Jeep Engines - Oljeep

T - n r i4.7L POWER TECH V-8 365EXHAUST SYSTEMExhaust ManifoldsExhaust manifolds are log style with ii patcnted flowenhancing design to maximir.e pcrfornimce. The exhaustmanifolds are made of high silicon molybdenum cast iron. Aperforated core graphite cxhaust manifold gasket is used toimprove sealing to the cylinder liead. Exhaust iiianitolds arecovered by a three layer larninated heat shield for thermalprotection and noise reduction. Heat shields are fastened witha torque prevailing nut that is backed off slightly to allow forthe thermal expansion of exhaust manifolds.Oxygen SensorsThe exhaust system uses oxygen wnsors to detect exhaustgasses. These gasses arc sampled to determine whether thesystem is rich (to much fuel) or lean (not enough fuel). ThePowertrain Control Module (PCM) then makes theappropriate ad.justnient to the fuel system.Muffler and TailpipeThe 4.7L engine uses a galvanized steel muffler to controlexhaust noise levels and exhausl backprcssure.The tail pipe is also made of gnlvani/ccl steel and channelsthe exhaust out of the muffler and out lrom under thevehicle to control noise and prevent exhaust gas luiiies fromentering the passenger compartment.IGNITION SYSTEMThe 4.7L V-8 engine uses a dedicated and individually l‘iredcoil for each spark plug (8 total). Each coil is mounteddirectly to the top of each spark plug. A scparate electricalconnector is used for each coil.Because of coil design, spark plug cables (secondarycables) are not used. A distributor is also not used.The ignition system is controlled by the Powertrain ControlModule (PCM), and consists of:Spark PlugsIgnition CoilsPowertrain Control Module (PCM)Crankshaft Position SensorCamshaft Position SensorThe MAP, TPS, IAC and EC‘T also have ;in et‘l’ect onthe control of the ignition system.Spark PlugsThe 4.71, V-8 engine is equippcd with “fired-in suppressorseal,” resistor-type spark plugs using a copper core grounde I cc t rode. To pre ve n t pos s i b I e pre- i g ni t i on and/ormechanical engine damage, the correct type/heatrange/nuniber spark plug iniist be used.4.71, V-8 engine spark plugs have resistance values rangingfrom 6,000 to 20,000 ohms (when checked with at least a1,000 volt spark plug tester). DO NOT use an ohmmeter tocheck the resistance values of the spark plugs. Inaccuratereadings will result. Remove the spark plugs and examinethem tbr burned electrodes and fouled, cracked or brokenporcelain insulators. Keep plugs arranged in the order inwhich they were reniovcd from the engine. A single plugdisplaying an abnormal condition indicatcs that a problemexists in the corresponding cylinder. Replace spark plugs atthe intervals recommended in your owner’s manual.Spark plugs that have low rnileagc may be cleaned andreused if not otherwise defective, carbon or oil fouled.Caution: Never use a motorized wire wheel brush to cleanthc spark plugs. Metallic dcposits will remain on the sparkplug insulator and will cause plug misfire.Because of the use of aluminum cylinder heads on the 4.7Lengine, spark plug torque is very critical. Refer to theproper service manual for procedure and specifications.Ignition Coils'lie 4.7L V-8 engine uses a dedicated and individually firedcoil (Figure 6-22) for each spark plug (8 total). Each coil ismounted directly to the top of‘each spark plug.Battery voltage is supplied to the 8 ignition coils from theASD relay. The Powertrain Control Module (PCM) opensand closes each ignition coil ground circuit at a determinedtime foi- ignition coil operation.Base ignition timing is not adjustable. By controlling thecoil ground circuit, the PCM is ahle to set the base timingand aci,iiist the ignition timing advance. This is done to meetchanging engine operating conditions.Thc ignition coil is not oil filled. The windings areembedcicd in an epoxy compound. This provides heat andince that nllows the ignition coil to beinounted on the engine.I3ccausc of coil design, spark plug cables (secondarycahles) are not uwd.