Testing fuel pressure on a 7.3 Super Duty.
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    56FordGuy's Avatar
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    Testing fuel pressure on a 7.3 Super Duty.

    I've been chasing a couple of small issues on my 2001 F-350, and put together a kit to test the fuel pressure. I know we have a few other 7.3 owners here, so I figured I would share the process. You can buy fuel pressure test kits for these trucks, but the ones I found were over $100 and you can assemble one yourself for less than half of that.

    Low fuel pressure can cause a number of issues, including low power and early injector failure. If your fuel pressure is less than roughly 35 PSI under load, the injectors do not receive adequate lubrication and can develop issues. Likewise, if pressure into the injectors is too low, you won't be delivering as much fuel into the combustion chamber as you should and the truck will feel weak. Ideally you want to be within 10 PSI of 60 at idle. Anywhere from 50-70 PSI at idle is pretty normal. Under load, which is accelerating, wide open throttle, etc you should see at least 35. If it's low there can be a few different causes, but for now we'll just focus on testing it. The process is the same for the 94-97 PowerStroke trucks, but the fuel bowl fittings will be different. There are a lot of different fitting/ hose combinations that can be used to do what we're doing, this is just what I did for a temporary test setup.

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    The fitting that threads into the Super Duty bowl is a #4 O-ring boss. I used a #4 o-ring to #4 JIC adapter, followed by a 90* JIC elbow into a JIC hose barb. I ran 48" of diesel rated fuel line to a 1/8" NPT hose barb, which was threaded onto a 0-100 PSI liquid filled gauge temporarily attached (aka, zip tied ) to the cowl. The fuel system is fairly low pressure at this point, so barb fittings and hose clamps will work. Some folks have installed fuel pressure gauges in the cab as a permanent fixture, but with my stock truck that's unnecessary. If I were doing a permanent install, I would mount the gauge where I wanted it in the cab, then measure and have a custom hose made with crimped ends to go from #4 o-ring to whatever fitting was on the gauge I used. Regardless of how you go from fuel bowl to gauge, this is the basic process.

    First, the fuel bowl. This is where your fuel filter is. It might have a stupid black, plastic cover over it with a little hinged lid. Take that dumb thing off and put it on a shelf, all it ever does is get in the way. You should see the fuel filter bowl in the center of the valley, behind the HPOP.

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    On the back (firewall side) left of the fuel filter bowl is a yellow lever to drain the bowl. Flip it backwards and drain the bowl. On the back right (driver's side) of the bowl is a plug.

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    Remove that plug. It takes a 3/16" allen wrench.

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    Install your o-ring fitting here.

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    From your o-ring fitting, attach the rest of your hose/ adapters. Don't use thread sealant on o-ring or JIC fittings, do use it on NPT fittings.

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    Check for leaks before you close the hood. Make sure the fuel bowl drain is closed, then turn the key on and let the fuel pump run. The pump will shut off in about 30 seconds, and you may have to turn the key off and back on for the bowl to completely refill and pressure to show on the gauge or a leak in your new system to start. Once pressure shows on the gauge, you can start the truck.

    I ran my gauge over and attached it to the cowl beside the windshield wiper. If you do this, make sure the wiper doesn't hit the gauge if it starts raining.

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    And you're done! My truck is holding a steady 70 PSI at idle which is in the right range, tomorrow I should have the horse trailer hooked up and see what it does under a load.
    Last edited by 56FordGuy; 12-14-2013 at 09:53 PM.
    -Blake

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    Good writeup.

    One item of caution, anything over 70 psi is known to cause injector issues.
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    56FordGuy's Avatar
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    Quote Originally Posted by psrumors View Post
    Good writeup.

    One item of caution, anything over 70 psi is known to cause injector issues.
    I was 10 PSI off in my post. Good catch!
    -Blake

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    On my OBS powerstroke I built a electric fuel system with adjustable fuel pressure regulator. It is amazing how these engine have a sweet spot for fuel pressure. Mine sits right at 64 psi and the engine engine responds beautifully. Any higher or lower and it just isn't the same.
    1025r TLB w 60D MMM & Independent Lift
    SN 114287 Built April '13 received 8/21/13
    180 degree thermostat
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    Artillian Forks (42")
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    Hey, I want a title too! ZachinCO's Avatar
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    Hey Blake,
    Are you still running the gauge on this? Still to the outside?

    Did you ever think of running it in the cab or was the thought of a fuel leak what made you mount it outside?
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    56FordGuy's Avatar
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    I'm not. Mine was just a temporary troubleshooting setup, not a permanent install.
    pcabe5 and Drifterbike like this.
    -Blake

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    Quote Originally Posted by ZachinCO View Post
    Hey Blake,
    Are you still running the gauge on this? Still to the outside?

    Did you ever think of running it in the cab or was the thought of a fuel leak what made you mount it outside?
    For inside the cab monitoring you would want to use an electric gauge or one with an isolator. You do not want to introduce fuel into the cab.
    pcabe5 and Drifterbike like this.
    1025r TLB w 60D MMM & Independent Lift
    SN 114287 Built April '13 received 8/21/13
    180 degree thermostat
    Omni Transformer w/ integrated weight bracket
    Single Point
    Ken's Bolt on hooks
    Artillian Forks (42")
    Full Compliment of Wheel Weights (340lbs)
    Custom Seat Springs

    Kubota 326H 72" deck ZTR

    Stihl MS361, FS250R

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    What kind of issues are you having with the truck?
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    Knuckles's Avatar
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    Interesting , all though I've never once needed to test fuel pressure on a 7.3 , usually the LPOP or HPOP systems cause most of the headaches I see aside from electrical


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    56FordGuy's Avatar
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    Quote Originally Posted by Jeff B View Post
    What kind of issues are you having with the truck?
    Well, it's been a few years so the list is a little longer now. The rear axle has an intermittent, unexplainable pinion seal leak. The vent is clear, the seal has been replaced twice and the yoke has had a repair sleeve put on it. There is no discernible set of circumstances that cause the leak, it can leak after 5 miles or it may go 500 perfectly dry. U joints in both front and rear driveshafts are new as well.

    The transmission synchros are worn, downshifting is a bit tricky. When you let off the throttle, especially going downhill there's a loud growling that I believe is either clutch or pilot bearing related. The front axle steering u joints are binding, and will intermittently cause the steering to pull in one direction or the other.

    The biggest issue I believe is fuel related and I suspect injector cups. The truck has very low power, single digit fuel mileage and smokes light a freight train under light loads. I don't even try it with heavy loads anymore. Intake is in excellent shape, fuel delivery to the rails is good, exhaust is good on both sides of the turbo with new up pipes and gaskets, manifold gaskets, etc.

    My patience with this truck has been exhausted. I'm done fixing it. I've been working on it literally from less than an hour after I bought it. Didn't even make it out of the town where the dealer was before I had to stop and fix the wipers. It's been one thing after another and I'm done. Been towed twice, left me on the side of the road 4-5 times that I was able to fix and have had numerous other issues that would have left me stranded if I hadn't caught them in time. Once I get the white truck ironed out in the spring, the F-350 will either be sold or maybe traded in on a Subaru to replace our Baja. I like the Crosstrek, I'm partial to the burnt orange color but the better half can't stand it. We're both okay with the desert tan though, so maybe that.

    If anyone wants a 7.3 F-350, call me around June. I can set you up.
    -Blake

    Your mileage may vary.

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