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3.0L timing adjustment

D

DJK55

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Following the manual instruction on setting the timing on a 1994 3.0L mercruiser engine when I jump the two white leads on the distributor there does not seem to be a change in timing advance. My understanding is that when the leads are connected the timing is returned to base which should be 1'BTDC. When the jumper wire is removed the timing should advance to around 12'BTDC. Any suggestions on why jumping the wires does not impact the timing. Suggestions?
 
3. Bypass the shift interrupt switch by disconnecting
wires at shift interrupt switch. Temporarily join the
engine harness wires together.
IMPORTANT: Do not fail to reconnect these two
wires to the shift interrupt switch when timing
procedures are complete.
4. With timing light connected, check timing. Timing
should be 1° BTDC.
5. If required, loosen distributor hold down clamp
and rotate distributor to obtain specified timing.
6. Secure distributor hold down clamp, and recheck
timing as above.
7. Reconnect the two wires to the shift interrupt
switch. Remove jumper wire at distributor white
leads.
IMPORTANT: Be sure to remove jumper wire before
 
Thanks for the reply. This the procedure I’m following. Steps 1-3 include jumping the two white wires in the distributor to put it into base timing. When I do that the timing doesn’t change from the 12’ BtDC that it is at now. Also, when I “join the engine harness wires together” , those going to the interupt switch, the engine dies. If I disconnect then it runs fine.
Any suggestions?



Bt Doctur said:
3. Bypass the shift interrupt switch by disconnecting
wires at shift interrupt switch. Temporarily join the
engine harness wires together.
IMPORTANT: Do not fail to reconnect these two
wires to the shift interrupt switch when timing
procedures are complete.
4. With timing light connected, check timing. Timing
should be 1° BTDC.
5. If required, loosen distributor hold down clamp
and rotate distributor to obtain specified timing.
6. Secure distributor hold down clamp, and recheck
timing as above.
7. Reconnect the two wires to the shift interrupt
switch. Remove jumper wire at distributor white
leads.
IMPORTANT: Be sure to remove jumper wire before
Click to expand...
 
Then you dont have electronic ign or the shift interrupt is wired wrong.
activate the shift interrupter, if it kills the engine your wired for points
The purple in the harness supplies 12v to the ign system to aid in shifting out of gear
your switch should be a button type
 
Last edited:
I'm inclined to agree with the Doctur....what color are the wires at the shift interrupt switch and the wires coming out of the harness going to that switch?
 
The wires to the interupt switch are purple and white/green.

I understand, I believe correctly, that the interupt switch momentarily cuts off the ignition to assist shifting. Would that not mean that disconnecting the wire to the switch and connecting them togetherwould do the same thing...cut off the ignition?

makomark said:
I'm inclined to agree with the Doctur....what color are the wires at the shift interrupt switch and the wires coming out of the harness going to that switch?
Click to expand...
 
That's the way the point style ignition wiring works with the interrupt switch....with the electronic ignition, the shift causes the module to change the timing to release the load on the prop shaft.

If the ignition advances, and is in the service range at the rated RPM, I wouldn't worry about it....it sounds like it is very close already...
 
Thanks for the responses. As it turns out it is all in the sequence of events. I got this on another site:

Start engine and warm up
- jumper 2 white wires on dist.
- jumper shift interrupt wires (engine stumbles and runs poorly going into base timing mode)
- adjust timing
- return shift interrupt wires, then unjumper dist. wires
- check ignition advance (should be 10-12* at idle)

Done in that order it works as it should.
 
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