The '86-'95 Mustang's in-tank electric fuel pump is easy to take for granted because it's something you never see or hear. It's good for at least 100,000 to 150,000 miles in normal use if you're running good fuel and perform regular preventative maintenance. If you drive your Mustang hard, fuel pressure and volume become even more important because one thing engines hate more than anything is a lean fuel mixture.
Late-model aftermarket Mustang electric fuel pumps come in 110, 155, 190, and 255 liters per hour capacities. The stock pump produced approximately 88 lph. If you've stepped up to more power, you need more pump. Which pump you choose depends on engine power. You don't want to come up short because engines don't like lean mixtures. Fuel starvation is the fastest way to a lean mixture and certain destruction at wide-open throttle. If your 5.0 is producing over 500 hp, plan for not only a high-capacity in-tank pump but also an auxiliary pump between the tank and engine.
Electric fuel pumps for Sequential Electronic Fuel Injection produce somewhere around 70 psi. Because you don't want that much fuel pressure, a return flow pressure regulator is installed between the fuel rail and return line. Pressure is regulated via the fuel pressure regulator, which gets its signal from intake manifold vacuum. This regulates fuel pressure to roughly 35-45 psi. If you've got too much fuel pressure, suspect the regulator. If you have too little, suspect the fuel pump.
Mustang fuel injection is a pressure/return system from '86-'97. From '98-'04, it's a non-return system with a different pump configuration. We will cover that system in a future issue.
What Kind of Pump Do I Need?
There are four basic types of electric fuel pumps available for '86-'04 Mustangs, ranging in price from $99.95 for the 110-lph unit to $129.99 for 255 lph. Mild street applications call for the No. 1526 110-lph pump. Capacity must increase as your appetite for power goes up. You must also have an appropriate sized fuel line for the capacity needed. Here's what's available: