Short, ordered theory + procedure (no extra questions). I’ll first cover the theory of what a camshaft does and common failure modes, then a concise ordered procedure for the two common Jeep Grand Cherokee engine families in WH/WK years (SOHC engines — 3.7/4.7 — and the pushrod HEMI 5.7). At each step I’ll state WHY you do it and HOW the repair fixes the fault.

Theory — what the camshaft does and how failures produce symptoms
- Function: the camshaft converts rotational motion into timed valve lift. Lobes push lifters/rockers to open intake/exhaust valves at precise crank angles to control air/fuel in and exhaust out. Correct timing (cam vs crank) and lobe profile determine cylinder filling, compression and combustion.
- Variable timing: some engines use cam phasers/solenoids to alter timing for torque/efficiency. Oil pressure runs phasers; clogged oil passages or bad solenoids/phasers cause timing errors.
- Failure modes:
- Worn/damaged lobes → short valve opening/low lift → loss of power, misfire, low compression, rough idle.
- Broken cam or journal wear → noisy operation, excessive oil clearance, dropped timing.
- Cam timing chain/gear failure or phaser failure → cam/crank relationship wrong → misfires, no-start, engine damage if valves contact pistons (interference engines).
- Cam position sensor failure → timing error codes (P0340 etc.) but cam may be OK.
- Why replacing/repairing cam/timing fixes faults: restores correct valve lift and timing relationship, removes worn surfaces/leaks and restores oil control for phasers, eliminating mis-timing, restoring compression and combustion timing.

Before you start (diagnostics + preparations)
1. Diagnose first:
- Read codes (P0010–P0016, P0340, P0365 etc). Cam phaser/position codes vs sensor.
- Compression/leakdown test to detect low valve lift or intake/exhaust sealing.
- Visual/noise inspection (valve cover removal) for unusual wear, broken followers, metal debris.
- Check oil condition/pressure and phaser solenoids/OMV operation (especially if VVT-related).
- If timing-related symptoms and evidence of wear/damage, proceed to replacement.
2. Safety & parts:
- Disconnect battery, cool engine, drain coolant/oil as required.
- Obtain factory service manual for your engine variant (critical for timing marks, torque specs and special tool use).
- Parts: camshaft (and bearings if required), lifters/tappets or followers, timing chain/belt/gears, cam seals, gaskets, phasers and solenoids if worn, front cover seal, valve cover gaskets, oil and filter.
- Tools & special tools: torque wrench, cam/crank locking tools (engine-specific), harmonic balancer puller, timing tool kit for Jeep engine, engine support/transmission support if needed, seal drivers, feeler gauges, compressing tool for springs (OHV overhead cams require rocker/lifter handling differently).
3. Clean area, prepare workspace, label/photograph everything you remove.

Ordered procedure — SOHC (3.7L, 4.7L PowerTech style) — general sequence and why
These are overhead-cam engines with timing chain and cam phasers on some models. Follow service manual for exact timing marks.

1. Safety, disconnect battery, remove intake and accessories that block valve covers.
- Why: access and prevent accidental starts.
2. Remove valve cover(s) and inspect valve train, lifters, cam phaser, chain slack, debris.
- Why: confirm damage and plan replacement; identify broken parts.
3. Rotate engine to TDC on #1 compression stroke; set crank locking tool if provided.
- Why: establishes reference for cam/crank relation and prevents accidental rotation.
4. Remove cam phaser actuator/solenoid electrical connector and any timing chain tensioner/guide covers (follow manual order).
- Why: expose cam gear and chain for removal and to relieve tension safely.
5. Lock camshaft (use cam locking tool per manual) so cam does not rotate relative to head when you remove bolts.
- Why: prevents valve/piston contact and preserves timing reference.
6. Remove camshaft sprocket/gear and timing chain in controlled order; label chain orientation.
- Why: remove cam from drive; preserves chain routing for reassembly.
7. Remove camshaft bearing caps in specified sequence (usually center to ends) and lift camshaft out carefully.
- Why: avoid bearing damage and keep journals/bore alignment.
8. Inspect cam journals, lobes, bearings, and lifters. Replace lifters/tappets if cam wear present (many engines require new lifters with a new cam).
- Why: worn lifters will score new cam; replacing both ensures longevity.
9. Clean oil passages and phaser oil control passages thoroughly. Replace phaser/solenoid if worn or clogged.
- Why: clogged passages cause variable timing failures; cleaning restores oil flow and phaser function.
10. Install new camshaft with new cam bearings/caps as specified; torque caps in the service-specified sequence and torque values.
- Why: correct bearing preload and alignment ensures proper oil clearance and cam rotation.
11. Reinstall cam sprocket, timing chain, tensioner, guides; set timing marks exactly; remove locks.
- Why: restores correct cam/crank phasing; correct timing fixes misfires and restores compression/valve timing.
12. Replace cam seals, gaskets, reassemble valve cover, reconnect solenoids, sensors.
- Why: prevents oil leaks and restores system monitoring.
13. Refill oil and coolant, clear codes, reconnect battery.
- Why: system fluids and electrical required to test.
14. Prime oil (turn engine by starter without injecting fuel or cranking fully where necessary) to ensure oil pressure to cam bearings/phasers before start.
- Why: avoid dry starts and cam damage.
15. Start engine, verify no abnormal noises, check timing with scan tool (cam/crank correlation), run compression/test drive and recheck for leaks/codes.
- Why: verify repair fixed timing and performance symptoms.

How this fixes faults (SOHC):
- Removes worn lobes/journal wear that caused low lift/low compression and replaces worn timing components (chain/phaser) that allowed cam-crank drift. Cleaning oil passages and replacing phasers/solenoids addresses VVT oil control failures that cause timing faults. Correct torque and clearances restore oil film and geometry so valves open/close at designed times.

Ordered procedure — Pushrod HEMI 5.7 (camshaft in block) — general sequence and why
The HEMI is a cam-in-block engine; cam drives lifters and pushrods to rockers. Procedure is different — more bottom-end access.

1. Safety, disconnect battery, support engine/trans if necessary, remove intake manifold and accessories to access valve covers and valley.
- Why: need access to front cover and valley for lifter/cam removal.
2. Drain oil and coolant as needed; remove valve covers and intake manifold, label connectors.
- Why: access lifters and pushrods; prevents contamination.
3. Rotate engine to TDC and use crank/cam locking tools per manual to set timing and prevent rotation.
- Why: needed for reinstallation timing reference.
4. Remove pushrods and keep them labeled to their original positions if reusing. Remove rocker arms as required (or replace with new set).
- Why: pushrods and rockers are matched to lifters; wear causes issues if mismatched.
5. Remove timing chain cover/front cover, harmonic balancer, and timing chain/sprocket assembly.
- Why: exposes camshaft for removal.
6. Remove camshaft retaining plate (if present) and carefully slide camshaft out from rear/front, supporting it to avoid damaging lifter bores.
- Why: camshaft removal from block; observe wear patterns.
7. Inspect lifters and lifter bores; replace lifters with new matched set if cam worn. Inspect block for scoring.
- Why: worn lifters destroy new cam; HEMI typically requires new lifters with cam.
8. Install new camshaft with new lifters (pre-lube lifters and cam lobes), ensure correct orientation and apply assembly lube.
- Why: proper lubrication prevents startup wear and ensures correct interaction with lifters.
9. Reinstall timing chain/sprockets, set timing marks and torque per manual.
- Why: restores correct cam-crank phasing for valve timing.
10. Reinstall rocker arms/pushrods, set valvetrain lash/specs (if hydraulic, ensure proper oiling; if adjustable, set clearance).
- Why: correct valve clearance ensures proper valve seating and timing.
11. Reassemble front cover, intake, valve covers, refill oil, prime oiling system, start and verify operation.
- Why: seals and fluids restored; priming prevents dry start failure.
12. Test drive and recheck for codes, noises, and oil leaks.

How this fixes faults (HEMI):
- Replacing a worn/broken cam removes damaged lobe geometry that caused low lift, restoring proper valve actuation. New lifters and re-established timing re-align valve events, restoring compression and combustion. Cleaning and replacing oil seals and chain fixes oil pressure/timing chain slack that contributed to the failure.

Important practical theory notes (concise)
- Always replace lifters/tappets when a cam is replaced if there’s evidence of wear — reusing worn lifters on a new cam will rapidly damage it.
- Cam phaser/clogged oil passages are a common cam timing failure cause on VVT engines; cleaning and phaser/solenoid replacement often fixes timing-related codes without full cam replacement if lobes are not damaged.
- Correct torque sequences and bearing clearances are critical; incorrect torque leads to cam distortion, bearing failure, oil starvation.
- Prime the oiling system before first start; cam journals and lifters need immediate oil film.
- Verify cam/crank correlation with a scan tool: cam angle vs crank reference must match factory specs after reassembly.

Final verification (ordered)
1. Clear codes, prime oil, start and idle while monitoring for noises and oil pressure.
2. Use OBD-II tool to monitor cam position, bank-to-bank balance, and misfire counts.
3. Run compression or leakdown test if prior low-compression symptoms existed.
4. Road test and re-scan; re-torque hardware if recommended after run-in.

That’s the ordered theory + procedure for cam replacement/timing repair on WH/WK Grand Cherokees (two engine families). For exact timing marks, torque specs, and special tool usage follow the factory service manual for your specific engine variant.
rteeqp73

Tools / parts needed
- Digital multimeter (DC volts)
- OBD-II scanner capable of reading/clearing DTCs and performing throttle body / TPS relearn (preferred)
- Ratchet + metric socket set (8mm, 10mm commonly)
- Torx bit set (T20/T25/T30 commonly used on TPS/throttle body fasteners)
- Small flat screwdriver or pick (for connector release)
- Extension, swivel if needed
- Needle-nose pliers
- Replacement part: TPS sensor (or complete throttle-body assembly if TPS is integral on your engine). Also new throttle-body gasket or O-ring if removed.
- Dielectric grease, shop rags, gloves, safety glasses
- Wheel chocks, jack stands (if you must get under vehicle)

Safety precautions
- Park on level ground, parking brake set; chock wheels.
- Engine cold before working around intake/throttle body.
- Disconnect negative battery terminal and wait ~2 minutes before unplugging throttle electronics to avoid accidental short or uncontrolled throttle movement. Reconnect battery only when instructed.
- Wear eye protection and gloves.
- Avoid dropping hardware or debris into intake.
- If lifting vehicle, use jack stands; do not rely on the jack.

Step A — Locate TPS and initial access
1. Open hood. Locate air intake tube and airbox on the driver’s side leading to the throttle body on the intake manifold.
2. Remove air intake duct and airbox cover as needed (loosen hose clamps, remove a few screws/bolts) to expose throttle body and electrical connector. Keep fasteners organized.

Step B — Diagnostics / test before removal
1. Connect an OBD-II scanner. Check for related codes (P0120–P0124, P2135–P2138, P2100–P2102). Note codes and clear only after repairs.
2. Backprobe the TPS connector with the multimeter (DO NOT disconnect the connector to read reference voltage).
- Set multimeter to DC volts.
- With ignition ON (engine OFF), identify: 5 V reference wire, ground, and signal wire (service manual pinout or visually compare wires).
- With key ON, signal should be about 0.4–1.0 V at closed throttle and increase smoothly to ~4.0–4.8 V at wide-open throttle. No sudden jumps or drops. If reference is not ~5 V or signal is erratic, suspect wiring/ECU or TPS.
3. If you have no smooth voltage increase or out-of-spec values, proceed to replacement/testing physical sensor.

How the multimeter is used
- Set to DC volts. Backprobe the connector pins (use paperclip or probe through the connector seam) to measure 5 V reference and signal. Gradually move throttle manually (throttle plate open) while watching voltage; it must change smoothly without steps or dropouts.

Step C — Remove TPS or throttle body
Note: On WH/WK many models use a drive-by-wire throttle body where the TPS is integrated. Check whether the TPS is serviceable separate — if not, you must replace the entire throttle body.
1. Disconnect negative battery if you haven’t already.
2. Disconnect the electrical connector(s) to the TPS/throttle body (press release tab and pull straight out). Use a small screwdriver to release clip if stuck; avoid prying on wires.
3. Remove intake duct to clear working area.
4. If TPS is a separate sensor: remove the Torx screws holding it (usually 2–3 screws). Support sensor and pull out gently. Note orientation and any O-ring/gasket.
If TPS is integrated: remove mounting bolts to the throttle body (typically 4 bolts). Support throttle body, disconnect any coolant lines (plug to avoid fluid loss) and vacuum lines, then remove throttle body from manifold.
5. Inspect mating surfaces; clean with shop rag. Replace gasket or O-ring.

Step D — Install replacement
1. Install new TPS or throttle body in the exact orientation. Replace gasket/O-ring. Do not overtighten screws — snug to manufacturer spec. If no spec available, tighten evenly and gently; sensor screws are low-torque.
2. Reconnect wiring harness until it clicks.
3. Reinstall intake duct and airbox. Reconnect any vacuum or coolant lines removed.
4. Reconnect negative battery.

Step E — Reset / relearn procedure
1. Use OBD-II scanner: clear DTCs, then perform any throttle body alignment / TPS relearn procedure specified for Jeep (recommended). Many scanners have "Throttle Body Alignment" or "Throttle Learn".
2. If you don’t have a scanner, perform this basic procedure (some models require a proper tool — this is a generic fallback and may not replace a full OEM relearn):
- With parking brake on and transmission in Park, start engine and allow to idle until stable (may be rough for a short time).
- Cycle ignition (OFF -> ON) a few times, and drive gently for several miles to let ECM adapt.
- If check engine light returns or driveability issues persist, do not rely on this — use a scanner or dealer tool.
3. Verify no related DTCs return and that throttle response is smooth.

Common pitfalls and how to avoid them
- Mistaking APP (accelerator pedal position) correlation faults for TPS — check pedal sensor codes too (P2138 etc).
- Dropping screws or debris into intake — plug inlet if throttle body out.
- Cutting wires or breaking connector tabs when forcing connectors — depress release tabs before pulling.
- Overtightening sensor screws (plastic housing can strip or crack) — snug only.
- Not performing relearn with correct tool — can leave poor idle/hesitation; use OE-capable scan tool if possible.
- Replacing only the sensor when TPS is non-serviceable (integrated) — confirm whether TPS is available separately; on many WH/WK engines you must replace the full throttle body assembly.
- Ignoring harness/connector corrosion — inspect and clean contacts; dielectric grease on reconnect is helpful.
- Not checking for vacuum leaks after reassembly (intake tubing seals, clamps).

Torque/info notes
- Sensor screws are low-torque; throttle body bolts are medium torque. If exact torque values are required, reference factory service manual for your exact engine (3.7, 4.7, 5.7, diesel etc.) — when in doubt, hand-snug then 1/8 to 1/4 turn further, or consult manual.

Final checks
- Clear codes, perform relearn, test drive and monitor for returned codes or drivability issues.
- Re-check connector tightness and for vacuum leaks.
- If problem persists after correct installation and relearn, suspect wiring, ECU, or pedal sensor and perform further diagnostics.

End.
rteeqp73

Tools & consumables
- Metric socket set (8–15 mm) + ratchet and extensions
- Torque wrench (0–50 ft·lb)
- Flat and Phillips screwdrivers
- Pliers (clamp and slip-joint)
- Hose clamp pliers or screwdriver for screw clamps
- Drain pan (3–5 gal)
- Funnel and clean coolant container
- Gasket scraper / plastic razor blade
- Wire brush or clean rag
- Rubber gloves & safety glasses
- Floor jack and jack stands (only if splash shield removal required)
- Shop towels
- Vacuum coolant fill tool (highly recommended) or long-neck funnel
- Penetrating oil (for stuck hose/clamp bolts)
- Replacement parts: engine-specific thermostat (3.7L/4.7L = mechanical; 5.7 HEMI = electronic thermostat assembly), new thermostat gasket or O‑ring, new hose clamps (recommended), coolant (Mopar‑specified long‑life coolant or equivalent — do NOT mix different chemistries)

Safety first
- Work only when engine is cold. Hot coolant under pressure will cause severe burns.
- Wear safety glasses and gloves. Keep open cuts covered.
- Support vehicle with jack stands if you raise it; never rely on a jack alone.
- Catch coolant — do not dump down drains. Dispose/recycle per local laws.
- Battery disconnect recommended when working near electrical connectors (especially with 5.7 HEMI electronic thermostat).

Overview & notes
- Location: thermostat housing is at the end of the upper radiator hose where it connects to the engine (passenger side). On 3.7L/4.7L it’s a conventional thermostat in a small housing; 5.7 HEMI uses an electronic thermostat assembly — part and procedure differ slightly.
- Always buy the thermostat specific to your engine. Replace the O‑ring / gasket with the new thermostat — do not reuse.

Step‑by‑step procedure
1) Preparation
- Park on level ground, set parking brake, chock wheels, engine cold.
- Open hood, remove engine cover and air intake components blocking access to the thermostat housing (often the airbox and upper intake snorkel; on some models you’ll need to remove the battery to gain clearance).
- Place drain pan under radiator drain or lower hose.

2) Drain coolant to below thermostat level
- Open radiator petcock (or loosen lower radiator hose) and drain enough coolant to drop level below the thermostat housing so you don’t spill when you open it. Catch used coolant.
- If unsure, remove only enough to avoid full drain; you can recover/replace remaining coolant.

3) Remove components for access (if required)
- Remove upper radiator hose from thermostat housing: loosen clamp, twist hose free. Use penetrating oil if stuck and pliers to compress spring clamps. Have shop towel ready for residual coolant.
- If access requires it, remove splash shield or brackets. Use jack/stands if needed.

4) Remove thermostat housing
- Locate and remove the housing bolts (usually 2–3 bolts). Use the appropriate socket and extension.
- Support the housing as you remove bolts — many housings are plastic and fragile.
- Carefully break the seal and lift the housing away. Expect residual coolant to pour; move drain pan.

5) Remove old thermostat and clean mating surfaces
- Note thermostat orientation before removal. For conventional thermostats: spring side faces the engine block (the thermostat valve faces the radiator outlet). For an electronic assembly, follow the part orientation instructions.
- Remove old thermostat and O‑ring/gasket.
- Clean mating surfaces on both housing and engine with a plastic scraper and rag until bare and flat. Do not gouge sealing surfaces. Remove old gasket material and corrosion.

6) Install new thermostat
- Verify new thermostat is the correct part for your engine.
- Install new thermostat in same orientation as removed (spring toward the engine for mechanical thermostats).
- Install new O‑ring/gasket — lightly lubricate O‑ring with coolant or clean engine oil so it seats without twisting.
- If replacing electronic thermostat assembly on a HEMI, make sure electrical connector harness is accessible and not pinched.

7) Reinstall housing and torque bolts
- Position housing carefully and start bolts by hand to avoid cross‑threading.
- Tighten bolts evenly in a crisscross pattern. Torque to manufacturer spec — if you don’t have the manual, torque small housing bolts to approximately 8–12 ft·lb (tighten snugly but DO NOT overtighten; plastic housings crack easily).
- Reconnect upper radiator hose and install new hose clamps if supplied.

8) Reassemble removed components
- Reinstall airbox, intake hose, battery, engine cover, splash shield, etc.
- Reconnect any electrical connectors you removed.

9) Refill and bleed cooling system
- Refill with correct coolant type to specified concentration.
- If you have a vacuum fill tool, use it — it makes bleeding straightforward and prevents air pockets.
- Without a vacuum filler: fill radiator/reservoir, start engine with heater on high, loosen any cooling system bleeder screw (if equipped on your thermostat housing or heater hose) until coolant flows steady, then tighten.
- Squeeze the upper radiator hose periodically to help dislodge trapped air.
- Monitor coolant level as thermostat opens (engine reaches operating temp) and add coolant as needed.
- Continue until no more air bubbles and level stable; top off reservoir.

10) Final checks
- With engine at operating temperature, inspect for leaks around housing and hose.
- Re‑torque bolts after cool down if necessary.
- After a short test drive, recheck coolant level and inspect for leaks again. Replace coolant cap and secure everything.

Common pitfalls & avoidance
- Opening hot system: always wait for cold engine. Hot coolant causes severe injury.
- Wrong thermostat orientation: always install spring side toward engine (mechanical). Double‑check part instructions for electronic assemblies.
- Reusing old gasket/O‑ring: leads to leak — always replace seal.
- Overtightening housing bolts: Jeep thermostat housings are often plastic — bolts strip or crack housing. Use correct torque and even tightening sequence.
- Not bleeding air: trapped air causes hot spots/overheating. Use vacuum filler or bleed procedure until no air.
- Mixing coolant types: mixing OAT/Dex‑Cool and other chemistries can cause sludge. Use manufacturer‑specified coolant.
- Damaging connectors/sensors: on 5.7 HEMI electronic thermostat, disconnect gently and avoid pulling wires.
- Ignoring corroded hoses/clamps: if hose or clamp is old/soft, replace to avoid future leaks.

Specific notes for HEMI 5.7L
- This engine uses an electronic thermostat assembly (often sold as a housing/thermostat/electronic valve). Replacement usually requires the whole assembly and may have different electrical connections and bleeding steps. Disconnect battery before replacing if working near electrical connectors. Use a scan tool if you get thermostat fault codes after replacement — some systems need the PCM to adapt.

Disposal & final
- Properly dispose of used coolant.
- Keep the vehicle monitored for several days for leaks and coolant level changes.

That’s the full, practical procedure. Follow torque specs from a factory or reputable repair manual for exact values for your engine.
rteeqp73