WS6" center caps. The GTA wheels were slightly restyled, and the convex 16-inch wheels were dropped as all Trans Ams received the 16×8" diamond-spoke aluminum rims, available in different colors (white, red, charcoal, and black) in addition to the GTA's gold. The GTA received new a steering wheel with integral radio controls. The Trans Am was made available with body-colored ground effects like those on the GTA. The optional convertible model also carried over, and now optional on the GTA was a new "notchback" hatch: rather than the large, glass hatchback that had been common to the Third Generation Firebird, the optional notchback consisted of a fiberglass trunk lid with a small, flat, vertical glass window. The notchback also incorporated redesigned rear seatbacks with integral headrests.
The notchback became popular with onlookers, who often assumed the notchback-equipped GTA was a Ferrari, thereby encouraging some notchback owners to dub their GTA notchback the "Ferrari Back." Many Trans Am owners were unaware that the $800 notchback option was even available, and for those who were, the vehicle typically had to be ordered from the factory, on a six-month waiting list, as the notchback was retrofitted to the vehicle. In rare instances, a dealership would get a notchback-equipped GTA on their lot. Another reason for the relative obscurity of the notchback is that the sales information was not very well disseminated to Pontiac salespeople, so many of them had no idea the notchback was available as an option.
As attractive as the notchback was, GTA owners were constantly plagued with structural and cosmetic issues with the notchback. The fiberglass would blister, causing surface bubbles resembling a bad case of acne. The Pontiac repair solutions were simply to sand the notchback down and repaint it, but the problem would always return, and GTA owners could expect multiple trips in order to achieve a final repair of the problem, or to have a new notchback installed. The notchback was intended to carry over and be standard-issue on the 1989 20th Anniversary GTA, but the plan never materialized; the aforementioned quality control issues apparently caused GM to discontinue the notchback forever.