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Is there a simple way to disable the secondary injectors?

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15K views 21 replies 5 participants last post by  Coyosso  
#1 ·
My 04 6rr is having some issues at high rpm, and I'm figuring it's the secondary injectors, or the fuel pump. So I'm thinking that if I can just not make the ECU tell the secondaries to turn on, the primaries won't emit less fuel, and I can immediately see if my secondary injectors are causing a problem, or if it's my fuel pump, or some other issue.

Since the 05/06 636s share a similar secondary injector system, I figured you guys might have found a way to do this.
 
#5 ·
Per Kawi's literature when the primary and secondary injectors are activated, they emit the same amount of fuel as the primary injectors alone emit. It just allows the fuel to mix with colder air so it's more condensed and more of the mixture gets into each cylinder.
 
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#6 ·
Where did you find that?

The temp difference in the small distance between the primaries and secondaries is basically nil. The secondaries are there to add more fuel during the part of the rev range they're active. Believe it or not (and I know plenty won't believe me), sportbike engines actually need slightly less fuel above 12K or so RPM than they do from 8-12K. The secondaries are there to get the primaries over that hump without having them work as close to their design limit (has to do a lot with the atomization of the fuel).
 
#7 ·
Chapter 1, page 11 of the 04 zx6rr service manual, it's technically page 21 though.

Here's the exact text:
Technical Information – Twin Fuel Injector System
This model has a twin fuel injector system to improve engine performance. The secondary injector
for each cylinder is installed in the airbox at the mouth of the throttle body. By spraying fuel further
upstream in the intake tract, the air is cooled down so the fuel mixture becomes more condensed,
allowing more of mixture to be drawn into the combustion chamber to increase power.
The primary injector closest to each cylinder is a fine atomizing type injector and produces a fine
fuel mist for better combustion and more efficient fuel consumption. The secondary injector is a conventional
type injectors.
While the primary injector operates whenever the engine is running, the secondary injector operates
only at high engine rpm and under heavy engine loads. The operation of both injectors is controlled by
the ECU.When both primary and secondary injectors operate, they inject the same amount combined
as when just the primary injector operates.​

I can see why they'd need less fuel at the higher rpms. The engines are designed to make power there so they're the most efficient in the range, needing less fuel to make each horsepower. I'd need a BSFC to compare with a dyno to verify, but assuming the BSFC is typical of other gasoline combustion engines I've looked at then you'd need around 1/3 of the fuel in the efficient range to make the same power as in the inefficient range. Although you usually end up making 3-5x the amount of power and use more fuel.
 
#8 ·
The problem I see is that our bikes do not have O2 sensors or a/f sensors. So by you unplugging the fuel injectors the ecu cannot add additional fuel to the primary's. It is not in the programming. If it were, when your secondary's went bad, it would simply compensate with primary injector pulse width, but it won't do that.
If it had an wide band, theoretically it could get there using fuel trim. Without any sort of feed back, it has no chance.
 
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#10 ·
As I pass the 9k-10k rpm threshold the bike doesn't necessarily lose power, but the hp curve feels like it's leveled off. And around 12k rpm the bike no longer has enough power to continue in that gear and I'm forced to upshift. And through each gear it's a similar feeling, around 12k rpm it just can't continue revving with the load. I did a pull on my private track the other day when I posted this and after hitting 12k in 3rd, I shifted to 4th, which was only around 100-105mph. In fourth the bike literally did not accelerate at all, so I shifted up and just let out of the gas.

The reason I'm thinking it's the fuel is because towards the end of the life of my last engine (hole in air filter sucked up sand/dirt and trashed it) I was having the same problems. I haven't been riding hard on this engine yet since the bike has been riddled with other problems of things breaking, but the only things I swapped from my old engine over is the entire fuel system.

Regardless, I'm about to ride an hour home to my garage from school today and do some diagnostics, luckily I have an entire extra air box including different secondary injectors so I should be able to find out rather quickly if those are the issue.
 
#13 ·
Well, after a rather thorough and exhausting diagnostic process, I'm going to go ahead and replace the fuel pump. It's hitting the proper pressure when priming and the lines aren't leaking anywhere, but when I did the flow rate test it fell flat on it's face. It's supposed to pump out 67ml in the 3 seconds of priming but was doing a max of about 52ml with a 12.8V reading off the battery terminals, and approximately 45ml with a 12.0V battery charge.

Everything else tested fine for the most part. My injectors were reading a little low on resistance (0.1ohms), but it's a good 30 degrees Fahrenheit colder then what the service manual gives the specs at. Just for good measure I hooked up the secondaries to the fuel line and jumped some power over to them so make sure they all worked, and the sprays were similar, which they were.

So yeah, I'm getting a new fuel pump, and spending another 300 bucks on this thing. In another year at this rate the entire bike will be brand new.

Thanks for the help guys.
 
#15 ·
rofl, this one is way worse. I think I've sunk more into this 04 in the last 12 months than I would have if I'd bought an 07.

Oh well, I love this damn thing. By the end of the year after I finish up my bachelors I'll just get a new bike and toss some track fairings on this thing. That'll justify the cost....somehow or another. :D
 
#17 ·
Just a little follow up, replaced the pump today which took me under 10 minutes since I'm so damn proficient and ripping my tank off. Replaced my plugs as well and I'm glad I did since the old ones looked terrible due to the fuel issue.

Did a pull on a highway onramp, cleared 14k rpm in first before shifting into second and lifting the front well off the ground. Look like my fuel issue is gone, thanks for the help guys.
 
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