"DCI" box ?

[turbocamino]

From Mr Pat.  " DCI (digital controlled ignition) uses a single pick up coil which were installed on the USA '88 to 95 FJ's
     The DCI boxes used a remote vacuum advance module (better design, easily replaceable) therefore, ""there is no vacuum port on the DCI box""                                                                                      I'm slightly confused ...as i thought the vacuum line, from Intake runner #2 on my 89, going up under the front nose fairing near the headlight, was going to the DCI box? 

[Pat Conlon]

No, the vacuum line was not going to the DCI box....the vacuum line was going to the remote vacuum sensor located under your fairing on the right side. There are 2 wires that run from this remote vacuum sensor back to your DCI box which located under the side panel on the right side.

Clear as mud?

[Pat Conlon]

See #24 for the remote pressure (vacuum) sensor

Although, I stand corrected....it looks like your DCI is located under your fairing, not side panel.

[turbocamino]

DCI box being #15, vac sensor #24... are both these related to emissions?  I searched around and can't find any info on what they do?

[Pat Conlon]

#24 and #15 work together to control emissions as I have previously posted. When the throttle plates close and the vacuum reaches a certain level #24 sends a signal (via 2 wires) to #15 to advance the ignition timing.

In the earlier '84-'87 FJ's (USA versions) #24 and #15 were combined into one TCI box. In those models when the vacuum diaphragm leaked air, you had to replace the whole TCI box (or abandon the vacuum advance)

When Yamaha went to the DCI ignition on the '89's they wisely separated out the pressure (vacuum) switch into a separate unit as you see above.

It is important to note that not all FJ's have this vacuum advance feature. I know the USA versions do, but I've been informed by my Aussie brothers that their bikes do not have this vacuum advance feature, nor do they have a side stand safety switch, small detail differences.

The FJ runs just fine without this vacuum advance, as the Aussies will attest. Again, this advance only happens when your throttle plates are closed. It has no performance benefits other than keeping your plugs clean (and white)

Cheers.   Pat

[Pat Conlon]

FYI, #29 below is your vacuum line run from #2 intake to your pressure (vacuum) switch.

[turbocamino]

  Thanks very much for the clarification.  Can one assume that if this "system" fails, it just won't advance timing as intended on deceleration...and no other issues could happen with timing function?     Ive never heard of it being a possible vacuum leak?

[Pat Conlon]

Yes, the advance system only works on closed throttle deceleration.

A failure in the system would mean a vacuum leak at either 1) the hose or 2) the pressure (vacuum) switch.

On your '89 you have 2 options.
1) cap off the vacuum port at the #2 intake manifold and abandon the vacuum advance system, or
2) repair the vacuum hose or replace the faulty pressure (vacuum) sensor.

How to tell? Disconnect the vacuum hose at the intake manifold, now suck on the hose...if you can draw air thru the hose you have a vacuum leak. Not good. Fix it or cap it off. You do not want unmetered air going into your #2 cylinder causing a lean condition.

I have the vacuum advance capped off on my '84, with no problems.

If you do cap off the vacuum port on the #2 intake, be sure to use the oem Yamaha heavy rubber caps on this port. It gets really hot in this area and the thin walled vacuum caps used for automotive applications are not suitable for this high heat area. You will end up splitting the caps....it's just too hot in this area. Ask me how I know.....

Cheers