Home How-to Articles Jeep® 4.0L Ignition Tune-Up and Injector Cleaning

Jeep® 4.0L Ignition Tune-Up and Injector Cleaning

by Moses Ludel
YouTube HD video coverage of a Jeep 4.0L engine diagnosis and tune-up can be viewed right here and also at the YouTube channel. How-to in depth diagnosis is followed by a comprehensive tune-up to restore performance and fuel efficiency. Fuel injector cleaning (Part 2) is found in the additional video below.

How-to: 4.0L Jeep® Engine Diagnostics and Major Ignition and Fuel Injector Service…

At 186,000 miles, our Jeep Cherokee 4.0L engine was due for mechanical diagnostics and a tune-up. This how-to covers our tests of the engine’s mechanical condition followed by performing a complete ignition tune-up and fuel injector cleaning. We upgraded ignition components during the tune-up work.

Spark plugs were still firing at close to 60,000 miles since the last major tune-up and 30,000 miles since the last spark plug and air filter change. No signs of oil burning, minor buildup of debris and little gap wear are typical for these EFI engines when in good operating condition. Parts wear is deceptive, as the strong spark and controlled fuel management keep spark plug tips clean. Carbon, however, is present at the plug shell, a sign of carbon buildup in the combustion area and likely around the valves. Compression was normal and within the 10% high-to-low spread for reasonable cylinder balance.

Engine tuning always begins with evaluating the engine’s mechanical condition. Before “tuning” an engine, make certain that compression, manifold vacuum, valve timing (chain/sprocket wear on a 4.0L engine) and oil pressure are okay. Eliminate engine mechanical trouble before performing ignition service or fuel injector work.

A compression check was once a part of every engine tune-up. This test can now be done with a traditional compression gauge or a lab oscilloscope. Using an amperage clamp, the starter motor draw during cranking can indicate the “relative” compression of each cylinder. If a cylinder is suspected of not pulling its load, low compression can be pinpointed with a compression gauge then a cylinder leakdown test or in-cylinder pressure transducer with automotive lab oscilloscope.

Distributor cap has considerable buildup on the brass contacts. The rotor was worn as well. An older breaker point distributor would not have bridged this gap and resistance. A contemporary high energy electronic distributor manages to fire through the resistance. The sign of trouble is poor fuel efficiency, possibly harder starting and less power under load when cylinder and combustion pressures rise. The worn spark wires, distributor cap and rotor cannot meet the challenge.

If the engine meets the basic mechanical standards illustrated in the video, with no more compression deviation than 10% between the highest and lowest cylinders, an ignition and fuel system tune-up can make a difference. Fuel economy and performance depend upon proper tune. Your choice of tune-up components can improve the engine tune and prolong the intervals between major tune-up work.

Taylor ThunderVolt® spark cables are advertised as the last set of plug wires you will need to buy. These well crafted 8.2mm wires serve in high performance vehicles and will outlast any OEM replacement wires—like the 7mm set that we removed. These Taylor wires are available in Red, Black and Blue. See installation details in the Tune-Up Part 1 video.

The ignition service video covers a complete engine tune-up, including upgrades like the Taylor ThunderVolt® 8.2mm ignition cables made in the U.S.A. Taylor has built quality ignition components since 1923 and is now part of the Pertronix® Products family. Follow the steps for spark plug, distributor cap, rotor and spark cable replacement.

Fuel Injector Cleaning

AUTOOL® CT200 Fuel Injector Cleaning and Testing Machine offers features found in machines selling for many times the price. For our top-feed EV1 and EV6 injectors, this is all the machine we need at this point. There are adapters for side-feed injectors and other AUTOOL® models available. This machine services common automotive and motorcycle electronic fuel injectors. The Jeep® 4.0L injector removal, cleaning and testing processes are clearly covered in this how-to HD video.

4WD Mechanix Magazine has stressed the importance of clean fuel injectors. The magazine has demonstrated the S.U.R.&R. FIC 903 upper engine cleaning tool plus the FIC 203 direct fuel rail injector cleaning kit. These tools are highly effective with Sea Foam Motor Treatment as the cleaning agent. When using the FIC 203 for a gasoline engine, Sea Foam is mixed 50/50 with gasoline. Diesel engines will run on pure Sea Foam through the FIC 203 canister. (Never run gasoline in a diesel engine—for any purpose!) The FIC 903 is for top engine cleaning on gasoline engines only. The FIC 903 uses pure Sea Foam introduced through the intake manifold, typically via the brake booster hose.

The S.U.R.&R. FIC 203 common rail injector cleaning kit does a great job of cleaning fuel injectors in place on the engine. We have demonstrated this system for both diesel and gasoline engines. Our XJ Cherokee engine’s fuel injectors have lasted 186,000 miles thanks to injector cleaning with the FIC 203 Kit. For details, see the HD videos and articles at the magazine’s URL links above.

To better demonstrate fuel injector performance and how to clean injectors off the engine, we invested in an AUTOOL® CT200 Fuel Injector Cleaning and Test Machine. The ‘Part 2’ video is devoted to removal, cleaning and testing of the 1999 XJ Cherokee engine’s fuel injectors. We test for spray patterns, fuel flow volume and performance from an idle to 7,500 rpm. Both ultrasonic and reverse flow cleaning are possible.

We purchased our AUTOOL® CT200 machine as a retail customer at eBay. This ad from AUTOOL® emphasizes the functions of the CT200 machine. With the optional adapters, on-vehicle injector cleaning is possible. With the injectors out of the engine and on the machine, spray pattern testing, leak detection, fuel flow volume, reverse cleaning and ultrasonic cleaning are possible. The bright back lighting of the six graduated tubes is excellent for viewing spray patterns. (Image courtesy of AUTOOL®)

These OEM injectors have been performing for 186,000 miles, and the cleaning results are impressive. The injectors are functioning as new from the ultrasonic cleaning process, and highway fuel mileage has gone up 2-3 miles per gallon since this injector service and major ignition tune-up. Throttle response has dramatically improved.

Ultrasonic cleaning method is unique. In the ultrasonic cleaning mode, the pulse signal leads that fire the injectors during spray and fuel flow volume tests send an ultrasonic vibration signal to the injectors. This “jitters” the injector pintles and is highly effective for cleaning the pintles, passages and nozzles. (Photo courtesy of AUTOOL®)

For our shop/studio, the AUTOOL® CT200 was a wise investment. Well built and affordable, the machine will pay for itself quickly by eliminating sublet labor costs for injector cleaning. We can quickly test and clean injectors in house. Testing flow rate and comparing volume on new or serviceable injectors enables matching the set of injectors for best air/fuel ratio balance and fuel trims. Any independent shop or serious DIY tuner should consider the value of this machine.

AUTOOL® CT200 Fuel Injector Cleaning and Testing Machine will clean up to six injectors at one time—ideal for the inline six-cylinder multipoint 4.0L injectors. This machine works with top feed injectors and will reverse flush if desired. The unique ultrasonic function uses signal pulses at the right frequency for an effective cleaning. AUTOOL® makes machines and adapters for side-feed injectors and on-engine injector cleaning. Our model machine takes care of Siemens Deka (Mopar™) and popular Bosch style top feed gasoline injectors. This works for our EV1 and EV6 style injector needs!

We also used a bore camera to look for carbon build-up in the lowest and highest compression cylinders. Both piston crowns showed the significant cleaning power of the S.U.R.&R. FIC 203 and FIC 903 equipment and Sea Foam®. The bore camera shows how piston carbon has been dramatically reduced and could be reduced further by more use of these top engine cleaning tools.

The low cylinder still has some carbon around the exhaust valve, which could be dropping compression slightly if that valve is not sealing perfectly. By any standard, 145 PSI at the low cylinder is fully acceptable, but another round with the FIC903 and Sea Foam might bump compression to the 150-155 range to match other cylinders. The high cylinder is at 160 PSI and could afford to shed some more carbon build-up. Rings and valves at that cylinder are sealing well.

Overall, the XJ Cherokee remains on course for at least another 75,000 miles of reliable service. The bore camera findings suggest the option of an in-chassis piston-and-rings changeout, using a professional grade hone like the Lisle 15000 series. A cylinder head sublet for valve work would be timely.

A stroker crankshaft with stock bore yields 4.5L instead of 4.6L. If the engine requires boring rather than an in-chassis overhaul with stock size pistons, 0.030″ oversize would be likely. With the engine out of the chassis, a stroker crankshaft would be a must, the end result being 4.6L. Injectors would be upgraded for more flow and four holes.

For now, this tune-up and fuel injector refresh on the stock 4.0L will do the job!

For More Information on Pertronix® and Taylor Cable Products visit:

https://pertronixbrands.com or https://taylorvertex.com

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