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Old 06-23-2013, 02:25 PM   #1
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Question Jeep 2.5 to Chevy 4.3 conversion?

I picked up a 95 YJ Rio Grande (originally 2.5 w/ stick) that had been converted to a Chevy 4.3 w/ TH350 Auto and 4bbl carb. It ran good, but when on the dunes going up hill would starv for fuel. So I cam across another 4.3 with TBI out of a '90 S-10. Asside from the wiring woes of the conversion everything went pretty smooth till I tried to start it. It seems to be getting too much fuel pressure in the supply line and the clear filter under the hood looks like it's under pressure until I pulled the fuel pump relay and pulled the gas cap.
Does anyone have any thoughts on what I need to do to relieve this pressure build up?

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Old 06-23-2013, 04:34 PM   #2
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What kind of fuel pump and lines are you running?

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Old 06-23-2013, 08:54 PM   #3
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I believe it is the stock fuel pump that was with the 2.5 has combination of rubber and steel lines from back to front.
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Old 06-23-2013, 08:58 PM   #4
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GM TBI needs 9-13 psi

Im pretty sure the 2.5 mpfi is around 40-50 psi.
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Old 06-23-2013, 09:18 PM   #5
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Maybe it's not the stock pump then. Is it true that a 4bbl carb only takes 10-15 lbs of pressure? It seemed to run fine with that. Was hoping I wouldn't have to pull the tank, but will if it comes to that.
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Old 06-23-2013, 09:20 PM   #6
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Quote:
Originally Posted by Bur View Post
Maybe it's not the stock pump then. Is it true that a 4bbl carb only takes 10-15 lbs of pressure? It seemed to run fine with that. Was hoping I wouldn't have to pull the tank, but will if it comes to that.


I ran my 4barrel edelbrock with a sbc350 at 4psi. Did you have a return line when you had it carbed?
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Old 06-23-2013, 09:29 PM   #7
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Yeah, it had a Schrader valve mtd on the firewall. But now with the TBI, I can't use it.
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Old 06-23-2013, 09:33 PM   #8
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You need to get a inline Fuel pressure regulator to cut the flow down. It doesnt have anywere to go now and is loading it up. I have had good success with the cheapo ebay fuel pressure regulators. They have a gauge and a feed and return line and are around $20

Other option would be a new fuel pump
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Old 06-23-2013, 09:42 PM   #9
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Is it possible that I need to replace or rebuild the Fuel pressure regulator inside the TBI?
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Old 06-24-2013, 05:20 PM   #10
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I wouldn't think you need to get a second fuel pressure regulator, the one in the tb would back in down enough on its own. But it needing to be rebuilt could be a possibility the spring could have gotten weak inside it. The tb should have a return line on it, there's two fittings on them. But having a gauge to get a reading on it would be best to see if the pump has been swapped out or not. Are the injectors spraying at all?
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Old 06-24-2013, 08:43 PM   #11
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That was the problem. The diaphragm was all dried out. put a kit in it for about $50 and it starts and runs fine now. Except, for some reason, now when I put it in gear, it wants to stall unless I give it some gas. Any ideas?
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Old 06-24-2013, 08:45 PM   #12
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Still need to put the timing light on it. Maybe it just needs a minor adjustment

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