2001 90TRLZ Bypass Mode & CDI

[94Burban]

hey guys
was researching why my 90hp ran one sunday just fine; and 36hrs later on tuesday morning if would not start. It will crank and fire for a second; but not run.
I found a post on here from 2012 that i don't believe was answered or resolved but i have the exact same issues. I have copied it here for reference. We have checked all coils; pulser coil; CPS; etc.
If we use the manual CDI bypass it cranks right up. I've also checked the key switch and harness and all seems to tone out fine.
We are running out of ideas.
Thanks

[94Burban]

Jeez- Tough Crowd
Thanks

[DennisG01]

Jeez- Tough Crowd
Thanks

Jeez, impatient much? It's only been a day. Good answers sometimes take time. Besides, it's not like you're paying for this service.

Seriously, though, there are some very knowledgeable people on this forum... but maybe they don't work on the same schedule as you do, you know? I'm being a little sarcastic with my replies, but give it some time. If someone that knows the answer reads it, they'll respond. You don't want to alienate anyone by appearing impatient.

[boscoe99]

One particular motor having the exact same issue(s) as a different motor means almost nothing. The same issue(s) can be the result of an entirely different problem. To think that what fixed one motor will automatically fix a different motor will lead one to go down deep into the rabbit hole.

[99yam40]

You say you checked everything, so give us some of that info.
does it have spark on all plugs or just some of the plugs when you test in both situations?

have you checked the peak voltages into and out of the CDI in both situations?
loaded and unloaded
can you give us those readings?

[boscoe99]

What results did you get when testing the following:

Crank position sensor output
Pulser coil output
High speed and low speed charge coils output
CDI outputs

Why was the key switch and harness checked?

[ausnoelm]

Not too sure about the term, "CDI bypass"

[boscoe99]

Not too sure about the term, "CDI bypass"

When the two yellow wires from the CDI assembly are disconnected so as to get the motor started.

[94Burban]

Hey Boscoe; that situation that old post described is VERY similar to mine at the moment. Just looking for ideas since I'm a shadetree mechanic. The key switch was checked to make sure the "run' circuit was not bad at the side mount throttle control.

99YAM40; I'm sure I have not checked everything but i listed the ones that have been checked.

I don't have the test readings on paper since a friend was helping and the info on the analog meter was showing the items we tested to be OK.
I'm trying to find a service manual to follow all the steps correctly; but don't have one yet. And I couldn't find the correct procedure to test the CDI unit anywhere so far.

thanks for the input and any help to lead me in the right direction.

[94Burban]

Oh I forgot to mention
We borrowed a working CDI off of another 90HP and same problems. So we assume not the CDI unit is causing the issue.
thanks again !!!

[pstephens46]

[QUOTE=boscoe99;n234082]

When the two yellow wires from the CDI assembly are disconnected so as to get the motor started.

What does that actually do to allow motor to run? Does it lower the amount of current needed to operate the engine?

[boscoe99]

[QUOTE=pstephens46;n234149]

When the two yellow wires from the CDI assembly are disconnected so as to get the motor started.

What does that actually do to allow motor to run? Does it lower the amount of current needed to operate the engine?

The CDI can detect certain input faults and put the motor into what is called the bypass mode. It then runs on fixed timing instead of variable timing.

Disconnecting the yellow wires manually puts the motor into the bypass mode. As a troubleshooting measure or a get home measure when things aren't going well otherwise.

Some manuals say to limit the RPM to X if and when operating in the manual bypass mode. I see that the 90 HP two stroke manual does not.

This is the 20,000 foot altitude view. About all that I know.