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Old 09-23-2010
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difficult vacuum problem

so i recently did an engine swap (4.0 form 95 explorer into 93 ranger that had a 3.0) and it runs great.... most of the time. my problem is what i believe to be a vacuum one because it runs fine with no throttle. here are the symptoms.

randomly loses and regains power at all rpm, on and off like a light switch.
if i flick the ignition off and then on it goes away, (resetting the computer?)

my guess is it has something to do with the EGR because that is a vacuum system controlled by the computer.

ive tried capping off various lines but nothing seems to work, please help me.
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Old 09-23-2010
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A vacuum leak will idle poorly and run great when you apply throttle. After of course it catches up.

Only way to reset the computer is disconnecting the battery.

If it is an EGR issue then it will have a CEL.

The 95 expo is an odd year for electronics. Its the OBD II setup but runs OBD I.

To me it sounds like a fuel pressure issue.
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Old 09-24-2010
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i never thought of that, is there a way to check my fuel pressure while driving around because it does not do it while idling in my driveway. it has not thrown a CEL once

so if i were to get a scanner i would need obd II?

thanks for the imput
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Old 09-24-2010
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Using the 95 computer in your 93 truck im sure you had to do some wiring to get to work. The OBDI port under the hood should still work. Im not sure how you got it wired up or what needed to be done.


Fuel pressure can be tapped off the fuel rail. I have a harbor freight test kit and it leaks on every vehicle I used it on. So i would avoid buying that. Check with your local parts store that loan tools. You may need to fab an extension hose and run it to a place you can read it. This would be very temporary. Option 2 would be an aftermarket fuel pressure gauge. They can be a tad expensive and really unnecessary if your not running boost or N2O

Cheapest digital/electric sender gauge I found.
Cyberdyne Gauges A012E351Y - Cyberdyne Gauges Digital Blue Ice Gauges - Overview - SummitRacing.com

Cheapest mechanical.
BBK Performance 1617 - BBK Fuel Pressure Gauges - Overview - SummitRacing.com


If you haven't changed the fuel filter in the last year that would be my first step.
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Old 09-25-2010
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fuel filter is brand new, I did it with the swap. I just changed the fuel pressure relay tonight, that didn't do anything. i'll look into renting a pressure tester
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Old 09-25-2010
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IIRC, your looking for 35-45 psi with the return style set up. I don't have a 93 manual to verify.

Is it possible you have a loose connection? That light switch analogy makes me think loose wire.
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Old 09-25-2010
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i'll run over my line from tank to engine today, make sure everything is good.
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