BUIZILLA

okay, i'm back for help with this malady again. Fuel pressure is way too high according to spec's. I get 58-60 at idle with vacuum source connected. NO BLACK SMOKE OR BLACK TRANSOM. It starts up at about 52#cold and slowly works it's way up to 58-60 (continually fluctuates about 2#) as the water temperature then gets to operating point. Regulator holds 36#-40# with engine off. The hotter the engine, the higher the pressure climbs. When I cycle the ign. key cold, the pressure goes to 50-52. When warm, 56-58, then settles back to 40#. I'm thinking it should only be 42-45 on cycling or running, no matter what temp.

Facts, and I have done the following>

1) Original fuel pump was very, very noisy, but engine ran great, so I replaced it as a precaution with new Merc unit. Did not have any issues up to this point, just hated the noise. Sounded on it's way out... Did not check the pressures at that time. Boat then ran great for 10 hours with new pump, new pump is reasonably quiet. Boat ran great b4 replacing the pump. Boat now runs great for about 30 minutes, then wants to shut off cruising, and then heavy surges at idle on restart. May, or may not, re-start. If it does start, it then idles perfect ... until raising it to 1000 rpm, then it surges to between 1000-2000. Docking is an adventure....

2) Removed and checked the original regulator thinking the diaphragm was stiff or dried out. (1995 boat with less than 72 original hours now) Removed return screen thinking this was a problem. Re-installed old regulator, same thing. Yesterday I replaced the original pressure regulator (and no return screen) with a new Merc unit, thinking this old one may have some trash. I still get the exact same readings. Checked it with another gauge, same readings.

3) Removed fuel return line and Merc filter head, and checked for return blockage. Perfectly clean. Replaced Merc filter with spin-on Racor setup, same thing. Pressure is regulated by the return fuel flow, so where the hell is the restriction???

4) Removed anti-siphon valve at tank thinking engine is starving under load and thats why it shuts off cruising (2 seperate problems maybe)... Blew back into tank with air thinking tank inlet tube is restricted.. no problems there.

Is it possible the new Merc fuel pump is simply overpowering the return circuit / regulator???

Is it possible the fuel cooler upper tube has a blockage somewhere's explaining why the pressure climbs as the engine heats up??

I'm kinda stumped... all opinions appreciated.

Ed Cozzi, PM me, I need a survey done on a Donzi Criterion to get insurance coverage.

Jim

Dave_N

Have you checked the vacuum at the regulator? Don't know what else to suggest.

Dave

NOBODY

I'm pretty sure this system has 2 regulators on it, The one on the intake manifold is a dummy one even though it has a vac line to it. Have you checked the one on the fuel cooler? This is the one that controls the fuel pressure.
It sounds to me like your having reg problems.
Even if you had a big efi pump that reg could still control the fuel pressure.
This system doesn't have a return line on the fuel rail.
The fuel is returned to the fuel filter.

Scott B

I'll bet dollars to doughnuts there's a second screen stuck in the hole where the the fuel regulator mounts on the cooler that you missed.. Pull the regulator and check it...

BUIZILLA

Fixed it..... about dammm time.

I removed the fuel cooler, fuel pump, all fuel lines, and water hoses completely as an assembly (more blood and skin removal) and after removing the regulator yet AGAIN, I found ANOTHER screen pushed way down in the cooler base of the regulator attaching base mount. It was somewhat dirty... Dammm thing must have had 2 screens from the factory, or someone b4 me did something stupid and added another one not knowing this one was hidden in there.... when I took out (dropped in the bilge really) the first OBVIOUS screen a few weeks ago, the pressure dropped from about 72 to 58.
Anyways, it now has 34 vacuum connected at idle, and 42 disconnected. Pump is quiet as a mouse. Runs perfect now. Very crisp.
The other *regulator* at the top of rail is just a dampner for the fuel pump/injector pulse stabilization.
Thanx to all for the help, and especially Ed Cozzi for insisting I take the cooler off and look closer, and Scott Baxter for helping with the surgery.

Jim

Scott B

Damn, thought I could beat ya here after dinner...

Edward R. Cozzi

I try to tell my own children to listen to the old man once in a while.

Glad I could be of help.

Nice to solve problems like that, isn't it?