90’ 2.5L TBI to carb SBC 350 - JeepForum.com
 
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post #1 of 9 Old 02-28-2020, 06:09 PM Thread Starter
90yjkrawler
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I know someone has done this same swap before. I’ve swapped my 90’ 2.5L with a carbureted SBC 350. I’ve got the new engine, trans, and transfer case bolted in and started on gauges but haven’t locked down the fuel yet. I’m not using a mechanical pump b/c I inherited a saddle style engine mount that is in the way. I have a Holley blue pump and Holley fuel regulator on hand to use. I’m wondering if I could still use my stock sending unit capping the return or use the sending unit from a 4.2L that doesn't have a return. Also, can I wire the new fuel pump using the same relay as my stock one? Thanks.

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post #2 of 9 Old 02-29-2020, 10:49 PM
Chrisnvegas
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More than one way to do it but I'd use a 4.2.
And I would also use an inertia/rollover switch (Mid 80's Mustang was trunk mounted) to stop the pump in case of a crash or rollover.
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post #3 of 9 Old 03-02-2020, 03:33 PM
1project2many
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You will need to remove the original pump to use the Holley inline with the 2.5 sender. Why not install a 4.2 pump in the 2.5 sender? It looks like you have a return type regulator so use the existing return line. Take some time to install a small cooler such as power steering cooler on the return line to keep the fuel cool. This will help ensure fuel is delivered to the carburetor very quickly and can help combat vapor lock.



The inertia / rollover switch is a great idea also.
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post #4 of 9 Old 03-02-2020, 10:51 PM Thread Starter
90yjkrawler
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I thought all the 4.2’s were mechanical fuel pumps? That’s why I thought the 4.2 sending unit would be less complicated to use and eliminate the return line. I didn’t think the Holley regulator I have was return style. Would that work though if it is a return regulator and reuse my old still in the tank unit from the 2.5 instead of the Holley pump?

Good call on the roll over switch.

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post #5 of 9 Old 03-03-2020, 09:11 AM
TheStevest
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The 4.2s are mechanical fuel pumps, however some still have a return line to the sending unit. They came stock with a pressure regulating fuel filter.
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post #6 of 9 Old 03-04-2020, 07:17 PM
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Quote:
Originally Posted by TheStevest View Post
The 4.2s are mechanical fuel pumps, however some still have a return line to the sending unit. They came stock with a pressure regulating fuel filter.
Sorry... typo on my part. I meant use a 4.0 in-tank pump.

Your regulator appears to have three lines which is typical of a return type regulator. The only problem you might run into using the complete 2.5 in-tank setup is that the pump doesn't provide enough fuel because it's from a lower power engine. With the in-tank pump you could remove the mechanical pump.

Folks like to use the mechanical pump because it's easy and because they feel the in-tank is less reliable. I've changed far more mechanical pumps before a vehicle makes 100k miles than electric. Plus with a fully circulating fuel system you have the option to build in fuel cooling. That can save a day when moving slowly offroad.
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post #7 of 9 Old 03-05-2020, 06:07 AM
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Originally I had a V8 carbed from a 2.5L. All you need is a pressure regulator. The 2.5L fuel pump is more than adequate.

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post #8 of 9 Old 03-11-2020, 04:46 PM Thread Starter
90yjkrawler
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Looks like I’ll need a bypass regulator. The Holley that I have has a single in and double out.
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post #9 of 9 Old 03-11-2020, 07:54 PM
1project2many
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That sucks. It looks like a return type but you actually have a three port "deadhead" regulator. The single "in" at the bottom and dual "out" at the top give it away. Find a 12-881 or equivalent return type and you'll be good to go.
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