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Ignition Upgrades The stock 4.0 ignition system is already very good right out of the box but there are a few upgrades that can be carried out to improve its reliability and longevity. A poorly-functioning ignition system will not completely burn the air/fuel mixture in each cylinder resulting in reduced performance, gas mileage, and poor emissions. Ignition system upgrades will not, by themselves, produce a horsepower/torque gain but they will regain HP/TQ that was lost due to poorly-functioning components. The '99+ Jeep Grand Cherokee WJ and the '00+ Jeep Wrangler TJ/Jeep Cherokee XJ 4.0 engines were upgraded to a distributorless ignition system with individual coils per cylinder, so the ignition upgrades (except for the spark plugs) outlined below do not apply to these models. |
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Autolite Double Platinum Spark Plugs Part no. APP985 Original OE design Platinum to platinum firing 30% more durable Maintains optimal performance longer Virtually no gap erosion Nickel-plated threads and shell Top fuel efficiency over the life of the plug 5-year unlimited mileage money-back guarantee |
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| Magnecor KV85 Competition 8.5mm Ignition Wires Part no. MAG-6595 Ignition Cables feature Magnecor's exclusive 2.5mm high capacity Metallic Inductance EMI Suppressed conductor consisting of stainless steel wire precisely wound at 200 turns per inch over a ferrimagnetic core. The insulating jacket is made entirely of Magnecor's exclusive TC-1500-HS high strength aerospace grade silicone rubber, and its single layer construction will prolong the jacket's insulating ability by conducting extreme heat away from hot-spots that occur near over-the-limit heat sources. The KV85 8.5mm jacket has a service heat resistance of 600 degrees F (320 degrees C) and up to 1,000 degrees F (540 degrees C) for short burst 3 minutes. The OEM ignition wires are only 7.5mm in diameter and have a much higher resistance. Their performance can also be reduced after just 10,000 miles so they can be considered to be the weak link in the stock ignition system. |
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Accel "HD Black" Distributor Cap Part no. ACC-120330 Accel distributor caps are the best way to help out your ignition. The compression molded caps with brass terminals are stress relieved immediately after molding in special fixtures to help ensure dimensional stability. The OEM distributor cap is good for 60,000 miles but has aluminium terminals that have a lower electrical conductivity than brass, resulting in a lower energy spark. |
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Accel Performance Distributor Rotor Part no. ACC-130229. The high conductivity corrosion resistant brass inserts and stainless steel rotor springs provide unrestricted spark energy flow. |
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MSD Blaster Coil Part no. MSD-8228. MSD Blaster 35,000V coils are designed with improved materials and windings to produce a stronger spark. This improved spark helps burn the fuel mixture more efficiently, resulting in a smooth idle and improved mid-range rpm power. The OEM coil is a reliable and durable unit, therefore consider the MSD Blaster coil as a good stock replacement. |
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