Engine Alarm 7.4 MPI

[BigDog98]

[FONT=Helvetica, Arial, sans-serif]Need your help guys! So Saturday I launched my boat for the first time this season and Sunday was the day for the maiden voyage. 7.4 MPI Mercruiser. A few issues that happened. 1) A beep tone alarm went off at cruising 3200 rpm and would not go away until I shut the engine off. It was occurring about every 5 seconds and would not shut off. Water temperature was at 170 which is what it always runs at, oil pressure was good in the 40 range and gear oil tank was full. After I shut the engine off and restarted, the alarm has gone off again and seems to come on at around 3000 rpm. Tested at idle speed and WOT. The engine however will still reach WOT with the alarm on so its not a rev limiter. I disconnected the gear oil sender to see if alarm would stop and nothing changed. Checked the thermostat with a infrared gun and read at about 155 at the time of the alarm going off. I basically did process of elimination at this point. Checked the battery volts and alternator, all was good. Checked the engine temp and oil pressure and that was good. Also checked all fluid levels, oil, power steering, trim pump, gear oil, trim tab pump and all that is good. I do not know what else to look for. If anyone can point me in the right direction would be greatly appreciated. Thank You [/FONT] [h=1][/h]

 

[tpenfield]

You can do some Googling and find similar issues ranging from faulty sensors to corroded wiring on the temperature and oil pressure sensors and even the knock sensor. At this point, it would be good to have the ECM (MEFI-3) read for any codes, etc.

 

[Scott Danforth]

have you tested the water pressure sender? they are a known fail early alarm sensor

 

[BigDog98]

have you tested the water pressure sender? they are a known fail early alarm sensor

I believe that my engine does not have a water pressure sensor. It is a MEFI2 Configuration. Serial Number is 0l085399.
The only senders it has is Water Temperature, Coolant Temperature (which I replaced last year), Oil Sender PSI (for the analog gauge), Oil Sender Switch (for the alarm), Knock Sensor. Is it possible that my oil sender switch is causing the alarm to go off but the oil sender for the gauge is still showing good 40 psi oil pressure?

 

[BigDog98]

You can do some Googling and find similar issues ranging from faulty sensors to corroded wiring on the temperature and oil pressure sensors and even the knock sensor. At this point, it would be good to have the ECM (MEFI-3) read for any codes, etc.

I believe that my engine is a MEFI2 style serial number is 0l085399... And i did consider scanning the engine but a merc dealer said that it does not store codes and he would be only able to scan it 2 months from now with his time .

 

[RichRab]

My guess is it was a pressure sensor on the power steering cooler.

 

[BigDog98]

My guess is it was a pressure sensor on the power steering cooler.

The issue actually went away for a good part of the summer and just came back recently. Still have no figured out what the alarm is coming from

 

[QBhoy]

IAC or SW pressure sensor likely culprit.

 

[scoflaw]

try pulling the wire off your oil pressure sensor. Get it read, it stores codes.

 

[BigDog98]

So I think I narrowed it down to what is causing the alarm. On further research I narrowed it down to the Knock Sensors. I plugged in a scanner tool / a homemade voltmeter code reader and got code 44 which is knock no detected. I however replaced both knock sensors in April and I know for sure the actual knock sensors are good. I did however find a cut / a few broken copper strands in the wire that goes to the port sensor. I pulled the plug from the ECM to locate to which pins those wires were going to and did a continuity test and was able to find both wires for both knock sensors in the ECM plug. I believe that even tho that one wire is intact enough to make continuity it still is damaged to show non proper knock reading to the ECM by my understanding that the wires draw voltage from the knock senors to the ECM and the damage in that wire is causing the code 44 to come up. I have ordered two new wires and connectors for the knock sensors and will replace and see if it resolves the issue. I believe that code 44 would also cause my loss in performance due to it retarding the timing when knock is not detected. Will update soon.