Port Engine is short on RPMs
 

Hoping to get feedback on where I might start analyzing to find out why I am 400-600 RMPs short on my Port engine. I am running 2 Merc 525SC in my 1997 38' Fountain, which I have had only since late last August, and do not have any familiarity with these engines. My fuel pressure, boost in addition to RPM are also low when I am at WOT.

Also, if any one can shed light on how to maintain these engines I would appreciate it; including how to check blower oil, etc. I received now information from the previous owner.

Sorry to be so dumb on this but I have not found anything on the Mercury site either and hoping someone can save me a lot of time tied up at the dock and more time on the water

-Kevin

Re: Port Engine is short on RPMs
 

If you have rev limiters make sure there the same on both sides.I checked mine last week, port side had 5600,star. 5200rpm . If you have msd boxes
it's just a chip you plug in.

Re: Port Engine is short on RPMs
 

From what have described, I would think the fuel pressure is the problem. Since you have twins, you could switch the fuel pumps and see if the problem follows the pump.
Be careful though if its too low. You are risking a lean condition that could cause an engine melt down.
If it was me, I'd just get a new fuel pump for the port engine.

Re: Port Engine is short on RPMs
 

what is the fuel pres? to lean to long to bad,, yikes...........
but
i had similar issue i just took delivery of a 35 fountain just bought from fl power boats and it had a bad stbd drive dragging one motor down about 2-300 rpm,, if so catch it before it blows.. its way cheaper,,,

Re: Port Engine is short on RPMs
 

Is it only low at WOT?

When I bought my boat I had one engine a little low all the way up to WOT. There it was 400 rpm less. My trouble was one prop had been replaced and the new prop had more cup to it.

Re: Port Engine is short on RPMs
 

Thanks for all the feedback and suggestions. The fuel pressure is down through out the RPM range, same goes for the boost, when I kick that in. I certainly am worried about the lean condition and know what that can do to an engine. I have a SC on my Vette and watch the Fuel pressure religiously. I thought that the fuel pump might be bad but the guy at the marina said he doubted it, he was saying the gauges might be off, seems a little strange that all the gauges would be off. The suggestion on swapping the pumps is a good idea, but to save time I guess I could just put a new one in to eliminate that possibility. Does anyone know a cost or a good place to check with? I should have my props detailed anyway so that is also a great suggestion.

Last, does anyone know where I can get a book on these engines? You know, where everything is and what are the torque specs on bolts, etc?

Re: Port Engine is short on RPMs
 

Direct from Mercruiser service manuals. I have one for motors and one for bravos. Guessing 40. each. Get serial #'s first.

Did you ck with Rod at Performance? He should be able to help diagnose that for you.

Re: Port Engine is short on RPMs
 

Yup....talked to Rob about it, he was on that said the guages might be off.

Re: Port Engine is short on RPMs
 

I've got the Merc manual for my 525sc. It a '96 engine. I think the only diff between 96 and 97 is they changed to CMI exhaust. Not sure if its the exact same manual or not.

It's Mercruiser Hi-Performance series manual #3. The part # on the manual is 90-848294

Re: Port Engine is short on RPMs
 

I assumed. Can he start by cking them first? I think his motives are good and not bad.

Also, when running is the boat pulling one way due to less rpms?
You should be able to hear, by ear, if your engines are synchronized together. I would start there before spending too much.

pm "10x" Frank on board and he'll tell you.

Re: Port Engine is short on RPMs
 

I agree, I am certain Rod's motives are good. He helped me out last year when I was in a pinch with my stearn drive. I felt bad after thinking about it for a while and was going to edit what I had written, I really did not mean to throw him under the boat so to speak, just started typing away with-out thinking. NOTE TO SELF: Do not respond to emails with a splitting headache and after waking up on wrong side of bed!

I never really paid to much attention to if it was pulling, if it is, it certainly is not pulling a lot that I notice it, but since the ride and handling of the boat are still so new to me, I could be missing it. As far as sound goes, I can not hear a difference at idle and at speed...it is anyones guess.

Thanks for the suggestion on PM 10x, I will do that.

Griff, thanks for the info on the fuel pump numbers.

Re: Port Engine is short on RPMs
 

That is the part# for my manual.

Re: Port Engine is short on RPMs
 

Most boat gauges are disappointingly inaccurate.

#1) verify tachs reading the same (which is different than "properly" but is more important). Run up to 75% WOT (wide open throttle). Play with the sticks until you get an audible sync. You can sync by ear very easily. Just listen for the out of phase sound and adjust a little at a time until it the phasing slows to an almost perfect sync. THEN take note of the tach readings. They should be showing within 50 rpm of each other. Some tachs have adjuster pots on the back. Some don't.

Okay, now that you are reasonably sure your tachs are reading close to each other, repeat your WOT run and note the differences in all of the readings. More than 100rpm difference is too much.

Fuel pressure: fuel senders are notorious for odd readings. You need to also have mechanical gauges in the engine compartment to double check your electric gauges. You should see between 5 and 7 psi of fuel pressure regardless of rpm or load (assuming this is a normal Merc 525SC). Less than 4 psi will allow the float bowls to run dangerously low and cause a lean condition. If you do NOT have 6 or 7 psi of pressure, then check your regulator and fuel pump and fuel lines and tank vents. Get that situation fixed before you do anything else. If you DO have 6 or 7 psi at all times, then set the float levels in all of the bowls (2 each carb). Pull the level plug on the side of the bowl and adjust the level screw on the top of the bowls (flame arrestor off and fuel pump running - if you have mechanical pumps the engine must be running so you will need to pack rags around the level plug to catch gas that spills out - also have a buddy with an extinguisher in hand: I've learned that if you have a manned extinguisher around you NEVER have a fire).

Boost? At WOT the two 525SC's should show the same boost even at 400rpm difference. Unlike a centrifugal supercharger, the blower on the 525SC should show pretty close to the same boost as the othwer motor AS LONG AS THE THROTTLES ARE OPENING ALL THE WAY (oh yeah, check your throttle linkages to make sure the throttles are opening up all the way). Leaking manifold gaskets or abnormal blower wear can of course change this.

Holler back when you check some more stuff.