Motor bogs unless trim button is pressed 96 Mercury 150 EFI

[Wildcat82]

Motor in question 1996 Mercury 150 EFI serial number OG396086

Here’s the issue I’m having and I know it’s strange. The motor will get on plane and then start losing RPMs unless I hit the trim button. When I press the button it will gain those RPMs back until I let off the trim. I can’t seem to find anything on the internet concerning this issue. It seems to be an electrical issue that I can’t figure out.

The battery is new as well as 2 new voltage regulators. Has anyone ever experienced this before? Someone mentioned maybe the bias circuit going bad? Any help would be appreciated. Thanks guys

[JOE54]

monitor fuel psi when problem is occurring

[Wildcat82]

Joe I initially was having a plane issue and it was in fact the HP fuel pump and was replaced. That fixed my plane issue, think that it’s possible it could be a faulty pump?

would it make sense that the voltage is getting high and when I’m using the trim it’s robbing voltage allowing the motor to run correctly? It’s odd that the problem clears while hitting the trim. This gremlin could be a major pain...

[kls2020]

Sounds like maybe high battery voltage or noisy charging current may be involved . When the trim motor in running the additional load may reduce the battery voltage enough to an acceptable level or help filter noise if that is the cause . I would suggest connecting a Digital volt meter to your cranking battery and monitor the charging voltage to the battery with and without trim motor running while driving the boat . If you have a meter with a "Frequency " function you could check for a smooth increase /decrease of charging voltage HZ with RPMs

[Wildcat82]

Would you happen to know off hand the voltage it should be running at WOT? I did hook a meter to it yesterday while running the motor in a tub. It’s would idle at around 12.8 volts to 13.5 volts. When I would give it some throttle the voltage would get up around 14.5 volts and I also noticed it would shoot up to 14.7 volts. When engaging trim at that voltage it did in fact bring the voltage down as to be expected. These new regulators could be malfunctioning out of the box.

[JOE54]

WHAT BRAND regs are they ????????

[Wildcat82]

WHAT BRAND regs are they ????????

They aren’t OEM I know that. They was put on at the shop when I had my HP fuel pump replaced. Upon further inspection the bottom regulator has a yellow and red wire connector. Both are brown and toasted already......

[EuropeanAM]

Oh boy.

BTW... you never said whether you were holding the trim button in the UP position, or the DOWN position?

Important question- as there are some "non-electrical" potential causes.

[Wildcat82]

Oh boy.

BTW... you never said whether you were holding the trim button in the UP position, or the DOWN position?

Important question- as there are some "non-electrical" potential causes.

Thanks for replying. The problem clears up If I press the up or down on the trim. It’s like an immediate change in the motor. Let go of trim and she’s dragging.. Other than that the boat is running good.

[JOE54]

oh boy. knew that was comming

[EuropeanAM]

Start with the obvious. Replace BOTH regulators and any damaged bullet connectors, using only OEM Components.

Verify clean, tight battery cable connections at BOTH ends of the cable, and verify a good, properly rated, WET-CELL cranking battery.

While you are at the regulators- verify that the grounds to the electrical plate are clean and tight (remove them completely, clean and re-secure them).

[Wildcat82]

Start with the obvious. Replace BOTH regulators and any damaged bullet connectors, using only OEM Components.

Verify clean, tight battery cable connections at BOTH ends of the cable, and verify a good, properly rated, WET-CELL cranking battery.

While you are at the regulators- verify that the grounds to the electrical plate are clean and tight (remove them completely, clean and re-secure them).

Will do and I’ll report back. Also I had someone else tell me possible bias circuit going bad. Is that also a possibility? I will need to check my switch boxes as well. Thanks Don

[EuropeanAM]

It is not IMPOSSIBLE. Normally if there is a problem in the bias circuit the ignition timing will be irratic (MOST of the time, anyway).

Bad grounds on the electrical plate could cause BOTH (can actually affect anything that is grounded to that plate).

[Wildcat82]

It is not IMPOSSIBLE. Normally if there is a problem in the bias circuit the ignition timing will be irratic (MOST of the time, anyway).

Bad grounds on the electrical plate could cause BOTH (can actually affect anything that is grounded to that plate).

Ok good deal, I’ll get to ordering some OEM parts and after a lake run I’ll let you guys know. Fingers crossed this issue will be history, Thanks guys!

[Wildride58]

It took me awhile to remember what was causing mine to do the same thing as Wildcat82. Mine would increase rpms when I trimmed up or down. It was the pre-detonation system. When I trimmed up or down the pressure of the trim system would smooth the vibrations from the motor and would think that the pre-detonation got better. I would gain 500 to 600 rpms when I hit the trim. The only part on mine that was still hooked up was the wire going to the EFI. Caused it to richen up while it thought it was having detonation problems. Most likely the sensor was faulty because I was running my WOT timing setting about 20 degrees btdc. I remember one of you very helpful people telling me to ground the EFI wire to the engine. After doing this my water temperature went up from running leaner, but not high enough to alarm. I changed the pump impeller and it got it back down better.

[kls2020]

I may be mistaken but I thought only the 200 and 225 EFI motors were equipped with the detonation sensor

[Wildride58]

kls2020, yep I'm pretty sure you are right on that. Mine is a 200 hp. Sorry for any confusion.

[JOE54]

know he is

[Wildcat82]

Alright guys after almost $500 later the boat is still doing the same thing... At this point I’m not sure what else to do. All of the grounds have been checked, and cleaned. I replaced the China regulators with OEM regulators that should have been put on in the first place. When my boat was worked on all electrical components was within specs as well. I’ve tried to upload the pictures but it says they are too big to upload. Any other suggestions would be welcome and I would appreciate it. Thanks guys

[EuropeanAM]

May need to email the pictures to yourself first (and limit the size of each picture to under 2MB). Not too small, though.

Did you look at the ignition timing to see if it was stable (or bouncing around)?