2011 Mercury 150 Pro XS - Losing power

[crawlerHarness]

2011 Mercury 150 Pro XS
Serial 1B804717
Model 1150P83HY
Water Pressure - 5-6 psi at idle, unsure at WOT
Analog gauges

I bought a boat in late May and back then it was reaching 4500 rpm and 38-40 mph on a 2011 Stratos 386XF - an 1850 lb fiberglass walleye boat. It has a 14.25 x 21P aluminum prop.

• But now it will only max out at 3500 rpm, and 34 mph when cold.
• After 10-15 minutes, she starts to bog down, until only going about 10 mph.
• I can shut it off for 10-15 minutes, and she again will start out at 3500 rpm and 34 mph, and gradually lose power.
• No audible alarms, and she does have the confirmation 1 second beep at startup

The bogging down happens much quicker when I use the tilt/trim. The motor loses the 200 rpm right away, and bogs down to slower rpm quicker than the 10-15 minutes.

I initially thought it may be battery related, so I added (2) new main batteries. They are connected by a Blue Sea 6011 Battery selector, which is OFF / ON / A+B, as well as a Blue Sea 7601 Auto Charging Relay that will charge the 2nd battery automatically when the Main battery is full. I usually see the 7601 green light after 5-10 minutes, which means the 2nd battery is charging. The 2 new batteries did not solve the problem. I also used a 3rd battery and left the jumper cables on during starting and for 10-15 minutes while the motor exhibited the same bogging down.

• 6 new NGK Iridium IZFR6J spark plugs
• new primer bulb (no change to rpms when pressed vertically while bogging down)
• had 105 psi on the fuel pressure / 90 psi on the air pressure (at startup)
• Idle water pressure at 5-6 psi.....unfortunately can't remember on WOT
• Compression on all 6 cylinders are 130-135 psi at WOT (cold)
• Water pump pees strong after 4-6 seconds

Another note, there is an audible droning / cycling of the engine at 1 second intervals when she starts to bog down. And she doesn't restart for 10-15 minutes after the bogging down.

NOTE - this is all I have gone thru so far. Have taken off and put back on the old fuel filter - waiting for new one. Ordered new fuel filter, 2 thermostats/gaskets, water pump, and 3 new relays for main motor / trim.

Looking for any help / advice on items to address.

[crawlerHarness]

Question - if it is going into Guardian mode.....shouldn't there also be an audible alarm?

Note that I do have the single 1 second beep at startup. But no alarm when I lose power.

[SilverFox579]

First off, your WOT rpms are WAY low, your engine needs to be propped to reach at least 5650rpm at WOT.

Second, you mention you added 2 new main batteries, your engine requires ONE main, and in a fishing application, it should have at least 950CCA.

Based on what you've posted so far, I would bypass the battery switches and ACR stuff, and connect engine leads direct to ONE battery that well exceeds engine required minimum capacity. Post results.

It would be helpful if you had Smartcraft data. At this point, based on the info provided, I don't believe Guardian has activated (you would know if it had) and you don't have a cooling related problem based on your idle pressure (even though analog).

[crawlerHarness]

Thanks Silver.

I haven't seen the 5500-6000 rpm's, but maybe the engine was not running right when I bought it. So I am not focusing on changing the prop yet.

My batteries are 840 CCA marine starting, but I have tried 2 of them in parallel (12V), with the same results. But I do take your advice, and BBC's as well, and will get one of the recommended 950-1000 CCA marine starting batteries. The 2nd battery is set up to handle the boat electronics. But they can be combined thru the switch. Whether the switch is faulty or not, I agree in trying to continue to prove it out.

I will be gettin the WOT water pressure the next time I am out (1-2 weeks)....when running good and when bogging down.

The other thing I haven't done (50 wet lashes) is removed and cleaned/flushed/replaced the Air Compressor strainer. I will do that.

I have also noted that my 9.9 kicker electric tilt relays are on the same battery as the 150 Pro XS trim. So my plan with that is to remove the relays and re-test.

Finally, I will also be ordering new fuel line from the bulb to the motor, as well as making sure the hose is warm prior to inserting on the barbed fittings. I can't be sure what type of gas was used prior to me buying the boat.

[JOE54]

report back

[SilverFox579]

There are some very helpful topics in the FAQ at the top of this forum with a wealth of Optimax information you can trust. To your benefit to spend some time there.

[crawlerHarness]

Performed quite a few maintenance items:

1) Put in new battery - Batteries Plus X2 Power - SLI31AGMDPM - 1150 CCA
2) removed automatic charging relay
3) cleaned Air Compressor strainer (some material to be cleaned off, but not terrible)
4) inspected air compressor intake filter
5) checked/tightened tilt trim connections, and tilt/trim fluid
6) replaced fuel line (the old did have the inner liner released and pinched)
7) Good spark at all 6 cylinders at idle and 1200 rpm
8) Cylinder drop test - Definite RPM / audible change at all 6 cylinders at idle at 1200
9) water pressure now 2-3 psi at idle, and 9-11 psi at 4500-4700 rpm.

No change at all. The motor still loses power after 10-15 minutes. RPM's go down from 4700 rpm down to 2000 rpm if you run it long enough / speed from 34-38 mph down to 10 mph.

Finally....

10) Once bogging down occured, we removed the upper cowling and belt cover, and sprayed gasoline into the air compressor intake. The motor took off for a second.

11) I HAVE NOT CHECKED THE FUEL PRESSURE AND AIR PRESSURE AT WOT WHEN BOGGING.

I suspect one of the fuel pumps.

Or is there something else you would be checking?

If it is the fuel pump(s).....what is the part number for the rebuild kit I need to order from EuropeanMarine? Looking at the parts list....it looks like there is (2) pumps inside the VST, as well as another fuel pump listed.

[JOE54]

first make sure you have no restrictions between vst and tank , inspect hose rebuild pulse pump , there is 2 pumps no kit, be sure you need pumps because they aint cheap ,call um with ser number theyll know what you need

[SilverFox579]

Excellent battery choice!

Since you had liner separation check out this FAQ topic, do everything recommended, all at same time skipping nothing - FUEL LINES AND PERFORMANCE PROBLEMS

Do not spray fuel into air compressor OR throttle body, BIG risk for damaging your engine. The compressor supplies pressurized air to the rails, no fuel whatsoever, I'd be concerned spraying gas into the compressor inlet may have washed oil away. Spraying fuel into the throttle body risks engine damage and potential for fire, throttle body meters air only, no fuel whatsoever.

It would be helpful to know air/fuel pressures when problem is occurring.

[EuropeanAM]

PLEASE do NOT spray gasoline into your air compressor again. The results could be CATASTROPHIC.

Based on what you've indicated, I would recommend getting an infrared temperature gun, and checking the EXTERNAL electric fuel pump's OUTLET fitting (top fitting) once the engine has lost power. This fitting should NEVER exceed 110 degrees F (if it does, the pump may be failing).

Also recommend a totally separate fuel source/tank with it's own separate line/bulb be connected directly to the pulse fuel pump to see if the problem persists. This helps to rule out any problems in the boat tank, pickup, anti-siphon valve, tank vent, line, bulb, etc.

[crawlerHarness]

We are set up to head out and test again.

1) rebuilt pulse pump - nothing noticeable regarding gaskets/residue when taking it apart - replaced with new rebuild kit
2) checked fuel line from bulb to pulse pump - nothing noticeable - no particles anywhere. Inner gas lining still clear / not amber. Replaced fuel line and bulb.
3) added fuel pressure gauges to both fuel schrader and air pressure schrader. Pressure at key turn to accessory - 15 fuel / 0 air. Pressure at idle - 100 fuel / 90 air. Removed fuel gauges for drive to boat launch - saw fuel spray out of air schrader gauge release.

Note....the engine will not restart for 2-3 minutes after shutting off.

Heading to boat launch to re-test. will report back this afternoon

[JOE54]

NO fuel on air side , were those gages positively fuel free before connection to air side from prior mtr

[EuropeanAM]

Also- are these Glycerin-Dampened DUAL pressure gauges? Be very critical of those pressures as 90 air 100 fuel would be an indication of problems.

[crawlerHarness]

Ended up taking it into the Marina as we couldn't figure it out. I will post what they find in a few weeks.

[JOE54]

[crawlerHarness]

The issue did turn out to be the High Pressure fuel pump inside the VST. Part #855427A-1

Ran well today on the water, but unable to get max rpm and max speed notes due to the 2' waves. Maybe tomorrow.

[crawlerHarness]

I was able to run the boat WOT again for just a few minutes.....due to the 2-4' waves this time out. Got her open behind an island. Only 4700 rpms and 39 mph.


So next step will be figuring out what prop to put on it now. Obviously a 17P prop instead of the current 21P, based on Mercury's prop selector. But I would like to think it is a little more complex.

[EuropeanAM]

If you can get a 17P on it, that will tell you.

[SilverFox579]

I have an "as new" 15 x 17 Black Max (purchased from European Marine), contact me via PM if interested and you can't find one locally.