Fuel Pressure Gauge Upgrade

Basic law of hot-rodding: the more you choose to modify, the more you have to modify. Build a 400-horse EFI 302 and you're going to need to update the five-speed, the radiator, the clutch, the diff, (perhaps the axles), motor mounts, fuel, ignition, computer mapping, hoses, etc. What else? Surely we've forgotten something. Okay, you'll need a fuel pressure gauge.

Fulmination Fix
This much-flogged Mustang sports a wicked new EFI 302 that had begun coughing back into the manifold. Fuel demands change with a new engine and, in most cases, you're starting from an educated guess. Break the engine in a little fat, start fiddling with pressure when there's 1000 or so miles on it, read plugs and listen for bad sounds. Tricks aside, though, it's good to have an idea where the pressure's at—EFI Fords have a particular range in which they're happy (38-46 psi @ WOT)—and within that there are a lot of variables to be concerned with. You need to know. With a backfire in the manifold, we had to be wrong on fuel.


Ford's sold a billion small-blocks, and the EFI variant is common. Fortunately, most of them were manufactured with a smart nipple on the OEM fuel rail that makes installing a standoff fuel pressure gauge simple. The factory rails are good for 400 hp on a small-block (the pump is the weak link, then the regulator, the lines under the car, and finally the factory rails) so you don't have to yank them if you're keeping things reasonable. Unfortunately, Ford chose to manufacture the fuel-T nipple with a strange 100-year old Saginaw machine thread that would have died an ignoble death had it not been on all those Fords.


A fuel pressure gauge is in direct contact with fuel. There's gas coming off the rail through the braided steel line attached to the back of the gauge, and you can't be routing raw 93-octane into the passenger compartment. Wouldn't be safe, or legal. Therefore, the gauge lives in the engine compartment, which isn't much of a problem as that's where you are while you tune. You've seen the FPG mounted on the cowling of some cars, above the hood and in front of the windshield, and you can buy isolator kits, which use a hydraulic link from the engine compartment to the cockpit that mirrors fuel pressure with a diaphragm, but both of these add complexity. Monitoring fuel pressure from the engine bay is fine. Why complicate?

Parts Improvisation
It's likely we're going to have some or all of what's necessary for little bolt-on jobs already in the garage. True to form, there was a lighted AutoMeter mechanical fuel pressure gauge in a box of 5.0 parts, and a length of braided stainless steel hose just perfect for fuel-pressure duties crawled out of some WRX parts (complete with standard 1/8th female fittings). We would fabricate a bracket out of some scrap steel, fasten things with pop rivets or bolts, and a trip to the parts store down the hill produced what we thought would be the correct unions. Correct, except for the weird little Saginaw-threaded OEM fuel rail "T" that none of the parts guys had EVER seen.