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Unread 08-19-2014, 06:57 PM   #1
DeanLM90
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Fuel Pressure Test: between the rails?

I don't have the test port on my 5.2 liter's driver side rail and don't want to buy the fuel line disconnect tool AND the additional line attachment with the valve built in. Can I simply cut the line between driver side and passenger side in half and insert the t shaped valve that came with my pressure testing kit?

Will testing it this way somehow disrupt the functionality of the fuel delivery system?

What happens to the air that inevitably gets trapped in the fuel lines/rails? Will it all get pushed through the injectors somehow? Air in the lines would affect the peak pressure values would they not?

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Unread 08-19-2014, 07:49 PM   #2
mrgimble
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I would not cut that line from rail to rail. It is quite hard and curved and you probably would never get it sealed right. Best to do it the right way.
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Unread 08-19-2014, 08:24 PM   #3
PolkaPower
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Not to mention the metal shavings.
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Unread 08-19-2014, 08:47 PM   #4
DeanLM90
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Thanks guys you prevented a mistake I did not want to make! Hopefully I can find a rail with the test port built in at the yard. Otherwise I have to track down the "kit" to attach the test line between the rail and the main line. If I could find the right fittings somewhere I could probably make one way cheaper and quicker. Not sure where I'd find those though. Looks like I'll be making some phone calls tonight.

Still curious how air works it's way out of the system (if at all)
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Unread 08-19-2014, 08:57 PM   #5
zjosh93
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Air in the rail just blows out the injectors. Especially since Jeep puts the regulator right next to the inlet so the air can't purge out the regulator. When the engine is running and the injectors are firing the fuel in the rails is pretty turbulent so the air gets out alright. On my 4.0 it takes a while to purge out but the test port is on top so I just give it a few taps to hurry the air out. I bought a junkyard rail a while back so I could move the regulator to the other side of the rail which would also keep the rail cooler but it's pretty low on my list of things to do.
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Unread 08-19-2014, 11:38 PM   #6
Uniblurb
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Isn't the fuel pressure regulator built right into the fuel pump module/assembly on both the 4.0/V8's from late 95 thru 98? Understand it's a separate part/device in the engine compartment on 93 thru early 95. Would agree the air's going to blow out through the injectors and even better if the regulator is clear back in the tank.
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Unread 08-20-2014, 09:36 AM   #7
zjosh93
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You're right, the regulator is in the tank on the later models but from what I've seen the bypass is in the tank so just one line runs up to the rails. No way for air to get to the regulator on those.

Last edited by zjosh93; 08-20-2014 at 03:21 PM.. Reason: grammar
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Unread 08-20-2014, 01:08 PM   #8
sebian
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That file line between the rails is a "non-servicable" part, meaning that it is not supposed to come apart from the rail.
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Unread 08-23-2014, 09:18 PM   #9
Scooteriggy
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What would be the issue with replacing the cross over line between rails with fuel line? or does it need to be that solid line insert?
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Unread 08-25-2014, 12:51 PM   #10
sebian
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The nipples on the rail connecting the line are hard plastic from what I remember, and it is not recommended to use those to clamp fuel line to. Having said that, when I did my plenum swap, I cracked the brittle fuel line, resulting in a fuel leak. I replaced it with fuel line, lightly clamped on with hose clamps...2 years ago and no probs so far. I didn't feel like spending the nearly $400 for a new fuel rail assembly, when $5 at the auto store fixed it.
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Unread 08-25-2014, 02:13 PM   #11
zjosh93
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Are the nipples plastic? I have the 4.0 but I was looking at pictures of the v8 rails earlier. It looked to me like the crossover was hard nylon line pressed onto steel nipples on the rails. If that is the case you can easily remove the nylon by warming it up and replace it with fuel injection hose and hose clamps. I have done this with some of the lines on my ZJ: high pressure hose and double clamps.
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Unread 08-25-2014, 02:32 PM   #12
sebian
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The nipples are plastic, which makes it sucky to work with, and they are ribbed to grab the fuel line, which makes getting off a pita. I had to very delicately cut the line that was left on there.
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Unread 08-25-2014, 03:51 PM   #13
McCloudsZJ
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Where are you seeing $400 fuel rail assemblies? Billet rails with allocations for full return plumbing are half that. DIY fuel rail stock is even cheaper.
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