Wish you could have a quick-reference checklist for those perplexing problems that crop up from time to time? Engine won't start. Battery won't stay charged. Transmission slips. Clutch chatters. Brakes pull to one side. Driveline squeaks like a spastic squirrel as you come to a stop. Instruments have stopped working. Left turn signal won't blink. Headlights have left you in the dark. Rear axle whining like a disgruntled politician.
Bewildering problems, yet most are simple to solve given a handy checklist. It's easy to get lost in the details to the point where we miss the most obvious things. Our goal here is to get you back on course as quickly as possible.
The best advice we can offer is to begin your troubleshooting with the simplest items first. When an engine quits, it's only natural to panic and think the worst. But, did you remember to put gas in the tank? Most of the time, it's a broken wire, busted distributor rotor, bad ground, cracked distributor cap, ruptured fuel pump diaphragm, faulty ignition switch, or you've run out of gas. So always begin your search with the most obvious stuff first. Start your troubleshooting at the source.
Engine Won't Crank
Even if your engine won't...
Even if your engine won't crank, make sure you have 12-14 volts of battery power. This may seem obvious, but it doesn't always get our attention right away. Start with the easiest item on your checklist.
- Check the battery, which should show 12-14 volts with a voltmeter.
If the battery has at least 12-14 volts, verifiable with a digital voltmeter, check the starter solenoid. When the ignition is turned to "Start," does the solenoid click? Clicking means power is getting to the solenoid.
2: If the solenoid clicks, is there power at the starter cable terminal?
3: If there's power at the starter cable terminal, check the starter cable and starter.
4: If the solenoid does not click, check for power at the "S" terminal with the ignition switch at the "Start" position.
If you have 12-14 volts of...
If you have 12-14 volts of battery power, check the starter solenoid and all related connections. The "S" connection should be live when you turn the ignition switch to start. The "I" connection, which should also be live in "start" mode, fully energizes your Mustang's ignition coil during starting.
If there's power at the "S" terminal with the ignition switch in the "Start" position and the solenoid does not click, replace the solenoid.
Other starting system items to check
1: Check engine to firewall ground strap for proper contact.
2: Check battery to engine block negative cable for proper contact.
3: Make sure battery terminals are clean and corrosion free.
4: If the battery is dead, have it deep cycle (trickle) charged, then load tested at your local auto parts store. If it fails the load test, the battery will need to be replaced.
Starter doesn't work
If the starter operates (spins),...
If the starter operates (spins), but does not turn the engine over, it's either starter drive (known as the Bendix) failure or a flywheel/flexplate issue (damaged teeth or improper starter drive engagement).
Give the starter a gentle whack with a hammer to jar brushes in order to improve contact. Sometimes, brush contact with the slipper is lost due to debris or oil. If that doesn't work, remove and inspect the starter.
2: Spray brushes and slippers with high-evaporation rate radio tuner cleaner or brake cleaner to rid them of debris and oil.
3: If it isn't poor brush contact, check all leads within the starter.
4: Have a reputable starter/alternator/generator shop check your starter.
Engine Cranks But Won't Start
Is there fuel in the carburetor?...
Is there fuel in the carburetor? Sounds elementary, but it's so easy to overlook when you fear it's something worse.
- Is there gasoline in the carburetor?
Remove air cleaner and work the throttle. Does fuel spray into throttle bore?
2: If not, is there fuel in the float bowl? If there is, you have a faulty carburetor accelerator pump.
3: If there's no fuel in the float bowl, is there fuel in the tank? Don't laugh, this happens way too often.
Don't forget to check the...
Don't forget to check the fuel strainers or screens found in some carburetors. They can clog, especially if they've been in use for quite some time. They're more common with Holley carburetors than Autolite and Motorcraft.
If there's fuel in the tank, disconnect the fuel line from the carburetor and have a helper crank the starter. If there's no fuel on the pressure side, check the fuel supply at the pump. If there's fuel, you have a faulty fuel pump or blocked fuel line. Check the fuel line between the tank and pump for debris, faulty hoses, or a damage (kinked or smashed) fuel line.
If there's fuel, check the ignition.
1: First, check for a spark by taking one spark plug lead and grounding the spark plug to the engine. Have someone crank the starter while checking for spark. (Don't lean against the car body or you could get shocked).
2: If no spark and you're still using traditional points (as opposed to an electronic ignition conversation), remove the distributor cap and inspect for badly pitted or damaged points, improper point gap, faulty breaker plate ground wire, cracked distributor cap or damaged rotor, or damaged ignition coil primary (-) lead.
3: If no spark and you've inspected the distributor, check for power at the ignition coil's positive terminal (+) with the ignition switch in the "on" position. Then check for power at the coil's positive terminal while cranking the engine.
Remove the air horn and examine...
Remove the air horn and examine the fuel bowl. A float set too high or a sticking needle valve will cause flooding and a no-start condition. Fiber floats eventually become fuel soaked and sink, causing flooding. Brass floats can develop a leak and sink, resulting in flooding. The smell of raw gasoline is your first clue.
If there's power at the positive terminal but no spark at the secondary harness, suspect the ignition coil.
5: If there's no power at the coil's positive terminal with the ignition on and while cranking, suspect the ignition switch or its resistor wire.
6: If there's no power at the positive terminal with the ignition switch in "start" mode, check for power at the "I" terminal on the starter solenoid. "I" is what fully energizes the ignition coil with 12 volts during start.
If there's spark and fuel, here are other items to check.
When there's no spark, check...
When there's no spark, check the obvious stuff first. New doesn't always mean a good part.
Does the engine crank normally or does it crank unevenly like a spark plug has been removed?
2: If it cranks unevenly, check compression. Compression should be close across the board. Unusually low compression on one or more cylinder indicates a serious mechanical problem such as failed timing set, broken camshaft, blown cylinder head gasket, cracked cylinder head or block, or damaged piston.
Check for proper grounding...
Check for proper grounding between the breaker plate and distributor housing. One mistake we see from time to time is PerTronix Ignitor installations without the ground strap. We also see point applications without their ground straps. Without the ground strap, your odds of getting an engine started are slim. Or the engine will start, then quit.
If there's a failed timing set, you will hear the tell-tale clicking of valve-to-piston contact along with an unfamiliar cranking pattern. Stop cranking immediately to prevent engine damage. Sometimes, there's also backfiring through the intake or exhaust system.
Engine Runs Rough
- Carburetor choke sticking (flooding with rich mixture).
- Idle-air mixture bleed(s) plugged or out of adjustment.
- Intake manifold vacuum leak-gasket, carburetor spacer, vacuum hose.
1: Manifold vacuum should be 15-22 inches at idle.
2: Spray carburetor cleaner around suspected vacuum leak area. If engine surges, you've found the vacuum leak. If engine operation does not change, keep searching.
When an engine runs rough,...
When an engine runs rough, check with a manifold vacuum gauge. At idle, your engine should make 15-22 inches of vacuum. If it is low or fluctuates in rhythm with engine exhaust pulses, you may have a vacuum leak or more serious mechanical problem.
Vacuum leaks at carburetor base and spacer are typically due to warpage or defective gaskets. Check surfaces with a straight edge. A machine shop can mill these surfaces to get them true.
4: Flaws in carburetor castings can cause vacuum leaks.
5: Throttle shaft vacuum leak - worn shaft and bushings.
Vacuum leaks happen where...
Vacuum leaks happen where we least expect them. This is a hot idle compensator used in some applications. It's a bimetallic strip and valve that creates a controlled vacuum leak and faster idle when the engine gets hot. If the rubber valve deteriorates, it can create an unwanted vacuum leak. Pony Carburetors can help with a replacement.
Vacuum leak at automatic choke.
7: Manifold gasket leakage. If underneath, engine oil is drawn into intake ports, which will cause blue or white exhaust smoke. This typically happens with engine rebuilds where heads and block decks have been milled, which creates manifold vacuum leaks.
8: A faulty PCV (or hose) valve can cause an irregular vacuum leak and rough operation.
The positive crankcase ventilation...
The positive crankcase ventilation (PCV) valve is a controlled vacuum leak where crankcase vapors are drawn into the intake and burned again for cleaner emissions. Although PCV valves virtually never fail, they can get dirty and stick. When they stick open from carbon deposits, you will get a rough idle.
Ruptured vacuum modulator at transmission (C4, C6, and FMX). Not only causes a vacuum leak, but fluid loss from the transmission because fluid is drawn into the engine intake and burned, also causing smoke from the exhaust.
- Idle Speed set too low.
- Vacuum leak (see previous).
- Ignition point or PerTronix Ignitor gap improperly set.
- Distributor breaker plate ground wire not installed.
- Ignition timing too late.
- Sticking float or float level set too high (flooding).
- Valve adjustment too tight.
- Vapor lock (hot weather).
- Frozen fuel line.
- Excessive water in fuel or other form of fuel contamination.
- Old fuel that's been sitting (will smell like varnish).
- Faulty spark plugs or spark plug fouling.
- Ignition wire insulation breakdown and crossfire.
- Weak battery.
- Improper ignition point gap.
- Weak distributor ground (check breaker point ground strap).
- Faulty ignition coil.
- Cracked distributor cap or rotor.
- Poor distributor rotor continuity.
- Wet ignition system.
- Intermittent short in primary or secondary ignition wiring.
- Blown head gasket between cylinders (do a compression check).
- Fuel mixture extremely lean.
Poor Performance Under Acceleration
A misfire is typically an...
A misfire is typically an ignition problem. Marvin McAfee of MCE Engines in Los Angeles stresses never to install anything right out of the box without testing. Here, Marvin checks a suspected ignition harness for poor continuity with a digital ohmmeter.
- Ignition timing too far advanced (pinging/pre-ignition).
- Ignition timing too late (runs like a slug and exhaust is loud).
- Improper centrifugal advance curve.
- Aggressive vacuum advance curve.
- Point bounce.
- Faulty ignition coil.
- Defective ignition wires.
- Throttle linkage improperly adjusted (not opening all the way).
- Secondaries not opening on four-barrel carburetor.
Smoke From Tailpipe
- Under acceleration, mixture too rich or excessive piston ring wear.
- When first started, excessively worn valve guides and/or valve seals.
- Steady smoke at idle means excessive piston to cylinder wall clearance and worn piston rings.
- Black Smoke: Rich fuel mixture.
- White Smoke: Engine oil or automatic transmission fluid via ruptured vacuum modulator diaphragm.
- Blue Smoke: Engine oil.
Spark Knock (Pinging, Detonation)
- Ignition timing too far advanced.
- Anything beyond 36-38 degrees BTDC total timing will do engine damage under hard acceleration.
- Fuel fixture too lean.
- Fuel octane rating too low for compression ratio.
- Hot spots in combustion chambers (carbon, sharp edges, spark plug heat range is too high).
Flat Spot or Hesitation
- Faulty carburetor accelerator pump or pump adjustment
- Fuel quality poor (low volatility from poor refinement or age)
- Hot fuel due to hot weather
- Late ignition timing
At highway speeds, the flow...
At highway speeds, the flow of coolant into the radiator tends to create negative pressure in the engine's water jackets, which makes this hose collapse. Overheating on the interstate and don't know why? Check the lower radiator hose.
- Stuck thermostat (a misconception; thermostats don't stick, they fail to open).
- Clogged water pump due to corrosion and/or debris.
- Clogged radiator or insufficient radiator capacity.
- Blown cylinder head gasket into water jacket.
- Collapsed lower radiator hose (only if overheating happens on the highway).
- Blocked water jackets (freeze plugs, iron particles, and other debris).
- Wrong pulley sizes, causing water pump to run too fast.
- Thermostat has been removed (engine will overheat in traffic only).
- Fan belt slippage.
- Wrong water pump for application, such as reverse rotation from a late-model 5.0.
Low Oil Pressure
- Excessive bearing clearances.
- Oil pump pressure relief valve stuck.
- Oil pump pick-up loose or bad gasket.
- Clogged oil pump pick-up.
- Oil galley plug loose or missing inside the engine.
- Loose lifter bore clearances.
Battery Won't Stay Charged
Baffled by overheating problems...
Baffled by overheating problems and think removing your thermostat will solve the problem? Don't kid yourself. The thermostat is there to regulate coolant flow and allow coolant to transfer heat to the atmosphere in your radiator. Remove the thermostat and expect a boil over in traffic.
- Alternator or generator not charging.
- Voltage regulator contacts open or open circuit inside regulator.
- Battery cells shorted out (known as dead cells; one dead cell causes a weak battery that runs down quickly)
- Belt slippage.
- Incorrect pulley size in front dress.
- Poor electrical connections at alternator, generator, or voltage regulator.
- Failed alternator diode(s).
Headlights/Taillights Inoperative or Cycle Off and On
- Defective headlight switch circuit breaker or short circuit.
- Short circuit can be anywhere between headlight switch and exterior lights.
- Heads-up: old headlight switches suffer from bad circuit breakers.
Turn Signals Won't Operate
Always use a 7-pound minimum...
Always use a 7-pound minimum radiator cap. And despite what your father told you ages ago, you can use a 16-pound cap on your classic Mustang. The higher your cooling system pressure, the less chance of a boil over.
- Defective turn signal switch.
- Blown fuse or other reason for no power to switch.
- Defective flasher.
- Bulbs burned out at parking or tail lamp.
Taillights/Parking Lights Keep Blowing Fuses
- Short circuit to ground anywhere between dashboard and lights.
- Short at socket.
- Internal short inside bulb.
Electric Clock Inoperative
- Clock rewind contact points pitted or burned.
- Clock main spring broken (cannot rewind).
- Fuse blown.
Parking Brake Will Not Hold
Taillight shorts aren't always...
Taillight shorts aren't always wiring, but can be caused by the bulbs themselves, which can short out internally.
- Cable adjustment required.
- Rear brake shoes excessively worn.
- Rear brake drums glazed.
- Rear brake shoe struts/springs require inspection.
Brakes Pull To One Side
- Improper adjustment (too tight on one side, drum brakes only).
- Stuck disc brake caliper piston.
- Improper proportioning valve adjustment (rear brakes will tend to come on first).
Pulsing Brake Pedal
- Warped brake drums or rotors.
- Damaged or excessively worn disc brake pads.
This is the instrument voltage...
This is the instrument voltage limiter, which regulates 12 volts down to 5-volts for proper instrument function. When fuel, temp, and oil pressure needles max out or the gauges stop functioning, the voltage limiter is usually the culprit.
- Worn-out clutch pilot bearing.
- Bent transmission input shaft.
- Bad input shaft bearing.
- Clutch disc contamination (oil, grease, debris).
- Clutch linkage binding.
- Clutch fork adjustment.
- Worn pressure plate or clutch disc.
- Contaminated clutch disc.
- Clutch adjusted too tight.
- Clutch disc installed backwards.
Manual Transmission Jumps Out Of Gear
- Maladjusted shifter linkage.
- Worn-out clutch pilot bushing.
- Defective detent mechanism (keeps transmission in specific gears)
- Worn synchronizers
Manual Transmission Noise In Forward Gears
- Lubricant may be low.
- Main and/or counter shaft bearings worn or damaged.
- Synchronizers worn or damaged.
Clutch Pedal Rattles and Pulses
The biggest power steering...
The biggest power steering leak culprit is damaged fitting mating surfaces. Even the smallest nick will cause a leak no matter how tight you get it. Check double flares at all line fittings. Even minute irregularities will cause a leak. Remember, your power steering pump makes 1,800 psi of hydraulic pressure.
- Out of balance clutch/flywheel.
- Release bearing adjustment too tight.
- Bent transmission input shaft.
- Worn or damaged clutch pilot bushing.
Automatic Transmission Slips
- Control pressure low due to defective front pump or damaged seals.
- Low fluid level (slips worse in turns).
- Extremely dirty or burned fluid.
- Clogged transmission filter.
- Sticking valve body pistons.
- Worn servo bands, clutches, or clutch piston seals.
- Defective or improperly adjusted vacuum modulator.
Automatic Transmission Slow To Engage (Any Gear)
- Low control pressure.
- Low fluid level.
- Clogged transmission filter.
- Extremely dirty or burned fluid.
- Leaking clutch piston seals and/or servo piston seals (rebuild necessary)
- Faulty torque converter.
Rear Axle Noise In Forward Gear
- Lubrication low.
- Improper viscosity.
- Excessive ring/pinion backlash.
- Pinion bearings worn or damaged.
- Loose fasteners.
- Rear axle bearings worn out.
Rear Axle Noise While Coasting
- Ring and pinion backlash too tight.
- Excessive pinion bearing wear.
Rear Axle Noise In Turns
- Differential side gears excessively worn or damaged.
- Differential side or pinion gears binding.
Steering Feels Tight
- Steering gear backlash too tight.
- Improper steering gear lubricant.
- Excessive caster (alignment).
- Steering linkage damaged.
- Ball joints binding or seized.
Steering Feels Loose
- Steering gear backlash loose.
- Excessive ball joint play.
- Excessive idler/Pitman arm play.
- Excessive tie-rod end play.
- Wheel bearings not adjusted.
- Excessive toe-in.
- Worn control arm bushings.
Intermittent Instrument Operation
- Instrument voltage limiter (voltage regulator) defective if all instruments involved (except ammeter).
- If problem exists with one instrument only, check sending unit.
- Binding speedometer cable.
- Speedometer head worn out.
- Damaged speedometer drive gear.
Power Steering Leaks
- Check hose integrity.
- Make sure fittings are tight.
- If fittings are tight, check fitting mating surfaces for nicks.
- Inspect control valve for leaks around Pitman arm and ball valve.
- Driveshaft out of balance.
- Driveshaft run out excessive (bent shaft).
- Universal joints worn or defective.
- Excessive slip yoke wear.
- Differential pinion yoke excessively worn or distorted.