1998 Mercruiser 5.7 bravo 1woes

[Chas0218]

So it all started with getting a free boat. Yeah for me right? We all know free boats usually mean bust out your wallet. Well i got this boat not running "fuel issues" with a a good lower unit.

Well long story short the upper housing input bearing locked up, they ground down the starter and teeth on the flywheel. So lucky me i got to pull the motor and get the outdrive fixed. The only good news the boat was pretty clean and all the electrical was intact and not butchered.

So back to the motor, i got her running but as soon as i did found out the power steering pump needed to be replaced. Fixed that, then found out the lines were bad. Replaced those. Carb was screwed, lots of "custom tuning" to the carb so i replaced with a holley 600 cfm vacuum secondary. I am very fimilar with holley carbs and have tuned enough to know what im doing. Got that rebuilt with apprioriate marine parts 0laced it on the engine and she purrrrrs.

Well after fixing and messing around with a dozen things she won't go over 2800 rpm. So my father in law said it's the prop "because the shop screwed up the gear ratio in the upper." So I buy a $300 stainless prop on everyone's recommendation and it would go up to 3200 rpm.


Here is what I've found! If you have been following sorry for being so long winded. I have been trouble shooting without advice of the internet and I could have saved a lot of time and money if i weren't so stubborn. Well my fuel pressure drops off after 2300 rpm it starts to fluctuate at 1500. At 2800 rpm i get 1psi on my gaugse but at idle 600 rpm it is at 7psi.

Sooooo here is my question, does that sound like the electric fuel pump going bad? I have new plugs, wires, cap, rotor. I have ran the motor off a seperate tank and same results. Checked timing 3 times and it is advancing completely and base timing set with grounded wire at 10* per motor cover spec. Any help would be greatly appreciated.

Chas

 

[alldodge]

Well my fuel pressure drops off after 2300 rpm it starts to fluctuate at 1500. At 2800 rpm i get 1psi on my gaugse but at idle 600 rpm it is at 7psi.

Sooooo here is my question, does that sound like the electric fuel pump going bad?

No, sounds like you have a restriction in the line/tank leading to the pump. Have you checked the antisiphon valve, tank pick up tube, and if the fuel line is collapsing inside?

 

[Chas0218]

No, sounds like you have a restriction in the line/tank leading to the pump. Have you checked the antisiphon valve, tank pick up tube, and if the fuel line is collapsing inside?

Yes i ran off a remote tank plumbed in right at the filter eliminating the on board tank, lines and anti-siphon valve. I was also loosing pressure on a remote tank at same rpms. I also changed the water fuel separator/filter with same drop in pressure.

 

[alldodge]

With that additional info then its either the pump, or a restriction between filter and pump, but most likely the pump

 

[NHGuy]

It's an electric pump. You can also check for voltage drop when the fuel demand increases.
ps. if replacing the pump seems to be the solution remove all the inter pump and filter and tank lines to check for debris in the lines and the inlets.
It also would be a good idea to just replace any rubber fuel lines. They are probably original to the boat, 20 years old. If there is a tiny leak in a fuel line it will suck air instead of fuel if it's between the tank and the pump.
Then if the problem is still there you can feel a little less apprehensive to change out the pump.

 

[tank1949]

Send prop bill to shop! You may have to run old gas through filter several times to get all the crap out of tank and lines.Trust me! If electric fuel pump is not marine grade but it is an automotive, pitch it. You have suckers and pusher type pumps. I learned the hard way after pitching anti syphion valve AND cheap ass automotive pump. I installed a sierra electric pump.

 

[Chas0218]

A little update, i replaced the pump and am getting 10 psi all the way up to 2800 rpm so that's good.

Unfortunately it still wont go above 2800 rpm. Compression is between 198 and 205 across all cylinders. Could it be running too lean? The attached picture is of new plug when engine was shut down at 2800 rpm.

 

[alldodge]

I think you may need better gauges. If your getting 10 psi fuel pressure then the carb float may not be able to keep all the pressure back and would flood. Pressure should be 7 psi max, and might get away with 8 but probably wouldn't last

Compression of 198 to 205 means you have liquid in the cylinders, and if the carb is flooding, then the plugs should be black (part is) and there should be a strong smell of fuel when running.

Plug looks a little steam cleaned (water) but enough gas can wash the plugs.

How is it idling now?

 

[Rick Stephens]

Just wondering, is the Holley 600 an automotive carburetor?

 

[NHGuy]

And if you are familiar with Holley carburetors you would know they are pressure sensitive. I believe they want 7 lbs of fuel pressure. My Holley derived carb does anyway. So if you are getting 10 psi get a regulator and gauge. Set the floats a little below the halfway point, set up your idle mixture, put the timing at 8 to 10 degrees at idle. or 32 all in.
Did you already verify the throttle blades are going wide open? Just look down the carb with the engine off.
Let us know how she does.
It's usually not the ignition, but if you run out of ideas and decide to get ignition get the DUI (Davis Unified Ignition).
My 383 LOVES that hot spark. I can idle really low. Love it with my kinda loud pipes.