2009 mercruiser 4.3mpi hard start when warm

[myentourage]

I have a 2009 4.3mpi that i am completely frustrated with. I have replaced the wires, cap and rotor, i swapped coils and ecm's with the twin sister motor, i have replaced the IAC, i have installed the mercruiser booster pumps to rule out vapor locking. I have tried everything and can't seem to solve the problem of this motor not starting when warm. If i go on a hot run and come to a stop to shut it off i will wait fifteen minutes and cannot start it. If i wait 2 hours or more it will fire right up. Has anyone ever heard of this? My mercury mechanic has checked the fuel pressure and has done vaccum test and everything seems normal. Where else should i go?

 

[Don S]

Re: 2009 mercruiser 4.3mpi hard start when warm

Have you considered getting it hooked up to a diagnostic computer and actually finding out what the problem is instead of just throwing parts at it?

Even before you do that, go for a run and get it good and warm. When you stop, open the engine hatch. Then see if it starts 15 minutes later.

Might also want to let the engine idle and cool down for a minute or two before shutting off. Then try 15 minutes later.

 

[alldodge]

Re: 2009 mercruiser 4.3mpi hard start when warm

I have a 2009 4.3mpi that i am completely frustrated with. I have replaced the wires, cap and rotor, i swapped coils and ecm's with the twin sister motor, i have replaced the IAC, i have installed the mercruiser booster pumps to rule out vapor locking. I have tried everything and can't seem to solve the problem of this motor not starting when warm. If i go on a hot run and come to a stop to shut it off i will wait fifteen minutes and cannot start it. If i wait 2 hours or more it will fire right up. Has anyone ever heard of this? My mercury mechanic has checked the fuel pressure and has done vaccum test and everything seems normal. Where else should i go?

Are you using pump gas which contains ethonal, if so you may be vapor locking. Only way to get rid of vapor locking I have found is to change the design which allows to fuel to circulate back to the tank and Mercruiser doen't do that. I have vapor lock several times and going from pump gas to marina gas helps a bunch, but also cost a bunch more. I have a VST setup and you should have cool fuel. While cool fuel helps it doen't get rid of it.

Vapor lock on an MPI/EFI it will crank and maybe hit just slightly every so often but not necessarly enough to start, Once it cools down it will fire right up because the fuel has condensed. The hotter it gets the more it happens.

This may not be your issue but sure sounds like it.

 

[Don S]

Re: 2009 mercruiser 4.3mpi hard start when warm

Only way to get rid of vapor locking I have found is to change the design which allows to fuel to circulate back to the tank and Mercruiser doen't do that.

I have to disagree. To many Mercruiser MPI engines running in warm/hot climates without changing the fuel system to go back to the tank.
Going back to the tank doesn't keep the fuel cool on the engines. There is fuel coolers on these MPI engines.

The problem with the newer boats is the tight engine covers/compartments for sound deadening, that is also cutting off any air circulation with the engine off. So all that hot air is trapped inside the engine compartment with no where to go.
Cars and trucks are open from the bottom and the front for ventilation.

 

[Don S]

Re: 2009 mercruiser 4.3mpi hard start when warm

Here is a service bulletin from Merc from 99. It may be almost 25 years old, but the facts are still there, probably more so today than when it was written.

View attachment Vapor locking.pdf

 

[alldodge]

Re: 2009 mercruiser 4.3mpi hard start when warm

I have to disagree. To many Mercruiser MPI engines running in warm/hot climates without changing the fuel system to go back to the tank.
Going back to the tank doesn't keep the fuel cool on the engines. There is fuel coolers on these MPI engines.

The problem with the newer boats is the tight engine covers/compartments for sound deadening, that is also cutting off any air circulation with the engine off. So all that hot air is trapped inside the engine compartment with no where to go.
Cars and trucks are open from the bottom and the front for ventilation.

Agree with the point your trying to make, but disagree with gas going back to the tank does not keep it cool. Heat and ethonal don't mix very well but I will yeild to your jugement.

 

[Dshow]

Re: 2009 mercruiser 4.3mpi hard start when warm

I had a vapor lock problem several years ago but took some steps to improve ventilation in the engine compartment and (knock on wood) haven't had the issue since.

Some of the things I did were:
1) I have two rectangular vent that have inserts for 2 - 3" blower tubes in them. I was only using 1 of the 4 tube holes so I removed one insert and cut the other in half to improve air flow.
2) On the sides of my engine, I had totes that pretty much took up all the space. I have much smaller totes now to increase air volume.
3) I leave the blower on when running to keep the air circulating.
4) I have a 'cool fuel' system and I read when you turn off the engine the cooling water can flow back down from the engine and actually heat the fuel. I installed a check valve to prevent that.
5) As Don mentioned, I try to idle a little bit after a hard run...

 

[myentourage]

Re: 2009 mercruiser 4.3mpi hard start when warm

Have you considered getting it hooked up to a diagnostic computer and actually finding out what the problem is instead of just throwing parts at it?

Even before you do that, go for a run and get it good and warm. When you stop, open the engine hatch. Then see if it starts 15 minutes later.

Might also want to let the engine idle and cool down for a minute or two before shutting off. Then try 15 minutes later.

I have had this engine on a diagnostic computer several times and it is not throwing a code and the problem is intermittent.

 

[Don S]

Re: 2009 mercruiser 4.3mpi hard start when warm

The problem isn't just the return fuel going to the tank, on marine engines all the fuel in the engine is hot, the fuel pumps are on the engine. In automotive, the pumps themselves are in the tank and the engine immediately gets cooler fuel.
You aren't going to get vapor lock until the engine compartment is 190? or more. The engine shouldn't be running more than about 175? on a raw water cooled engine.
I would bet that it works fine when the engine hatch is opened. Which just means he needs more air when he shuts it off, and cooling the engine down some before shutting it off. Cars and trucks aren't usually run under full load at 4000 rpm and immediately shut off. Would bet they would vapor lock too.

 

[myentourage]

Re: 2009 mercruiser 4.3mpi hard start when warm

I had a vapor lock problem several years ago but took some steps to improve ventilation in the engine compartment and (knock on wood) haven't had the issue since.

Some of the things I did were:
1) I have two rectangular vent that have inserts for 2 - 3" blower tubes in them. I was only using 1 of the 4 tube holes so I removed one insert and cut the other in half to improve air flow.
2) On the sides of my engine, I had totes that pretty much took up all the space. I have much smaller totes now to increase air volume.
3) I leave the blower on when running to keep the air circulating.
4) I have a 'cool fuel' system and I read when you turn off the engine the cooling water can flow back down from the engine and actually heat the fuel. I installed a check valve to prevent that.

Those are some good ideas i will try. I installed two rectangular vents in the engine compartment under the gunwal. I cut out a 5 inch hole in my stern with a dc fan sucking the air in. I also reversed my 2 three inch blowers to blow air in. I have not tried running them for my full run though. I will try this tomorrow.

 

[Don S]

Re: 2009 mercruiser 4.3mpi hard start when warm

I have had this engine on a diagnostic computer several times and it is not throwing a code and the problem is intermittent.

It may not be something that will set a code. It could be a sensor that is telling the ecm something completely wrong.

As an example, You might find no codes, but see the ECT shows the engine temp on the diagnostic tool at 10?F so the ecm tells the fuel system to run like it's really cold. This would flood a really warm engine. But, it will NOT set a code.
That is a problem with a lot of shops, they look for codes only, not false information from sensors.

 

[myentourage]

Re: 2009 mercruiser 4.3mpi hard start when warm

The problem isn't just the return fuel going to the tank, on marine engines all the fuel in the engine is hot, the fuel pumps are on the engine. In automotive, the pumps themselves are in the tank and the engine immediately gets cooler fuel.
You aren't going to get vapor lock until the engine compartment is 190? or more. The engine shouldn't be running more than about 175? on a raw water cooled engine.
I would bet that it works fine when the engine hatch is opened. Which just means he needs more air when he shuts it off, and cooling the engine down some before shutting it off. Cars and trucks aren't usually run under full load at 4000 rpm and immediately shut off. Would bet they would vapor lock too.

I have 160 thermostats so i know the engine temp is between 160 and 170. I did make a 16 mile run the other day and when i returned i left the hatch open for about 10 minutes. I then went to start it and it fired right up. I am definately agreeing with you here but i just don't know what else i can do to get cool air in there. I can't keep opening the hatch every time i stop, i run a charter business with the boat and there is just too much going on to do that. I wish i could instal a ac unit in there. Lol

 

[Dshow]

Re: 2009 mercruiser 4.3mpi hard start when warm

To prove vapor lock is the problem, before you do anything else, as mentioned you should leave the hatch up after a hard run so the heat can't build up and see if you still have the issue...

...Never mind... Just read your post.

 

[Don S]

Re: 2009 mercruiser 4.3mpi hard start when warm

Leave the blowers on for a while after you stop see if it helps, maybe add an additional vent or two for the engine compartment so the hot air can get out.

 

[NHGuy]

Re: 2009 mercruiser 4.3mpi hard start when warm

What about leaving a blower on as you prepare to shut down and while the motor is off and hot?
And don't forget your running cool down. Run the motor without load at the dock for a couple of minutes before shutting it off, bring the rpms up off idle to circulate some coolant. The cooling system will remove some of the stored heat from the block and the blower will help keep the remaining block heat from heat soaking the rest of the system.

 

[myentourage]

Re: 2009 mercruiser 4.3mpi hard start when warm

Thanks everyone for the quick responses i will keep in touch to let know what happens. Great forum with knowledgeable members. Thanks again.

 

[alldodge]

Re: 2009 mercruiser 4.3mpi hard start when warm

Engine with a 160-170 degree thermostate once stopped allows engine to radiate heat to all areas. We can all see the post about opening hatches, increase air flow with blowers, etc. Gas boils between 100 to 400 degrees Which depends on octane (higher the octane high boil point), ethonal boils at 173 degrees. Winter fuel is worst because it contains stuff which lowers the boiling point so it will vaporize quicker for a cleaner burn in cold weather. Once the engine shuts off the fuel lines, pump, and everything else on the engine soaks up heat. As heat increases the gas forms and gas replaces liquid, now the engine will not start. If the engine is cranked liquid is trying to replaced a presurized gas area. With no way to bleed off the gas it still will not start. If the return fuel line returns to the tank after the pressure regulator gas and liquid goes back to the tank allowing more liquid to replace gas.

Note: I have stopped for 3 hours and still had issues because I was using winter fuel blend and outside temp was 95 degrees. Note to self which worked, pay the extra price for Marina non-ethonal fuel and no vapor lock. This has worked for the last 2-years. This is only 2-years but it is a start, other waise I add a hole to my fill lone and move my return VST tank line to my fill neck.

Cheers and have fun

 

[UncleWillie]

Re: 2009 mercruiser 4.3mpi hard start when warm

... I cut out a 5 inch hole in my stern with a dc fan sucking the air in. I also reversed my 2 three inch blowers to blow air in...

You do NOT want to blow air Down INTO the Bilge.
You want to suck the heavy fuel fumes up and overboard.
If you blow air down, the air will mix with the fuel vapors and may produce an explosive concentration.
The fuel vapors will still be in the bottom of the boat.

Heat rises and the hottest air is at the top of the compartment.
If you want to add a blower to remove it, suck it out of the top of the compartment.
Move the hot air out, Moving cold air in does not control where the hot air goes.
The cold air could just as easily drop directly to the bottom and leave all the hot air on top.

 

[Fun Times]

Re: 2009 mercruiser 4.3mpi hard start when warm

I have a 2009 4.. I have replaced the wires, cap and rotor, i swapped coils and ecm's with the twin sister motor, Where else should i go?

Maybe onto the engine cooling system. Also, bear in mind that the crankshaft sensor can be heat temperamental when becoming defective.

i run a charter business with the boat.

There must be a lot of hours on this boat by now? did this just start happening? and the other engine seems fine?

Do you know if your standard cooling system is a Single or Three Point Drain System that looks like this, http://www.mercruiserparts.com/Show...+Cooling+System,+Single+and+Three+Point+Drain

Or do you have the seven point drain that looks like this, http://www.mercruiserparts.com/Show...sc=Standard+Cooling+System,+Seven+Point+Drain

If you have the "seven" point drain system, Take note of item #13 the "check valve". If that valve becomes defective, it could allow hot water to flow down to the fuel pump cooler assembly after engine shut off.

Are the sea water pump impeller's new?

Do you have a Bravo or Alpha drive system?

 

[myentourage]

Re: 2009 mercruiser 4.3mpi hard start when warm

I swapped the crank sensors from motor to motor and did not make a difference. There are 875 hrs on both engines. This started about 150hrs ago about the same time they started adding even more ethanol to the fuel. It is a seven point drain system. I just pulled the check valve out the other day and it seemed to be working properly. Impellers are new just replaced this season. I have bravo drives and have also come to the conclusion if i open the engine hatches right away from a hot run they will start no problem at any time. I have to find a way to get more air in the compartment.