496ho help!
 

I have a 2002 496ho that ran fine when put up for winter..now after full service for this season want run past 3500 rpm..starts surging like running out of fuel and sounds like its spark knocking. .will fire up and idle fine...run great all day under 3500rpm..but as soon as u try to speed up starts cutting out and rattling. .has new fuel filters and full service. . The port motor runs fine..boat has dual tanks but got fresh fuel in both..any help would be much appreciated!

Spark knock could be indicative of a lean condition. I would check the air intake for a possible obstruction. Have the injectors been cleaned and inspected? A simple switch of fuel tank lines would eliminate the fuel as a suspect.

Is it throwing codes? Is it beeping every two minutes?

Have you tested your fuel pressure? Could be a fuel pump. They are not that hard to replace. I had to replace both of mine (496HOs) after untreated ethanol fuel damaged my fuel systems. (Bought fuel that was not supposed to have ethanol, but turns out it did.)

No beeps..no codes..new fuel filters..just changed plugs..hope to check fuel pressure today. .ran great last trip out before winter. .motors have 300hrs..also pulled fuel pump off and cleaned screen going in pump..there was nothing in them..

Where is best place to get pump if I need one

I would have someone check to see if there are any codes in it. I had a similar problem and checked everything I could without scanning it and it turns out the beeper on my boat wasn't working. It was setting codes for low water pressure at higher RPM's and sea water pump was causing it. Replaced pump housing and impeller and ran great.

Had codes scanned nothing..just put new impellers in with service. .all gauges read good..oil pressures good temps good ..

It does sound like a fuel issue, but make sure plug wires and coils are good, no corrosion and good contact (I see you already did plugs).

When I changed plugs they looked good almost like new with good color. .didnt look lean or anything. .Both motors seem to be burning about the same

Just pulled my fuel pump off the part # 861155-2 is whats on both motors but when I look up this number it says its for non efi carb 5.7 motors..these are 2002 496ho efi motors..I know these are the original pumps..are these correct?

Try looking up the part in BAM's site. Great place to deal with too.

http://www.mercruiserparts.com/selec....asp?type_id=8

If you just changed the plugs i would pull them all out and check and see if you cracked one.. had same issue and i cracked one of of pita plugs on the outside.if its cracked it will have black line in the white part of the plug..

also make sure the gaps are right may have squished one down alittle

Thanks for all the replies. .plugs look good..runs and sounds great on hose..how many fuel pumps are on this engine..ive only found one on the side by the canister filter..this motor is before the cool fuel...looked up pump by serial # on BAMs site and its the same part # but every where I look it says its for a carb motor..these are early serial# motors..when u look up by part # it says its a low pressure pump 10-15psi..am I missing something here. . Doesn't seem to be enough psi for efi...but damn if I see another pump..

Some searching gave me this,

496 Mag & HO 496/ V-8 2001 - 2004 (0M025000-0W059999) 861156A03 (2) 861155A3 (1) N/A

Found that from here:
http://www.sterndrives.com/fuelpumps.html

Your fuel rails probably rusted on the inside and one or more of your injectors is clogged. GM made a "plated" rail in the later years so look into that. Could also be crank sensor but with yours being an early model 496 I'd say put a fuel pressure gauge on that schrader valve and watch your fuel pressure. Your rail is probably nasty....

Crank sensor generally throws codes.