89 Mustang 5.0 highly modified balks when hot

[Ron Fisher]

I've just purchased an 89 Mustang from a guy who rebuilt the motor with a FRPP cam no. E303. It also has Power heads, shorty headers, low restriction exhaust, underdrive, and fuel pressure regulator. The car runs good when it's cold, but as soon as it hits a certain temp. it will balk under a load. At first I thought it was lack of fuel, but when I put in the fuel pressure regulator and adjusted it to 40psi. it didn't make a difference. And after thinking about it, if it runs good when cold, wouldn't that mean it has enough fuel? Anyway, if anyone has an idea why it won't run right, please email me. Thanks.