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adding an electronic fuel pressure sensor to a ‘96 XJ
i hope this is the right place to ask…
i have a 1996 XJ and want to add an electronic fuel pressure sender to monitor the health of my fuel delivery system and have read some cautionary words about fuel rails cracking due to vibration and the extra mass of the sensor, and some other content about inserting it to the fuel line, tapping into a 5V lead from an existing sensor, etc, but have not found any write-ups/videos of anyone doing it on a ‘96… has anyone done this, or seen a good write-up on it? |
Sounds interesting.
I think I'll follow this one. |
If your '96 XJ has a returnless fuel system, I'm not sure how you'd attach a fuel pressure sensor to the rail. Are you thinking of making a hard adapter to the fuel pressure measurement port? If that is the intent, how about making a soft (hose) adapter?
No problem to tap the 5 V from another sensor. |
no return line, so was originally considering adding the sensor where the schrader valve is, but I'd read concerns about vibrations leading to cracks after adding the mass of the sensor to a component that wasn't designed for it. I've seen some other posts where people have installed a sensor on non-Jeep vehicles by cutting the hard fuel line and using compression fittings, but I'm now thinking of fabricating a simple bracket for the sensor and replacing the circled bolt that secures the fuel rail with one a bit longer so I can mount the bracket there so any vibrations will go to something more solid than the fuel rail itself and using flex tubing between the end of the hard fuel line and the fuel rail to avoid having to cut it.
https://cimg2.ibsrv.net/gimg/www.che...9a19805be7.jpg |
I think you'd have no cracking issues if you mounted an adapter to the schraeder valve, and then put a rubber hose between the adapter and the pressure sensor housing.
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i like that idea even better--so maybe a hose with 4AN ends, one end with a 90 elbow screwed on to the schrader and a 4AN to 1/8 NPT adapter at the other end for the sensor held in a cushion clamp on a bracket...
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Check the flare on that schrader, a fuel fitting should be SAE 45* instead of JIC/AN 37*.
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it seems kind of hard to find a definitive threadsize for the outside of the shrader valve on the fuel rail, but i checked with a 4AN fitting and it threaded right on... sure seems like it's larger than the normal shrader valve stem O.D. and the threads appear coarser to me...
the concern about flare mismatch is noted, but I'll give it a shot with white plumbers tape on the threads and keep an eye out for any leaks. RIFE 60 psi pressure sensor, a 2' braided steel leash (rubber coated), and a voltmeter panel gauge (that turned out to me much larger than what it looked like online) arrived this week, so hope to get it installed in coming days... |
4 JIC and 4 SAE are both 7/16-20 thread size.
Dont use thread tape on hydraulic/fuel fittings. a little loctite sealant might be acceptable but really shouldnt be needed. Theyre supposed to seal on the flare. Even if the flares are mismatched, it might seal up OK. We have had to mismatch parts in hydraulic systems before. |
i searched the web for an 1/4 SAE 45 to AN adapter and came up empty... i did find one that sold for $75 but was a) 3/8 or 3/4 and b) was out of stock...
the closest i found was SAE to NPT, but that would then require thread tape/sealant, which is what i would need since the flares of my current hardware are different... going to give your suggestion of thread sealant a try and see how it goes... |
All the fuel pressure tester kits at auto parts stores have the correct fitting. Have you rented a kit to see what the fitting is?
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i have a BETOOLL fuel pressure test kit, which includes a fitting for 7/16-20 UNF (and happens to have an o-ring and a pin to depress the shrader valve) and it doesn't leak. as i understand it, 7/16-20 UNF is the same thread size as SAE-4 and 4AN and it feels like the 4AN threads work just fine, so the only issue appears to be a mismatch of the flare angle of 8 degrees between the SAE-4 and the 4AN fitting. i wouldn't mind using a SAE-4 to 4AN adapter, but those seem non-existent in this size, so going to take 89Laredo's advice and use thread sealant instead of relying on the flare...
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Thread sealant is intended for compression threads. I wouldn't count on it being effective for straight threads, especially for a fuel system. If an appropriate adapter can't be found at a reasonable price, I would put a tee in the hardline before trying to use thread sealant on the pressure test port.
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I wasnt really advising using sealant. It COULD be used if you had to. It is applied to the male flare, not the threads. Yes the fuel pressure testers usually have a soft seat so they will seal on 45* or 37*. Have you confirmed that it is actually a 45* fitting anyway? It should be, as that was the standard on fuel and brakes for a long time, but who knows what chrysler was doing back then so it may actually be a 37*.
Even if the flare is mismatched, you could try it. We recently made a brake hose for a loader that had a 4 SAE 90* end on it, eaton doesnt make those anymore so we just made it with JIC fittings and it has held up fine so far, probly 1500 psi on it. Another option if you dont want to cut into the hard line is a SAE to NPT adaptor, and then adapt to your sensor. Use liquid sealant/dope on the NPT threads, NO thread tape. |
i ended up using Loctite 577 on the threads of the schrader valve port to attach the 4AN fitting on the end of my sensor leash.
i used the ground and power wires that used to go to the audio system as input power to a 12V to 5V/3A buck converter to supply power to the sensor. the sensor signal, power, and ground wires pass through the firewall using a grommet that fits a 5/8" hole i made with a stepper drill bit. current sensor location is above the brake booster to try to get it away from the vibration and close-proximity heat of the engine. signal and ground are then attached to a simple 5V voltmeter. turning the key primes the system and the whine from the pump drives the voltmeter up to about 4V (about 52psi) and it stays there after starting. if i leave the key in position without starting the engine, the voltage slowly decreases as the pressure bleeds out. mods:
help diagnose any rough running and to serve as reference to the existing MAP/IAT values i get from OBD2 thanks for everyone’s feedback! happy to answer any questions... some links: sensor: https://motionraceworks.com/products...8-npt-52-60psi gauge adapter: https://www.summitracing.com/parts/fra-495000bl 4AN plug: https://www.summitracing.com/parts/fra-480604-bl sensor leash:https://www.summitracing.com/parts/fra-4121224bl voltmeter: grommet: https://www.summitracing.com/parts/qcr-57-810 loctite 577: have had it installed for a few days--no seeping fuel evident at fuel rail, gauge, or plug https://cimg7.ibsrv.net/gimg/www.che...520d00c0bb.jpg no leaks with 4AN onto the schrader connection with loctite 477 https://cimg8.ibsrv.net/gimg/www.che...31540b2331.jpg no leaks with white PTFE tape (per Motion Raceworks tech support) haven't added the zip tie to secure it to the loom yet... https://cimg9.ibsrv.net/gimg/www.che...306e0785c9.jpg 4V is about 52 psi for this sensor |
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