GM Iron Duke Engine - Tech IV

Tech IV

Iron Dukes were fitted with fuel injection (TBI, via a single injector in the throttle body) in 1982. This version was christened the Tech IV, though Car and Driver later ridiculed it as the low-Tech IV. Power output remained at 90 hp (67 kW).

This was replaced by a swirl-port head with 9.0:1 (instead of 8.2:1) compression ratio in 1984 for a 2 hp (1.5 kW) gain. Other additions for 1985 included roller lifters, improved bearings, and a new crankshaft.

Several significant changes were made in 1987. These included an improved cylinder head, intake manifold and throttle body injection module, a more-modern serpentine belt with an automatic spring-loaded tensioner for the accessories, and a distributorless ignition system (DIS). This revision to the engine increased power to 98 hp (73 kW). In 1988, a balance shaft was added to smooth engine vibrations. Further improvements in later years included new pistons, rods, crankshaft, and an in-pan oiling system. The most powerful variant of the Tech IV raised the rev limit to 5500rpm, and achieved 110 hp (82 kW).

The Tech IV uses the same bellhousing pattern as the 2.8 L 60-Degree V6.

Over the years, the Tech IV engine has proved to be a reliable, if noisy, workhorse for owners when not pushed to its limits. All 1978-1990 Iron Duke L-4's are outfitted with a micarta camshaft gear that meshes directly with a steel gear on the crankshaft (no timing chain). 1991-92 VIN R and U engines received a timing chain. The timing gear has a tendency to crumble a tooth anytime after 80,000 miles. The cam gear simply shears a tooth at startup and the engine won't start; because of the non-interference design of the engine, no further damage occurs. When the cam gear loses a tooth, the camshaft AND distributor stop rotating during engine cranking. Replacing the gear requires heating the new gear in hot oil and quickly installing it for a press fit on the cam stub.

A few Tech IV owners experience minor driveability issues with the engine. There are several cheap/easy repairs that the shadetree mechanic can perform to keep this engine running at its best.

Inspection (and replacement, if necessary) of the MAP sensor, and its accompanying vacuum hose, is often a solution to many driveability problems. This sensor largely controls the engine's driveability. Stuck EGR valves are also very common on the Tech IV.