2006 Chaparral 190SSi Mercruiser 5.0 has perplexing alarm/power loss

[crepko]

I bought a 2006 Chaparral 190SSi w/5.0 Mercruiser carbureted last fall. It had a blown head gasket and cracked port side head. I replaced the bad head and head gaskets and put it all back together, changed the oil 5 times to get out all the water etc. We have had it out on the lake 3 times this year and we are getting occasional alarms that we have traced down to the water temp alarm sender on the right side of the thermostat housing. The strange thing is the gauges always show normal water temp of 170 degrees, oil pressure is also good, gear lube level is topped off. If I unplug the right water temp sender the alarm never goes off. The gauges use the water temp sensor on the left side. So why would one measure too hot and the other measure normal 170 degrees?

Also this is the first boat I have owned. I am very familiar with car engines as I have rebuild many of them, but boats, this is the first. Another issue that perplexes me is that sometimes it seems hard to get this boat on plane. I can hold the throttle full for longer than a minute, rpm will stop at 3000 and it still will not be on plane. Other times it quickly gets on plane. The engine always sounds good, no pinging, or bad noises whatsoever. It kind of acts like and engine that is not advancing its timing enough. I did bump up the initial timing from ten to 14 degrees but the problem persists. Also the service manual mentions that if there is any kind of audible alarm some of the ignition advance functions will be disabled, maybe this is what this issue is? Also I changed the prop from a 3 blade with 21 pitch to a 4 blade with 19 pitch which seemed to help a bit.

Any help is appreciated.

Chris

 

[JASinIL2006]

Weird... you should be around 4400-4800 RPM WOT. Does it ever get above 3000 RPM?

 

[crepko]

Weird... you should be around 4400-4800 RPM WOT. Does it ever get above 3000 RPM?

Yes, once it is on plane the rpms go up. Not sure if it gets all the way up to 4800 though. It definitely wont get past 3000 until its on plane. Is that not normal?

 

[Bondo]

The gauges use the water temp sensor on the left side. So why would one measure too hot and the other measure normal 170 degrees?

Ayuh,..... One is a sensor, the other is a switch,....
Change the switch,.....

Another issue that perplexes me is that sometimes it seems hard to get this boat on plane.

Sounds like a fuel delivery issue,.....
Check the contents of the fuel filter in a clear vessel for anything but clean fresh gasoline,....

 

[crepko]

Ayuh,..... One is a sensor, the other is a switch,....
Change the switch,.....

Sounds like a fuel delivery issue,.....
Check the contents of the fuel filter in a clear vessel for anything but clean fresh gasoline,....

Thanks Bondo for your input. I did change the water separator filter when we replaced the heads, as well as the cap, rotor, wires, plugs, oil pressure switch and gear lube switch and reservoir. I set initial timing to 14 degrees trying to get more power, which is a bit more than the service manual recommends which is 10 degrees. If the power problem were fuel related would you expect more of a stumble or bog (like a carburated car?). This is not what we are observing, its more like there isn't enough power to come on plain, kind of like a car would exhibit with its timing advance too low. Also how much rpm is typical of a Mercruiser 5.0 when its not yet on plain? I cant seem to break 3000 rpm until I am on plain, and sometimes I can't get on plain, other times it seems easy. Thanks for any help!

 

[crepko]

Update on the alarm situation. It is definitely the sensor on the right side of the thermostat housing (the two wire sensor). This sensor controls the audible alarm. The sensor on the left side is a one wire sensor and controls the gauge. When I disconnect the left side one wire sensor the gauge reading goes to 0. The gauge seems to work well and you can see the engine come up to temperature normally and see when the thermostat opens at 170 degrees. The two wire sensor on the right is triggering the alarm as verified by disconnecting it and no more alarms. The alarms seem to happen only after we have been out on the boat for awhile. Typically we will go out and run the boat around for 60 minutes or so, maybe pull a tube or skier, then we will anchor for an hour or two, and then on the way back to the boat ramp the alarm will be going off quite a bit, if not constantly. It doesn't seem to matter if the boat is on plane or not, it also doesn't seem to matter what the trim position is. Also the gauge reads a normal 170 degrees the whole time the alarm is going off. In a desperate effort to solve this issue I have replaced both temp sensors and the thermostat, yet the problem still persists? Any ideas? Is it possible one sensor is really reading hot on the other side of the thermostat housing (I mean its all connected right). Also I have used an IR thermal scanner to check the engine and both risers seem normal as well as the thermostat housing.

 

[nola mike]

You verified the 170' at the sensor and the switch? What temp stat did you install? What ignition system do you have? I can't find a wiring diagram for a TB-V with knock sensor, but the normal TB-IV/V doesn't tie into the alarm at all. If a TB-V or other, the ignition needs to be put into base timing mode to set the timing. I'm also not certain at what temp the switch trips at, didn't see it in the manual...

 

[crepko]

You verified the 170' at the sensor and the switch? What temp stat did you install? What ignition system do you have? I can't find a wiring diagram for a TB-V with knock sensor, but the normal TB-IV/V doesn't tie into the alarm at all. If a TB-V or other, the ignition needs to be put into base timing mode to set the timing. I'm also not certain at what temp the switch trips at, didn't see it in the manual...

Hi Mike,
The gauge reads 170 once the thermostat opens. I replaced the gauge sensor with a new one just to be sure and it reads the same. I have a 160 degree thermostat which I also replaced during troubleshooting. I also replaced the springs and check balls in the thermostat housing as well as the sensor (switch) that controls the alarm. I basically replaced everything but the thermostat housing itself. I used an IR sensor on the thermostat housing while running and it it read 120 degrees or so. Risers are reading about 160 max.

 

[nola mike]

Hi Mike,
The gauge reads 170 once the thermostat opens. I replaced the gauge sensor with a new one just to be sure and it reads the same. I have a 160 degree thermostat which I also replaced during troubleshooting. I also replaced the springs and check balls in the thermostat housing as well as the sensor (switch) that controls the alarm. I basically replaced everything but the thermostat housing itself. I used an IR sensor on the thermostat housing while running and it it read 120 degrees or so. Risers are reading about 160 max.

Didn't answer the other questions about setting timing and what ignition you have...
But did you check temps at both the switch and the sensor with the IR thermo?
Only thoughts I have about the temp might be to test what temp the switch closes in some hot water (again, I don't know what temp it's supposed to close at, anyone have those numbers?). If the closing temp isn't near where you're actually running, the only thing left is that you have a short to ground somewhere between the switch and where it joins the other sensor wiring.

 

[crepko]

Didn't answer the other questions about setting timing and what ignition you have...
But did you check temps at both the switch and the sensor with the IR thermo?
Only thoughts I have about the temp might be to test what temp the switch closes in some hot water (again, I don't know what temp it's supposed to close at, anyone have those numbers?). If the closing temp isn't near where you're actually running, the only thing left is that you have a short to ground somewhere between the switch and where it joins the other sensor wiring.

Not sure if it is a TB-V. Can you tell from the attached picture? I have the timing set at 12 degrees advance using the procedure in the service manual where you ground the purple and white wire to engine ground. I set to ten originally but it seems to run better at 12.

 

[crepko]

Not sure if it is a TB-V. Can you tell from the attached picture? I have the timing set at 12 degrees advance using the procedure in the service manual where you ground the purple and white wire to engine ground. I set to ten originally but it seems to run better at 12.

Also Mike,

Do you know where the Alarm circuitry is located? Is it under the driverside dash area? -BR Chris

 

[nola mike]

Not sure if it is a TB-V. Can you tell from the attached picture? I have the timing set at 12 degrees advance using the procedure in the service manual where you ground the purple and white wire to engine ground. I set to ten originally but it seems to run better at 12.

Can't tell, but if you have base timing it's a TB-V. Question is if you have a knock sensor or not, and I'm not sure if knock sensor ties into the alarm at all--I don't have a wiring diagram (@alldodge ?).

Also Mike,

Do you know where the Alarm circuitry is located? Is it under the driverside dash area? -BR Chris

I mean, there isn't any real alarm circuitry. The buzzer has 12v to it (IDK where, follow the buzzing...), and the switches ground to complete the circuit.

 

[alldodge]

Verified it is TBV (Part number on port side elbow) but do not see knock sensor mounted. Don't think the motor has one installed

The boat gauge is off because IR measuring 120* on thermostat housing and gauge shows 170*. Measure temp at the temp sender and not on top of the housing

Not good seeing 160* on elbows, they should be cooler.

The alarm is under the helm and has 12V full time applied to one side when key is ON. Alarm sounds when the Tan/Blue wire is grounded

Motor low on power, suggest compression test and what do the plugs look like?