3L Runs On/Dieseling

[kidafa]

Engine: 2005 Mercuiser Turn Key Start, Alpha One Gen 2 Drive Serial: 0W356097

Some of you may recall my previous thread about my tub running on... Anyway; I've recently started using the boat for skiing and its running on for about 5 or so seconds each time I turn it off....

Plugs are correct
Timing is fine
Running regular unleaded fuel (91RON here in Australia)

My Idle speed is set at about 700rpm, BUT if I throttle up and come back to idle it sits a little bit higher (say 750rpm)? Does this mean that the throttle plate isnt closing properly?

What can I do to fix this?

Do i need to lower the idle and turn the mixture screw CCW?

Thanks in advance,

Chris

 

[Don S]

Re: 3L Runs On/Dieseling

Disconnect the cable and see if the idle drops down. The throttle cable needs adjusted to preload the throttle lever slightly against the stop. You might even try adjusting the idle speed screw down to 650 rpm, then adjust the cable. There should be a lock over the idle mixture screw.

 

[98Shabah]

Re: 3L Runs On/Dieseling

I've got a '98 and ended up having to run one step colder plugs in it to stop the dieseling. The timing was correct, as was the idle speed. I believe there was a bulletin from Mercruiser regarding the dieseling and going with colder plugs, but I don't recall what years were included.. I can't seem to find it though.

 

[Don S]

Re: 3L Runs On/Dieseling

He has the TKS carb, colder plugs is the last thing you want on this engine, the biggest problem is it's running so lean because of all the enviornmental laws. Ones that weren't a problem in 98.

 

[kidafa]

Re: 3L Runs On/Dieseling

The Idle stays low with cable disconnected and is fine when its connected; it only jumps up once I've throttled up and come back to a stop...

Ok if there is a lock over the idle mixture screw I meant the mixture screw that you got me to buy that tool for

 

[Don S]

Re: 3L Runs On/Dieseling

The Idle stays low with cable disconnected and is fine when its connected; it only jumps up once I've throttled up and come back to a stop...

Does it work ok with the cable removed when you give it throttle using the carb linkage and not the throttle lever?

Does it diesel after the engine has been idling at 700 rpm or lower for a minute or so?

 

[kidafa]

Re: 3L Runs On/Dieseling

Doesn't diesel after engine has been idiling at 700rpm or so NO

Not sure if it works ok when you give it throttle using the carb linkage and not the lever.... Will check

Boat is currently on the hose atm warming up to fix this gremlin

 

[98Shabah]

Re: 3L Runs On/Dieseling

You're saying colder plugs are a bad idea with the newer TKS carb then?

He has the TKS carb, colder plugs is the last thing you want on this engine, the biggest problem is it's running so lean because of all the enviornmental laws. Ones that weren't a problem in 98.

 

[kidafa]

Re: 3L Runs On/Dieseling

Ok this is how I have it idling with the throttle cable removed at the moment

Is the small hunting around of a bout 30rpm common?

See when I throttle up and then put it back to the idle stop it takes a while to come back down to the set RPM?

Also when I turned it off and restarted after taking that video it idled around 540 rpm for 5 to 10 seconds before it settled itself out at around 620.

 

[Don S]

Re: 3L Runs On/Dieseling

I try to get them idling on muffs at 675 to 700, any lower and when in the water the back pressure kills them. Mixture is a fine line, to rich and you get a hesitation, to lean and you get a hesitation. The TKS carb is a real piece of work, it tries to use an outboard priming setup on a carb for an IO, works as good as their idea of using an outboard charging system on the 470's. Now add a bunch of electronics and wiring to make it work part of the time, and you have problems.

 

[Pete104]

Re: 3L Runs On/Dieseling

How long has it been since you've had it out on the water to get HONEST operating temp? Anytime I think I 1 dialed on land, sure as heck , I change something again. TKS or not.
Don was being kind with his "real piece of work" comment!
Do you start the engine the way it was (in theory) designed or more like a conventional carbed engine?
I would get the tool, get rid of that cover on the air adjuster & dial it in where like it. With a hot engine! That way, as they say, it is what it is!

 

[kidafa]

Re: 3L Runs On/Dieseling

none of those posts really answer any of my questions....

Is the small hunting around of a bout 30rpm common?

See when I throttle up and then put it back to the idle stop it takes a while to come back down to the set RPM?

Also when I turned it off and restarted after taking that video it idled around 540 rpm for 5 to 10 seconds before it settled itself out at around 620.

 

[achris]

Re: 3L Runs On/Dieseling

none of those posts really answer any of my questions....

That's true, but it has given you a lot of new information.

Is the small hunting around of a bout 30rpm common?

That could be as a result of the idle mixture not being set right, but you're doing all your tests with the engine running on muffs. No results are valid. Unfortunately the only way to set the carburettor up is for the boat to be in the water, with the 'normal' exhaust back pressure. You can't simulate that on the trailer.

See when I throttle up and then put it back to the idle stop it takes a while to come back down to the set RPM?

That might be a part of the emission requirements. According to 'those who know', engines that are allowed to return to idle quickly produce an unacceptable level of Nitrogen oxides in the exhaust, so a system was devised to slow that return to idle. Usually it's done with a dashpot, but sometimes it's done within the carb, using jetting and drilling....

Also when I turned it off and restarted after taking that video it idled around 540 rpm for 5 to 10 seconds before it settled itself out at around 620.

That would indicate the carb mixture is not set right, probably too lean.

HTH,

Chris.....
(where in OZ?)

 

[kidafa]

Re: 3L Runs On/Dieseling

Thanks for the in depth response

Can you run me through the correct way to set the idle speed and the mixture please?

Im in Adelaide, South Aus.

 

[achris]

Re: 3L Runs On/Dieseling

First and foremost the boat needs to be in the water, in forward gear, un-tethered (not tied to anything). Get the engine warm, put it in forward gear with the throttle cable removed and set the idle speed and mixture. Then adjust the barrel on the cable so there is a SLIGHT amount of preload (pushing the throttle most closed) and put the cable back on. Check to make sure you don't have any hesitation on acceleration... Job done. If you have hesitation it will indicate the mixture is incorrect, usually too lean... Adjust accordingly...

 

[Fun Times]

Re: 3L Runs On/Dieseling

AMkidafa, Your engine idle is to low, Service manaul number 41 calls for, # 4. Allow engine to warm up (6-10 minutes on first start of the day). The engine will initially idle at 650-900 RPM and then return to normal idle RPM for the engine.

(3.0 L is 800 RPM Idle in Neutral) & 750 RPM Idle in Gear.

& the 4.3 L, 5.0 L, and 5.7 L are 650 RPM In Neutral) & Idle in Gear is also 650 RPM.

TKS Starting Characteristics
On 3.0 L models - If the engine has not run for a long period of time, it might require a
couple of attempts while the fuel bowl refills. Once the engine has started, it will idle at 700-900 RPM.

achris, I believe you were thinking about the highlighted areas below? On the 4.3 L, 5.0 L, and 5.7L models - If the engine has not run for a long period of time, it might require a couple of attempts while the fuel bowl refills. Once the engine is started, it
will idle around 650 to 700 RPM in idle stabilization mode. If the idle exceeds 700 RPM,
the ECM adds spark, thinking that the operator is trying to accelerate, which could cause
the engine to idle at 700-900 RPM. After the TKS module has shut off the enrichment circuit,
the carburetor will function like a standard carburetor. If the engine is out of idle stabilization
mode, (engine below 700 RPM), you will hear and feel a slight drop in RPM. After the TKS
module has shut off the enrichment passage, the carburetor will function like a standard
carburetor.

Good luck with it.

 

[kidafa]

Re: 3L Runs On/Dieseling

Check to make sure you don't have any hesitation on acceleration... Job done. If you have hesitation it will indicate the mixture is incorrect, usually too lean... Adjust accordingly...

So I set the idle speed and then just use the mixture to adjust if there is hesitation on take off?

When the cable is disconnected should I be able to move the end that connects to the throttle lever (the black end) back towards the brass adjuster say 10mm?

(3.0 L is 800 RPM Idle in Neutral) & 750 RPM Idle in Gear.

That's CONSIDERABLY higher than what everyone else has recommended on here for 3L

 

[kidafa]

Re: 3L Runs On/Dieseling

this is the play in the cable im talking about:

 

[achris]

Re: 3L Runs On/Dieseling

So I set the idle speed and then just use the mixture to adjust if there is hesitation on take off?

Yes, but if the idle speed changes significantly, adjust it back with the idle speed screw.

When the cable is disconnected should I be able to move the end that connects to the throttle lever (the black end) back towards the brass adjuster say 10mm?

I watched your video and that amount of movement looks to be about normal. Adjust the black plastic barrel while pushing the cable in.

That's CONSIDERABLY higher than what everyone else has recommended on here for 3L

800 in neutral, 750 in gear is the book spec for a TKS. Anything lower is the sepc for the older 3 litre....

Do you have the manuals?
If not...
Drive -> http://www.4shared.com/document/dPQUcyn_/Service_Manual_14.html
Engine -> http://www.4shared.com/document/xEKlzP-s/Service_Manual_26.html
TKS system -> http://www.4shared.com/document/SNqPsoNI/Service_Manual_41.html

Cheers.....

 

[Don S]

Re: 3L Runs On/Dieseling

1. In the real world, if you set a 3.0L engine at 750 to 800 rpm idle speed, it will diesel every time you shut it off. Even with the TKS.
Lots of people quoting the book, but who has real world experience with those carbs on a 3.0?
2. From your first video, that 30 rpm movement is typical with digital tachs, the engine sounds smooth, but I don't have fancy speakers either.
3. Cable is fine, as I said right to begin with, your throttle cable needs adjusted.

Remember this thread. http://forums.iboats.com/showthread.php?t=516170