fuel pump wiring and bypass of ECU

Doced · Sep 25, 2023

Recently the fuel pump stopped working. Took to shop and they found a rat / mouse had chewed wires and shorted fuel pump and probably the ECU ?
They were unable to get the fuel pump to turn on to see if there were other issues. They checked wiring harness continuity, fuel pump works when directly connected, said the crankcase position sensor was working, the kick stand sensor was functioning along with the bank angle sensor. Their conclusion was ECU. I want to bypass the ECU and see if the bike will at least start.
There are 3 wires from fuel sensor, which color is what function, hot, ground, common? Also what is the name of the type of connector so that if I can direct wire it, I get the correct wire to the correct connection.
I have attached photos of wires and the plug. The wire colors are yellow with red stripe, Red, black with white stripe.

I do not have a service manual so any help is appreciated.
Ed McKnight

mikesim · Sep 25, 2023

Ed, I'm afraid that trying to get the bike to start by bypassing the ECU is nigh impossible. The NT is fuel injected so the fuel to the engine is controlled by the fuel injectors which are controlled by the ECU. The fuel injectors meter fuel to the engine based on inputs to the ECU from the throttle position sensor, crankshaft position sensor, coolant temp sensor and oxygen sensor. You can still test for spark by pulling a spark plug and grounding it against the engine and looking for the spark. You can test the injectors for continutity and if you have a voltage source, the injectors can be tested off the bike. You can attempt to start the bike using starting ether in the air intake and if it fires then you know that the ignition portion of the system is likely OK and then can concentrate the fuel issue. I wish I had better news or advice. I will look in my manual and see if I can determine the wire colors you are looking for. One thing to consider however is that if you have full coverage insurance, rodent damage is likely covered minus your deductible.

Mike

mikesim · Sep 25, 2023

Ed, Y/R is 12V+ to pump, B/W is grd and R/Bl is fuel sender to fuel gauge. B/W is common ground to both the pump and sender. Hope this helps.

Mike

ARKNT · Sep 25, 2023

Ed here is a link to an electrical schematic from another post. With your issue and what you are trying to do you may need it. I don't know what wires the critters chewed up but there is a relay and the wiring itself in addition to the ECU.

Good luck,
Arknt

https://www.nt-owners.org/forums/attachments/nt700v-wiring-jpg.21134/

mikesim · Sep 26, 2023

ARKNT said:
Ed here is a link to an electrical schematic from another post. With your issue and what you are trying to do you may need it. I don't know what wires the critters crewed up but there is a relay and the wiring itself in addition to the ECU.

Good luck,
Arknt

https://www.nt-owners.org/forums/attachments/nt700v-wiring-jpg.21134/

Very good point about the relay. I neglected to consider that when I gave you the wire colors.

Mike

Doced · Sep 26, 2023

ARKNT said:
Ed here is a link to an electrical schematic from another post. With your issue and what you are trying to do you may need it. I don't know what wires the critters crewed up but there is a relay and the wiring itself in addition to the ECU.

Good luck,
Arknt

https://www.nt-owners.org/forums/attachments/nt700v-wiring-jpg.21134/

Awesome and where is that relay located? This is a big help.
Ed

Doced · Sep 26, 2023

mikesim said:
Ed, Y/R is 12V+ to pump, B/W is grd and R/Bl is fuel sender to fuel gauge. B/W is common ground to both the pump and sender. Hope this helps.

Mike

This is what I needed in addition to your previous recommendation. I have contacted my insurance agent to see what the scoop is on my coverage. I will also try the starter fluid process. With fuel injection, the starter fluid works?
Thank you again
Ed

Doced · Sep 26, 2023

Doced said:
Awesome and where is that relay located? This is a big help.
Ed

Is this relay located under seat back by the tail light?
Ed
PS I grew up in Cross County Arkansas

ST1100Y · Sep 26, 2023

Doced said:
Is this relay located under seat back by the tail light?

I'd rather expect it being one within the array of 5 relays under the LHS upper faring ...

mikesim · Sep 26, 2023

Doced said:
This is what I needed in addition to your previous recommendation. I have contacted my insurance agent to see what the scoop is on my coverage. I will also try the starter fluid process. With fuel injection, the starter fluid works?
Thank you again
Ed

Yes, starter fluid will work, but, you have to lift the fuel tank and remove the air cleaner cover to gain access to the intake horn. If it attempts to start that's a good indication that ignition wise the bike is OK and you can concentrate on fuel delivery.

Mike

dnktng · Sep 26, 2023

Both the FI/Ignition and Fuel Pump Relays are located near the voltage regulator between the LHS saddle bag and subframe for the seat.

What exactly is (or is not) your NT doing when you turn the Ignition switch(key) on?
Take the seat off and listen for the FI/IGNITION and FUEL PUMP relays clicking when the key is turned on.
Any dash indicator lights coming on?
headlights?
Is the fuel level indication working? If it works that means the ground for the fuel pump is working.
Is the speedo cycling up full range and back as part of the automatic self test?
Is the MIL check engine light coming on and then going off or is it staying on after the self check? Does the engine crank using the starter button?

The circuit to make the fuel pump come on is below. If if was mine, I'd work on getting the Fuel Pump to work before looking at the ECU or anything else because its 1) simple and 2) possible that fixing whatever is preventing the fuel pump from running is also causing any other problems, and 3) your going to need a fuel pump to start it.

rc_heli_nut · Sep 27, 2023

Bottom line is, you need to rewire where the mouse chewed on the wires. I can't really tell from your original picture, but is there enough undamaged wire at the 3-pin connector just past the pins and shell where you can get to some clean copper? If so, I recommend you get some of the heat shrinkable butt splices with the hot melt glue in them, available at any auto parts store, and cut out the damaged wire sections. Sometimes the metal crimp barrel length is long enough to make up for the missing copper that got chewed, otherwise also get a spool of 16-18 gauge primary wire and cut back towards the main harness as needed so the pump feed wire is same length as it already is. Keep in mind it has to fold down without getting too bend out of shape at the rear tank bolt where it pivots as you lower front of tank down. Worst case scenario, you may have to find a wrecked NT in a boneyard and have them let you cut that pigtail out of the harness, and wire that in with the aforementioned butt splices.

The ECU is fine, all the inputs and outputs are protected from damage/overcurrent/etcetera internally. Also check all the fuses under the seat. As others have noted the fuel pump will run momentarily with key first turned on to pre-charge the fuel rail. If that works and the fuel gauge reads right, you got it fixed. Hope this helps.

mikesim · Sep 28, 2023

Here is a good source for replacement connectors and terminals.

Motorcycle Terminals, Connectors, and Wiring Accessories

Cycle Terminal - We have Your wiring Needs. OEM Style Japanese Motorcycle Wiring Terminals and Connectors for Yamaha, Kawasaki, Suzuki and Honda Motorcycles, from the 60’s to the 90’s. Motorcycle electric products and accessories, Motorcycle Fuse Box's, Bullet Terminals, Spade Terminals and...

cycleterminal.com

Hope this helps,

Mike