The 1991 Suburban with 5.7L TBI is a workhorse GMT400 platform known for longevity, but suffers from predictable fuel system issues, transmission cooling failures, and upper engine wear from inadequate oil delivery to the top end.
TBI Fuel Pump Failure in Tank
Common · high severityTypical onset: 100,000-150,000 mi
Symptoms: intermittent stalling when hot, no-start after sitting, loss of power under load, surging at highway speed
Fix: Drop the 42-gallon tank (2.5 hours labor alone due to straps and filler neck corrosion), replace pump assembly and strainer. Smart move: do fuel filter at same time since tank is already down.
Estimated cost: $450-750
Upper Engine Wear - Piston Scuffing and Ring Failure
Occasional · high severityTypical onset: 150,000-200,000 mi
Symptoms: excessive oil consumption (quart per 500 miles), blue smoke on startup, loss of compression, rattling from cylinders on cold start
Fix: TBI 350s starve the top end if oil changes are stretched. Requires engine-out rebuild: pistons, rings, hone or bore, head gaskets, timing set. Budget 18-24 hours labor for full teardown and assembly. Many owners opt for reman short block swap (12-14 hours) instead.
Estimated cost: $3,200-5,500
4L80E Transmission Oil Cooler Line Failure
Common · high severityTypical onset: 80,000-140,000 mi
Symptoms: transmission fluid leaking at radiator connections, burnt ATF smell, slipping between gears, no movement after sitting (low fluid)
Fix: Steel lines rot where they attach to radiator; rubber hoses crack. If not caught early, starved trans overheats and clutches burn. Replace all cooler lines and external filter (3-4 hours). If trans damaged, rebuild runs 12-16 hours labor.
Estimated cost: $400-800 for lines only, $2,200-3,800 if trans rebuild needed
Rear Transmission Mount Collapse
Common · medium severityTypical onset: 90,000-130,000 mi
Symptoms: clunk when shifting into drive or reverse, vibration at 45-55 mph, visible sag of tailhousing, driveline angle change causing u-joint wear
Fix: Rubber mount deteriorates from heat and age. Requires trans support and crossmember removal (1.5 hours). Cheap part but awkward access under vehicle. Ignoring it accelerates driveshaft and u-joint failure.
Estimated cost: $180-320
Intake Manifold Gasket Leak (Lower Plenum)
Occasional · medium severityTypical onset: 120,000-180,000 mi
Symptoms: rough idle when cold, coolant seeping at intake valley, oil contamination in coolant (if gasket fails internally), poor fuel economy
Fix: TBI manifolds use paper gaskets that fail from heat cycling. Requires intake removal, new gaskets, RTV application. 4-5 hours labor. Check distributor seal and cap while in there.
Estimated cost: $550-900
Front Brake Rotor Warping and Caliper Seizing
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: pulsation in brake pedal, pulling to one side, brake drag causing wheel heat, grinding noise even with pad life remaining
Fix: Heavy vehicle plus single-piston calipers equals rotor distortion. Resurface rarely works long-term; replacement needed. Caliper slide pins seize from lack of greasing. Budget 2.5 hours for rotors, pads, caliper service both sides.
Estimated cost: $420-680
Fuel Tank Sender Unit Corrosion
Occasional · low severitySymptoms: fuel gauge reads empty when tank is full, erratic gauge movement, gauge pegged at full or empty
Fix: Ethanol fuel eats the rheostat windings and float arm. Since you're dropping the tank for fuel pump anyway, replace sender at same time (adds 0.5 hours). Sold separately from pump on this year.
Estimated cost: $220-380 if done with pump job, $450-650 standalone
Buy one with maintenance records showing religious oil changes and recent trans service; budget $1,500 immediately for deferred fuel system and cooler line work, but the chassis will outlast two engines.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.