03 ZX7R fuel supply issues - ZX Forums
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post #1 of 2 (permalink) Old 07-17-2019, 06:54 PM Thread Starter
Joined: Aug 2014
From: Vancouver Island
I Ride: 2003 ZX7R

Posts: 6
03 ZX7R fuel supply issues

Got a 2003 ZX7R that starves for fuel on occasion. Last time out I managed to limp it home after three incidents that left me roadside on the shoulder. It did get a new Quantum HFP-181 pump before that last time out. To get it running and home, I removed the pump from its mount and removed the back cover exposing the contacts. What I found was I could get it working temporarily by “helping the contacts together and it would flutter until the bowls were full and return to a normal pulse every second or so, then fail.

Now I’m poking around at the relay.

This is what I’ve concluded... there is a 0.7volt drop to the red wire at the relay when the bike is running, likely in the kill-switch and to be investigated. Still getting 13ish volts to the relay when the bike is running with 13.8 volts at the battery.

A black/red wire coming from the crank circuit that energises the relay while cranking, a black wire that energises the relay while running that is tied to the primary of one of the ignition coils, and a black/blue wire that feeds the fuel pump from the relay.

So, this isn’t your typical electromechanical relay but rather a solid state relay that operates like a transistor?

When I bought the bike 4 years ago, there was a spare relay tucked in the tool kit. Dug it out of the parts bin and gave it a try. Acts just like the first with about a 4 volt supply to the pump at idle and about 6 volts above 5000 rpm. Thought that was strange and bought another relay that’s doing the same thing. 3 relays all working in the same fashion. Something is amiss!

While poking around the relay with my Power-Probe (cool tool) I noticed that while probing the fuel pump power feed with the bike running and the 4-6 volts present, the min/max feature is showing 0-14 volts there too. Without a labscope I’m assuming the 4-6 volts I’m seeing is the average of the relay being pulse width modulated by the black/red trigger from the coil primary.

Anyhow, just wondering if anyone can confirm that’s typical relay operation... pulse-width modulated square wave giving me the 4-6 volt “average” depending on RPM?

I thinking I’ll have to throw the new fuel pump back at Amazon before the return date expires and buck up for a new pump from Kawasaki. Tossed around the idea of swapping the fuel pump contacts from the new pump to the original but that’d kill any chance of returning it to Amazon.

I’m an automotive tech and quite knowledgable with modern automotive electronics. Technical replies very welcomed! Let’s get crazy with the Cheez-Whiz!!
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post #2 of 2 (permalink) Old 07-17-2019, 06:58 PM Thread Starter
Joined: Aug 2014
From: Vancouver Island
I Ride: 2003 ZX7R

Posts: 6
I will remember to avoid contractions and quotation marks in future posts. Not sure what caused the goofy characters where I placed apostrophes and quotation marks. It was sent from my phone. Hope it is readable :-/
SoftTaco is offline  
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