Fuel pressure

Tiny
PACIFICISLANDER
  • MEMBER
  • 1996 TOYOTA COROLLA
  • 1.6L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 100,000 MILES
Unhook fuel return line, disconnect fuel harness car still running. Seems the fuel return line is feeding the throttle body how can this happen return line should not sucks fuel in?
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Saturday, August 29th, 2020 AT 1:56 PM

126 Replies

Tiny
ASEMASTER6371
  • EXPERT
Good evening,

The return line only sends excess fuel back to the tank for re use.

Dis connect the harness? What harness?

Roy
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Saturday, August 29th, 2020 AT 5:15 PM
Tiny
PACIFICISLANDER
  • MEMBER
I disconnected the fuel pump wiring harness and it continues to run also disconnect both output and return line but gas it coming out of the return line. Could it be the fuel pressure regulator sticking closed?

My car problem is that when I start it up, it idles real low and when I kick the gas pedal it shuts off.
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Saturday, August 29th, 2020 AT 5:41 PM
Tiny
ASEMASTER6371
  • EXPERT
If the regulator was closed, no fuel would be coming from the return line.

As far as the pump still running, does fuel come out of the outlet of the pump? It should not pump any fuel with the connector disconnected.

Roy
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Saturday, August 29th, 2020 AT 6:02 PM
Tiny
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  • MEMBER
Fuel comes out of outlet port. No, it's not throwing out fuel.
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Saturday, August 29th, 2020 AT 7:20 PM
Tiny
ASEMASTER6371
  • EXPERT
Okay, then the pump is not running?

Roy
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Saturday, August 29th, 2020 AT 7:39 PM
Tiny
PACIFICISLANDER
  • MEMBER
Fuel comes out of outlet port. No, it's not throwing out fuel, when connected it throws out fuel. When outlet pipe disconnected and return line still connected the car is still running. How is it, still running?
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Saturday, August 29th, 2020 AT 11:05 PM
Tiny
ASEMASTER6371
  • EXPERT
Without fuel pressure it should not run at all.

It makes no sense for it to run with no fuel going to the engine.

Can you upload a video of it running with the lines disconnected?

Roy
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Sunday, August 30th, 2020 AT 4:01 AM
Tiny
PACIFICISLANDER
  • MEMBER
I don't understand it either. When outlet pipe disconnected no fuel is coming out and to include fuel pump wiring harness disconnected and return line still connected the car is still running. How is it, still running? The return line feeding the engine or what?

With both lines disconnected it will not start but hook up the return line and it will start while the fuel pump wire harness is connected.
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Sunday, August 30th, 2020 AT 2:22 PM
Tiny
ASEMASTER6371
  • EXPERT
Can you upload a video of this happening?

Roy
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Sunday, August 30th, 2020 AT 3:22 PM
Tiny
PACIFICISLANDER
  • MEMBER
Here it is, it's unplug but stay running.
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Sunday, August 30th, 2020 AT 9:32 PM
Tiny
PACIFICISLANDER
  • MEMBER
Even if both lines are connected it shouldn't run if the fuel pump wiring harness is disconnect as shown, but it does run but very low idle.
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Monday, August 31st, 2020 AT 12:07 AM
Tiny
ASEMASTER6371
  • EXPERT
Did you trace the lines to be sure someone did not add another inline fuel pump into the system?

Roy
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Monday, August 31st, 2020 AT 3:32 AM
Tiny
PACIFICISLANDER
  • MEMBER
Don't know about that on this make/model but I'll check let you know.
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Monday, August 31st, 2020 AT 4:01 AM
Tiny
ASEMASTER6371
  • EXPERT
Sounds like a plan.

Roy
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Monday, August 31st, 2020 AT 4:02 AM
Tiny
PACIFICISLANDER
  • MEMBER
There's nothing to find the original piping is still there, no fuel pump. Don't know about you but this one is a nightmare. I believe this one is an electrical problem.
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Monday, August 31st, 2020 AT 7:14 AM
Tiny
ASEMASTER6371
  • EXPERT
I agree. Wish I was there to see it and help but it it's tough from doing it from a virtual communication.

Roy
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Monday, August 31st, 2020 AT 7:31 AM
Tiny
PACIFICISLANDER
  • MEMBER
Can you give me what the EFI relay powers and what terminal? Also could this be a computer problem in your own opinion? For me it's coming down to this but I need more info to be sure. Thank you.
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Monday, August 31st, 2020 AT 2:29 PM
Tiny
ASEMASTER6371
  • EXPERT
No, not at all. The pump cannot work without power.

I attached the diagrams you requested.

Roy
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Monday, August 31st, 2020 AT 4:17 PM
Tiny
PACIFICISLANDER
  • MEMBER
What do you meant by this; No, not at all. The pump cannot work without power.
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Monday, August 31st, 2020 AT 6:30 PM
Tiny
PACIFICISLANDER
  • MEMBER
It seem like the return line is sucking fuel back to the fuel rail when fuel pump disconnected. What do you think is doing it?
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Monday, August 31st, 2020 AT 7:45 PM

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