underpsi68

I went out yesterday for the first time of the season. I just installed a mechanical water pressure gauge and oil temp gauge. Drive it about an hour with no issues. As I get back to the dock I was getting the 2 beeps every minute. Put it on the trailer and flush on the hose, no beeps hummmm. I went out today and shortly after I left the dock the 2 beeps a minute returned. Drove around at my usual 3500rpm cruise. Good readings on gauges, oil pressure, oil temp, water pressure, voltage, exhaust cool, good flow out of pipes etc. Engine never skipped a beat. I had to pass someone so I went wot. After a short period the alarm went to a constant. So I backed down to an idle. Alarm went back to 2 beeps a minute most of the time. Getting close to dock later in day I went wot again, constant alarm returns ahhhhh. I don't think there was reduced power when it went to a constant alarm, although I backed right down. It didn't nose over at all.

I don't have a scanner YET. I was looking over the winter but kind of slipped my mind. Will be buying one shortly!!!!!

After doing some research on the alarm beeps of a 496 it leads me to the wp sensor.

Does anyone know the ohm reading vs pressure of the 496 pressure sensor? I would like to check to see if it this and get back on the water for memorial weekend.

Fwiw it's a 2002, I just changed the impeller and wear plates in the Hardin marine stainless water pump as I do at the beginning of every season, I checked every plug on the harness, no burnt wires or connectors, even the iac. The engine starts right up and idles fine.

Ryan00TJ

iTrader: (8)

The seapump sensor measures water inlet pressure or water block pressure. It is located
at the seapump inlet hose. Normal diagnostic tool ranges are 1-5 psi (7-34 kPa) at idle and
7-17 psi (48-117 kPa) at WOT. To check if sensor is within range, the diagnostic tool reading
with key ON should be approximately zero. The normal resistance value for the water pressure
sensor at 70 degrees F (21 degrees C) is A to B 31.5 kohms and A to C 42.9 kohms.
A malfunction of the seapump sensor will set the fault of Seapump CKT Hi, Seapump CKT


Pm me your email or cell # and I'll send you the 555 pcm troubleshooting Merc fsm.

underpsi68

PM sent

BUP

iTrader: (9)

I have notice that Hardin kits now have a different impeller IMO it looks and feels and bends like a cheap made impeller. The other impeller they had or possible still do as well was more like the exact Merc impeller. I ordered some kits like I do and this year there was 2 different made impellers - one like the Merc Impeller and the other one inwhich I think is cheaply made. Cheap impellers do not flow very well as rpms increases. Just saying and something I noticed this year about the Hardin rebuild kits.

Anyways you can test water pressure with a psi style gauge in place of the sensor also you can use an air gauge to pump air into the water pressure by fabing a fitting correctly to do so and pump air into it - you can watch on the scan tool the psi change with the air you are pumping into it - does the alarm go away doing this testing ?

Next is you can test the Merc spec testing of water volume into a pal for 15 seconds to see if it matches the correct amount of water flowed volume. Search up here as I least have brought it about 5 times on how to do so and the output specs for volume.

You really need a scan tool and know how to use it plus know how to read it. The understanding of all parts from the scan, can lead you to your problem area.

IMO and throw out a really good guess with a dart on the board ---- POSSIBLE EMCT sensor and or EMCT OVERHEAT --- when was the last time you changed out the heat exchanger end cap gaskets as well. These gaskets will restrict water flow to the exhaust manifolds but your engine temps will be spot on normal good readings. When was the last time you changed out completely the engine coolant ???

Just an FYI, I have NEVER ever seen water pressure at correct dead idle for OEM bone stock ECM 555 and PCM 555 anything 3 psi and above. Never and I have scanned marine engines in the thousands.

underpsi68

John I changed the end gaskets and o rings last season. I changed the antifreeze 2 years ago.

I kept checking the exhaust manifold temp byfeel and they were just slightly warm to the touch.

I installed a tee for the new wp pressure gauge inline with the factory sensor at the back if the sea water pump. The gauge won't read at idle, I'm assuming because there is a small 25ft hose feeding the gauge and a lb or 2 won't get threw such a small line with that pressure., common from what I was told.

I get 3 lbs at 1100 and it jumps right up after that. At 3500rpms it reads 28 and at wot it was about 45. I forgot the readings between 1100 and

Thanks Ryan for the info and as always a big thanks John!!

BUP

iTrader: (9)

your welcome water pressure sensors come is 2 different psi ratings - one is 100 psi and one is 50 psi you have to use the correct one per your app - it goes by engine serial number inwhich inreturn the cal in the PCM.

Also do not rule out a bad EMCT sensor(s) really need to scan the engine to read all parameters.

Also you might have more than 1 problem going on as well. Not saying you do but sometimes 2 different warning horns can mean that or one alarm is soft alarm and then it turns into a hard alarm ( the same fault) The same works with guardian mode and available power..

Also there is 4 or 5 different diagnostic manuals for the 496 thru out the 10 year run of them in the marine world.

The first couple of service manuals really were average at best.

underpsi68

Update

I checked the ohms of the emct's and they were correct. Checked wp sensor obm reading and it was pretty far off. I went to local mercury dealer and got new sensor per serial number. Checked ohm reading on new sensor, just about the same as the old sensor. Installed the new sensor because I'm sure they wouldn't take back electrical part, still the 2 beeps.

Going to order a scanner Tuesday morning. Don't want to just keep throwing parts at it.

John I know you are spot on with your info. I'm thinking the emct sensor/s are a good possibility. Just confused the sensors have the correct ohm reading.

If I unplug the emct's will the alarm go away or be constant? The emct's can throw both the 2 beeps and constant beep. I'm almost tempted to pick up 2 new emct sensors, at least they are cheaper than the wp sensor lol.

Ryan00TJ

iTrader: (8)

Without being able to scan the PCM it's just a wild guess at this point. FYI when I had a bad IAC it had the same symptoms as you have right now. It had a 2 beef soft alarm at anything under 4000 RPM. Anything over 4,000 it would throw a constant hard alarm. Only visible sign the Iac was bad was when it was removed the pentil was in a different position versus the new one. Getting the scan tool should get you on the right track.

underpsi68

It's funny that you mention the iac. I recently lowered my idle rpm because it was a little high. I turned the stop screw 1/4-1/2 turn. I wonder if this has anything to do with it???? It ran for about an hour mostly at cruise before the alarm started going off?

BUP

iTrader: (9)

John not picking on you but your last post - HUGE details that were left out from the start. Very important to tell all what you did to your engines before and during when they have problems and in full details plus what exactly you have for engines and set up - OEM stock or not. .

Anyways the throttle plate setting also effects the IAC PWM % and the TPS outputs along with IDLE control. So possible the cause of the problem but not 100 % without a scan and see those parameters.

Also now reading into your whats going on in more details - Possible IAC sensor or another sensor fault (2 beep ) that is putting the engines into guardian mode and by continue running the engine at half throttle or above settings or whatever throttle setting depending on available power % will activate the OVERSPEED fault. - hence the solid WARNING horn. I would bet that you will see OVERSPEED fault(s) in the scan matching the timeframe of the 2 beep warning fault,