06laser

ok thanks ray. do you reccommend any shops up in the corona/riverside area?

Raylar

Yah, talk to Gary @ G& S Marine in Corona, he should be able to scan and maybe help locate your issue. Hope its easy and inexpensive fix.

Best Regards,
Ray @ Raylar

06laser

Thanks I'll give him a call.

thirdchildhood

iTrader: (6)

Is there a normal amount of water coming out the exhaust? Does the exhaust feel hot when the alarm sounds? Backflushing of the raw water side components is easy and good maintenance even if that isn't the problem.

An infra-red heat gun is really handy to have on board to check engine and oil temps. Point it on the oil pan to get oil temp. Point it at the oil filter too.

http://www.amazon.com/Raytek-MT4-Non.../dp/B0002198GY

downtime270

Seriously - Don't overlook the routing of the knock sensor wires. I know it sounds goofy, but I can't stress this enough. My boat has twin 496's and the port motors issue, - similiar to yours- was fully documented with Merc and they were unable to identify a problem over the course of 3 years. Its a freebie to look at, just make sure the wire routing is nowhere close to a plug wire.

Eric

06laser

Ok I'll take a look at it today when I get home. Thanks

06laser

Does the knock sensor sit right behind the starter? If it is the wire is pretty much resting on one of my spark plug wires.

downtime270

So on a 496 MPI motor there are 2 knock sensors, one on each side of the block. I attached a picture to help you visualize it, however it will have a bolt through the center. Think of it this way - its just a microphone looking to detect any type of detonation. If it gets interference from the High frequency plug wires - it sends incorrect signal to the ECM and the ECM attempts to adjust the timing or fuel supply to compensate for what it thinks is detonation.. There is a very small greyish/white single wire coming off of it to a black connector. It should be routed very closely along the edge of the block around to the back of the bellhousing where it connects. If the wire is coming off at a funny angle - just loosen the bolt and rotate it to help you route the wire better. All I can tell you is I chased this issue too long to find out this was the problem. I had certified merc mechanics run the boat, tech the boat, and converse with Merc to no avail...Until I stumbled across a technical article that lead me to this...Good Luck!


jpeg image hosting

low_psi

I had a few grains of sand jammed in the water pressure sensor on the impeller housing. Guradian alarm would go off if I ran it over 3000 rpm it would reduce power until i brought it back to idle, then the alarm would fo off.

I bought a new sensor and while replacing I inspected the old sensor. I tapped it a few times and the sand came out.......

TWIN-SPINS

http://www.mercruiserparts.com/Show_...ft+and+Pistons #12 is knock sensor,,one on each side of block