4.3l Mercruiser cold starting problems (HELP)

Rhinodecals · May 21, 2012

I have seen a number of posts on this problem and thought I would post anyway. I just did a Carb Kit rebuild today it will start up the run for 10 to 15 sec. then die. I am new to the boat world worked on a lot of car engines in my passed. It has been an long time scents I did a rebuild and not sure if I got choke arm in the correct positions. When the boat is in the not running the butterfly level should be in the close positions on the carb is that correct. I got it running this afternoon and came back about 4 hours later and it started doing the same thing again. gave up because it got dark and I was about to hit my head on something!

achris · May 21, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Welcome to iBoats....

Can I ask you to read this -> http://forums.iboats.com/showthread.php?t=220416 and get back to us with the required information....

The very least we need is...

1. Engine year.. (the 4.3 litre engine's been used by Merc since 1985, so there are about 20 variations)
2. Heat riser choke or electric?
3. Weber, Rochester or Mercarb carburetor?
4. 2 barrel or 4?
5. Electric fuel pump or mechanical?

Chris.......

Rhinodecals · May 22, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

1. Engine year 1998
2.electric choke
3. Mercarb carburetor
4. 2 barrel
5. Electric fuel pump

Don S · May 22, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Sounds like a faulty oil pressure switch or wiring to the sender that controls the fuel pump. The oil press switch provides power to the fuel pump so it doesn't run when the engine is not running.
This wiring diagram should help.

Rhinodecals · May 22, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Ok how do I test the oil pressure switch? Also I unplugs the fuel pump and pumped the bowl dry on the carb then turned the key on to see if the pump pumped gas back into the bowl. And there was gas back in there.
Could it be a bad plugs? it try's to start then dies took the throttle cable off the carb and tried to manual get it started but it would not stay running.

Rhinodecals · May 22, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Engine Serial Number 0L039643 If that helps any

Don S · May 22, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Pressurize the switch and check for continuity between the two terminals.

Typically, if you have power to the terminal with the purple wire on it, and the other terminal is clean and tight, and it won't stay running you just replace the switch.

Rhinodecals · May 23, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

looking at getting a new presuure switch today just in case. What would I look at next if that does not fix the problem?
Spark plugs? Coil? fuel pump leak on the inside?

Rhinodecals · May 23, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Ok update on my problem. I cleaned the gas out bowl on the carb. Found the purple wire and checked voltage I had 12VDC at the switch. Checked the other side of the switch and no voltage. Took both wires off and put a jumper on and turned the key on the pump did not turn on and no gas in the carb. Could it be a bad pump or diaphragm on the fuel pump?

Don S · May 23, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

I would check the pump by running it straight from a battery. If it doesn't work then, it's bad.
If it does, then you have wiring problems. Could be a bad ground, or a bad wire splice.

Rhinodecals · May 24, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

ok let me start again.
did a carb kit.
Boat will turn over and run for about 10 sec. then die
Things i have checked.
Elect. fuel Pump is worked jumped out to battery and is pumping gas
pumped all gas out of bowl.
pulled wire off pressure switch and jumped out
Turned engine over and checked bowl on carb full of gas.
pumped out all gas out of bowl.
hooked pressure switch back up
turned engine over. checked bowl on carb has gas in it.
what am i doing wrong

Don S · May 24, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

pulled wire off pressure switch and jumped out

If you hook all the wires from the oil pressure switch together, does the fuel pump keep running with the key in the run position? Or does it stop. (No need to run engine)

If it does keep running, then start the engine (on muffs of course) and see if the engine stays running along with the pump.

Rhinodecals · May 24, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

i think it stops. when I had the jumper wires on the wire got really hot

Come to think I did not hear the pump run like it did when I had it hooked up to the battery

Don S · May 24, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Make yourself a jumper wire for the oil pressure switch wires, and put a 15 Amp fuse in it and run the pump and see if the fuse pops.
I'm thinking the pump is bad, but not sure why the 15A fuse to the ignition switch at the helm didn't blow.

Rhinodecals · May 24, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

would i still be getting gas in the bowl of the carb if the pump is bad?
Is it not pumping enough gas to the carb?
But will try that tomorrow when I get home from work to dark out there now.
thanks
The other thing I remember also is when I had the fuel pump hooked up to the battery it was making spinning noise. I never did hear that same noise when I has the wires from the pressure switch jumped out. I had the supply line that goes to the carb disconnected and it was pumping gas out. I did not do this when I jumped around the switch

Rhinodecals · May 28, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Ok jumped the pressure switch with a fuse link and a 15 amp fuse. Engine started right up and ran like a champ. Put the wires back on the pressure switch and the engine would not start. Bad pressure switch?

achris · May 28, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Rhinodecals said:
Ok jumped the pressure switch with a fuse link and a 15 amp fuse. Engine started right up and ran like a champ. Put the wires back on the pressure switch and the engine would not start. Bad pressure switch?

Certainly sounds like it...

Don S · May 28, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Replace the pressure switch, why it doesn't blow the fuse I don't know, but it seems to be killing the ignition too. The fact that it won't even start when you hook up the pressure switch is the problem. There should be enough fuel in the carb to run it for 15 to 20 seconds without the pump running.

Rhinodecals · May 28, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

It run for about 15 sec. But when I had the fuse link it ran great

Don S · May 28, 2012

Re: 4.3l Mercruiser cold starting problems (HELP)

Ok then, a new switch and you are good to go.

4.3l Mercruiser cold starting problems (HELP)

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