I have a 98 Mustang GT, PI swapped heads, manifold, and comp cams.

My car is running fine under low vacuum, but when I get on it it vapor locks and does not pull. I just replaced the plugs and wires so I know that it is not misfiring. My only guess would be a vacuum line or a Fuel Filter? I checked the fuel pump and it is working properly.

Thank you all for any help.

 

The car has been running very lean too.

 

Bump.

 

What size injectors are you running?

 

24lbs I'm pretty sure.

 

Hmmm...well you say the pump is working properly...but what duty cycle is it running at? It may be working but just working too hard and can't pump enough fuel?

Is it a stock pump?

 

Vapor lock is an extremely unusual occurrence in moder EFI automobiles, incorporating in-tank fuel pumps, and higher fuel line pressures as compared to carbureted engines. I doubt very much that is what you are experiencing.

What you describe sounds more like fuel starvation from insufficient fuel pressure--have you monitored the f/p?

Do you have the return-type or returnless fuel system--as I understand 1998 was when Ford switched to the returnless system and some of each were produced for the 1998 MY.

A bad return-type FPR would create just the problem you describe...

 

Yeah it is a stock fuel pump.

 

I will be sure to check this, thank you for your help!