1990 GMC SONOMA

Typical onset: 80,000-140,000 mi

Symptoms: Slipping between 2nd and 3rd gear, especially under load, Delayed engagement into drive or reverse, Burnt transmission fluid smell, Metal shavings in pan during service

Fix: Rebuild or replacement required. Factory 700R4 units behind the 2.8L are particularly weak. Expect 12-16 hours for R&R and rebuild, includes new torque converter, bands, clutches, seals. Many shops recommend cooler upgrade simultaneously.

Estimated cost: $1,800-3,200

Typical onset: 120,000-180,000 mi

Symptoms: Deep knocking sound from bottom of engine, worse when cold, Sudden loss of oil pressure, Metal flakes in oil during changes, Catastrophic failure leaving you stranded

Fix: The 2.8L suffers from inadequate oiling to rod and main bearings, especially cylinders 4-6. Repair requires full teardown: connecting rod bearings, mains, often crank machining. Most opt for used 4.3L swap or remanufactured short block instead. Engine R&R plus rebuild: 18-24 hours.

Estimated cost: $2,500-4,500

Typical onset: 60,000-100,000 mi

Symptoms: Coolant seepage at intake manifold base, visible orange residue, Overheating or running hot in traffic, White smoke from exhaust on cold starts, Coolant loss with no visible external leaks

Fix: The composite intake gaskets on both 2.8L and early 4.3L deteriorate, allowing coolant into crankcase or external leaks. Must remove upper plenum, fuel rails, vacuum lines. Replace with updated Fel-Pro gaskets. 4-6 hours labor.

Estimated cost: $400-750

Typical onset: 90,000-150,000 mi

Symptoms: No-start condition with cranking but no fuel pressure, Intermittent stalling at operating temperature, Whining noise from fuel tank area, Engine stumbling under acceleration

Fix: In-tank electric pump. Requires dropping fuel tank, which on 4WD models means dealing with skid plates and exhaust routing. Replace pump, strainer, and rubber fuel lines at tank simultaneously. 3-4 hours labor.

Estimated cost: $350-650

Typical onset: 80,000-120,000 mi

Symptoms: Power steering fluid dripping from steering box, Excessive play at center (more than 1 inch at wheel rim), Wandering on highway requiring constant correction, Groaning noise when turning at low speeds

Fix: Saginaw recirculating ball units wear internally and seals fail. Rebuilding rarely holds long-term; replacement with remanufactured box recommended. Requires alignment after. 2-3 hours labor.

Estimated cost: $400-800

Typical onset: 100,000+ mi

Symptoms: Black smoke from exhaust, running extremely rich, Raw fuel smell from tailpipe, Poor fuel economy (dropping 30-40%), Rough idle and hesitation

Fix: Diaphragm inside regulator ruptures, dumping excess fuel into intake. Easy diagnosis: pull vacuum line from regulator and check for fuel. Regulator replacement is straightforward, 1 hour labor, but often injectors need cleaning at same time.

Estimated cost: $150-350

Typical onset: 70,000-110,000 mi

Symptoms: Brake fluid on inside of rear wheels/drums, Soft or spongy brake pedal, Reduced braking effectiveness, vehicle pulls to one side, Parking brake ineffective

Fix: Wheel cylinders corrode and leak internally. Once one side fails, the other follows within 6 months. Replace both sides, turn drums, replace hardware. Good opportunity for complete rear brake overhaul. 2-3 hours labor.

Estimated cost: $250-500