Idle issue

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Re: Idle issue

Postby fvkagi » Sat Jan 04, 2020 7:39 pm

underscore wrote:I opted to use the jumper from a 5SFE in place of the relay to bypass the resistor system. If the fuel system cuts out or switches to the wrong mode at the wrong time the results could be catastrophic, and by all accounts here the only supposed benefit is reduced fuel pump wear. When everything was shiny and new I'd have no problem with it but when parts are approaching 30 years old simplicity seems safer.


I like the sound of this option, can I just get a fuel pump relay from like a 1998 Camry or something and use that? Or is there some other part I need to use?

Thanks again for all the help!
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Re: Idle issue

Postby 93celicaconv » Sun Jan 05, 2020 1:23 am

underscore wrote:I opted to use the jumper from a 5SFE in place of the relay to bypass the resistor system. If the fuel system cuts out or switches to the wrong mode at the wrong time the results could be catastrophic, and by all accounts here the only supposed benefit is reduced fuel pump wear. When everything was shiny and new I'd have no problem with it but when parts are approaching 30 years old simplicity seems safer.

Just realize though that the ECU injector duration time is based on an estimated fuel pressure. When not under full-throttle, the ECU utilizes the resistor to slow the fuel pump down, which results in a lower controlled fuel pressure, and the injector duration is based upon this lower pressure. Yes, there is +/- fuel trim capability, but typically only within a +/- 25% range. If you eliminate the resistor on an ECU made to operate a resistor, you may get very rich idle condition and low speed conditions even up to highway speeds. Negative sustained fuel trim adjustment may not completely correct this. I'd be "concerned" about this aspect if purposely eliminating a fuel pump resistor on a vehicle with an ECU designed to control electronic fuel injection with one.
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Re: Idle issue

Postby underscore » Sun Jan 05, 2020 3:39 am

I noticed no change in the AFRs on my wideband when I made the switch, it has datalogging capabilities so at some point I could do the same drive with and without the relay to see if there's a noticeable difference. I'm curious just how much the flow/pressure of the pump is changed by the resistor, somebody with a fuel pressure guage should be able to compare the with/without pressure at idle to see.
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Re: Idle issue

Postby 93celicaconv » Sun Jan 05, 2020 11:20 am

There is a fuel rail pressure regulator on these engines too, which may help maintain fuel rail pressures in the range the ECU was programmed to control fuel injector duration. That being the case, the fuel pressure regulator may just open more at low RPMs/low engine loads to keep fuel pressure low if the fuel pump isn't allowed to run off of its resistor in these cases. So you have a good point there, Underscore.
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