1990 GMC JIMMY

Typical onset: 80,000-140,000 mi

Symptoms: White smoke from exhaust on cold start, Coolant loss with no visible leaks, Overheating under load, Milky oil on dipstick or oil cap, Rough idle when warmed up

Fix: Both head gaskets require replacement, heads should be pressure-tested and resurfaced. Budget 12-16 labor hours. While heads are off, smart to replace intake gaskets, thermostat, water pump, and all coolant hoses. The 4.3L's iron heads warp if overheated even once.

Estimated cost: $1,800-3,200

Typical onset: 60,000-120,000 mi

Symptoms: ATF puddles under front of vehicle, Pink or red fluid mixing with coolant in overflow tank, Transmission overheating, Slipping or delayed engagement after cooler line ruptures

Fix: Steel cooler lines rust through where they connect to radiator or run along frame. If fluid mixes into coolant, radiator replacement is mandatory (internal cooler rupture). External line replacement is 2-3 hours; radiator adds 4-5 hours plus full flush of cooling and trans systems.

Estimated cost: $400-1,400

Typical onset: 70,000-110,000 mi

Symptoms: Hard starting when engine is hot, Black smoke on acceleration, Fuel smell in oil, Rough idle and stumbling, Poor fuel economy suddenly worsens

Fix: Diaphragm in TBI fuel pressure regulator splits, dumping raw fuel into intake. Requires TBI rebuild or replacement. Also change oil immediately if fuel contamination suspected. 3-4 hours labor including cleaning and recalibration.

Estimated cost: $350-650

Typical onset: 90,000-150,000 mi

Symptoms: Cylinder misfires on specific cylinders, Loss of power on hills, Check engine light with lean or misfire codes, Uneven idle, Fuel trim values way off

Fix: The central port fuel injection system uses poppet valves that stick or clog. Upper intake plenum removal required. Replace entire spider assembly, not individual poppets. 6-8 hours labor. Common enough that updated poppet-less injector kits exist.

Estimated cost: $800-1,400

Symptoms: Sudden no-start with no spark, Intermittent stalling while driving, Engine dies and restarts randomly, No codes stored, but tach drops to zero

Fix: Plastic reluctor ring inside distributor cracks from heat cycling, causing total ignition failure. Requires distributor replacement or rebuild. 2-3 hours labor. Aftermarket units often fail quickly; OEM AC Delco preferred.

Estimated cost: $300-550

Typical onset: 80,000-130,000 mi

Symptoms: 4WD won't engage or disengage, Service 4WD light illuminated, Grinding or popping when trying to shift into 4WD, Stuck in 4WD or 2WD

Fix: Encoder motor on transfer case fails or shift fork wears. Encoder replacement is 2-3 hours; if fork is damaged, transfer case must come out (8-10 hours). Fluid contamination or low fluid accelerates wear. Often the motor connector corrodes first—check that before parts replacement.

Estimated cost: $400-1,800

Typical onset: 100,000+ mi

Symptoms: Oil drips from bell housing area, Oil coating on transmission, Steady oil consumption without visible leaks up top, Oil spots on driveway centered under engine

Fix: Two-piece rear main seal design leaks as rubber hardens. Transmission must be removed (6-8 hours labor). Oil pan gasket also seeps on high-mileage units; add 2-3 hours if doing both. Consider doing clutch or torque converter seal while trans is out.

Estimated cost: $800-1,600

Typical onset: 80,000-140,000 mi

Symptoms: No-start with cranking but no fuel pressure, Sudden stalling and won't restart, Engine sputters and dies under acceleration, Whining noise from fuel tank before failure

Fix: Tank must be dropped to access pump. 3-4 hours labor. Replace fuel filter and strainer sock at same time. Running tank below 1/4 regularly kills these pumps early.

Estimated cost: $500-850