Possible Voltage Drop Issue? (1 Viewer)

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Joined
Jun 22, 2018
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Location
Houston, TX
Not another crank but no start thread!

I may be looking at this wrong, but jumping 12.5v off the battery to fuel relay socket pin 3 forces fuel to come out of the reg. return. Key crank with the relay in = no fuel. From pin 5 I get 10.5v coming upstream from the battery. Downstream from the relay at the resistor I get 9.5v with a key crank.

It's a newish denso pump just outside of the warranty period. Are these pumps that picky on supplied voltage?

Is this likely a crusty circuit issue or a failing fuel pump?

Thanks all.
 
What year vehicle, any check engine codes?
Not another crank but no start thread!

I may be looking at this wrong, but jumping 12.5v off the battery to fuel relay socket pin 3 forces fuel to come out of the reg. return.

This indicates your fuel pump is fine.

Key crank with the relay in = no fuel. From pin 5 I get 10.5v coming upstream from the battery. Downstream from the relay at the resistor, I get 9.5v with a key crank.

12v should be present at terminal Pin 5 when the ignition is in ON and START
View attachment 1576391
Pin 5 should be closer to the battery voltage, Not surprised that you got 9.5v after the .73Ω resistor. Are your battery terminals clean?/ Clean them now. Check your battery voltage if it is 12.5v then proceed with the next step below.

The fastest way to test for a faulty Fuel Pump Relay (common issue) is to remove the relay and put a jumper wire between terminal 5 and terminal 3 then try to start the engine. If it starts the FPR is bad.

If that doesn't work then trace the EFI power circuit back from the FPR to the Open Circuit Relay. It's behind the dead pedal side panel, check your voltage at terminal 1 and terminal 2 when cranking If it's still low, then trace it back to the EFI main relay test terminals 4 and 2..
1) CoR
COR.JPG
2) EFI
EFI.JPG


If the voltage is low at terminal 1 but not terminal 2 of the circuit opening relay then replace it. If the voltage is low at terminal 4 of the EFI relay but not at terminal 2 then replace it.
If both those are fine and your battery terminals have been cleaned recently then it's likely your fusible link.
FSL.JPG


Let me know what you figure out.
 
Last edited:
My man smoking rocks! FPR is the issue using that jumper method.

It's a little more complicated by looking at your screen shots than what I thought. I have one in the mail.

Thanks
 
Glad to hear that helped! I'd still clean your battery terminals.

Also if you don't have it download your vehicles FSM here:
FSM's
 

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