1998 Ford Explorer Problems: 8 Known Issues

On the 1997-1999 Ford Explorer 4.0L SOHC V6, the 4.0L SOHC V6 (introduced in the Explorer for 1997) uses a complex three-chain system: a crank-to-jackshaft chain and a jackshaft-to-left-camshaft chain at the front, plus a jackshaft-to-right-camshaft chain at the rear of the engine, all riding on plastic guide 'cassettes' with hydraulic/spring tensioners. The plastic cassettes and the spring-loaded tensioners are a chronic weak point. Tensioners lose spring tension (often by ~75k-100k miles) and the plastic guides embrittle and shatter, dumping debris into the oil pan. This is one of the most-reported failures on the SOHC engine and is the single biggest reason to prefer the older OHV engine of the same displacement. The rear cassette job is extremely labor-intensive because it sits against the bell housing, requiring engine or transmission removal.

On the 1993-1999 Ford Explorer, the 4.0L (both OHV and SOHC) drives the camshaft position sensor off a gear-driven 'synchronizer' assembly in place of a conventional distributor. The synchronizer's shaft/bushing wears or gums up with varnish, developing play and producing a distinctive squeak/chirp that is often mistaken for a belt or bearing noise, and eventually causing erratic CMP signals - rough idle, misfires, hesitation, and intermittent stalling or no-start. The chirp is typically worst when warm and persists with the serpentine belt removed, which is the standard field test to isolate it.

On the 1997-2000 Ford Explorer 4.0L OHV V6, the 4.0L OHV V6 uses a camshaft synchronizer (a gear-driven cylindrical housing that also drives the oil pump intermediate shaft) with the camshaft position sensor mounted on top. The plastic vane/'flag' on the synchronizer and the sensor's internal magnet wear or come apart, mangling each other. This sets a P0340 (and often P0344) cam sensor code, produces a hard misfire, rough running, and stalling. Owners report the sensor magnet falling out and destroying the vane. Because the synchronizer shaft also drives the oil pump, a badly worn/seized unit is more than an electrical nuisance.

On the 1997-2001 Ford Explorer, the 5R55E five-speed automatic (behind the 4.0L before the 5R55W/S arrived for 2002) commonly loses reverse and/or slips in Drive/1st as the low/reverse sprag, reverse clutch pack, and forward clutch wear. A broken tab on the pressure-regulating (EPC) solenoid in the valve body drops line pressure, so reverse — which needs the most pressure — engages late or not at all, and the engine flares on deceleration. High-mileage owners search this heavily as the truck 'won't back up.'

On the 1991-2001 Ford Explorer, the 1991-2001 Explorer was factory-fitted with P235/75R15 Firestone Radial ATX, ATX II and Wilderness AT tires that suffered tread-belt separation, especially in hot climates and when underinflated to Ford's low placard pressure. A rear tread separation at highway speed frequently sent the tall, relatively narrow-track Explorer into a rollover. NHTSA linked the failures to hundreds of deaths and over 700 injuries, triggering the August 2000 recall of 6.5 million tires and the 2000 TREAD Act. Owners of surviving high-mileage examples still search this because any period-original or old-stock Firestone AT tire is suspect.

On the 1991-1999 Ford Explorer, in salt-belt climates, 1991-1999 Explorers rot in predictable structural areas: the inner rocker panels, the tops of the front hangers of the rear leaf springs (dirt packs between the hanger and inner rocker, which the factory welded only at the bottom), rear spring hangers/shackles, and the body-to-frame mount areas. Owners have documented rear subframes 'literally falling apart,' with detached sway-bar mounts and shock mounts losing support. Rocker/cosmetic rust is common; the safety-critical concern is corrosion at spring hangers and body mounts, which compromises suspension attachment and crash structure.

On the 1997-2004 Ford Explorer, on 4.0L Explorers (both the OHV Cologne and the later SOHC V6) P1506 is a common high-idle complaint on higher-mileage trucks. The idle air control valve sits on the throttle body and meters bypass air around the closed throttle plate. Crankcase vapour routed through the PCV system, plus normal intake carbon, gradually coats the IAC pintle and its seat. The pintle stops seating fully, so even when the PCM commands the valve to its minimum duty cycle, more air keeps bleeding past than the strategy allows. The PCM compares commanded position against actual RPM, sees idle running above the target, and stores P1506. The second pattern on this platform, and the one that catches people who have already thrown an IAC at the truck, is an EVAP canister purge valve stuck partly open. The purge valve is plumbed into intake vacuum downstream of the throttle plate, so a leaking purge solenoid is functionally an uncommanded vacuum leak the IAC cannot compensate for. Ford's diagnostic material for P1506 lists the EVAP purge system among the causes, and Explorer owners repeatedly report replacing the IAC, clearing the code, and having it return until the purge valve is addressed. Owners describe a cold-start flare that will not come down until the transmission is put in gear, a hanging idle on deceleration, an idle that stays elevated when warm, and a slight lurch when shifting into drive. Fuel economy drops and the truck can creep against the brakes at a stop.

On the 1995-2010 Ford Explorer, the cable-drive window regulators on the Explorer/Mountaineer/Sport Trac fail as their plastic cable guides crack and the steel lift cable frays or jumps off the drum. The window then binds, drops crooked, or falls down inside the door — the motor often still runs. The front door regulators are the most common, and the original glass/regulator is riveted, complicating the repair. A very high-frequency 'window fell down' search across the whole 1994-2010 range.