2000 Mercruiser 5.0 Thunderbolt 5 Ignition idle issue.

[Yannih]

G'Day all,

I have a 2000 Sea Ray 190 CC with a Mercruiser 5.0 Thunderbolt 5 ignition.
I am having idle issues where the engine idles okay for approximately 1-2 minutes then slowly reduces rpm till it stalls.
I have adjusted the idle rpm adjustment screw with no joy.

Any idea's?

Thanks heap...

 

[04fxdwgi25]

That sounds like a fuel delivery situation.
If engine is a carbed engine, then maybe low fuel pressure to the carb or a bad float adjustment?
Or perhaps the engine is running too rich and dying. Is the choke opening up as it should when warming up?

Kind of difficult to diagnose with the limited info.

Or maybe coil is going bad, breaking down as it heats up, or the ignitions system is doing that same thing.

 

[alldodge]

Welcome

I am having idle issues where the engine idles okay for approximately 1-2 minutes then slowly reduces rpm till it stalls.

Sounds like the oil pressure switch but could use motor serial number

Motor cranks and during this time the fuel pump runs with power coming from starter.

Once motor starts connection is removed from the starter and oil pressure builds. The oil pressure switch "should" now send power to fuel pump but my guess this isn't happening

 

[QBhoy]

Is this a tks ? Regardless, I’d suggest you might have a fuel delivery or quality issue. I’d also check the plugs for condition and/or signs of water ingress, perhaps from manifolds or similar..causing less than idle running at low rpm.

 

[Scott06]

Welcome

Sounds like the oil pressure switch but could use motor serial number

Motor cranks and during this time the fuel pump runs with power coming from starter.

Once motor starts connection is removed from the starter and oil pressure builds. The oil pressure switch "should" now send power to fuel pump but my guess this isn't happening

this is most likely cause based on info given. When it dies look down carb and stab the throttle see if any gas squirts in would bet carb bowl is dry until next cranking and fuel pump gets power off the starter.

Oil pressure switch is above oil filter has two wires on it - I think it is purple and yellow. Jumper the switch out and see if it stays running.

 

[Yannih]

Well here's the thing.
When I had the idle issue it was cold. About 0 degrees celsius.
Ran the boat again today and it was much warmer at 12 degrees celsius with no issue at all with idle.
Is that standard with the setup I have that it doesn't like cold weather?

 

[alldodge]

Well here's the thing.
When I had the idle issue it was cold. About 0 degrees celsius.
Ran the boat again today and it was much warmer at 12 degrees celsius with no issue at all with idle.
Is that standard with the setup I have that it doesn't like cold weather?

This would have helped in first post

So after the motor stalls at 0*C can you get it to restart by pumping the throttle?
Will the motor keep running once it's warmed up at 0*C?

If the above is correct need to adjust your choke

 

[Yannih]

Hi and thanks for the reply.
I didn't add the temperature in the first post as I assumed Mercruiser engines were designed to run efficiently regardless of it being hot or cold.
I guess never assume.
Apologies.

Restarting the engine was not an problem as long as some throttle was applied.
Everything was good.
Except the idle stalling issue.
And I ran the engine to operating temp hoping this would resolve the stalling at idle but the same thing.
And yet at the higher outside temperature all ran well with maintaining idle...

 

[alldodge]

Motor needs more fuel when cold because the fuel doesn't vaporize very well when cold

Adjust the choke so it takes longer to open

 

[Yannih]

Wow, thanks so much for the advise and how to diagram.
I will give it a go.
We are into spring here so probably will struggle to get the lower temps to test though...

 

[Scott06]

Wow, thanks so much for the advise and how to diagram.
I will give it a go.
We are into spring here so probably will struggle to get the lower temps to test though...

Adjust the choke as AD lays out , but if it stalls in colder temps when engine is warm you may to turn the idle mixture (not idle speed) screw out and fatten up the mix a hair. In colder conditions and warming up need a richer mixture. Can look at your spark plugs to see if they look white/lean after idling a couple minutes

 

[Yannih]

I guess the obvious question is if I adjust the choke to allow more fuel in the cold, will this new setting be detrimental when the temp is warm or hot?

 

[Scott06]

I guess the obvious question is if I adjust the choke to allow more fuel in the cold, will this new setting be detrimental when the temp is warm or hot?

Maybe. Adjusting the notches on the choke element only makes it stay closed longer, so it gives it more time to warm up to operating temp.
is the thermostat working and the engine warming up to proper operating temp?

 

[alldodge]

I guess the obvious question is if I adjust the choke to allow more fuel in the cold, will this new setting be detrimental when the temp is warm or hot?

Only if it's adjusted to far, if set correctly there will be no issue

It's a metal coil spring sort of thing. When temps get colder the metal shrinks pulling the choke closed. The colder it gets the more it shrinks. Same thing happens in reverse when temps get warmer.

 

[Yannih]

Only if it's adjusted to far, if set correctly there will be no issue

It's a metal coil spring sort of thing. When temps get colder the metal shrinks pulling the choke closed. The colder it gets the more it shrinks. Same thing happens in reverse when temps get warmer.

So as a final question and to confirm, I should be adjusting for more choke and turning the choke adjustment clockwise (according to the above diagram from alldodge)? Also there seems a very limited range adjusting in this direction...

 

[alldodge]

Yes, adjust for more choke
The internal spring gets stretched out a bit over time and needs a bit more. If the wire gets tight so it won't rotate enough, remove and adjust. If wire can not be reconnected then add more length

 

[Yannih]

Thanks heaps again alldodge.

I also think my idle speed is a little too high as shifting into gear from neutral (directly and quickly) brings a substantial and concerning crunch.
I think it's at around 800rpm. Needs to be closer to 650-700rpm?
Would the 100 odd rpm be the reason for the excess crunch or is it something more sinister?
P.S.
The engine and leg just went through major services...

 

[alldodge]

Idle 650
Timing 10* BTDC

 

[Yannih]

Is that idle 650rpm while in gear neutral or out of gear neutral please?

 

[alldodge]

In neutral, the in gear idle are for 4 cyl