Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide



An engine tune-up is a service designed to restore the maximum capability of power, performance, economy and reliability in an engine, and, at the same time, assure the owner of a complete check and more lasting results in efficiency and trouble-free performance. Engine tune-up becomes increasingly important each year, to ensure that pollutant levels are in compliance with federal emissions standards.

The extent of an engine tune-up is usually determined by the length of time since the previous service, although the type of driving and general mechanical conditioning of the engine must be considered. Specific maintenance should also be performed at regular intervals, depending on operating conditions.

Troubleshooting is a logical sequence of procedures designed to lead the owner to the particular cause of trouble. Service usually comprises two areas; diagnosis and repair. While the apparent cause of trouble, in many cases, is worn or damaged parts, performance problems are less obvious. The first job is to locate the problem and cause. Once the problem has been isolated, refer to the appropriate section for repair, removal or adjustment procedures.

It is advisable to read the entire section before beginning a tune-up, although those who are more familiar with tune-up procedures may wish to go directly to the instructions.

It should be noted that the diesel engine does not require tune-ups in the conventional sense. The diesel does not use spark ignition to fire the fuel (it uses compression ignition) so it has no spark plugs, distributor, or ignition wires. On the other hand diesels are much more sensitive to clogged air and fuel filters and should have their engine oil and filter changed more frequently as well. Diesel owners simply need to redefine "tune-up" to be the inspection and replacement of fluids and filters on a regular basis.

A complete tune-up inspection should be performed every 30,000 miles (48,000 km) or 24 months, whichever comes first. This interval should be halved (as a rule of thumb on certain items) if the truck is operated under severe conditions, such as trailer towing, prolonged idling, continual stop and start driving, or if starting or running problems are noticed. It is assumed that the routine maintenance described in General Information & Maintenance has been kept up, as this will have a decided effect on the results of a tune-up inspection.

A tune-up inspection for models covered in this guide may consist of the following:

Inspecting the drive belts
If necessary, checking and adjusting valve clearance
Cleaning the air filter housing and replacing the air filter element.
If equipped, replacing the PCV filter.
Inspecting or replacing the fuel filter assembly.
Inspecting all fuel and vapor lines.
Checking or replacing the distributor cap, rotor and ignition wires.
Replacing the spark plugs and making all necessary engine adjustments.
Always refer to the Maintenance Interval Chart for additional service information.