3.0 Mercruiser Alpha One Base Timing Issue

[Bridgerecording]

Hi all, here's hoping someone out there can shed some light on my latest challenge...
I have a 3.0 mercruiser running EST ignition.
I have set the base timing as per the manufacturers recommendations -
1. Start engine and allow to reach operating temperature.
2. With engine running, install a jumper wire across
the two WHITE leads on the distributor.
3. Bypass the shift interrupt switch by disconnecting
wires at shift interrupt switch. Temporarily join the
engine harness wires together.
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.
8. With timing light still connected, and engine at
IDLE, verify that timing did advance to 12? BTDC,
(plus or minus 2?). At 2400-2800 RPM maximum
(total) advance is obtained and should be 27?
BTDC (plus or minus 2?).

All this goes fine except when I recheck the timing with all wires back to default I find the timing is still at 1 degree atdc.
When 1st start the engine and check the timing it is at 8 degrees btdc then the rpm drops and the timing has shifted to 1 degree atdc??
It seems that it is going back into base timing by itself...
When I increase the rpm it advances as per normal specs...
Any ideas??
Cheers
Mark

 

[Don S]

Re: 3.0 Mercruiser Alpha One Base Timing Issue

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.

You seem to be missing part of step 6 which is missing from the manual.

After rechecking the timing, you need to shut off the engine.

THEN you move on to step 7.

 

[Bridgerecording]

Re: 3.0 Mercruiser Alpha One Base Timing Issue

Hi Don
Well I have rechecked the timing using the procedure you added but still it is not convincing me...
Please correct me if I'm wrong ...
The shift interrupt switch is designed to reduce engine rpm and load on the gearbox when it is being taken out of gear. It does this by retarding the ignition which in turn drops the rpm, (only momentarily).
The base ignition timing, (in my case 1 degree ATDC) is what the timing returns to when the interrupt switch is activated, (or by passed and as in the timing procedure).
So again if I am correct after the timing has been set and the normal configuration is returned the timing should then advance back to 10 +/- or minus 2 degrees.
Well what this is doing is after completing the timing procedure I check the timing and its still at 1 degree ATDC then if I start to bring the rpm up to around 800 -900rpm the timing jumps straight up to approx 8 degrees which in turn raises the idle speed to around 1000rpm
So then I try reducing the rpm with the idle screw. It starts dropping then it suddenly drops again and the timing is back at 1 degree.
This doesn't seem right to me and it makes the boat a bit touchy to control.
So, I'm thinking it must be the module, ($320 or there about for genuine) though I would like to be sure...
Does it sound like the module could be at fault or could it be the wrong module??
I have tried confirming the part number on it (below) but have had no success, do you recognize it as being genuine? -

MG-9-29800R
3410 CN

Engine Serial Number OM651424
Engine Model Number 4-111021N2

Thanks for your help
Mark