engine sputters and shuts off at random times

[hottuna1]

i have a 25' Renken repowered in 2005 with a 2004 350 MPI Horizon ( Bravo 2 outdrive). lately it has been sputtering and then shutting off . it will restart and may or may not run at low rpm. If i let it set for 1/2 hr. or longer , it will restart and run at low rpm fine. Fuel pressure is at factory specs . this is a cool fuel model . Can the ECM be checked while the boat is in motion? That being said , has anyone else experienced this problem?

 

[alldodge]

Re: engine sputters and shuts off at random times

i have a 25' Renken repowered in 2005 with a 2004 350 MPI Horizon ( Bravo 2 outdrive). lately it has been sputtering and then shutting off . it will restart and may or may not run at low rpm. If i let it set for 1/2 hr. or longer , it will restart and run at low rpm fine. Fuel pressure is at factory specs . this is a cool fuel model . Can the ECM be checked while the boat is in motion? That being said , has anyone else experienced this problem?

:welcome: to iboats

How did the fuel pressure get set?
Yes, the output from the ECM can be read on a scan tool while running or stopped.
It may be the IAC
What all has been checked/replaced?

 

[hottuna1]

Re: engine sputters and shuts off at random times

fuel pressure was set by factory. i have replaced high and low pressure fuel pumps and rebuilt raw water pump. had to replace the thru transome plastic water pickup tube ( that was an engineering marvel -NOT). What exactly does the IAC do . Thanks for the reply.

 

[alldodge]

Re: engine sputters and shuts off at random times

fuel pressure was set by factory. i have replaced high and low pressure fuel pumps and rebuilt raw water pump. had to replace the thru transome plastic water pickup tube ( that was an engineering marvel -NOT). What exactly does the IAC do . Thanks for the reply.

Your comment of the fuel pressure was set at the factory is that you just replaced the fuel pumps and it had no effect, correct? What caused you to believe the fuel pumps needed to be replaced?

The Idle Air Control (IAC) valve controls the air flow at idle rpm. If it is sticking it will cause the engine to sputter and/or die.

Can you locate a Merc scan tool or do you know if any codes have been thrown?

 

[Fun Times]

Re: engine sputters and shuts off at random times

fuel pressure was set by factory. i have replaced high and low pressure fuel pumps and rebuilt raw water pump. had to replace the thru transome plastic water pickup tube ( that was an engineering marvel -NOT). What exactly does the IAC do . Thanks for the reply.

Do you have your engine serial number handy by chance?

IAC = Idle air control valve.

Both Your fuel pumps are inside a cool fuel module by the sea water pump correct?

 

[hottuna1]

Re: engine sputters and shuts off at random times

high pressure pump was not putting out correct pressure , replaced high and low pressure pumps about a year ago and had no trouble until the problem recently. The high pressure pump is near the cool fuel box and the low pressure pump is located forward starb. on the engine

 

[hottuna1]

Re: engine sputters and shuts off at random times

Would a faulty Idle Air Control cause an engine to shut off even at different RPM's and or speeds ?

 

[hottuna1]

Re: engine sputters and shuts off at random times

I am having a friend ( also a certified Merc mechanic) take a ride with me and hopefully diagnose the problem , as soon as we can get together. He seems to think it could be a fuel problem ( i think its electrical). I have run the boat two times since i had the sputtering/ shutoff problem. The first time i ran 20 miles and then i had the problem. last time i ran about 3 miles and had the same problem.

 

[alldodge]

Re: engine sputters and shuts off at random times

I am having a friend ( also a certified Merc mechanic) take a ride with me and hopefully diagnose the problem , as soon as we can get together. He seems to think it could be a fuel problem ( i think its electrical). I have run the boat two times since i had the sputtering/ shutoff problem. The first time i ran 20 miles and then i had the problem. last time i ran about 3 miles and had the same problem.

The fuel pressure should be 43PSI at 1800 RPMs at the Schrader valve. Your first post stated your problem was when it was idling, there was no mention of having issue at higher RPM. If this is the case I would lean toward the IAC. You could pull it out and see if the valve is clean, if not clean it and reinstall. Do you have throttle body or multiport injection?

 

[hottuna1]

Re: engine sputters and shuts off at random times

sorry, i looked back and saw that i made no mention of problems at higher speeds . the engine has multi port injection. I will pull the valve and clean it . Thank you for your input

 

[Fun Times]

Re: engine sputters and shuts off at random times

Would a faulty Idle Air Control cause an engine to shut off even at different RPM's and or speeds ?

While normal no the IAC should not affect the engine at higher RPM, it still can't be ruled out as some engine models have been know to do unusual things at all speeds with the newer MPI engine models.

You may want to check the distributor cap for any signs of carbon tracking or damage as that style cap has been known to cause issues like you are describing.

Also be sure your ignition coil isn't getting too hot and have a timing light hooked up to the coil wire so that you can quickly tell if the coil seems to be failing while under way.

 

[jcbache]

Re: engine sputters and shuts off at random times

Sounds like possible crank position sensor. They get hot and won't get the job done. Once temp drops they start acting right again. IAC won't cause stalling while running at RPM's. Carbon tracking causes misfires and rough running, usually not stalling and then symptoms go away (temporarily) after cooling down. Good luck

 

[Fun Times]

Re: engine sputters and shuts off at random times

Sounds like possible crank position sensor. They get hot and won't get the job done. Once temp drops they start acting right again.

Excellent thought, thanks for bring it to light. The crank sensor is much more susceptible to failure then the newer design coil your engine model has.

If you do decide to check your flat crab style distributor cap, be sure whoever pulls of the distributor cap follows the quote below due the distributor housing is susceptible to failure as well. Be sure not over tighten as it's real easy to over tighten and break the housing.

On the HVS style cap and rotor, you'll need both a Torx T20 and T15 driver. On the cap hold-down Torx screws, loosen, tighten, loosen, tighten, then loosen all the way to help avoid wrecking the cheap POS plastic distributor. Cheap design, not cheap to replace if you break the 'ears' off that hold the distributor cap hold-down screws. Try not to lose the screws down into the bilge either. When replacing the cap, please just do one wire at a time from the old distributor cap to the new cap.Original style caps had aluminum terminals vs. brass, which was a terrible idea regarding longevity

A must read, Flat Distributer Caps - Boat Talk - Chaparral Boats Owners Club

http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/gmefi-nostart.PDF