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The Fuel Rail Banjo-Bolt Fuel Pressure Gauge Mod

Since TRD came out with their supercharger for the Tacoma, there has been quite a furor over whether the stock fuel system supplied enough gas to prevent detonation. The consensus opinion now is that the stock fuel system is on the weak side, and that it's a good idea to do some upgrades and monitor your fuel pressure at the fuel rail. Here's how to do it.

There are several ways to mount the sender for the Autometer electronic fuel pressure gauge sender.



One way involves removing the supercharger (assuming you're so equipped) and replacing the stock fuel line with length of custom-made steel braided hose. I invented a different approach for three reasons. One, I didn't want to have to go through the hassle of taking off the supercharger. Two, I didn't want to have to order custom parts because I wasn't sure everything would work out correctly and there's nothing worse than a two hour job turning into a two-day job while you try to track down the correct parts. And three, due to the fact that the fuel pressure regulator cuts back the fuel pressure to whatever it is "supposed" to be, I believe that getting a fuel pressure reading after the fuel pressure regulator is a better solution than reading before the fuel pressure regulator.

If the gauge is showing low pressure at redline, you know that for whatever reason your fuel delivery system is not up to the task. I figured that mounting the gauge sender on the fuel rail would give the most accurate reading, and that is what I did. In the picture below you can see the fuel injector rail. It's running vertically through the center of the picture.



This is a side view of the fuel rail. It's still centered, but running horizontally. I originally ordered from Toyota the dual-banjo-nut assembly that connects the two fuel rails together, but when I took it to a machine shop to have a 1/8" NPT fitting attached, I was told that there was not enough straight section of the connecting pipe to work with. That's when I got the idea for the banjo bolt itself. You can see the head of the bolt below as it goes into the fuel injector rail.





There are two parts you need to order from Toyota, plus a 90-degree elbow of the appropriate size. First, the Toyota parts. You'll need a new banjo bolt, part number 90401-12036. Don't take your original one off unless you have alternate transportation, as the truck could be out of commission for a few days. A new one costs about six bucks.




And it looks like this:



You'll also need new gaskets for the fuel rail where the banjo bolt and nut connects. These part part number 90430-12026. I think they were three bucks.



Finally, here is a picture of the appropriate 90 degree elbow. It's a male to female 1/8" NPT elbow. Make sure you get one that's one-piece, not a cobbled-together two-piece design like they sell at NAPA. The NAPA part is too big and too darn expensive (4 bucks versus 99 cents). You only have 1.13 inches of clearance between the end of the banjo bolt and the timing belt cover so unless you want to make more work for yourself, take a tape measure to the hardware store and measure the overall length of the elbow you find. It should be one inch or less. The one I finally found was .83 inches and it worked perfectly.



This is how to make a six-dollar bolt into a thirty-six dollar bolt. Take the banjo bolt to a decent machine shop and tell them that you want a 1/8" NPT threaded-hole machined into the end of it. My local shop told me they have a 60-dollar minimum (!) but they agreed to do it for half that (hooray). This is how it should look when finished. (before installation, be sure to check that there are no metal shavings tied up in the threads or you could have some interesting fuel-injector experiences.)

Now, you could certainly drill out the bolt yourself and thread it with a tapping set, but then you run the risk of not getting it quite right and going back to square 1.





Move your spark plug wires to the side and saw a piece out of the timing belt cover for the fuel pressure gauge sender to sit up through. The remove the stock bolt and screw in your modified bolt. Don't worry about fuel leaking from the rail, it's not much and a rag under the bolt should soak it all up. Then tape the end of the elbow with teflon tape (it does not degrade in gasoline) and screw it in. Tape the end of the fuel pressure sender and screw that into the upright end of the 90-degree elbow. Here's how it should look:



This is a zoomed-out picture of the end of the sender poking up through the spark plug wires:



Clip on the wire harness:



And if you want to be really cool, drill a hole and route the wire through the spark plug wire loom:



I mounted the box on the top of the firewall, since it's supposed to stay out of sand and water. (follow the red wire). Toyota was nice enough to leave an unused, threaded hole in the firewall so it's only necessary to drill one additional hole.



I understand that the new fuel pressure gauges don't use this box, so maye this will save you a step. But if you have the old style:

I ziptied the wires the along the way and sealed the heck out of the control box with silicone caulk after all the connections were made. It's been working perfectly ever since.



Now just run wires to the gauge inside the truck and you're done. Fire your truck up and be sure to check for fuel leaks.

I invented this mod before I added a larger fuel pump, and it was gratifying to see the needle slamming back and forth as the system leaned out..even though good ol' TRD said the stock fuel pump flowed plenty of gas.

If you need additional space to mount gauges, I do custom dash gauge mounts for TTORA members as seen here. If you're interested in a similar setup or want to have this type of sender installed on your truck, you can reach me at sam@samsonfab.com .