Warm start problems... but wierd o.0

Starter heat soak is a very common problem. A very real possiblility that your starter is just getting weak. Also wouldnt hurt to check over all your grounds very closely

No Crank checklist for 5.0 Mustangs

Revised 05-Oct-2010 to update Fluke references.

No crank. slow 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 unstick 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://assets.fluke.com/appnotes/automotive/beatbook.pdf 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.


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.

you might also want to try this as well.. scroll through the 1st few bits, its from a responce I gave to another member with a starter problem.



An often overlooked cause of these kinds of problems is excessive resistance.Loose, corroded or damaged battery cables or ground straps can choke off the normal flow of current. Testing the battery is always a good idea but also the connection may read good because all you're measuring is continuity -- not the ability to handle a high amp current load. The connection may pass a small current, but when a heavy load is applied there may not be enough contact to pass the extra current.


you are going to have to perform a voltage drop test has another step before sinking money into a starter. A voltage drop test is the only effective way to find excessive resistance in high amp circuits and it not hard to do ( but you need a DVM)

1st thing even though the battery is new means nothing, check the state of teh battery. To get the starter spinning at normal speed the battery needs to be at 75% state fo charge (12.4 volts or higher idle) anything lower battery is no good for starting.

The test.. important make sure to disable the engine so it will not start just crank ie pull the fuel pump relay, etc) and only crank for short duration

set the DVM to the 20 volt scale and connect the + postive lead to the + postive side of the battery and the negative lead to the negative side, crank the motor and record the reading you see on the meter.

Next, connect your meter positive + lead to the battery terminal stud on the starter, and the meter negative lead to the starter housing. crank the motor and record the reading from the meter. Compare the two voltage readings. If both are the same, there are no excessive voltage drops on the positive feed side.If available voltage at the starter is not within one (1) volt of battery voltage, there is excessive voltage drop in the circuit.


next is testing for voltage drop on the + postive side of teh starter circuit..

Set DVM on 2 volt scale.Connect meter positive + lead to positive + battery post, and the meter negative lead to the battery terminal stud on the starter. While cranking the engine, record the voltage reading on the DVM.The maximum allowable voltage drop including the solenoid in the starter circuit should be 0.6 volts or less.If you find more than a 0.6 volt drop in the starter circuit, you can isolate the bad connection by using the following voltage drop tests.

Check the positive battery post and cable connection by measuring the voltage drop between the two while cranking the engine. Connect the meter positive lead to the battery post and the meter negative lead to the cable clamp. A good post/cable connection should have zero voltage drop.

Check the positive battery cable by measuring the voltage drop end to end while cranking the engine. Connect the meter positive lead to the clamp on the positive battery cable, and the meter negative lead to the end of the cable at the starter. Crank the engine and note the voltage reading. A good cable should have a voltage drop of 0.2 volts or less.
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To check the starter solenoid or relay connections, connect the meter positive lead to positive battery terminal on the solenoid or relay, and the meter negative lead to the starter motor terminal. Crank the engine and note the reading. A good connection should have a voltage drop of 0.2 volts or less.

Next, you need to check the negative side of the starter circuit....
To check the entire circuit, connect the meter positive lead to a clean spot on the starter motor case and the meter negative lead to the negative battery post. Crank the engine and note the reading. The voltage drop on the negative side should be 0.3 volts or less.

If the voltage drop is too high, set your DVM to the 2 volt scale and start checking each connection on the negative side to find the bad connection or cable. Use the DVM leads to check across each connection while cranking the engine as before.

Check the negative battery post/ground cable connection (should be zero voltage drop).

Check the negative ground cable from the battery to the engine (should be 0.2 volts or less).

Check between the negative battery post and starter housing (should be 0.3 volts or less).

Check between the engine block and starter housing (should be 0.10 volts or less).


if all the cables, wiring, etc check out and you are still eating starters from heat soak if you don't have one might also be a good idea to switch over to a mini starter. I had huge heat soak issues with the fat OEM starter and went to a mini, very easy. I then had a hard start issue about 2yrs later and had to do the drop down test to find a bad cable. The tests are very good for finding issues but also in the end it just may be the starters them selves.

hope this helps