SeaRayCaptain

Hi guys, I am new to the forum and need your expertise.

Have and Sea Ray 340 and have repowered from Twin Mercruiser 6,2L to 496 HO engines, Hurth V-drive and new ACME 4-blade CNC-cut propellers.
Engines from 2001, 400h

Have owned the boat for two summers but one engine is causing me problems....
Symptoms:
Engines starts fine and runs great at idle. If I only go slow, 1200 rpm I can travel a long time without problems
But when I take the boat up to plane it works perfect at first, strong and easy up from the water.
Regardsless of rpm (3000-4500) can I only drive the boat for a approx 4minutes!, then the starboard engine start to cut/bog down, rpm jumping, loose power and pop. Then stop....
Easy to restart but will cough and stop if I go over 1000rpm.

I have read a lot about problems with these engines, but nothings helps...=(. No beeps and no stored alarms when hooking up computer.

I have
-Changed water separating filters many times
-Changed both fuel pumps (fuelboost and inside cool fuel)
-Emptied the gastank och refilled with new fuel.
-New fuel lines
-New sparkplugs and cables
-Cleaned injectors and fuelrail
-Changed regulator inside cool fuel module (Gen2)
-New IAC
-Lifted the engine during the winter and sent it to Mercruiser Service, they sad that some cables to the injectors where in wrong order and vacuum hoses where connected wrong, but no alarms. Testrunned the engine
indoors and sad was OK, but I still have the same problem now when I am back in the water.....


Tearing my hair, can anyone help me?? Canīt continue to run the boat in 5 knots....what can I do/test?

Sydwayz

iTrader: (1)

Have you done a compression and leak down test?

motor

iTrader: (3)

most fuel tank pickups have a small screen in them that can become stopped up .How much trouble to swap hoses at pickups and see if problem follows swap.. You didn't say you had run boat with a fuel pressure gauge attached,,, have you?

SeaRayCaptain

Sydwayz: Yes I did, within range, think it was 160-165psi on all cylinders. Pulled all sparks when did the test.

motor: Got the tip to check the 90 degrees elbows that connect the fuelline to the tank. There where wide open....Have also taken away the fuel shut offs.
My next step is to try and external tank and connect to the engine. Have also ordered a fuel pressure gauge that I can connect on the fuelrail. So I can se if the pressure drops when this occur.

Sydwayz

iTrader: (1)

Good call.

Maybe even (safely) rig up a test tank in the cockpit and take it out for a run. You could do this with a cheap 6 gallon tank from WalMart, some fuel line, and appropriate outboard fittings for the tank.

ezstriper

ck fuel pressure 1st under load..see what it does when falls down

28Eliminator

The early models had a problem with the crank position sensors. you could swap from one motor to the other to see if it makes any difference. They are easy to get to, right on the back of the motor behind the intake. Check the temps on both exhaust risers for overheating.
Last year my friends 496 had a similar problem and we changed the sensor, but still had the problem. We scanned everything and didn't find any real issue other than one exhaust coolant temp was higher than the other. 1 was running 120 and the other was 150-160. We found out that manifold was way hotter by the touch, and that's where the problem was at. We flushed it out and it ran, but it still was hot. I finally pulled the bottom hose off the manifold while reving the motor upto about 2000rpm, and it finally blew out a bunch of sand.

Yours may not be sand, but could be blocked by any number of reasons. The point is that it had low water flow to it and we couldn't see any valid alarm indicating this was the problem, but the ECU was shutting it down regardless. I hope you get if figured out, sounds very frustrating.

FIXX

iTrader: (2)

could be crank sensor like mentioned but usually they wint start...it sounds like the fuel tube has a crack in it,,if the fuel tank has aluminum pick up tubes check the threaded part that threads into the 90* fitting that screws into the fuel tank..i have replaced alot of those...if their nylon tubes then you have the replacement's if not check and replace both..

What your discribing is sounds like fuel pressure problem,,also if you have a fuel pressure gauge that would be a good diagnostic tool for you ..

28Eliminator

After rereading this, your first thing (as stated) should be to check fuel pressure while running.

SeaRayCaptain

Thanks so far for your replies. Did a fuel pressure test. Had 31 psi at idle....to low right? Took the boat for a run, couln't see the pressure drop when the engine stalled. Was about 35psi under run. Have know taken away the check valve in pressure tester to see if this changes the result. Will also try external tank to rule out that factor. If I only have 31 at idle, does at mean I still have problem with the fuel boost?