We are gathering data to find out what's wrong with harness that's causing engine to die. We already KNOW it's voltage drop that's doing it. But what we DON'T know is how much of voltage drop that is. And where the short is located. So put all bulbs back in and do these tests:

1. measure battery voltage with bike running, volts =???
2. keep probes on battery and step on brakes, volts when engine dies = ???

3. measure voltage at ECU blk/wht power wire with bike running, volts = ???
4. keep probe on ECU blk/wht power wire and step on brakes, volts when engine dies ???

 

if it is indeed a short, it should be blowing the fuse though. have we verified that he has a 10a fast acting fuse and that it has been ohmed out to ensure its good? one thing I question during his last test is this.



he is using his positive lead to probe the wires, but is the negative lead at the battery or is he on the green wire at the ECM?

I get that you want to see the extent of the voltage drop with the bulbs in, but when it kills the bike you are only going to see battery voltage and not rectified voltage so its going to drop regardless.

 

Results from Oct. 24, 2023:1. measure battery voltage with bike running, volts = 14.54 volts

2. keep probes on battery and step on brakes, volts when engine dies = 12.49 volts

3. measure voltage at ECU blk/wht power wire with bike running, volts = 13.89 volts

4. keep probe on ECU blk/wht power wire and step on brakes, volts when engine dies ??? = 11.89 volts

All fuses under the seat in the fuse block are all the same, red color 10A mini-fuses that were each checked out to be good by using a multimeter.

My results for the tests below were obtained yesterday by connecting my COM "black" multimeter lead to the negative lug of the battery and back-probing the ECU blk/wht wire with the red lead of the multimeter.

3. measure voltage at ECU blk/wht power wire with bike running, volts = 13.82 volts

4. keep probe on ECU blk/wht power wire and step on brakes, volts = 13.82 volts with brake light bulbs removed, front brake lever pulled in. Doing this test with brake lights installed causes stall.

Doing this test with only one brake light bulb installed causes a small reduction in power = 13.74 volts.


Should I have connected the COM (black) lead from the multimeter to the green wire at the ECM for the tests above?

 

True, this is start of test sequence with battery as control sample. Then measurements at other locations can be compared to this. With working wires and connector, supply voltage at any power wire cannot drop below battery voltage. Only difference is percentage of current supplied by either battery or RR. With sufficient RR output above battery, ~14-14.5v, all operating current comes from RR with RR supplying additional amount to recharge battery. At low RPMs, if staror can't supply enough to be above battery, say only 12.9v, the battery's 13.7v will still be what ECM is supplied, 100% current from battery. And some percentage in between when RR output rises to match battery's.

Maybe "short" isn't quite term I'm looking for, maybe "drain" or "hole" might be more appropriate. What we're trackjng down are sections of wiring with higher resistance at connectors due to poor terminal connections from corrosion or insufficient clamping. This will result in certain voltage drop when going across. The higher the current flow across, the higher voltage drop. Based on V=IR equation.

So clue is ECM dying when all brake bulbs are in place when brakes are applied. Yet highbeams don't cause this effect. So we can rule out forward section of harness. Trouble may be in section of wiring that supplies power to both brake-light circuit and ECM.

 

Nov. 10, 2023 Update
Extremely frustrated with my 2000 CBR 600 F4 not running properly, and with influence from some friends, I caved, and took my motorcycle into my local private owned motorcycle service and repair shop for their mechanic to complete the trouble shooting and repair. The mechanic, with 15 plus years of experience had never witnessed a CBR with the conditions of my bike. At first with the engine running, he started pushing and pulling on connectors of all exposed relays, ignition control module, and any power plugs that could be reached to find no problems. The steering was turned many times full right to left motion without any change in the RPM or sound of the engine running at idle. When the brake lights come on, the engine would stall. The engine runs but not well.
I left the motorcycle with the shop and the next day was called and informed that the factory original ignition control module had been replaced and the stalling problem with the brake lights or other power draw, was resolved but the engine still sputtered and back-fired when revved up. Mechanic suggested the spark plugs and fuel filter be replaced and I gave the approval to proceed.
Following day, stopped in to find the mechanic had replaced the spark plugs, all four ignition coils as he said there was corrosion found on the top of two of my old spark plugs and also had replaced my new July 2023 installed fuel pump and the power relay. The engine still ran like crap so the problem was not resolved and many of the parts installed were not needed.
Can ride the motorcycle but sputters at all RPMs, not constantly but often. Could say it stutters like Elmer Fudd. Left with a huge repair bill and a s h I t bike.
I feel the problem is due to poor spark control. Ignition control module (ECM) replaced so the other item recently touched was the pulse pick-up coil that was an aftermarket China made unit. I plan on replacing the pulse coil with another brand in hopes that that corrects the poor engine operation.
The only other item I worked on was the ignition key switch and only to replace the Zener diode. The motorcycle key works and controls as it should, but could the diode that I installed potentially cause poor engine operation? I am thinking that this diode works as a "pink wire" permissive to the ECM so it would satisfy and allow spark or not, and have no other impact on engine operation.
Any suggestions for additional checks?

 

No diode only tells ECU if key was used to turn ignition switch ON. If not, ECU won't turn on pump or fire sparks. As test:

1. key ON

2. measure power at pink wire at ECU connector. volts = ??


Runnjng poorly can be caused by numerous things:

- low compression
- mis-adjusted valves
- clogged fuel-filtre
- mis-adjusted TPS
- clogged injectors
- ignition-coils out-of-spec
- bad wiring between ECU to injectors and/or ignition coils

All of these have a number specified in manual that you can measure to determine where problem is.