Mercruiser pushbutton start + compression test?

[stephenm27]

Does anyone know if the “cranking cycle” started by the Mercruiser pushbutton start can be cancelled?

Background: I’m preparing to do a compression test but have never attempted to prematurely cancel a start of this engine. According to the manuals, the computer takes over when the start button is pressed and I’d like to be sure it doesn’t attempt to crank for 15 to 20 (or more) seconds before the computer decides to stop. Wondering if a second press of the start button stops the cranking...?

 

[Espos4]

I’m not sure, but you could just enable the starter by putting power to the “S” wire. That way you can control the cranking duration.

 

[scoflaw]

 

[stephenm27]

So, I like the idea of using one of these, but I don’t initially see where to connect it. This is a DTS engine so more electronics to contend with.

I did find one of the 5 automotive-like plug-in relays on the intake manifold labeled as “start”. Others are labelled “trim up”, “trim down”, “main power”, and “fuel pump”. I would assume if I rigged up 12V to this relay properly, I can cause the starter to engage...

 

[scoflaw]

how bout just putting 12v to the starter. We're not trying to put a man on the moon here. LOL

 

[stephenm27]

how bout just putting 12v to the starter. We're not trying to put a man on the moon here. LOL

Perhaps you can access the starter on your boat...it’s under my engine, against a bulkhead/stringer on the starboard engine.

Saying I don’t know is always ok. LOL.

 

[scoflaw]

That button works fine on the slave solenoid on top of the engine as well. Y/R wires

 

[stephenm27]

That button works fine on the slave solenoid on top of the engine as well. Y/R wires

That’s what’s confusing to me—I don’t appear to have a slave solenoid on the top of these engines, at least compared to those I can find on youtube and the internet. These 5 relays, the ECM, a 50A breaker and wiring harnesses are it.

I’m currently guessing this relay is switched by the computer at start which activates the starter solenoid.

 

[Espos4]

Remove the relay marked “start” and press the green button to see if the starter engages.

if it doesn’t, then one of those terminals IS your “S” wire on the starter.

 

[stephenm27]

So the start relay is indeed the "S" wire it appears. So I removed the relay and rigged up a handheld switch to jumper the wire for doing the test. This worked out much better than fooling with the pushbutton start. Thanks @Espos4 and @scoflaw for the guidance!

 

[pyro]

I can confirm that you can cancel the cranking by pressing the pushbutton start again. I don't exactly know how fast you can press it, but I would say I have canceled it approx 1 sec later.

 

[stephenm27]

I can confirm that you can cancel the cranking by pressing the pushbutton start again. I don't exactly know how fast you can press it, but I would say I have canceled it approx 1 sec later.

Thanks—good to know info!