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Unread 08-19-2014, 05:57 PM   #1
DeanLM90
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1997 ZJ 
 
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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, 06:49 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, 07:24 PM   #3
PolkaPower
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Not to mention the metal shavings.
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Unread 08-19-2014, 07:47 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, 07:57 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, 10:38 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, 08:36 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 02:21 PM.. Reason: grammar
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Unread 08-20-2014, 12:08 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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