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DIY (Do-It-Yourself) Guides For all DIYs.


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Old 08-30-2017, 01:59 AM   #1
armstrom
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DIY fuel pressure gauge install

I recently needed to check my fuel pressure while trying to diagnose a problem. Our fuel system does not provide an easy place to install a fuel pressure gauge so I put this together.

Standard disclaimer
Do this at your own risk. Opening/modifying the fuel system is risky business. Make sure your engine is cold and that you have a suitable fire extinguisher handy. Don't blame me if you burn your car to the ground!

Tools
  • 5/16" fuel line disconnect tool (I use this one)
  • 5/32" allen key
  • Open Ended wrench or adjustable wrench
  • Rags to absorb any spilled fuel]
  • Eye protection (here's gas in your eye!)
  • Fire Extinguisher (I'm serious, don't skip this!)

Parts
  • 5/16" fuel line adapter with 1/8" NPT ports from Cobb or NX (One of these would work as well... but you would also need to buy a -6AN plug for the big hole so I don't think it's worth all the extra cost.)
  • Some sort of fuel pressure gauge or sensor. They pretty much ALL have 1/8" NPT fittings. Make sure you get something that reads at least 80PSI (Nominal fuel pressure is ~57 PSI) Most of the gauges you find in your local auto parts store are for carburetors and only read up to 15-16 PSI. I ended up building my own gauge using a pressure sensor, microcontroller and LCD.
  • Thread sealant. I used this but any fuel-safe sealant should work. You can even use teflon tape in a pinch but I wouldn't recommend it.

Process
  1. Prepare the adapter. Apply thread sealer and install the supplied plug into the unused 1/8" NPT port. Apply thread sealer and install your gauge/sensor in the remaining port. Keep in mind, NPT is a tapered thread so these things will NOT thread all the way in. Torque them down well. You will need a 5/32" hex key for the supplied plug, the wrench you need for your sensor/gauge will vary but an adjustable wrench will usually suffice.
  2. Depressurize fuel system (Pull F/PMP fuse, start car and wait for it to die, try to start again to confirm it can't get fuel). I actually didn't do this step but it is best practice. If your car has been sitting for a while the system will usually depressurize on its own, just make sure you have rags handy.
  3. Disconnect fuel line using 5/16" quick disconnect tool. (Remember to use those rags!) You can tap either the feed line to the HPFP (closer to front of engine) or the feed to the port injector rail (closer to back of engine). I chose the port injector rail. (See image below)
  4. Attach the fuel line adapter to the hard line first. The adapter can be a tight fit so it has to be inserted perfectly coaxial to the hard line or the metal spring-clip-thing will bind. Take it slow and don't force it.. it will go.
  5. Make sure the fitting is properly seated. It should click into place over the ridge on the line. Give it a little tug to make sure it's attached properly.
  6. Connect fuel line to the male side of the adapter. You want to do this only after you've confirmed the adapter is properly attached to the hard-line. The shape of the adapter will make it more difficult to remove the fuel hose since most of the tools are too long to clear the larger diameter body. If you decide to bail out of the install you don't want to have to fiddle around trying to remove the adapter from the flexible fuel line. Removing it from the hard-line is significantly easier.
  7. If you're installing an electronic gauge then route the wire into the cab through one of the existing grommets in the firewall. I won't cover the steps of installing an electronic gauge inside the car...
  8. Re-install the fuse removed in step 2.
  9. Turn the key to the on position but do not crank the car (keyless start: press button twice without stepping on the clutch/brake)
  10. Check for fuel leaks make sure everything is secure and to your satisfaction before you start the engine. You can also confirm your fuel pressure gauge is working at this stage.
  11. If everything checks out you can crank the engine and enjoy your new gauge

You may want to keep your fire extinguisher handy for the next little while (keep it in the car). After driving a bit re-check the fuel line and make sure there are no leaks at all. Make sure you do this immediately after turning off the engine or with the ignition on (pump running) since fuel evaporates quickly.

Like I said, I built my own gauge using a microcontroller and electrical pressure sensor. If anyone is interested in my setup I can elaborate a bit, but there are lots of options out there.

-Matt

Last edited by armstrom; 08-30-2017 at 10:04 AM.
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Old 05-21-2018, 03:18 PM   #2
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Thoughts on doing this with a mechanical gauge directly into the Cobb adapter?
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