hot starting when hot help 91 mustang


New Member
Dec 15, 2022
Hi everyone I have a 91 mustang hot start problem when running after 20 minutes the battery is new but it’s not a big one? I would like a bigger one like a ?group 65 battery with more cranking amps .

it’s been a very big headache for me any help or tips to try I would greatly appreciate it . The car has the battery relocated New 2 gauge wire to factory locations up front . then from the solenoid I did a 4 gauge wire to starter. With a new a 14gauge? Signal wire.

This what’s all New new on it ? Starter distributor coil plugs wires
Map sensor
headers that are warped. Long tube
Tin diy heat Shield. Heat warped the starter wires too
I added 2 ground wires in the back
New alternator 3G set up
Tps sensor set
Timing at 10

I did the volunteer drop down test and got a
With coil off got 9.63 volts off the battery

But it seems like it starts gd cold no problem so its ? My wires to the back of car 2 gauge then to 4 gauge to the starter and alternator?
It’s something electrical?

But I’m at not sure what test to do ? Next or what video to watch for more help ? Was even thinking? A relay ?
Please help me or give ideas and information on what I should do .thanks guys and girls..
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
polk county florida
This is a hard one because there are a lot of variables. Condition of cables, battery condition, ground locations.
Best I could advise would be a voltage drop test starting at the battery, just a thought, next time the hot start problems occur feel the cables starting at the battery up to the starter, this may give you a hint.


That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
Just to be clear, when hot, the starter is struggling to crank the engine over?

Or does the starter easily turn the motor, but it just won't fire?
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Founding Member
Oct 28, 2001
Jenks, OK
Search voltage drop test on YouTube. Once you have confirmed the cables are good then this thread may be of some help.



Active Member
Dec 17, 2021
Check to see if your 22kohm resistor at pin #4 is still good by doing a ohms check between pin #4 on the ECU plug and Pin #2 on the TFI plug....


Another thing I would do is clean up the grounds for the ECU thats bolted to the unibody and change the ground wire between the battery and the engine block.

Sometimes the wires in the tfi plug lose connection and theres one wire on the TFI called the "Start Signal In" wire thats responsible for retarding timing while the engine is cranking..........

When the key is turned the "start signal in" wire at the TFI plug should show between 10.5 and 12.7volts