1991 CADILLAC ELDORADO

Typical onset: 80,000-140,000 mi

Symptoms: Slipping between gears, especially 2nd to 3rd, Delayed engagement when shifting to Drive or Reverse, Transmission fluid in coolant or coolant in trans fluid (cooler failure), Shuddering or harsh shifts

Fix: The TH440-T4 is notorious for torque converter lockup issues and internal oil cooler failures that cross-contaminate fluids. Often requires rebuild or replacement. Expect 12-16 hours labor for R&R plus rebuild. External cooler upgrade recommended during repair.

Estimated cost: $2,200-3,800

Typical onset: 120,000-180,000 mi

Symptoms: Low-frequency knocking on cold start that may fade when warm, Metallic ticking that worsens under load, Low oil pressure at idle (below 10 psi hot), Metal flakes in oil or on magnetic drain plug

Fix: The 4.5L uses aluminum main bearing caps that can wear into the block if oil changes are neglected. Requires teardown to inspect crank journals and main saddles. Short block replacement often more economical than machining the block. Figure 18-24 hours for short block swap including all gaskets and seals.

Estimated cost: $3,500-5,500

Typical onset: 100,000-150,000 mi

Symptoms: White smoke from exhaust on startup, Coolant loss with no visible leaks, Oil in coolant or milky oil on dipstick, Overheating or erratic temperature gauge readings

Fix: The 4.5L head gaskets fail between coolant and oil passages more often than into cylinders. Common to do both sides when one goes. Resurface heads if warped. 10-14 hours labor plus machine work. Always replace intake manifold gaskets at same time.

Estimated cost: $1,800-2,800

Typical onset: 70,000-120,000 mi

Symptoms: Stalling at idle or when coming to a stop, Surging idle (500-1200 rpm oscillation), Hesitation on acceleration from stop, Check Engine Light with codes 21 (TPS) or 35 (IAC)

Fix: The TPS wears out its resistive track and the IAC valve carbon-fouls. TPS replacement is 0.5 hours, IAC is 0.8 hours. Both are common enough you should just replace both if one fails. Clean throttle body at same time.

Estimated cost: $250-450

Typical onset: 60,000-100,000 mi

Symptoms: Intermittent misfires, often when engine is hot, No-start with spark missing on multiple cylinders, Rough running that moves between cylinder banks, Codes for multiple misfires or ignition control

Fix: The C3I (Computer Controlled Coil Ignition) uses three coil packs on the ignition module. Module cracks with heat cycling are common. Diagnosis requires checking for spark on each tower. Module replacement is 1.5 hours, individual coil packs about 0.8 hours each. Replace plug wires if over 60k miles.

Estimated cost: $300-700

Symptoms: Window moves slowly or only in one direction, Clicking or grinding noise from door when operating window, Window drops into door or won't stay up, Motor runs but window doesn't move

Fix: The cable-style regulators stretch and the plastic pulleys crack. Driver's side fails first from most use. Requires door panel removal and drilling out rivets. 2-3 hours per door. Aftermarket regulators are hit-or-miss quality.

Estimated cost: $350-550

Typical onset: 80,000-120,000 mi

Symptoms: Clunking from front end over bumps, Creaking noise when turning steering wheel at low speed, Steering feels notchy or catches at center, Uneven tire wear on inside edge

Fix: The strut mount bearings seize and the rubber isolators separate. Requires strut removal to replace. Do both sides and consider new struts if original. 3-4 hours labor for both sides including alignment.

Estimated cost: $600-950