Mercruiser 5.0L TKS idling and low rpm problems

[ricmat68]

I bought my Maxum just about 6 weeks ago and have been using it around 25 hours during this time. The boat is a 2007 Maxum and only had 26 hours when I bought it so it has been sitting around quite a bit the past few years. It worked great until 2 days ago when all of a sudden, when entering a no wake zone, it did not want to run evenly at idle speed. If you don't use the throttle to increase rpm's it will just die. It starts up ok and idles ok when not in gear but as soon as you put it in gear it will die almost right away. When moving the throttle forward there is quite a long gap before the engine reacts and then all of a sudden it revs up to around 1800-2000 rpms and the boat "jumps" forward. After a lot of throttle adjusting it is possible to find a spot where it will run at around 1200 rpm but engine is not running 100% smoothly. Above 2000 rpm it runs just fine though.

So far the fuel filter has been changed, the tiny "peanut" filter which was 100% clean, alternator cable renewed.

Does anyone out there have any ideas? Everything is appreciated.

[pascavone]

if its an MPI then is either bad fuel or leaking manifolds.

There is always a reason why a previous owner stops using a boat.

so, I'd rule out an electrical problem, because electrical is rarely intermittent.

I'd pull the oil filler cap off and look for white foam under it. the would indicate water in the engine.

If your manifolds are leaking, then the plugs are wet and that is your idle problem, so pull out a plug in the morning and see if they are wet.

then try the fuel issue again, unscrew your fuel separator, and remove it full, and then dump it in a bucket and see if there is water in it.

water sinks to the bottom, and it could be in your tank sloshing around .

start with that.

[mmwjr]

If I recall TKS is a carb that has type of built in primer so that you don't need to pump the throttle to set a choke. Turn key start. Sounds like there may be something wrong with this function.

Have you tried googling the issue?

[ss3964spd]

So, turn the key and the engine starts and idles right away? What is the idle RPM once the engine is warmed up but not in gear? Does it seem to idle smoothly and normal once warmed up and not in gear?

Given the age of the boat, the very low hours, and the described symptoms I'm inclined to say poor quality fuel (water in it).

[mmwjr]

Yep, quick blurb I found.

TKS (Turn Key Start) is nothing more than a primer system similar to what is used on carbed outboards for starting purposes. The rest of the carb is the same. Just a lot of extra stuff to go wrong. instead of just the automatic choke

[rodrigo]

check idle air valve and fuel pressure regulator at the fuel pump, check for paint clogging the fuel passages, I had that issue myself.

[mmwjr]

TKS is a carb with an enrichment circuit that uses a enrichment injector mounted to the base of the carb and also has a temp sensor so it knows when it is cold. I beleive one of these two components is at fault.

PS: this is not fuel injected so no idle air valve. Not sure if these engines use a mechanical or electric fuel pump, if manual then no regulator either.