5.7 liter EFI Won't idle after running at high speed

[Ryland3210]

This is a 2003 Bayliner with a 5.7 liter Mercruiser EFI 260 HP engine.

Engine starts fine and runs up to speed fine. After running at 3500 RPM for about 30 minutes, the tachometer began to jump erratically higher, while the engine ran steadily. I gradually slowed down to 1100 RPM as I approached a marina. The engine died suddenly. I gave it a little throttle as I normally would, and it started after a few seconds struggling. I did not want to idle, so I gave it lots of throttle. It would run at 2,000 or more RPM, but died again when I tried to drop down to 600, its normal idle RPM.

Once I got it running again, I ran a steady 3300 RPM back to home port, which took about 30 minutes. It ran fine until I started to slow down again. The engine quit again. It took a number of tries to get it going. I smelled gas and immediately turned on the blower. Then I got it to idle at 600 RPM and decided to limp all the way back to port without even using more throttle. Whew! Made it!

Suggestions anyone?

 

[alldodge]

Howdy
If you can give it throttle and keep it running (above 1000 to 1500 rpm) and dies when you idle down, they my first thought is the IAC valve. The issue I am having is the smell of gas but this could have been done just from throttling it so much.
When was the last time you replaced the fuel filter?

 

[Ryland3210]

Thanks for the fast reply. I just bought this boat from a used boat dealer. The engine has about 150 hours, about half of which was at low RPM. Not sure how long it was sitting or when the fuel filter was changed. Upon launching, it ran good at all RPM's, but it leaked near the tiller, so the dealer replaced about half the outdrive assembly, which required pulling the engine. I had only run the boat once up on plane for maybe 15 minutes at this point.

The first time I got the boat back, I ran it again about 30 minutes to a nearby fuel pump and filled up. I ran good all the way there and back to home port, and no leaks.

My second run, today, was the first time there was any problem running.

I haven't contacted the mechanic yet to ask whether he changed the filter. I sure don't mind changing the fuel filter, but there is also the erratic tach reading, which seems to me to indicate an electrical issue.

 

[Mischief Managed]

Sure sounds like a flakey IAC to me. Even if it's running OK now, I would replace it. They heat up in use and can fail intermittently. They are cheap and easy to swap. The tach issue is quite common (especially with Faria) and has nothing to do with the engine. Just smack the tach with your knuckle and it will start reading right again. I don't think it's the fuel filter, they normally allow it to run at low RPM OK but restrict fuel at high RPM when they are clogged.

 

[alldodge]

The fuel filter question is more to find out if maintenance was done then the cause being the filter with an EFI engine. As before if you can start the engine by giving it more throttle and it dies when returned to idle position, then that is a classic IAC issue. You can pull it off and try cleaning before replacing. The Merc IAC is around $140 (Item 14) but these can be obtained at a auto parts store or rock auto for $41

Don't know what your serial number is so I used the one found for late model of 862998

 

[Ryland3210]

My serial number is OL687277 I plan to replace the IAC valve. There are several different style IAC valves on the website I found. The one that appears to be for my engine comes with a gasket that looks like it is for the injectors. Looking at the exploded view of the throttle body, it looks like that should not be necessary. Are there tricks to this?
Thanks.

 

[alldodge]

With your serial number your IAC comes up as 805224A1 and Rock auto doesn't show one. There is next to nothing to replace it, remove the 2 number 8 screws and washers and wires. It will come with an o-ring. I like to put a drop or two of oil on it and put it back together.

 

[Ryland3210]

I found the IAC valve in stock at a local marina. I used to build hydraulic machinery and have designed O-Ring grooves for extremely high pressures pulses. Lubricating O-Rings is essential for them to seat properly and to avoid cutting them during installation. In cases where pressures change over a wide range, they can move as compression varies with pressure. Therefore, grooves should be polished to avoid long term abrasion in those applications.

 

[skippy2235]

before buying one, you should clean yours and test it. Look at youtube on this. there is lots of info.

 

[Ryland3210]

the new IAC valve fixed the problem. Next time, I'll see if simply cleaning will do the job, and check the youtube.
Thanks!

 

[Rick Stephens]

AllDodge nails another one.