Running out of ideas... Hot start issue.

The only time I've had this issue was with old and or poorly connected battery cables and/or a weak battery. Any light wisps of smoke coming up from under the hood when trying to crank?

I know you said you had new battery cables, but a loose connection could cause this problem. Always good to start with the most basic solution and work backwards. Is the battery holding a full charge?

Did the old starter do the same thing?

Is it a piggyback-solenoid starter and is that style OEM to your car?

No, actually hot-cranking issues is often a starter with heat-soak issues. That wasn't a bad call.

I'd go back to the earlier thoughts about wiring connections.

How is the starter cable? When you're doing testing, I'd do a voltage drop test on the starter cable itself. If near or over 1/2 V, that's not good. Also be real sure the battery ground pathway is super clean. The stock configuration can suffer issues with galvanic corrosion.

I'd check the battery and even though it's a new cable, the resistance on the power cable next, though if it's the cable resistance, mine produced a puff of white smoke (I assume the heat melting the rubber). Experienced that twice.

My guess right now is that a short drive is draining the battery just enough to where it won't start again (not holding a full charge from the alt). Let it cool, and it's got just enough juice to go again.

I had this problem several times on my old 5.0 and it was always the battery or the cable, so I'm not going to have any other suggestions other than those two.

Good luck!

Resistance checks on high current cables aren't reliable with a common garden variety DVM or ohmmeter. There is too little resistance for the meter to read accurately. Use a voltage drop test with the circuit loaded just like it would be when it is in use. For starter wiring, this means you measure the voltage drop across connections and wiring while the starter is actually trying to crank the engine.


[ No Crank checklist for 5.0 Mustangs

Revised 09-July-2009 to reorder stuck solenoid help.

No crank and stuck starter solenoid problems have the same root causes – low battery voltage and poor connections. For that reason, they are grouped together.
Use the same initial group of tests to find the root cause of both no crank and stuck solenoid problems.

Since some of the tests will bypass the safety interlocks, make sure that the car is in neutral and the parking brake is set. Becoming a pancake isn’t part of the repair process…

1.) Will the car start if it is jumped? Then clean battery terminals and check battery for low charge and dead cells. A good battery will measure 12-13 volts at full charge with the ignition switch in the Run position but without the engine running.
A voltmeter placed across the battery terminals should show a minimum of 9.5-10 volts when the ignition switch is turned to the Start position and the starter engages or tries to engage. Less than this will result in a clicking solenoid, or slow cranking (if it cranks at all) or a starter solenoid that sticks and welds the contacts together.

Most auto parts stores will check your battery for free. It does not have to be installed in the car to have it checked; you can carry it with you to the auto parts store.

The battery posts and inside of the battery post terminals should be scraped clean with a knife or battery post cleaner tool. This little trick will fix a surprising number of no start problems.

The clamp on with 2 bolts battery terminal ends are a know problem causer. Any place you see green on a copper wire is corrosion. Corrosion gets in the clamped joint and works its way up the wire under the insulation. Corroded connections do not conduct electricity well. Avoid them like the plague...

If the starter solenoid welds the contacts, then the starter will attempt to run anytime there is power in the battery. The cables and solenoid will get very hot, and may even start smoking. The temporary fix for a welded starter solenoid is to disconnect the battery and smack the back of the solenoid housing a sharp blow with a hammer. This may cause the contacts to unstuck and work normally for a while.

A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection while trying to start the car: more than .5 volts across a connection indicates a problem.

See http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103 for help for help troubleshooting voltage drops across connections and components. .



2.) Check the battery to engine block ground down near the oil filter, and the ground behind the engine to the firewall. All grounds should be clean and shiny. Use some sandpaper to clean them up.

3.) Jump the big terminals on the starter solenoid next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.

The rest of the tech note only concerns no crank problems. If your problem was a stuck solenoid, go back to step 1.

4.) Then pull the small push on connector (small red/blue wire) off the starter solenoid (Looks like it is stuck on a screw). Then jump between the screw and the terminal that is connected to the battery. If it cranks, the relay is good and your problem is in the rest of the circuit.

5.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then you have wiring problems.

Typical start circuit...
Diagram courtesy of Tmoss & Stang&2birds



6.) Pull the starter and take it to AutoZone or Pep Boys and have them test it. Starter fails test, then replace it. If you got this far, the starter is probably bad.


Starter solenoid wiring for 86-91 Mustang



Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.


Electrical checks for the switches and starter solenoid

Remove the small red/blue wire from the starter solenoid. Use a screwdriver to bridge the connection from the battery positive connection on the starter solenoid to the small screw where the red/blue wire was connected. The starter should crank the engine. If it does not, the starter solenoid is defective.

If the starter does crank the engine, the problem is in the clutch safety circuit (5 speed) or Neutral Sense Switch (auto trans) or ignition switch.

Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.


Typical start circuit...
Diagram courtesy of Tmoss & Stang&2birds


You will need a voltmeter or test lamp for the rest of the checks. Connect one lead of the voltmeter or test lamp to ground. The other lead will connect to the item under test.
Look for 12 volts on the white/pink wire when the ignition switch is turned to the Start position. Check the ignition switch first.
No 12 volts, replace the ignition switch.

The next step will require you to push the clutch pedal to the floor (5 speed) or put the transmission in neutral (auto trans) while the ignition switch is turned to the Start position.
Good 12 volts, check the clutch safety switch (5 speed) or Neutral Sense Switch (auto trans) for good 12 volts on both sides of the switches. No 12 volts on both sides of the switch and the switches are defective or out of adjustment. Check the wiring for bad connections while you are at it.

I don't follow your drop-test analysis. How are you doing the tests?

If you have less than about 9 V while cranking, it won't turn over fast enough to catch.

If you turn the key on and jump the solenoid, it should turn over at the same speed as it does while cranking it with the key. The difference you saw was that all of the nominal systems (ignition, fuel pump, etc) were not powered up while you were jumping the solenoid (key off), and that left more power for cranking.

This really does sound like a bad battery issue or ground issue.You mentioned that the battery was 5 years old and i imagine up where you live you got a few good cold nights, might of been enough to take that battery out.

Do at least make sure you charge the battery. You noted 12.0-12.3 V, and both are very discharged.