Volvo Penta 7.4 gsi going into SLOW down mode. Please help!

[pnaauto]

Hello there. Recently purchased Carlson csx23 with 7.4l gsi vp engine and dpx duoprop drive. boat has 340hrs. Seems like boat goes into Slow down mode when cruizing on the lake.I am an auto mechanic so have knowlege how stuff works. So far i figured out that in order for the ecu to go into slow down mode there have to be 2 sensors out of spec (low oil press or high temperature). So i noticed that everytime i am cruizing and boat cuts off the throttle my temp gauage jumps to 250deg. then when i take gas lever down engine rpm goes down below 1200rpm the temp gauage goes back to 110deg. and boat has power back on, sometimes this happens one a day sometimes every 30seconds. Boat is for sure not overheating. It would look like there is wiring issue between temp sensor and ecu. I checked all wiring, even tried to wigggle wires around while having my dvom hooked up to see if there is broken wire somewhere inside, all wires look good. Next i replaced temp sensor with autozone sensor that fits 7.4 gm motor(sensors looked exactly the same) but no luck i think that it even got worse? bad sensor out of the box? or the issue is getting bigger, last night we were on the lake and it was the worse ever she was going into slow down mode everytime i wanted to go above 2500rmp. What do you guys think? Should i start looking for a new ecu or try to get another sensor from VP.? Also how can i read codes from it? Any feedback welcome. Thanks!

 

[Tail_Gunner]

The good new's its a very simple system there is a model number on the ecu housing post it a i will post the manual's

Here's a link as to how mefi works..1..2..3..4 the operation's are essentially the same foundation

http://www.pleasurecraft.com/manuals/L510004.pdf

http://www.offshoreonly.com/forums/...e-marine-efi-code-tool-less-than-$1-00-a.html

 

[DCinVA]

My 7.4 GSI has 2 temp sensors. One is for the temp gauge and is a single wire, the other is for the ECU and is a 2 wire sensor. The ECU temp sensor can be removed and tested by checking resistance across the terminals at different temperatures. Start by putting the sensor in ice water and gradually warm up the water and compare to the spec in the manual. I also have 2 oil pressure sensors. Again one for the gauge, the other for the ECU. The ECU oil pressure sensor is a a binary switch (on / off). If grounded you have no pressure, if the circuit is open, there is pressure. You can disconnect the wire to the ECU oil pressure switch to by pass that circuit.

I would start diagnosis by disconnecting the ECU oil pressure switch to eliminate that circuit the system.
Then, there is a procedure in the manual for testing the ECU temp circuit. I believe the ECU sends 5 volts to the sensor, and the other wire should provide a good ground. Check the manual to be sure. I am not sure I understand the relationship with your limp mode problem and your temp gauge pegging at 250 degrees. That might indicate an issue with a bad ground somewhere.

Good luck

 

[pnaauto]

Ok so i understand that there are two sensors for each oil and temp.But question is why temp sensor jumps all the way to 250deg when boat goes into that slow down mode?? Wouldn't that kinda show us that the issue is with temp circuit?? Or you still thinkn that oil press might be the issue?? Also can you send me pics of sensors. I know where temp sensor is for ecu but not sure of other sensors. I did find the oil press for ecu and tested the wire it looks good. Also DCinVA do you have volvo penta or merc?? And what kind of temp do you normally have when cruizing on the lake??