1995 90HP Yamaha - Bypass Mode

[90HPYam1995]

Been reading this forum for some time and decided to post - this issues appears several times, but no where has the actual problem been found - or at least shared.

1995 2 Stroke, 90HP, TLRT

Runs great in Bypass Mode, two yellow wires on CDI box disconnected - when hooked up - motor fires but does not stay running.

Bypass Mode - runs on Cylinders 1 and 3. The box says this is a timing issue.

What has been replaced so far by two different dealers are: New CDI Box, Pulsor, Stator, Charge, Crank, Rectifier - the only think remaining is the Flywheel.

THis is not an electrical problem, harnesses has been isolated and still have the same problem.

When in Bypass mode there is no spark going to Cylinder 2 - this is normal and should be.

Compression/Fuel Good - but engine runs great in bypass mode.

Sometimes I can disconnect the crankposition sender and the engine will also run on 1 and 3.

Can this timing issue be caused by weak mags in the flywheel?

Any help would be great - also every wire has been traced out, and goes where it should, and not shorted to ground.

Thanks so much....

[rodbolt17]

get ign timing out of your head.
its not a timing issue.
get the fact it runs great on 2 cylinders out of your head, it doesnt.
its broke.
its had parts chunked at it.
use the dealer locator function from yamaha and find a dealership near you that employs a master tech, take it there.

[90HPYam1995]

Understand

Problem is where I live, not easy getting to these places - I am not going back to the two local ones that tried. I did make an appointment with one in Charleston - call and made appointment 4 June - they have me penciled in for July 17th as the first opening - just was hoping for some help prior.

[99yam40]

what box says it is a timing issue ?

A motor needs Good compression, good spark at the proper time, and proper air/fuel ratio to run properly.
Compression spark and timing can all be measured. Without some info from you we have no idea what any of them are.
You say timing issue, but what is the timing problem?

I hope you did not have to pay for all those parts if they were not needed

[robert graham]

I have a very similar 90C Yamaha, and sorry for your problems, and will be interested to hear the outcome. Seems you've spent a small fortune on replacement parts, and no real solution yet. Hopefully a real Yamaha Technician can be found to isolate this issue. I'm assuming you've checked many of the more obvious culprits like electrical/battery connections. I've found it's a good idea to remove each connection, clean/polish with a 3M Pad, a dab of grease, and re-tighten. Good Luck!

[90HPYam1995]

Thanks for reply

Compression is 118, 118 and 120 on 1, 2 and 3.

Carbs cleaned, and fuel checked by a dealer.

This motor is unique in that there is only one pulser that controls cylinder 1 and 3. The ignition time for cylinder 2 is entirely con*****ed by the computer. The book says that when any problem occurs and the computer automatically goes into bypass mode, cylinder 2 will not fire and time will be fixed.

Charge coil output: 170v, in spec at 1500 rpm
Pulser Coil: 14v, in spec at 1500 rpm
Lighting Coil: 25V, in spec at 1500 rpm
Crank Position Sensor: 25V, in spec at 1500 rpm

[90HPYam1995]

Robert

Yes, went hand over hand every connection, cleaned, tested to ground, tested between every other wire.
I have isolated the entire engine, every harness that runs forward removed, basically a stand alone engine being started with a starter switch.

I don't have the ability to run to a dealer, the one I finally got is 3 hours away that has a master tech as rod bolt recommended - but he has a 5-6 week wait.

[99yam40]

Does the manual say what kind of problems will cause it to go into bypass mode?
That would be where I would be looking.

Is this bypass mode different than the safe mode from overheat or low oil level?

[90HPYam1995]

Yep

Bypass is different then safe mode - safe mode is oil or high temp which it is not, I have traced that until blue in the face.

As for Bypass - the book says a timing issue - and all of that has been replaced, recommended by the dealers I have had to use to this point.

[99yam40]

crankposition sender is the only thing I can think of that would make any sense to cause it to go into bypass mode.

If it does not know what that was doing it just faults into bypass

Sensor or wiring maybe

[robert graham]

That's for sure a curious problem, especially since you've replaced about everything electrical on the motor....it's way beyond my skills. I'll be very interested learning the outcome. Good Luck!

[90HPYam1995]

Crank Sensor

I agree, but it has been replaced, I know the position is critical, and is .8mm away from teeth on flywheel, book says .5 to 1.5mm.

I know this sensor counts the number of teeth passing the pickup and able to calculate engine rpm, and also detect crank phase angle from a specified point on the flywheel, that is why I asked if something could be wrong with my flywheel - just guessing there.

[90HPYam1995]

Here other other posts with exact same problem - and no resolution

http://www.yamahaoutboardparts.com/f...n-th12805.html

http://www.yamahaoutboardparts.com/f...d-th16616.html

http://www.yamahaoutboardparts.com/f...s-th11253.html

[90HPYam1995]

Rodbolt

Do you see anything common in these other posts - just some direction while I wait a month to see a tech on this?

[robert graham]

I wish I had some great new ideas for you, but sounds like you've checked, cleaned, tightened or replaced about everything in the electrical system. Hope it doesn't turn out to be some super-simple, obvious and very cheap to fix item, but I'll be very interested in hearing what it is. Least you've got a nice collection of extra/spare parts! Good Luck!