98 mustang gt wont start when warmed up

On a 98 this can be a number of things but the most common one will be one of heat.

When integrated components get hot they expand, when they get old they can expand enough for one of the electrical connections to break connection and cause your car to 'not start'.

This is a likely problem for your car. If your control module is mounted on the side of your distributor you can unplug it, and using the the special little 7/32" removal tool, sold at most parts retailers for under $10, you can un-plug the unit and take it down to your local parts house and have it checked.

Of course if you have a circuit tester available you can check it yourself for any high resistance levels. This would be a sure sign that yours is bad.

If yours checks bad, buy a new one and install it in the reverse order that you took it off.

However, if it checks good, you may want to call a wrecker and have it towed to a shop for some TLC.

Good Luck!

How are you warming it up if the car don't start? There can be a million different reasons why your car isn't starting.

Another reason could be coil packs, tps "Throttle Position Sensor" even your fuel pump which can be checked at some auto stores, they hook up a psi gage to your fuel rail. if you can get it to run it should be at about 67 to 85 psi it it shows 35 psi or sowe your fuel pump or o-rings are bad. this its self will be around $140.00 for the pump and about $200.00 to install. but it could be in the ign. switch. there are a lot of reasons most likely you need to get a mec. to look at it,,,sorry