Before I posted this thread I thought of removing the resistor from a relay to see if I could reproduce the problem, but I wasn't sure if that would result in damage to the computers. Would it?
It might damage the ICU although I think that risk is very low. The resistor is for damping the voltage spike that occurs when power is removed from a relay coil. The risk is that removing this damping resistor will possibly take our a transistor driver in the ICU from the resulting voltage spike that occur when the bike is powered off. As I said, this is a low risk. You probably could do it and see if it changes the nature of the failure.
The time I had it running with the pump disconnected, I rode it around the block, about one kilometer, which seems to have done no damage.
However if I remove the wire from pin 12 of the fuel injection unit (earth to injectors) and earth it, would that be a way to test it without risking damage to the computers, or anything else?
Or leaving it connected and earthing the injectors some other way?
Removing the wire from Pin 12 of the ECU plug would not be catastrophic. What you’d be doing is removing the ability of the ECU to control the injectors. If you grounded this free floating wire, then all the injectors would open up fully for the duration of time that the lead was grounded.
OK, might cop some flak but anyway...
Another beautiful day... another beautiful ride... an historic day too... riding along... all of a sudden a thought bubble from nowhere... disconnect the injector earth's and earth them, then earth the injectors.
That should be a way to provide constant earth to the injectors without risking damage to the computers.
Yes?
Yeah. As I mentioned above, grounding the Yellow/Grey wire from Pin 12 will open all the injectors fully for the duration of time you ground the wire.
I suspect that the engine vacuum combined with the injectors being open 100% of the time would permit enough fuel to enter the cylinders to support combustion. If the fuel pump was to be started, the additional pressure would flood the engine and stall it. I think this is what you saw originally.
It’s perplexing to me how this problem was solved with replacing the FI relay. The FI relay supplies power to the injectors but doesn’t control their dwell time; that’s done by the ECU. The injector dwell time is influenced by the TPS switch and engine temperature. If the TPS is at WOT, then the ECU will set the injector dwell time to almost 100%. Did you test the condition of the TPS?
Another condition that could cause fully open injectors is if they are dirty. I guess your injectors are clean because you claim to have a perfectly running engine at the moment and you didn’t touch the injectors. So, that’s not a possible cause.
I’ve gone through the startup sequence from Bert’s page, thinking “what would happen of the FI relay was defective?”. Here’s a normal sequence.
1. The starter relay and Fuel Injection relay close, Hall sensors get power.
2. The FI relay energizes (+) the fuel pump, the idle switch, the injectors and the air flow meter.
3. The Jetronic receives (pin #4) the signal that the engine is starting and it sets itself on starting mode (enriching the air/fuel mixture)
4. ECU pin # 9-10-14 send power to the ignition coil
5. ECU pin #8 send engine rpm info to pin #1 of FI computer
6. ECU pin #7 sends ground to the coil of the FI relay as soon as the starter switch is depressed. The ground will stay on after the starter switch is released as long as the ECU receives a signal from the Hall sensors.
Let’s say one of the 87 contacts on the FI relay is defective but the other works. That means injectors get power but the temp relay and fuel pump don’t get power. When you crank, the ECU thinks the engine is cold and enriches the mixture, increasing the injector dwell time. Since the injectors are open, cylinder vacuum draws fuel into the system and combustion happens (ICU tells the plugs to fire, AFM meters correct amount of air, etc.). So your engine fires and keeps the RPMs up, drawing sustaining fuel from the fuel system. But the engine temperature remains “cold” so the injectors remain open. Replacing the FI relay corrected this broken contact situation and brought the system back to normal.
Well, that's my half-baked theory. Maybe someone else has a better one.