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Engine stops running, but starts

GlastronGary

GlastronGary

Member
2000 Mercruiser 4.3 with Thunderbolt V ignition.
Was out cruising down the river last night did a 20 mile run to a restaurant on the river. Everything was running great,when we started back home the engine just died after about 10 minutes. It will start but only runs for about 20-30 seconds than dies again. I can pump the throttle and it starts just just fine but dies like it runs out of fuel. Just wondering where I should start looking first, fuel pump, fuel filter or maybe the distributor. Any help is always appreciated.
 
First check the fuel filter/water separator for water ( dump contents into a wide mouth jar and wait 20 mins)
T'bolt disti caps/rotors good for 2 seasons at best.
 
Ok that’s my next step, jumped out the fuel pump directly to battery and it pumped fine into a container (disconnected fuel line from carb) fuel looks good.
 
Did some more checks, fuel filter seems ok and distributor seems ok. Ran the motor on the driveway on muffs, noticed that my voltage gauge was bouncing, put a multimeter on the batttery and noticed it was at about 15 volts, when I increased RPM’s to about 1300 the voltage was about 16 volts and the motor stalled. Could a bad alternator with high voltage output cause a stalling issue.
 
Never mind about the voltage issue, found a disconnected wire at the alternator. Fixed the wire and test ran the motor, voltage readings are back to normal range but engine still dies after about 30-45 seconds of running. Oil pressure is good, engine temperature is good, voltage is good, starts fine and sounds good. Just can’t figure out why it stops running.
 
1st find out if its fuel or spark..very easy..take off air filter and when the engine starts dying spray carb cleaner or use propane from torch(not lit) if it stays running longer you have a fuel problem.
 
oil pressure switch controlling the fuel pump???

hook up a test light to the +12VDC side of the fuel pump....
 
Thanks for the info, will try the 12v light tomorrow. I’m assuming if the oil pressure switch is faulty it will cause the fuel pump to shut off.
 
FOR TESTING ONLY,
Remove wires from oil pressure sensor and jump together.
This will allow fuel pump to run with out sensor.
(ONLY A TEMPERARY TROUBLESHOOTING TEST)

If engine continues to run the sensor is bad.
If engine still stalls and your sure there is adequate fuel to carb,
Check gas tank vent and anti syphon fitting
 
Found the problem, it was a faulty oil pressure switch. Connected a 12v light to the pressure switch circuit and started motor, light was initially on after about 30 seconds the light started to flicker and then finally went off, then the engine shut off a few seconds later. Then I jumped out the pressure switch and started the engine again, it ran without issue for a few minutes until I turned it off, tested again and it ran without any problems.
Thanks for everyone’s input.
 
Merc Cruiser 1997 V6 New Safety Switch, new oil sending unit new oil and filter, new coil, spark plugs and wires and new fuel pump, new starter ( I messed up the old one) new safety witch, carb has been rebuilt, fuel pump was tested outside, new anti siphoned valve, new 55 gallon tank, new fuel lines. All that being said. Engine starts runs abut 30 seconds then it shuts down from lack of fuel. When it starts runs smooth until it stops.


Read all response on this, stll haven't solve my problem.
 
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New Safety Switch- What safety switch are you speaking to? Neutral safety switch? Other?


New oil sending unit- What sending unit are you speaking to? Pressure sender or Pressure switch?



This topic you jumped into the root cause was the Oil Pressure Switch which has two connections ( original/older style )
It is an On/Off switch based on oil pressure.

Low to no pressure switch is open. (no voltage to pump)

Pressure threshold reached pressure switch is closed (voltage to pump)

Oil pressure sender typically has One wire connection (variable resistor to gauge)
 
The oil pressure switch with a gauge on single connection. The safety switch that works with oil pressure which sends the current to the electcric pump when it closes
 
All other stuff replace because it was old. Took gas filter out and electric pump, filter is new and the pump is new and ran fine outside. No sediment in fuel filter. Engine stop running because the old tank rusted out and the sediment clogged up the carburetor. I rebuilt carb float adjustment by the manual 14.3 level, 28 mm drop but for some reason appears needle with spring gets stuck, or at least thats what I see, fuel bowl empties am waiting for A SPRING KIT for the spring that goes under the t in the venturi squirts fine but I think is the wrong spring and my wife just gave me the package with the new spring kit. Guess Saturday carb comes apart again. All check balls in place one under the plunger and the other under the T check ball, spring then the t then the venturies.
 
Angel Rondon said:
All other stuff replace because it was old. Took gas filter out and electric pump, filter is new and the pump is new and ran fine outside. No sediment in fuel filter. Engine stop running because the old tank rusted out and the sediment clogged up the carburetor. I rebuilt carb float adjustment by the manual 14.3 level, 28 mm drop but for some reason appears needle with spring gets stuck, or at least thats what I see, fuel bowl empties am waiting for A SPRING KIT for the spring that goes under the t in the venturi squirts fine but I think is the wrong spring and my wife just gave me the package with the new spring kit. Guess Saturday carb comes apart again. All check balls in place one under the plunger and the other under the T check ball, spring then the t then the venturies.
Click to expand...


and i assume you replaced the rusty fuel tank?
 
chs said:
and i assume you replaced the rusty fuel tank?
Click to expand...
The tank is brand new and all its hardware is brand new, it was custom made by a professional tank manufacturer. Am starting to think I need a new carb. The starter which i just purchased a few weeks ago, the by pass circuit stop working so the pump doesn't send fuel when starting. I don't get 12 volts when cranking to start the pump. I by pass the solenoid and jumped the pump from the slave relay (yellow /red) engine fired up, but only runs for about 4 to 5 minutes then dies. I think the tank sediment mess up the carb. Gonna rebuild it again one more time, if it doesn't work, I ll buy a new one. Engine runs very nice when running considering is 97 Merc Cruiser with a 2 bbl carter. But its having fuel issues with the float. When properly set no fuel comes into the bowl.:mad:
 
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