2009 Indmar Assault 340 hp starting, idle and surge problems.

[Graeme]

Hi,

I have a 2009 5.7 340 hp engine.

It starts very hard, I have to give it lots of throttle. Sometimes it backfires. Sometimes I have to hold the key to start for a while because if I let it go the engine will just shut off.

Initially it seems to idle ok, but as it warms up itidles lowers are lower and rougher. Exhaust smells and looks normal.

At 1000 to 2000 rpm the engine surges up and down about 400 rpm.

Engine will enter a limp mode after about 10 minutes of use.

I have replaced the spark plugs, the inline fuel filter, the cap and rotor, upstream O2 sensors. No joy. Also seafoamed and replaced as much fuel as I could.

Next I will try the MAF/MAS. PCV valve. Any ideas? This boat has been a complete piece of garbage. But it would be nice if it worked. The dealers here in Canada are completely useless and don't know/won't try to fix it.

Help.

[CJD]

If it is going into limp mode, it should be storing a fault code. Reading that code may help get you started in the right direction.

[Graeme]

According to the dealer it shows no codes. Even though it says "SERVICE REQUIRED" and goes into limp mode. I have lost faith in the dealer however, so no sure if they even can read a code.

[CJD]

This early in the season, water in the tank would be high on my list of possible causes. After that, cleaning or replacing the MAF would be my next course. I still find it hard to believe it gives you the light with no code.

Your symptoms have the indication of both lean and rich mixtures. That really sounds like bad gas.