Keep your engine running right
Some of these are gonna seem pretty basic. But everybody from the beginner to the seasoned engine-tuning veteran has probably been guilty of misdiagnosing a poor-running engine at some point in time. Engines are pretty simple critters when you strip away all the outlying accoutrements. All you need is fuel, air, and spark and then it’s suck, bang, blow. Larger tires sap power and a poor-running engine drinks more fuel. So check off a couple of these items the next time you’re poking around under the hood of your Jeep. Some more pep and better mpgs just may be the reward for a little time and money spent.
The ignition system can range from a basic points-type mechanical operation working inside an engine-mounted distributor to a complete distributorless setup with the coils on individual plugs actuated by a mixture of camshaft and crankshaft position sensors and an electronic control unit (computer). Assuming all your parts are in good working order, here are some ways to ensure proper operation and maybe even eke out a little more performance.
Electronic Ignition Conversion: If you’ve so far resisted the urge to convert to an electronic ignition, be well versed in checking your point gap and dwell every so often. If you’re not, mechanics who know how to work a set of feeler gauges and a dwell meter are getting fewer and farther between. A tip is to find a motorcycle or air-cooled VW mechanic since many of these vehicles retained points-type ignition systems longer than others. If that’s a no-go, several companies from Petronix to Crane to Accel to others offer electronic ignition conversion systems that will easily drop into your points-type distributor to convert its workings to solid-state operation.
Cap and Rotor: Sounds stupid, but many ignition woes are caused by moisture or corrosion inside the distributor cap. Pop off the distributor cap every other oil change and take a peek, especially if you frequent mud or water crossings.
Wires: Bad plug wires can cause erratic idling, backfiring, misfiring, and all sorts of other issues you may not immediately attribute to the wires. You should have a multi-meter in your tool box. You can pick one up at just about anywhere they sell electronic computer or auto parts. Or, Harbor Freight sells very inexpensive multi-meters with a high degree of accuracy. Pull your plug wires every so often and check the resistance in Ohms. Generally, anything under 7,000 ohms-per-foot means the wire is still good. Excessive resistance means the wire is corroded or breaking down inside and should be replaced
Plug Gap: The specs for the distance between the two sparkplug electrodes varies from engine-to-engine, but in any case, as plug life increases, the gap grows. Generally, every 30,000 miles or so you want to pull at least a couple plugs and make sure the plug gaps are still within factory-spec. If you’re running a hotter ignition coil and lower-resistance aftermarket plug wires, you can generally increase the plug gap over stock for a hotter spark. However, if your ignition system is still stock, it’s generally best to keep your plugs close to the factory gap-spec as possible.
Mechanical Advance: Non-computer-controlled ignition systems rely on mechanical centrifugal advance within the distributor to increase ignition timing as engine speed increases. The trouble is the factory advance spec is generally tailored more towards resistance to knocking than performance. Also, corrosion and wear can limit or restrict the advance mechanism’s operation. Pop off the cap and rotor and (normally) the points or electronic ignition plate to expose the mechanical advance. You’ll see eccentrics held in place by springs. Lighter-weight springs are available from companies like MSD, ACCEL, and others to allow the ignition advance to come into play sooner in the rpm range. Just be sure to test drive cautiously, as pulling too much ignition timing too soon can cause knocking and pinging.
Advanced Timing: If you don’t want to crack open your distributor to mess with your mechanical advance, you can still gain a bit of performance by loosening your distributor hold down and advancing your initial timing up a bit. Normally a 3- or 4-degree bump won’t harm anything. However, if the engine cranks hard or labored you’ve put too much initial timing in and should pull out a couple degrees.
Adjustable CPS: If you have a computer-controlled ignition system, the computer uses data from the cam and crankshaft position sensors to determine where in the rotation it should fire the plugs. You can’t spin the distributor to advance the timing in these engines, but you can either modify your crankshaft position sensor (or buy an adjustable one) to trick the computer into thinking the engine is farther into its rotation so the ignition fires earlier. Most Jeep engines position the CPS sensor in the bellhousing. Slotting the mounting tabs will allow you to either advance or retard the initial timing and, therefore, the timing throughout the entire rpm curve.