You’ve got questions. We’ve got answers—the Summit Racing tech department tackles your automotive-related conundrums. This week in our Mailbag, we’re tracking down the cause of hard starting and gasoline odor.

Q: I have a third-gen Firebird with a 305 TPI engine. I installed a Hypertech Thermomaster computer chip and thermostat, plus an MSD ignition box.

My problem is very hard starting and a constant strong gasoline odor. I haven’t found any fuel system leaks, and I traced the gas odor to the fuel filler cap. After I shut the engine off, I can hear pressure leaking out of the cap. If the car sits for about 10 minutes, it takes about three tries to get it started again.

When I turn the ignition key to the first position, the fuel pump kicks on and fuel pressure is at 41 psi. When I pinch the fuel pump inlet line, pressure goes up to 42 psi; when I release the line, pressure drops back to 39 psi.

When I start the engine, fuel pressure is 38 psi. When I pinch the fuel pump outlet line, the pressure shoots way up, then drops to 34 psi when I release the line. After letting the car run a minute, the pressure evens out at 36 psi. When I shut the engine off, the pressure comes up to 40 psi, then goes down about one psi a minute until it settles at around 20 psi.

Is this loss of fuel pressure after shutoff normal? Could the computer chip or MSD box be causing the problem? Could you tell me why fuel is backing up and out of the fuel tank?

J.S. Doylestown, PA
Pontiac Firebird, Gen 3

A: Actually, we think the problem could be centered on fuel pressure being bled off at the fuel rails. This is most likely due to a leaking fuel injector. If an injector is leaking when you shut the engine off, the pressurized fuel in the rail would bleed through the injector and into the cylinder. When the engine is semi-warm, those leaking fuel droplets can create a lot of fuel vapors which can ultimately flood the engine. That can make the car hard to restart and can cause that strong gas smell.

We’d also check for a bad fuel pressure regulator valve or fuel pump, but we really think the problem is with one of your injectors.