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Fox Body Tune-up Guide

By:  Connor MC  / Jun 5 2019
Fox Body Tune-up Guide

A spring tune-up is a great way to insure the car will perform to its potential all summer long. For those of you that are luckily enough to be able to drive your Mustangs all year long, a tune-up, often overlooked, is a good idea for you as well.

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When it comes time to tune-up your aging Foxbody AmericanMuscle has everything you need to keep your car running at peak performance. Treat your Mustang right and it will certainly treat you well in return. Shop maintenance products from the top brands in the Foxbody aftermarket.

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Why Should I Tune-up my Fox Body?

It’s that time of year again folks. For those of you that have a real winter (sorry, anything above 32F degrees is not a real winter), spring is just around the corner. With it comes the smell of moist air, thoughts of warm sun rays and of course most importantly, the excitement of rolling the Fox out of the garage and hitting the pavement with 5.0L (or more) of fury. Just like you prepare the car to be stored, it is a good idea to have a once over to check that everything is still functioning (and not leaking) as it should.

The ignition components on an older Mustang are often neglected because hey, if the car starts and runs, everything is probably OK. While there is definitely some truth to that, it is a very good idea to check once a year the condition of each ignition component.

Blue Foxbody Spark Plug Wires
Fresh wires, plugs, cap and rotor can have a major impact on how the engine runs

Fox Body Ignition Conponents to Check:

  • Distributor
  • Wires
  • Coils
  • Spark plugs
  • Cap and rotor

Perhaps the Fox Body is running well as is, but there could be room to improve. The stock Duraspark II ignition system is not bad at all, quite the opposite actually. However, years of use and heat cycles will result in lower voltages being produced and less efficient electricity transfer. This can lead to degraded engine performance, a rough running engine or even an engine that refuses to start. Replacing the parts gives peace of mind that the engine is operating efficiently and smoothly. The best part is, ignition components are not that costly and can easily be found. Maybe even better news than that is that proper ignition components can turn a barely running ‘Stang into a galloping race horse, simply by changing the plugs and wires.

Under the Hood of a 1993 Foxbody Mustang

Changing Fox Body Spark Plugs

Over time, constant use and heat cycles deteriorate the spark plug and increase its internal electric resistance, lessening its ability to create a strong, clean spark. Reading the spark plugs from your Mustang can tell you a lot about how the engine is running. When removed, a healthy engine should color the spark plug reddish-brown and show slight electrode wear. Black deposits indicate an engine running rich (too much fuel) whereas white deposit accumulation signifies a lean condition (not enough fuel). Excessive electrode wear (which is normal after years of use) means it’s probably time to order a new set. Motorcraft (OEM) or NGK (Iridium series, G-Power series, V-Power series) both fabricate readily available, inexpensive and high performing spark plug sets. For a heavily modified engine, you’ll want to pick a set of plugs with a colder range. Cold range plugs better expel heat and deal with slower burning, high-octane fuel than stock ones and are thus recommended for higher horsepower engines.

Mustang NGK Spark Plug Set

Fox Body Spark Plug Wires

Just like the spark plugs, over time constant heat cycles affect, at the atomic level (boy, we’re getting technical here), the ability of the wires to pass an electrical current due to increasing internal resistance is substantially reduced. Swapping wires with Taylor Street Thunder 8mm, Ford Racing 9mm or MSD Super Conductor8.5mm performance wires can have a drastic effect on how the car runs, especially at idle and wide open throttle! All 3 companies use premium insulated copper wires precut to the proper length for each cylinder, thus making the install fast and painless.

Ford Racing 9mm High Performance Red Spark Plug Wires

Mustang Distributors, Caps, and Rotors

Another painless procedure is to replace a Fox Body Mustang's worn distributor cap and rotor with new ones. Surprisingly, the stock pieces are actually very good, but like all the other ignition components, they too degrade over time. Aftermarket cap and rotors are popular replacement choices as they provide advanced spark and performance and are tailored to provide the best connectivity and protection against arcing and ignition crossfire. Or, altogether you can replace the whole distributor. Distributors from MSD and Accel exceed OE specifications and include their proper cap and rotor. Simply drop into place with the correct orientation as indicated by the instructions.

Mustang Distributor

Fox Body TFI Coils

We’re really getting repetitive here… but I’ll reiterate it one more time. Extended use and attack from engine heat take their toll on the stock TFI coil (a good piece from the factory) and it will no longer be able to produce the voltage it did when new. Motorcraft , MSD TFI Performance and the Accel TFI Supercoil are all popular, good performing replacement coil packs that fit into the stock location with no modification necessary and will provide more juice than the stocker. Again, engine smoothness will increase all over the range, from idle to redline.

Foxbody Stock Ignition Coil

MSD Digital Ignition Module

On a side note, if your Mustang is pushing more power than stock or operates at or above 4000-5000 RPM, if you haven’t already, consider purchasing an aftermarket digital ignition module. The reason being, at higher RPM’s the coil will have a difficult time recharging fast enough to provide sufficient voltage. MSD’s 6AL digital ignition module is an ignition controller that will help regulate and alleviate the loads on the coil thus guaranteeing the car receives a strong spark at a quick enough rate during higher operating ranges. Furthermore, an electronic rev limitation can be set to guarantee that your motor never spins higher than it is supposed to.

Mustang MSD Ignition Module

Tuning-up Fox Body Mustang Fuel Systems

Another recommended idea, particularly if it has never been done before, is to flush the fuel system using a fuel system flush kit. A proper flushing of all the fuel lines, rails and injectors will remove any deposits and sludge buildup along the way, once again allowing the free flow of fuel. It can even help restore the pump! An alternative method, one that is much cheaper, easier to do and will not be as effective as a full system flush, is to simply pour a little fuel injector cleaner into your gas tank. This too will remove deposits, just not as effectively or completing as a proper flush kit. Regardless, proper fuel delivery is essential to smooth and reliable operation.

Mustang Fuel Rail Kit

General Fox Body Tune-up

Air filter: Whether running the stock airbox or not, it is a good idea to check the condition of the air filter. A good cleaning (if it is a reusable filter, some are not) will usually take care of any issues with the filter and can have a noticeable impact on throttle response. If ripped or otherwise damaged, it is a good idea to replace the filter. K&N, BBK and Stack Racing offer air filters, depending on your setup (stock airbox, aftermarket CAI) that are less restrictive than stock but yet better filter the air. The result is cleaner air entering the engine and a smoother operating engine with improved throttle response.

Edlebrock Cone Air Filter

Performance Mustang Tires Are Part of a Good Tune-up

Tires play a very important role in the overall safety and handling of the car. A damaged or worn tire significantly reduces braking and steering ability and greatly increases risk of a blowout and consequently, a crash. Tires are considered unusable when the tread is below 2/32 of an inch. Cracking or rot on the sidewall of the tire means the tire should be replaced. If any tires do indeed need replacing, NITTO Extreme Performance NT555’s or Sumitomo Performance HTR Z tires are a great choice for high performance summer driving. They won’t break the bank either. If the tires otherwise check out OK, verify they have enough air. The correct pressure level is marked on sticker located on the driver side door (usually ~30 PSI).

Oil: If you didn’t do this before you stored the car, you should definitely do it now! A quick oil change with a quality oil and oil filter such as Royal Purple will extend engine life and reduce wear on moving parts by being properly lubricated. 10W30 is the factory recommendation for most climates.

Nitto NT555 Mustang Tires

Battery and Battery Cables

A critical, and very obvious, part to every car’s functionality is of course the battery and battery cables. Verify the battery terminals are clean as well as the cable connectors. Also trace the length of the cables looking for breaks in the insulation or corrosion. If you suspect or witness a bad connection, replace the cables with the likes of a PA Performance Premium cable package. Age and heat will reduce the old cables electrical capacity, causing harder starts and even arcing.

Foxbody Mustang Battery with Terminal Corrosion
See the build-up on the terminals and cables? This caused poor contact and thus hard starting until the terminals were cleaned and the cables replaced.


Doing these basic preliminary checks and replacing any worn parts as needed is a sure fire way to have a headache free summer driving the Mustang. Once tuned up, simply add gas, check the oil and tire pressures once a week and you’ll be cruising for the entire summer (or winter, for those lucky guys that don’t really know what a REAL winter is) in a smoother operating car, problem free!

Fitment includes: 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, GT, Cobra, LX, SVO