Twall7

I've got 496 ho I was wondering if any one could tell me how much could the fuel pump put out if the regulator(s) went bad. I checked the fuel press with key on motor off with what I assume is a good gauge (it's a whole setup made to check fuel press ) but I swear it was showing over 100psi does that sound odd to anyone ? I also talked to a local mechanic he said no way the pump won't put out that much press so...... Any help

4bus

iTrader: (4)

Absolutely, at dead head pressure it can build up to 100 psi. The regulator is only needed at low rpm, once the vacuum is gone at high rpm the regulator lets full fuel flow. My engines run at 30 psi idle, I had a bad reg and was running 60psi pinned on the gauge.

Change the reg, and now you will most likely need to change the spark plugs. 496s with COP ign are very sensitive to fouled plugs for some reason. My friend dropped a sparkplug wire years ago, and the boat would not plane until he changed the plugs.

Twall7

Now if I'm not mistaken there r two regs on that motor one by the pump and one on the rail they said they had the one by the pump in stock

BUP

iTrader: (9)

Fuel pressure regulator and a fuel pressure dampner as they both look the same just to clarify what is on these MPI marine engines..

Rich running conditions could also mean bad MAP sensor also Mercruiser years ago had a campaign to remap the PCM for rich / sooty running conditions.

Twall7

So any one know which one I should change ? Also the fuel psi was still over 100 with the motor running

GO4BROKE

iTrader: (1)

The fuel pressure regulator.

BUP

iTrader: (9)

I take it you have the Gen II cool fuel system. Serial # will determine exactly what you have. Your problem might not be the regulator but would not rule it out. I am almost sure your app has the Gen II cool fuel system. If so problem might be under the regulator. Completely clogged screen and or bad o-ring and or the regulator itself. Have to ask where are you testing fuel pressure on your motor ?

Keith Atlanta

Off memory it should be 42 PSI running and about 45 key on not running.

You are getting into a bad place. Something weird is going on. First, you need to hook a computer to it to see if there is something else alarming. Then, assuming you are hooking it up to the schrader valve on the rail, go rent a different fuel pressure gauge from an auto parts store to confirm your numbers. I dont see how a 496 would run at 100PSI. Mine smoked like crazy at 55 psi.

The fuel pressure regulator is on the rail... it is a piece of junk. Yes, you can buy a new one. But I would assume you have another problem. Maybe even a clogged return? Just seems like you have something else going on like water in the gas and the rust messed up your regulator somehow. (maybe)
FWIW - I converted mine to a full Aeromotive system with Aeromotove pump and regulator. I didnt get along with the #10 star allen adjuster on the regulator after I made upgrades it wouldnt stay consistent.

You have several things to check:
-Fuel Pressure (again)
-Computer
-Pull the regulator apart (I dont recommend this, I doubt you will get any consistency out of it unless you install all new guts and o-rings and I still doubt that)
-Possibly pull the return line off the rail to see if there is debris in it?
-Change the fuel/water separator

BUP

iTrader: (9)

If your motor is truly built in 2002 or 2003 or 2004 it will fall under these engine serial ranges 0M025000 thru 0W059999.

These serial ranges all have the Gen II cool fuel system with a spin on water fuel filter and a boost pump. The cool fuel system here has the fuel pressure regulator mounted on the cool fuel cooler. I know what I am talking about here or look up these parts to verify and parts diagram.

If you pull up the parts list for your engine serial # you see it a 43 psi fuel pressure regulator part # 861126A1 or if you have the Mercruiser 496 OEM service manual # 30 it will show you the whole cool fuel set up with fuel pressure regulator 43 psi on page 5A-6 part # 4.. Under that is the small screen and sealing O-ring, if the screen becomes clogged it can cause high fuel pressure and rich running conditions. Also I am not ruling out the 43 psi fuel regulator as well,

The regulator on the intake fuel rail is no longer available for the serial # ranges listed above and was used as fuel dampener. If you look up later years of this motor the new part # 8M0046753 and LISTED as dampener on the intake fuel rail. Good luck. .

Twall7

I just took off the water step and dumped the fuel in a glass jar to see how it settles out I've got a new one on order from local shop.i guess I don't understand why a clogged screen would cause higher pressure ?! And I think I will rent a pressure gauge from a local parts store to verify the press and yes I did hook onto the fuel rail to get my numbers. What does the fuel dampener do? And can I get one or not? Thanks for all the help serial om637193 I did have a lot of soot and it didn't like running at all