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1998 502 MEFI 1 Cool Fuel II low fuel pressure

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1998 502 MEFI 1 Cool Fuel II low fuel pressure

Old 07-12-2020, 12:34 AM
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Default 1998 502 MEFI 1 Cool Fuel II low fuel pressure

New to me boat. (1998 Cobalt 252) Never been in water yet and lots of Jerry Rigging done. Appears the engine was removed at 1 time. 497 on the hour meter with 390 stored in the ECM scan.

Trying to figure this one out.

Fuel tank drained of old fuel. 1/3 tank of fresh 92 octane in it now
New fuel hose form tank to water seperator/filter.
New Sierra fuel pump (Merc recommended).and Merc fuel regulator.
All new O rings and filter under regulator
Injectors professionally cleaned/flowed

Only getting 30 PSI at idle. Supposed to be 36 PSI.

After about 10 mins of run time, the fuel pump is whining.

This is the second new Sierra fuel pump I've installed. Same problem with first, so I replaced with the second and new regulator. (First fuel pump install was a cluster "F". Figured I messed up the install)

Second pump install went smooth. after letting it idle on the garden hose for a few to get oil warm for oil change. I heard it.....

What would cause 2 new fuel pumps to start whining after 10 mins of run time?

SUSPECT #1 When draining the fuel tank, found it extremely difficult to siphon fuel from the tank via the fuel outlet.

How hard should it be for fuel to bypass the anti siphon valve? Or how do you know when 1 is bad?

SUSPECT # 2 When replacing the fuel supply hose from the fuel tank to the water seperator/filter I saw a strange fitting.. Someone installed a quick disconnect coupler (for air tools) on the water seperator for the fuel supply hose.. I removed that and installed a normal 3/8" barbed brass hose fitting. Could this be causing me a problem?

While trying to diagnose the low fuel pressure problem, I installed my Snap On digital multi meter on the fuel pump wiring harness. Then turning the key on to "prime" the pump. (it runs for like 2 seconds) I would only see 10.8V on the meter. Now this may not be accurate as the digital multi meter needs to "zero" itself before displaying the reading. So it may actually be taking a reading just before the fuel pump "prime" stops. (it takes a second for the meter to "zero" and the fuel pump only runs for 2, so it might be only taking a reading of the pump shutting off)

New batteries fully charged. (12.9V prior to starting the engine and have seen 13.2V after running the engine)

Alternator reading 12.9V at + and negative posts while sitting there and 14.7V when running

12.9V at starter

12.9V at the 50 amp circuit breaker in the elec "box"

No resistance from the gray wire that powers the fuel pump up to the fuel pump relay.

No resistance from the black wire that grounds the fuel pump to the engine block

I'm going to try replacing the anti siphon valve and taking a reading of the fuel pump voltage while it's running to see if I am getting 12V to it.

Anyone else got any ideas for me to look into?

I really appreciate and help on this as I'm not familiar with this FI stuff at all. Thank you
.
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Old 07-12-2020, 06:47 AM
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A pump whining means it sucking air or vacuum in most cases.

The antisiphon valve should be easily pass fuel toward the filter. Could put a hand vacuum pump on it after cleaning to see how much it takes. For testing could replace with straight thru barbed fitting.

Some tanks came with filter screens in the pickup tube. Take some string trimmer line and push into the pickup tube and see if it makes it into the tank
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Old 07-12-2020, 06:54 AM
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Didn't realize there was a cool fuel I and II, so i may be off here, but isn't your fuel module hanging off the port side of engine down by oil pan? How did you ever get that out to change the pump? Wow. There is a thing on the fuel rail on top of the engine that looks like a regulator that is actually a fuel damper I think. You did change the regulator on the module down by the pump?
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Old 07-12-2020, 08:51 AM
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Pretty sure I inspected the pick up tube when i drained the fuel tank, but I will check again when I install the anti siphon valve.

Think I'll try vacuum pump testing the anti siphon valve that's on there just for testing purposes.

Liberator, gen I was the VST system they used, Gen II is known as the cool fuel II, and after that, they came out with the cool fuel III

Yes, mine is hanging low on the port side of the engine. Very difficult to get at while in the boat. It's really not too bad once you know how to do it and have all the new O rings you will need to re-install. The whole unit comes out as 1 piece. You replace the fuel pump on the work bench, then re-install it into the boat as a whole unit.

Yes, I have that fuel regulator looking piece on the top of the engine also. Not sure what it actually does? So I don't know if that can be bad.

Yes, replaced the fuel regulator mounted to the cool fuel copper pipe.


Regulator looking part mounted on fuel rail.

Fresh rebuild just done

Cool fuel II removed as whole unit
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Old 07-12-2020, 09:00 AM
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about .060 gap on this one

Broken impeller vanes found inside the cool fuel cooler

Quick disconnect fuel lines? Who's idea was that? Oh yeah, no thread sealer either. What a great idea...

Just a few examples of the fine "craftsmanship" I'm finding on this boat.
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Old 07-12-2020, 09:02 AM
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Thanks for the help guys
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Old 07-12-2020, 09:14 AM
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The Reg is the one on cool fuel (30 psi), the one on the rail is a damper (860349A1 or Mallory 9-33207 unable to find pressure setting)
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Old 07-12-2020, 09:15 AM
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a air chuck fitting.............lol, be thankful its a single, I changed that fuel pump on the starboard engine in a 33 Outlaw.......no fun
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Old 07-12-2020, 09:23 AM
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Knew of VST, was not aware that was cool fuel 1. Thanks
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Old 07-12-2020, 10:47 PM
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Well today was very disappointing.

New anti siphon valve opens around 1" of vacuum on my gauge. The old brass one i replaced opened around 2". Not as difficult as I remember

Pick up tube was clear and fuel comes out easily with minimal vacuum

SIDE NOTE: when I removed the fuel supply hose from the anti siphon valve, it wasn't full of fuel

Installed multi meter on fuel pump elec. connector and have 13.7V while running. So it's getting full elec power to the fuel pump.

Installed fuel pressure tester and get 36 PSI when I turn the key on and the fuel pump primes the lines. As soon as the pump stops, it immediately drops to 32 PSI. I can repeat this over and over.

There is no fuel leaking or smell of fuel anywhere. Where is the 4 PSI going?

If I remove the pressure regulator vacuum hose from the intake manifold, the pressure goes up to 40 PSI. The whining quiets down some, but still is whining. Apply vacuum and pressure drops back to 32 PSI. I can repeat this over and over as well.

When I raise the engine RPM to 2000, the fuel pressure actually drops down to 28 PSI

This might be worthless, or it might be a clue but when I released the pressure on the pressure tester, no fuel came out the clear tube. It was just a big fart of air

I've got a couple short videos showing what I've described. Once I figure out how to get them off my phone and post here, I will.

I guess the big question is why did both pumps run quietly for about 10 mins and then start whining

Thank again guys

Last edited by xlint89; 07-12-2020 at 10:51 PM.
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