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496 mercruiser will not start

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Old 07-14-2008, 03:08 PM
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Default 496 mercruiser will not start

Hi guys, great forum!

I have a problem with my mercruiser 496 w/ blower. This season I have had som problems getting it started. It turns around but there is no spark. If I try a couple of days later it suddenly works.

Last weekend it stoppet for me while running at cruising speed, and it didn't start after that. Had to leave at my summerhouse.

I am going there in a couple of days to drive it back, but I want to find out what the problem is and fix it.

I have read the if one of the 5v sensors get a short to ground, the engine won't start and it will stop if it is running. I think this might be the problem. Where do I find all the "5v" sensors on this engine, so i can start troubleshooting?

I have a Rinda tech. Diacom software tool that I can hook up to the engine, if this will help me.

All help is appreciated!
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Old 07-15-2008, 11:43 AM
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Quote:
Originally Posted by Roger Eriksen View Post
I have read the if one of the 5v sensors get a short to ground, the engine won't start and it will stop if it is running. I think this might be the problem. Where do I find all the "5v" sensors on this engine, so i can start troubleshooting?
This is correct, if the sensor power circuit is shorted to ground, the engine will not run. However, you should get an alarm and Sensor Power Ckt Low fault if that were the case.

When it won't start, connect your Diacom software and check to see which codes are active. If you can't establish communications, then you don't have power to the ECM, and that could be caused by a bad lanyard switch, ignition switch, main power relay, ect.
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Old 07-15-2008, 12:21 PM
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thanks for the reply Dave!

I connected the Diacom to the engine today before I tried to start it, so it would show me the errors from last time it stopped. This is a part of the report. STEER, FUEL and PITOT errors are not included here, but was in the report as well.

The engine actually started after 3 attempts. I have recordings of this from the Diacom software too.

Could it be the "lake/sea temperature" that is causing the engine to stop and refuses to start?

3 TRIM CKT HI
--------------------------------------------------------------------
FF Baro Pressure 14,27 PSI
FF Battery Volts 11,95 VDC
FF Sea Pump Pressure 0,00 PSI
FF Boat Speed 0,00 #
FF Manifold Air Temp 57,20 F
FF Coolant Temp 55,40 F
FF Demand 0,00 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0,0 Counts
FF Frequency Count 45
FF Fuel Level 0,00 %
FF Gear Position Neutral
FF Lake Temp 429,80 F
FF Engine Load 0,00 %
FF Main Pwr Relay Requests 32772,0
FF Manifold Air Pressure 14,27 PSI
FF Oil Level 0,00 %
FF Port Tab Pos 0,00 %
FF Available Power 100 %
FF Run Time 160,37 hrs
FF Starboard Tab Pos 0,00 %
FF TPS Percent 0,00 %
FF Trim Position 0,00 %

4 HORN OUTPUT
--------------------------------------------------------------------
FF Baro Pressure 14,19 PSI
FF Battery Volts 12,25 VDC
FF Sea Pump Pressure 0,00 PSI
FF Boat Speed 0,00 #
FF Manifold Air Temp 75,20 F
FF Coolant Temp 64,40 F
FF Demand 0,12 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0,0 Counts
FF Frequency Count 0
FF Fuel Level 0,00 %
FF Gear Position Neutral
FF Lake Temp 429,80 F
FF Engine Load 0,00 %
FF Main Pwr Relay Requests 32768,0
FF Manifold Air Pressure 14,20 PSI
FF Oil Level 0,00 %
FF Port Tab Pos 0,00 %
FF Available Power 100 %
FF Run Time 153,15 hrs
FF Starboard Tab Pos 0,00 %
FF TPS Percent 0,12 %
FF Trim Position 0,00 %

Fault Log Data
Fault Descriptions Seconds

Battery Range High: 0
Battery Range Low: 0
Block Pressure is Low: 0
Compressor Temp Overheat: 0
ETC Motor Open: 0
ETC Motor Short: 0
Fuel Pressure Sensor Input High: 0
Fuel Pressure Sensor Input Low: 0
Guardian Strategy: 0
Knock Sensor 1: 0
Knock Sensor 2: 0
Low Oil Pressure Strategy: 0
Low Oil Remote Strategy: 0
Low Oil Reserve Strategy: 0
MAP Sensor 1 Input High: 0
MAP Sensor 1 Input Low: 0
MAP Sensor 1 Idle Rational: 0
Oil Pump Output: 0
Overspeed: 0
Port Clnt Overheat: 0
Starboard Clnt Overheat: 0
Warning Horn Output: 88
Water In Fuel: 0

Engine Run Time History:

Total engine run time: 160,37 Hours
0 - 749 RPM: 42,58 Hours
750 - 1499 RPM: 42,42 Hours
1500 - 2999 RPM: 39,98 Hours
3000 - 3499 RPM: 16,08 Hours
3500 - 3999 RPM: 14,68 Hours
4000 - 4499 RPM: 3,18 Hours
4500 - 4999 RPM: 1,25 Hours
5000 - 5499 RPM: 0,18 Hours
Over 5499 RPM: 0,00 Hours
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Old 07-15-2008, 12:25 PM
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This is a part of the report when engine is running normal at idle after a quick warm-up.

2. PERFORMANCE DATA

Parameter Description Value Unit

Engine Speed 523 RPM
Available Power 100 %
Coolant Temperature 118,40 F
Fuel Flow Rate 0,86 GPH
Port Exhst Cool Temp 32,00 F
Sea Pump Pressure 0,54 PSI
Starb Exhst Cool Temp 32,00 F
IAC Duty Cycle 99,98 %
Manifold Absolute Pressure 7,71 PSI
Trim Position 1023 #
Baro Pressure 14,27 PSI
Trim Volts 5,10 VDC
Manifold Air Temperature 80,60 F
Pitot ADC 0 #
Oil Pressure 22,11 PSI
Paddle Wheel 0 Hz
Throttle Position 0,00 %
Sensor Power 5,01 VDC
Throttle Sensor Voltage 0,59 VDC
Lake/Sea Temp 429,80 F
Spark Advance 14,00 DEG
Fuel Level 1023 #
Battery Voltage 13,43 VDC
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Old 07-15-2008, 12:37 PM
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The sea/lake temp is a default value and not an issue. The only thing I see is that your battery voltage is pretty low (11.95v) . If your battery is weak and the voltage is too low during cranking, the engine won't start. I would start with replacing the battery.
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Old 07-15-2008, 01:01 PM
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wow you're quick

So low battery voltage is the reason there is no spark? It does crank pretty good.

I don't see why the voltage is the reason why it suddenly stopped at cruising speed.

Can it be the wiring from the ignition key that is bad?
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Old 07-15-2008, 02:19 PM
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Quote:
Originally Posted by Roger Eriksen View Post
So low battery voltage is the reason there is no spark? It does crank pretty good.
I can't say for sure, it's just the only thing that was a little unusual in the data that you posted. A battery with one bad cell can still turn the engine over ok, but the voltage will be low and EFI engines don't like that. In addition to that, the symptoms are consistant with low voltage, with the exception of stalling at high speeds which usually isn't battery related.

Quote:
Originally Posted by Roger Eriksen View Post
I don't see why the voltage is the reason why it suddenly stopped at cruising speed. Can it be the wiring from the ignition key that is bad?
Yes, it could be the ignition switch, lanyard switch, 10 pin connector, ect.
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