496 mpi HO question
 

Hello all.

I have a pair of 400 hour merc 496 HO mpis and at 1000 rpm one burns twice as much as the other according to vesselview. Was up with that? What should I check?

also see a little fuel sheen on thirsty motor’s side when I shut em down. Not sure if related.

thanks

Swampy

Check Fuel pressure.
Check spark plugs to see if one or more look like its running rich.
Send injectors to Smitty/arcticfriends to be cleaned and flow tested.

Thanks Griff. I assume my Rinda tool cant tell me which injector might be having issue.

1K rpm is idle, whats it seeing at cruise ?

400 hours, and 'something' awry...
...I'd pull ALL of the injectors and have them professionally cleaned, inspected, refurbished, and flow tested.

www.injectorpulse.com (Typical turnaround is a week. Xavier is a trusted resource and does the racecar injectors for a bazillion fellow racers. He can do any injectors.)
or
https://www.boatunlimited.com/marine...ting-cleaning/ (Not sure on turnaround time, but reach out and John will tell you. He has forgotten more about 496s than any of us will ever know.)

Can you check fuel usage at other rpms ?

I'm not sure what a Rinda will show for the PCM555's. I have MEFI 3's and it doesn't show much.

Ran boat a bit yesterday - both motors using same at 1,000, 1500, 2000, and 3000 this time .... couldnt do more as weather was rough in ICWW was packed!

When I tun STBD motor off, fuel sheen on water surface. Will check plugs next.

It cant be the idle sensor IAC thingy can it?

I would check your engine oil level. You might have a leaking oil cooler that is letting oil get into the raw water side of the oil cooler and out the back of your boat.

Uh oh!!!

I can almost guarantee you have the Cool Fuel paint peeling problem and it has now entered into the fuel rail and injectors. You need to pull everything fuel related on that motor!. Get a new Cool Fuel module, pressure regulators and clean, clean clean. I HIGHLY recommend new injectors. The other motor is probably right behind this one. So I would do both.

This is the EXACT same thing that happened to my HO's. One started burning WAY more fuel, sheen on the water, etc etc.

Sorry....good luck!

bummer - will do some checking around. At 400 hours the oil coolers should be replaced anyway - been shopping - as I do not know if the last guy rinsed the salt water motors out every time (he was a pilot but .....)

If after oil coolers I still see a sheen - injector route for sure.

thanks everyone for the diagnostics/ideas.

What's a set of injectors run these days for the 496?

Swamp,

Send them to Smitty (ArcticFriends). You'll get a "new" set of injectors back.

Thanks. Brad.

Get a fuel pressure reading at the shrader valve on the fuel rail. I bet 100% it is reading very high.

Don't just deal with the injectors. If the Cool Fuels are sending paint up stream, it won't matter what you do. This is a well known problem with the 496's.

To my knowledge, vessel view does not know what the fuel pressure is or what the injectors are doing, it only knows what the computer is commanding the injectors to do and calculating from there. Since vessel view is showing more fuel usage, this tells me that there is a sensor that is not sending the correct information to the computer and it is commanding more fuel.

Someone please correct me if I am wrong.

Techman,

You're not wrong, but.... Getting the injectors refreshed is pretty cheap insurance and should indicate if the CoolFuel is sending paint flecks downstream.

OP could just ditch the CF altogether and assemble it with reliable parts and solve the issue for good,

Thanks. Brad.