Mercruiser 350 won't start - low voltage error

[Graemep]

Hi all, thanks for reading!

I have a SeaRay Sundancer 275 with a Mercruiser 350 in it. It's been unused for the last 6 months.

Came to try it last week - the engine cranked but the belt didn't turn. Turned out to be due to a siezed alternator.

We freed the alternator (by turning with a spanner).

The engine then started, wee let it run for a good while and could see the voltage increasing. The alternator didn't heat up so all seemed well.

Next day it wouldn't start at all. There was a error shown against the battery - "Voltage is low - sensor power supply voltage is low 13.9V"

We figured it may be the battery so put in a new one - no difference. We did get it to start at one point - it ran for a minute then dies.

I've now had a computer put on it & it gives the error "5 VDC PWR LO"

The error comes up even when just turning the key so I can't image it's the alternator?

Can anyone give me an idea where to look? My mechanic is a bit stumped too.

 

[alldodge]

Howdy

Turned out to be due to a siezed alternator.

We freed the alternator (by turning with a spanner).

Finding a seized ALT and your not going to replace it, or have it rebuilt, things that make me go Hummmm

Now your getting "5 VDC PWR LO"

The 5V comes from the ECM which gets its power from the battery and ALT. Once the flag (5 VDC LO) has been set it won't go away just by turning the key ON.

If you start the motor, what reading are you getting from the ALT?
Also what is your engine serial number?

 

[Graemep]

Hi, thanks

The mechanic said the alternator was OK but yes I will get a new one, they don't have stock. I was concerned that the problem was something else.

When we had the motor running last week we were getting 14.5V from the ALT. Since then we haven't managed to start it to check the voltage.

The mechanic did a MEDScheck whih showed the 5V fault - it also said that the fault is cleared every time with the ignition. I it's the alternator I can't understand why it would be there without the engine running. If it's not cleared by the ignition, how is it cleared?

Engine serial no is 1A080456

Thanks

 

[alldodge]

Thanks for the serial number, it tells me you have the 555 ECM.
Agree, if you find out where your loosing 12V the 5V LO will clear and allow the motor to start. The 5V LO will not allow the motor to start. Start with checking the battery cable connections on both ends, make sure they are clean and tight.

Next take a voltmeter and check for 12V on both sides of the 50 AMP breaker. Then check pin D on the DLC connector which is a 4 pin connector where the scan tool was attached, pin A is ground. Check for 12V on the output post of the alternator (orange wire). Check fuses up by the ECM.

 

[Bt Doctur]

low voltage comes from dirty connections no matter what the alt puts out.you pulling over 200 amps with the starter and that is a load,add a corroded connection and nothing will work

 

[Graemep]

Thanks for the serial number, it tells me you have the 555 ECM.
Agree, if you find out where your loosing 12V the 5V LO will clear and allow the motor to start. The 5V LO will not allow the motor to start. Start with checking the battery cable connections on both ends, make sure they are clean and tight.

Next take a voltmeter and check for 12V on both sides of the 50 AMP breaker. Then check pin D on the DLC connector which is a 4 pin connector where the scan tool was attached, pin A is ground. Check for 12V on the output post of the alternator (orange wire). Check fuses up by the ECM.

Well unfortunately all that seemed ok. All I noticed was the voltage was slightly lower (12.4 instead of 12.7 elsewhere) on the D connector.
The smartcraft guage says "BATT OK" when switched on then cycles through & changes to "!" then I get System fault - "STBD SYSTEM FAULT 133"

 

[bman440440]

code 133
POWER 1 VOLTS (5VDC) LOW ALL ENGINE SENSORS (+5V) POWER
SUPPLY LOW
Check for:
1. Excessive Current Draw on the +5V DC Circuit
2. Circuit or Sensor Shorted to Ground

 

[alldodge]

All your sensors use 5V, start pulling them one at a time to see if it can be found. Don't start the motor, just try to find out when it goes away. Suggest start with water pressure which is on the cooler behind the motor. MAP. TPS, IAC ect. Hope its not the ECM.

 

[Graemep]

All your sensors use 5V, start pulling them one at a time to see if it can be found. Don't start the motor, just try to find out when it goes away. Suggest start with water pressure which is on the cooler behind the motor. MAP. TPS, IAC ect. Hope its not the ECM.

Hello sorry missed your post. My problem is that I'm from the UK but the boat is in Spain so I am floundering to get help here particularly when I haven't bothered to learn the lingo! ;-) Time moves very slowly here....

I had been trying as you suggest - although I don't know what's a sensor but I'm not too daft so if it has 2 wires and goes into a casing I'm guessing it's a sensor!

I disconnected all the alternator leads & that made no difference.
The "sensors" I disconnected were - fuel filter, one on the starboard exhaust near the throttle cable.
A single wire on the water manifold at the top (starboard) . There's also a 2 wire one on the port of the water, when I disconnected that I got a temperature warning.
Other than that no difference.

Where are the other ones?

I take it the ECM would require a new mortgage???

Everything looks pretty clean to be honest - except for the "Mercathode" unit - as that's in amongst water pipes I haven't fiddled with it.

The mechanic is supposed to be coming on monday to move wires around!

Appreciate all the help by the way - I may be asking one of you to come to Spain soon ;-)

 

[alldodge]

The 555 ECM cost around $1600 in the US, overseas even more.
Your motor has several sensors and each one run off of 5V. The throttle body has 2 (TPS and IAC), manifold has the MAP and coolant temp, next to the harmonic balancer is the CPS. There are several and if you have digital shift and not mechanical, there is more. All power is connected at splice 101

On the back of the motor and on top the bell housing there is a tube. The tube is the power steering cooler, and on the cooler there is the sea water pressure sensor. All the Gray wires supply 5V to all senders. Remove the connector a put a volt meter on the Gray wire and with key on see if you have 5V. If its low, then something is pulling it down. If it is 5V there is a good chance the ECM is the issue

 

[Graemep]

No Title

Hi

Making progress I hope - I found the sensor at the back of the engine. Disconnected it and there is 5V on the grey wire. I also got a "Water pressure sensor not working properly error".

So then I measured a different wire (There's a Paddle/Fuel connector that just has one connection). Again I got 5V.
I plugged back the sensor wire - the sensor alarm went away & the low voltage alarm came back. The voltage went down to below 3V.

Does this indicate the sensor is faulty? It's the one in this pic

 

[alldodge]

If you remove a wire and the low V goes away, you see 5V and when its plugged back in low V comes back and you see 3V, my thought is you found the sensor.

And the one in the pic appears to be on the power steering cooler and would be the water pressure sensor. The one which caused the 3V was the Paddel/Fuel

 

[Graemep]

Great (it was when I unplug the water pressure sensor that the 5V comes back). Now the challenge is to find a new one in Spain! (Completely impossible at the weekend) so we'll see if I can find one tomorrow!

 

[alldodge]

If you can find it, the part number is 8M6000623

 

[Graemep]

Thank you so much. Found the part - 170 Euros, engine started first time!

 

[alldodge]

Way cool. sounds great and thanks for letting us know. :thumb: happy boating

 

[SİMİRNAMARİN]

Verado 350 hp x2 engine available. It gives the fault in the picture and passes. When it gives the fault, the trim indicator and the engines do not match.