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First thread topic! Fuel question for seasoned V8 swappers!

XJ6 & XJ12 Series I, II & III 1968-1992

First thread topic! Fuel question for seasoned V8 swappers!

 
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Old 06-22-2014, 02:35 PM
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Default First thread topic! Fuel question for seasoned V8 swappers!

Before anybody bashes me on the fact this project 1986 XJ6 has a 355 Chevy motor in it, be aware my dad bought this rust free Texas car as is with a V8 swap already done-sort of. Now, I build my own stuff and this is my first Jaguar build of any sort to to make life easy for my dad, I'm taking this project on.

So, being as though this was a FI 3.5 6cyl car, are the oem tanks setup with internal pumps? If so, I doubt then that one can simply run a mech pump like this car is setup for, correct? I thought above running an external pump after verifying what psi I would need then regulate it down to 6 psi at the engine-assuming the tanks aren't rusted will this plan work? What has everyone else down with this scenario? I could design and build a fuel cell but would rather keep this car as much factory appearing as possible. I like the dual tanks and have no problem with them so long as they are clean and unobstructed.
 
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Old 06-22-2014, 03:34 PM
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Originally Posted by gmachinz View Post
Before anybody bashes me on the fact this project 1986 XJ6 has a 355 Chevy motor in it, be aware my dad bought this rust free Texas car as is with a V8 swap already done-sort of. Now, I build my own stuff and this is my first Jaguar build of any sort to to make life easy for my dad, I'm taking this project on.

So, being as though this was a FI 3.5 6cyl car, are the oem tanks setup with internal pumps? If so, I doubt then that one can simply run a mech pump like this car is setup for, correct? I thought above running an external pump after verifying what psi I would need then regulate it down to 6 psi at the engine-assuming the tanks aren't rusted will this plan work? What has everyone else down with this scenario? I could design and build a fuel cell but would rather keep this car as much factory appearing as possible. I like the dual tanks and have no problem with them so long as they are clean and unobstructed.
Welcome to the forum. I'm ElinorB and it's nice to have you with us. When you get a chance drop by the New Members section and post an introduction.
https://www.jaguarforums.com/forum/n...-intro-must-5/

Every once in a while someone gets their shorts in a bunch over those of us with GM powered Jaguars, but it's quiet on that front for the moment. Mostly, people in here feel it's your car and you have the right to do what you want with it. Stick around and you'll see lots of mods falling by.

I think it's very cool that you're taking on your dad's project, if for no other reason than it's for your dad.

I have a Chevy 350 in my car, I also got it that way, but it has a stock fuel pump that operates off the cam, it not being FI. Originally there were pumps in both tanks (I think) but the PO had those removed, plumbed the tanks together and removed the tank switching valving, whatever that's called, so the engine draws off both tanks at once.

Well not exactly, it draws more from the left tank until the fuel reaches a certain level and then the right tank flows. I think that's a quirk of the plumbing but I haven't checked that out yet.

I have another car (not a Jag, Chrysler 440) that has the exact setup you mention here; external pump with regulator feeding the carb. It works *Very* well and has for several years.

If this doesn't answer your question someone will be better able to address your problem. I wish you success with your project and hope we hear more about it.
(';')
 

Last edited by LnrB; 06-22-2014 at 03:55 PM.
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Old 06-22-2014, 04:35 PM
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Fuel injected cars had a single and central high pressure pump in the spare tire well. Series 1 and carburated Series 2 cars had a low pressure pump in each tank. In your case you should eliminate the high pressure pump and replace the tank switch over mechanism because its wrought is reliability issues. You have many options some are detailed below.

1. Bridge the tanks using a T fitting and plumb the tanks to simultaneously supply the engine's mechanical fuel pump. Good option if you want over all simplicity but you loose tank select-ability.

2. Install two Holley low pressure carburator compatible fuel pumps, one for each tank to supply the carburetor directly. Use the cars selector switch wiring to power each pump based on switch position. Be sure to use a 1 way check valve to ensure proper fuel flow and prevent back flow. Good option if you like electric fuel pumps.

3. Retain the mechanical pump and use a 3 port pollack valve as a tank selector. The Jag fuel tank selector wiring is not directly compatible with the pollack valve so a relay, separate switch or some creative wiring will be required. This is a good option if you want to retain rock solid tank select-ability allow by the pollack valve and want the bullet proof reliability of a mechanical pump.

4. Just plumb one tank. Chances are one is less rusty than the other. 11 gallons is good enough for occasionally driving and local trips.

Using a low pressure electric or mechanical pump will allow you to have the right fuel pressure to begin with and you can simply cap or plug the return line for each tank. If you use a regulator to lower the fuel injection 40 PSI to the 6 psi needed for a carb you run the risk of flooding the engine at best or starting a fire at worst should something cause the regulator to fail. In all cases don't forget a quality fuel filter somewhere in the system, preferably right before the carb.
 

Last edited by icsamerica; 06-22-2014 at 04:47 PM.
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Old 06-22-2014, 07:54 PM
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Wow....didn't realize stock FI pressure was upwards of 40 psi. Hmm....I may see about trying to locate 2 stock carb equipped fuel tank sending units. Would that be easier? Then I could simply run a T-fitting from both tanks....that would make my life easier....lol
 
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Old 06-22-2014, 09:32 PM
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Originally Posted by gmachinz View Post
Wow....didn't realize stock FI pressure was upwards of 40 psi. Hmm....I may see about trying to locate 2 stock carb equipped fuel tank sending units. Would that be easier? Then I could simply run a T-fitting from both tanks....that would make my life easier....lol
Carb fuel tanks are different and not necessary in your case. It's not a sender issue. You can simply T the tanks in the spare tire area and use the 3/8 line forward of the fuel pump to supply a mechanical fuel pump. The suction of the mechanical fuel pump is plenty strong.
 

Last edited by icsamerica; 06-22-2014 at 09:36 PM.
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Old 06-22-2014, 11:49 PM
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Ok. I'll just have to check the interior condition of the tanks then. Thanks! I'll get some pics up asap...just have a long checklist of things to go through and the fuel system is first followed by an electrical overhaul.
 
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Old 06-23-2014, 07:49 AM
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Lotsa ways to skin a cat. Carb'd Jag to carb'd GM is simplist. Fuel pump output psi isa close enough. No real need for the GM mechanical one unless one wants belt and suspenders!!


FI Jag to carb'd GM a tad different. Jag pumps too much PSI for a carb. Can be regulated, though.


I like the twin tank and selector system in my car. And, that is because it works properly. If it didn't I'd think differently. Fix it or get a better selection valve as already mentioned.


Now the "T the tanks" sounds simple and generally I like things simple, it has a serious draw back. If one parks side hill and the tanks are near full, the high side will drain to the low side and it will spill over. Messy as well as dangerous.


Carl
 
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Old 06-23-2014, 08:14 AM
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Ahh, a fellow Iowan with a lump! I was beginning to feel a bit lonely. I also see you are a capable CAD operator; same here. Welcome to the forum.

I've been operating my SIII for years off only one tank. May be able to get the other one operable soon, hopefully.

What year is the XJ6?
 
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Old 06-23-2014, 05:34 PM
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This one is an 86. I just pulled a really nice black console and other misc. interior from an 83 in a local salvage yard today. The interior in my dads is tan with the top padded dash and center section being black along with the seatbelts. But, I like the look of a black console to create a better interior transition.
 
 
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