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Discussion Starter · #1 ·
Hi guys and Gals, I'm hoping you can help me out here. I'm working on a 2004 GSX-R 750 K4 for my boss. It's throwing up FI codes C25 & C26. The bike revs up to about 8000 rpm then looses power and drops to about 6500rpm and picks up again to 8000rpm and repeats. like a rev limiter cutting in but slower.
Checking on this forum and the book those codes are for the ignition signal to no# 2 and no# 3 cylinders.
So I swapped out the plugs........ No change, still C25 & C26
I swapped the coils about ......... No change, still C25 & C26
I checked resistance in the coils... All good.
I checked coil wiring and all seems ok.
This all leads me to the Crankshaft Position Sensor (CKPS), The ECM or Wiring in between.
My questions are...
Rather than strip the whole wiring loom out can anyone tell me where the common joints and plugs are that I can check?
Also Does this GSXR run a "Wasted Spark" type of firing order i.e cylinders 1 & 4 spark at the same time (1 on power and 4 on exhaust) and the same for 2 & 3? Because I'm thinking if the CKPS was at fault it would throw up faults for all 4 cylinders.
Thanks in advance
 

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If it was the CKPS or the CMPS, you'd get those codes. Codes 25 and 26 are the coils from #2 and #3. If you swap 1&2 and 3&4, but still get those two errors, it's most likely wiring. Check the connectors at the coils first, then the connectors at the ECU.
 

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Discussion Starter · #3 ·
Thanks The Geek, that's what I thought. There's a fair bit of wiring on this bike so I guess it's start at one end and work through it. The coil wires seem ok so will start at the ECM and work forward :)
 

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Discussion Starter · #5 ·
I have both a Haynes and a Suzuki Factory manual. They are where I got the codes and test specs for the coils from. What puzzles me also is that they state that if 2 or more of the codes for the ignition signal are present the bike will not run. But it does, just with the faultering at 8000rpm. I'll just keep on at it :).
 

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Wouldn't be the first misprint in the manual (4-20). It might just mean the component detection signal though. I don't know about "just keeping an eye on it". Misfiring like that is hard on the engine, and riding like this is just asking to get stranded somewhere. I'd encourage you to dig deeper until you find a solution before taking her out.
 

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Discussion Starter · #7 ·
You're right there, it wouldn't be the first miss print, I've seen a fair few in manuals over the years. The bike is sti stripped down so not going anywhere till I've got to the root of the issue. Time is an issue at the moment though. I'll keep at it and report what I find.
 

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Discussion Starter · #8 ·
Finally we've got round to double checking everything and came to the conclusion it was the ECM. We got another one and just tried it. The bike is still the same :-(.
We have yet to get the Fi light to come on to see if it's the same codes that come up with the same codes.
All parts check out ok to the book specs.
Any other suggestions???
Cheers
 

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Discussion Starter · #10 ·
OK, good thought but this problem started about a year ago and the fuel pump was changed then to no effect. I've only known my boss and his bike for the last 6 months. we've learnt a lot in the last 6 months about the "dealer Mode" and how this bike works.
This fault is very precise and has not changed. He can't afford to just keep changing parts. What we need is a perfectly healthy bike to borrow bits from to find the offending part.
After it was last pulled apart to run the meter over it, with the original ECM in, was when the Fi light stopped coming on. but the fault persists. Our local bike workshop said "All they could do is throw bits at it until they find the fault"
 

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Your local bike shop are idiots. The ECU function checks everything. No FI light, but a problem running means a mechanical condition.

When you say fault, you're talking about the behavior of loosing power at 8k, then dropping back to 6500. If there's no code, it's not getting enough fuel, enough air, or enough compression to function properly. Any decent mechanic could find that problem in a couple hours topps.
 

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Discussion Starter · #14 ·
Since this problem started the fuel pump + associated parts have been changed. More recently coils, plugs and ECM have been changed. The problem has never changed, it always cuts out at 8000rpm (indicated).
 

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I had a 01' 600 throw C25-C27 because of a charging issue that killed my ECM. Only one pin on the ECM, for #2 ignition wasn't working. I bought another ECM for 01-03 GSXR 600 and the bike worked but threw a C29. It turned out to be the wrong ECM. Bought the right one and everything was ok. I'd check to make sure correct ECM, check the original ECM pins for cyclinders 1 and 4 and the wiring harness for cylinders 1 and 4. You shouldn't have to check the whole harness just the wires causing C codes.

You shouldn't feel obligated to replace parts that aren't the cause. The 8000rpm cut is common STVA problem prior to complete failure that cause C29.
 

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Discussion Starter · #16 ·
Hi Jodydaniela, we've never had a C29 code come up. After the fuel pump was changed the next thing that was suggested was the STVA. The butterfly valves work exactly as described in the book. With the airbox open we've watched them and run a meter over the whole assembly, the STVA checks out fine. According to all information gathered the ECM will only fit K4 and K5 (2004-2005) models. I've had a Google hunt and found a pic that identifies what each pin is for so will check the appropriate wiring. Visually they all look fine, all clean and straight. Thanks for the information :)
 

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Discussion Starter · #17 ·
Hello All, We have finally solved this problem. It was the connection to the ECU from the wiring loom. after changing the connectors (which was a right pain) the symptoms changed slightly. So a decent used loom was eventually sourced and fitted. the K4 is as right as rain now. Thanks again for all your input. :)
 

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Hello All, We have finally solved this problem. It was the connection to the ECU from the wiring loom. after changing the connectors (which was a right pain) the symptoms changed slightly. So a decent used loom was eventually sourced and fitted. the K4 is as right as rain now. Thanks again for all your input. :)
Hi, i have same exsctly issue with yours, since you already find how to fixed it. Do you have a picture of the connection ? And where did you bought that ?
Thanks
 
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