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Discussion Starter · #1 ·
2006 GSXR 750
Low voltage going to injectors causing them not activate

I have a little over 9 Volts metered directly on my fuel injector harness (fuel injectors not connected).
If I keep my positive lead connected to the harness and meter directly to the ground on the frame I get 12 + volts.
If I keep my positive lead connected to the harness and meter to the negative on the battery I get 12+ volts.
If I keep my positive lead connected to the harness and back probe the ECU ground I get 12+ volts.
If I keep my positive lead connected to the harnes and back probe the negative output on the ECU that leads to my injector that I'm working on I get 9 volts.
There's no resistance on any of the ground wires that I just mentioned.
This problem is happening on all the injectors causing them not to activate during startup.
My battery is good.
Any ideas?
Thanks in advance for your help.
 

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Hey, probably won't be able to help you much. Electrics is not my forte.

If I keep my positive lead connected to the harnes and back probe the negative output on the ECU that leads to my injector that I'm working on I get 9 volts.
Are you measuring this while cranking the bike? There will be a voltage drop while cranking.
Getting any codes? Whats the dash say?
 

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Discussion Starter · #4 ·
Thank you for the reply.
I've metered the harness without the injectors connected while the keyswitch is in the off position; 0V.
Keyswitch on position for first 3 seconds fuel relay is activated 9+V.
Keyswitch on while cranking 9+V.
The current codes I get are related to the sensor on the air intake being disconnected. I temporarily connected it to clear all the codes but the voltage output issue is still there.
 

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So the only codes you are getting is C21 and C22?
Can you hear the fuel pump prime for 3 seconds? Whats the voltage at the fuel pump when priming (Y/R wire)?
I thought 9 volts would be enough to open injectors? I could be wrong though.
I can check on my bike what voltage I get tomorrow. Bit dark here at the moment.

Is this how you bought the bike, or did it just start happening now?
 

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Discussion Starter · #6 ·
I can hear the pump prime and when my fuel tank is on the bike and I apply 12v directly to the injectors I get a nice even spray.

I'll confirm the voltage going to my fuel pump and codes a little later on today.

9v doesn't open the injectors and 10v doesn't ethier.

If you could meter the voltage going to your injectors that would be super helpful.

I've been the only person to own this bike. It sat for awhile because I live in California and its a 49 state compliant bike. I just want to get it running to sale it since I can't register it here. I can spray starter fluid and it runs long enough to burn off that fuel.

I did replace the fuel pump due to it not priming. I also just replaced the fuel fuse because it was blown.
 

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Discussion Starter · #7 ·
I currently have c21 and c46. The plastic that holds the cable broke for my exhaust actuator. The issue was happening prior to the actuator plastic being damaged.
The fuel pump voltage is at 12+V.
 

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Ok. just did some testing and I'm getting similar results to yours.

The fuel pump when priming = 12v.
Next, I "unplugged all" the injectors. Injector (+) to Battery (-) when priming = 12v.
(NB. Fuel pump and Injectors share the same 12v feed from relay).

Now, here's the tricky bit. I used 4 multimeters. Two cheap ones and two decent ones.
Injector (+) to Injector (-) when priming = 8.90v. For the 2 cheap multimeters.
Injector (+) to Injector (-) when priming = 11.4v. For the 2 decent multimeters.
(All measurements were done with injectors "all unplugged". Forgot to check the codes but probably had the codes for the injectors).

Next, I "plugged all" the injectors back in. I back probed No4 Injector.
No4 Injector (+) to Injector (-) when priming = 0.0v
Fuel pump priming, still at = 12v.
(NB. Did a visual inspection, Injectors do not squirt fuel into throttle body when priming. Did not check it when cranking, but obviously they do it when cranking).

Bike started up first go. Tried to measure voltage at No4 Injector when running, but of course the digital multimeter cannot keep up with the pulses, fluctuating rapidly, I'm guessing there
is about 12v there when running.
 

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Discussion Starter · #9 ·
That is extremely helpful to know that a functioning bike has the same output on the injectors; it rules out my ECU. It's also helpful to know that it doesn't spray during priming. That was the basis of my test.

I have ran a test by temporarily hooking up my airbox, connecting my gas tank and the bike doesn't start. One thing I haven't done is put my air box back on and tighten the screws to the throttle bodies and try to start it. Maybe the sensor in the airbox although connected recognizes an issue (its not mounted to the throttle bodies) and the injectors won't work (could be a fire hazard in an accident). I'll put it together tomorrow and give it a try.
 

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Discussion Starter · #10 ·
I put the air box and tank back on and connected all fittings and hoses. I turned over the bike a couple times and it didn't start. I could hear the pump priming.
I had my old battery hooked up and it quickly died. I was in the process of connecting my new battery when I tapped the poative lead too many times on the battery terminal causing my 30A fuse to pop. I already used the extra one in the plastic cover. I'll get another fuse hopefully in a couple days and try again with the new battery. I did turn it over 2 or 3 times and it didn't start. :/ I have a video of this test; if you want I can put it on youtube and post a link.
 

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When removing the Battery, make sure everything is turned Off.
*When disconnecting the Battery, disconnect the (-) Battery lead first.
*When connecting the Battery, connect the (+) first and the (-) last.
(This is in the Workshop Manual).
Basically, if there is any sparking, you want it to occur on the (-) negative side.

You mentioned that the fuel fuse was also blown. They don't usually blow for no reason. Maybe you
accidentally touched the wrong wires when installing the new pump?
Has the bike started or ran with the new pump??

You said that you can spray starter fluid and the bike runs. That's good, it means the Ecu is working (the ignition side at least). It's also priming the pump and giving codes. All good signs.

Maybe the sensor in the airbox although connected recognizes an issue (its not mounted to the throttle bodies) and the injectors won't work
I had my airbox off too, with the sensors disconnected and the bike ran fine.(It ran Ok). As far as I know, the only sensors
that will prevent starting are the crank sensor and tip over sensor and maybe the cam sensor. And, you would get codes on the dash if they weren't working.(Fingers crossed).

Another thing to note is that I have the K4 600 which I am familiar with. I have not worked on the K6 750. I also don't have the workshop manual or wiring diagrams for your model. It's hard to find them these days (For free). I understand that your bike has primary and secondary injectors?(K4 only has primary). I am assuming that you were conducting testing on the primary injectors and found 12v there?
I can hear the pump prime and when my fuel tank is on the bike and I apply 12v directly to the injectors I get a nice even spray.
You said the bike sat for a while.
It sat for awhile because I live in California
Is this the first time you are trying to start it? How dirty was the tank and the old fuel pump?

NB: I'm new at this too, so if I say anything incorrect, feel free to point it out.👍
 

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9V across the injector lead is probably just due to your meter not being fast enough to see the 12V spike. You almost need an oscilloscope to do the type of testing you're describing.

Be very careful doing this test, but hold a Q-tip down into the throttle body and cover the primary injector tip with the swab. Crank it for a few seconds, then see if the swab has fuel on it.
 

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Discussion Starter · #14 ·
When removing the Battery, make sure everything is turned Off.
*When disconnecting the Battery, disconnect the (-) Battery lead first.
*When connecting the Battery, connect the (+) first and the (-) last.
(This is in the Workshop Manual).
Basically, if there is any sparking, you want it to occur on the (-) negative side.

You mentioned that the fuel fuse was also blown. They don't usually blow for no reason. Maybe you
accidentally touched the wrong wires when installing the new pump?
Has the bike started or ran with the new pump??

You said that you can spray starter fluid and the bike runs. That's good, it means the Ecu is working (the ignition side at least). It's also priming the pump and giving codes. All good signs.


I had my airbox off too, with the sensors disconnected and the bike ran fine.(It ran Ok). As far as I know, the only sensors
that will prevent starting are the crank sensor and tip over sensor and maybe the cam sensor. And, you would get codes on the dash if they weren't working.(Fingers crossed).

Another thing to note is that I have the K4 600 which I am familiar with. I have not worked on the K6 750. I also don't have the workshop manual or wiring diagrams for your model. It's hard to find them these days (For free). I understand that your bike has primary and secondary injectors?(K4 only has primary). I am assuming that you were conducting testing on the primary injectors and found 12v there?


You said the bike sat for a while.

Is this the first time you are trying to start it? How dirty was the tank and the old fuel pump?

NB: I'm new at this too, so if I say anything incorrect, feel free to point it out.👍
 

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Discussion Starter · #15 ·
Thanks for the tips on proper installation and removal of the battery; I dont want to burn any more fuses up.

The bike hasn't started with the new pump.

I tested the voltage on all of the injectors.

The gas was old and the fuel pump had small amounts of surface rust. I inspected the inside of the tank and didn't notice any major rust spots. I removed all of the old fuel and and added new gas.

I have the FSM for this bike on my phone. I can send it to you if you'd like 👍

@TheGeek Thanks for the information about the lack of sensitivity on basic meters; that's probably why Peter079 nicer meter was able to read the higher voltage. I'll try the Q-tip test later this afternoon.
 

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Assuming you were correctly on the lower set of injectors, not the uppers? If all your test data is accurate, it's rare, but it sounds like the injectors are all stuck.
 

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Discussion Starter · #19 ·
I was testing based on that picture I just posted. I tested all primary injectors just to be on the safe side; I can watch the secondary ones not spray. You mentioned the possibility but unlikely hood of the all injectors being stuck. Earlier I had tested the injectors by 12vdc directly into the injectors and they worked. Can they still be stuck and be working with 12v?
I've detailed my test but I could of done something wrong any suggestions? Thank you for your help!
 

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Going by what I have read on this site, the secondary injectors don't come on until higher rpms.
They are not used when starting. That's why you should be testing the primaries for 12v and operation.
 
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