diagnostic CPU running wild!

Well, I decided to do the battery sensor wire mod a couple of weeks ago, and it works great! No more annoying flashing!

I still have an ailment though, and that is that the CPU goes through the laundry list of checks everytime the engine gets up past about 4500 RPM. The warning light does not come on, but it will just keep cycling through "STAND" on down, and won't stop until the RPM's fall below 4500. Weird. What up with that?

Oh- and it tends to stay on "STAND" much longer than the other checks. Like it will stay there for 3 or 4 seconds, then will continue the cycle as normal.

BTW, bike is a 81 750 Seca.

Thanks, Chad

 

It would seem that the "latch" circuit is possibily fried. When the bike is first turned on, the cycle begins and runs through it's self-test routine. After one cycle, the computer is supposed to "latch" and hold there untill the key is cycled off and back on. I'm puzzled as to how it is affected by RPM. Did you or the P.O. possibily miswire the connection? Have you recently replaced the instrument cluster? The Haynes says that use of bulbs of the incorrect wattage, connecting accessories to the CPU or related circuits, water intrusion, shocks or pressure on the face of the LCD, or magnet (magnetic field) exposure can all cause damage to the LCD or CPU. Any of those symptoms fit?

 

I'd try a heavier resistor on your bypass. Maybe the CPU is seeing too much voltage.

 

Mine started doing that when the Speedo was unhooked.. like it kept detecting something was fubar..

I also notice it when my tail lamp light comes on
(think i got a marginal bulb or bad connection.. works so havent tracked it down yet)

Maybe it runs when it detects a fault ?

 

I used a 4.7ohm resistor when I did the battery mod, I'll take a reading with my multimeter to see what kind of V that wire is seeing.

I'm starting to think it may be something to do with the "CHECK" switch. Like the vibration of the bike when it gets up to high RPM's makes the connection go haywire or something, cause I just recently noticed it will run through the check menu even when I hit a bump at low RPM's.

I'll look at my wiring diagram and try to hunt down some connectors that probably need a good cleaning or something.

 

I was going to suggest investigating your 'Check' switch - that was the first think that popped into my head.

 

best guess is what obliv mentions.

 

clean the switch!

if that doesnt solve it, try swapping your tci box with a known good one ( if a friend has one) other wise, perhaps a loose wire too the switch.

i had similar problems on my 750 seca, it was infact the switch