I have a 90 mercury that is smoking and alarm goes off and is constant,water pump was replaced and i

I have a 90 mercury that is smoking and alarm is constant when it goes off,water pump was replaced and injectors recently any thoughts?

When you say smoking, you mean the engine block is so hot that smoke is rising from the block? Or do you mean the tell tale water stream is smoking, like steam...water vapor? When you say alarm, do you mean the Over Temp horn?

Under what conditions is this occurring? You just started up to launch off the trailer, sitting at the pier subsequently at idle, exiting the harbor in the no wake zone at idle rpms, clearing the zone powering up to get the boat on plane, on plane running for some period of time at moderate rpms.....max rpms, have you experienced a similar problem before?????

Sounds like we need more information, Lisa. Do you have the serial # off the motor?.....or at very least do you know the year? We need to determine if it's a 2 stroke or 4 stroke. Also.....who did the work on it and when and why was the work done?

After running for about 30 min on plane it starts to constant high pitch alarm I turn off engine and there's smoke coming out of back where water spurts out

Its a 2005 90 hp mercury

Is this an optimax? Is this motor new to you?

Its a 2005 90 4stroke mercury outboard,I have it serviced every year in fl but I reside in SC now

Since you had the water pump done and you were able to run that long (per outing) without a problem, I would suggest that your water pump replacement was done correctly. That leaves a bad thermostat and/or high flow pressure relief valve (designed to increase water through the block at higher rpms) if it has one if it doesn't then it would be the thermostat or salt water corrosion blocking your cooling passages...assuming that your time in Florida was on salt water. If fresh water could be moss ingestion rather than corrosion.

One would assume that you haven't changed anything about your boat/engine that might cause the problem other than engine getting marginal cooling at the higher rpms/flow rates.

What are your wide open throttle (WOT) engine rpms (smooth water, throttle max, engine trimmed for max rpms) and what is in your owner's manual specifying the WOT operating range of the engine....like a range of 5000-6000 rpms.

Was this problem apparent prior to the water pump replacement? If so, was it apparent in Florida also? What is your approximate elevation...sea level, couple hundred feet, in the Smokey's....little rusty on the Eastern states and my Geography/topography.

It looks like not enough water coming out back its trickling out? How can I unclog it?

Depends what and where. Some folks backflush with the water hose if i's something removable.....piece of your old impeller if damaged and blade(s) broken off not caught in the water pump repair (a possibility, not necessarily the norm), weeds, running in a sand bar and picking up a lot of sand possibly. If running in salt water and not flushing after use it could be Barnacles, salt deposits that would require the water jacket covers to be removed from the block at the rear where the spark plugs are located and the flat cover on the left, looking forward from the rear, side of the engine. Another option would be to drop the lower unit and force water up the water tube that goes up into the bottom of the block with the thermostat and popoff valve (both under the same cover on the plate you removed that surrounds the spark plugs.

The Pop off mentioned above regulates the cooling above 2500 rpms and that valve could be stuck and not opening properly, or the flow path through it could be blocked. It is closed at the lower rpms and the thermostat adjacent to it controls temp there. Opening temp on my 90 was 143F stamped on the pellet part of the device. 143F is about the temperature of a US domestic hot water heater set to Normal for an idea as to how hot that is. Since water boils at 212F at sea level, there would be no steam if working properly.

Others could help more with this. I never had a clogged OH problem. I did have a thermostat stuck closed once but that caused the warning horn to sound at the low rpms where it is supposed to be controlling cooling. Once the boat got up on plane and rpms were high enough, the Pop off valve opened and allowed for proper cooling and the horn shut off.

Had a 50 this year , was going into limp mode, and giving 6 beep alarm. Tps,map & iac code.
What ended up being problem was over heating, ecm got cooked and was sending 6 beep code , instead of solid alarm. After checking and double checking ( codes : says voltage to high for those sensors) well ecm delivers 5 volts to these sensors. Luckily had another customer's boat with same single ecm plug. He said he was ok if I tested with it. Swapped ecm, put boat in water and boom , solid alarm. Overheating not 6 beep . pretty sure it was a '05
Pulled termostat it was full of sand and grass. So I back flushed motor with lower unit off replaced termostat and unfortunately ecm, cause it kept throwing 6 beep. Motor is running great.