350 horizon Hard start when hot

[dan313]

Im at my wits end. I have a 05 207AJ. My rebuilt 350 horizon will not start when hot. The engine was replaced two years ago. I had the issue before it was replaced. The motor was replaced because it Hydro locked. Also the fuel rails were sent out for cleaning. Anyway my issue is that when the motor reaches operating temp it doesn't want to start. I have to push the throttle forward in order to get it started. This is an Fuel Injected motor. I shouldn't have to do that.
Now when I run the boat i can't get more than 4200 rpms out of the motor. I was getting 4600 rpms at the beginning of the season. I don't usually go above 4000 rpms when i'm running the boat. I found this out last week when i opened it up.

Any suggestions will be greatly appreciated,

Lenny

 

[Espos4]

Having to push the throttle all the way open could be a clue.

You may have a leaking fuel injector. When an injector leaks after shutdown, the intake manifold becomes very rich with fuel vapors, too rich to ignite when trying to start the engine. The fuel injectors are also firing when cranking the starter, which only adds to the problem. Opening the throttle allows extra fresh air to be drawn in, which leans out the mixture, but more importantly, full throttle during cranking sends a signal to the ecm to shut the fuel injectors off during cranking. This is a "clear flood" command, allowing the engine to be started using just the rich mixture in the intake manifold.

Low fuel pressure could also cause hard starting.

To test for a leaking injector, you could attach a fuel pressure gauge and observe the pressure drop after shut down. It should only drop 2-3 lbs in the first few minutes. If the pressure goes to zero in just a few minutes, that could be from an injector leaking fuel.

If this is happening, you could remove the fuel rail with the injectors still attached, activate the pump to pressurize the rail, and observe the injectors.

 

[dan313]

I've had three mechanics check the fuel pressure and it was good. The last mechanic put a computer on it and said the motor is working within specs and doesnt know what is wrong with it. I've had the rails cleaned and injectors checked out. I called Merc Cruiser they said to check the cool fuel pump to see if water was circulating thru it. They said you may have a vapor lock condition. The pump was cool to touch after running the boat.
I was able to adjust the the throttle cable and the boat would start, but i created a hard shift condition. so i put it back to its original spot. My new issue is i'm only getting 4200 rpms. at wide open throttle.
I'm pulling the boat today. Ill have all winter to try and figure this out..

 

[Espos4]

So when you “adjusted” the throttle cable, the hot start issue was cured?

 

[dan313]

Yes the motor started every time because their was a little gap in the throttle body flapper to allow air in. But it shifted like crap. so i put the setting back to where it was. I'd rather have a smooth shifting boat especially when I'm docking. When I spoke with Merc Cruiser they said that the flap on the throttle body should always be closed tight for Hot or Cold starts.

 

[juggernaut1]

Does this motor have an IAC valve?

 

[skibum]

Does this motor have an IAC valve?

And was it swapped from the rebuilt engine to the new one?

 

[dan313]

i'm on my 3rd IAC valve. As I said in my earlier post. I've had 3 mechanics check out the motor since the rebuild. I only have 90 hours on it. I shouldn't be having these issues. Not one of them have an idea as to what is wrong with the boat. The last mechanic that worked on it is a certified Merc mechanic with 40 + years that works for Marine Max and he has no idea what's wrong with it..

Also when i do have the hard start condition i can do any of the following and the motor will start right up. (remove vacuum hose from the regulator, unplug the IAC valve, or unplug the TPS sensor. Do anyone of the three and it starts.

Its a mystery...

 

[Espos4]

In your original post, you said that you have to push the throttle forward in order to get it to start.

Is that just slightly forward, like enough to just open the throttle plate slightly?

As far as the 3 options you just listed

1. Removing a vacuum hose allows air to enter, like a properly functioning iac valve.

2 & 3. Unplugging the iac or tps......it’s possible that one or both of those is being affected by the heat. Next time out, run the motor till it’s hot. Shut it down.
Remove the tps and iac valve.
Put them in a cooler of ice for a few minutes. Once they’ve cooled, quickly reinstall and start the motor.

 

[dan313]

Thanks for the info. The boat is home now and winterized. This is going to have to wait until spring. The cup filter in the gen 3 canister was black. I only put 15 hours on the motor for the season. I wouldn't think it would be that dirty. This also is a contributing factor as to why i have this issue. I didnt see anything floating around in the fuel. I was thinking about removing the gen canister and rebuilding it. I'v read too many post that say that the paint breaks down and causes all kinds of havoc. Has anyone removed one and on a scale of one to ten how hard of a job is it?

 

[scoflaw]

Thanks for the info. The boat is home now and winterized. This is going to have to wait until spring. The cup filter in the gen 3 canister was black. I only put 15 hours on the motor for the season. I wouldn't think it would be that dirty. This also is a contributing factor as to why i have this issue. I didnt see anything floating around in the fuel. I was thinking about removing the gen canister and rebuilding it. I'v read too many post that say that the paint breaks down and causes all kinds of havoc. Has anyone removed one and on a scale of one to ten how hard of a job is it?

The black in the cup is from your fuel line dissolving. It would be a good idea to tear into that CF3 and do some upgrading.
Bead blast the paint off the inside of the cover.
Upgrade to the thread in water line fittings
Seal the water jacket side with POR fuel tank sealer, so it doesn't breach into the fuel section.
1 or 2 of the mounting bolts can be a PIA to remove, the rest is relatively simple

 

[dan313]

Thanks, I will work on it over the winter..