strange stalling issue (Mercruiser mechanics are stumped)

I have a 2003 Mercruiser 4.3 L with a 2bbl Carb. It has a strange stalling issue which happens randomly at idle, partial or full throttle. When it is running, it runs great. When is stalls, it will stall a few times in a row and then run great for a few minutes up to 40 minutes of idle. I have run it at full throttle for 5 minutes or more.

I have replaced the distributor sensor, cap, rotor and plugs. It has a new water separating fuel filter and fresh oil change. I have poured the gas out of the fuel filter and there is no water in the gas. I by passed the oil sensor and it still stalls, I unplugged the shift sensor (did not shift it) and it stalled at idle.

It is currently in the Mercury boat shop and they are stumped. They have a fuel pressure gauge on it and it stays steady on my tank and the shop tank. They said when they have it hooked up to a shop tank and when it starts to stall they can save it by pumping a primer bulb. So they are thinking it is a fuel delivery problem and want to tear apart the carb, but I don't think that makes much sense, since when it is running it runs great. Can a carb have an intermittent stalling problem? I have never heard of such a thing.

I still think it is an electrical issue. Bad coil (not likely), bad ignition module (maybe, approx. $500.00). They don't have any spares to try. I am hoping they will test with new ones so I don't have to buy them it they are not the issue.

I need help before they charge me a fortune in labor trying to figure this out. This is the second time in the shop. They said it was the distributor sensor the first go around, but that was not it. Please help!!!

Re: strange stalling issue (Mercruiser mechanics are stumped)

tezaks said:

...................... when it starts to stall they can save it by pumping a primer bulb. So they are thinking it is a fuel delivery problem ...............................

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Rebuilding the carb won't make any improvement.

Most likely there is an air leak allowing air to suck into the fuel system, the fuel pump is pumping more air than fuel and the carb runs dry.

I'd like to see where and how they attached the aux tank as the air leak must be within the original hoses remaining before the fuel pump.

Re: strange stalling issue (Mercruiser mechanics are stumped)

Great idea! Makes a lot of sense. I left a message with the boat shop. They are closed so I will have to wait until tomorrow.

Re: strange stalling issue (Mercruiser mechanics are stumped)

tezaks said:

They have a fuel pressure gauge on it and it stays steady on my tank and the shop tank. They said when they have it hooked up to a shop tank and when it starts to stall they can save it by pumping a primer bulb.

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With a carb I don't see an air leak causing an issue at idle, I could see it at higher rpm. Opinion (everyone has one) it's an electrical issue and something is breaking connection.

Re: strange stalling issue (Mercruiser mechanics are stumped)

Dirt in the carb float bowl would do that, it gets sucked into jet and blocks it, when motor stalls it floats free again. Pumping primer when it happens may cause it to wash free temporarily and produce same result.

Re: strange stalling issue (Mercruiser mechanics are stumped)

tezaks said:

... They said when they have it hooked up to a shop tank and when it starts to stall they can save it by pumping a primer bulb. ...

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There's the answer right there. If it was electrical, that wouldn't fix it. If it was a clogged jet, that wouldn't fix it also (if the fuel bowl is full then priming the bulb wouldn't push any fuel into the carb as the needle would already be closed).

Tell them to put a section of clear line in the fuel line immediately before the carb. If they see air (and I'm betting they will), go find where it's leaking in... If they don't see any air, suspect the fuel pump, and check it has voltage still present when it starts to stall.

I seem to remember a service bulletin about the electrical connectors on those pumps... Check up on that too...

Chris......

Re: strange stalling issue (Mercruiser mechanics are stumped)

They now are thinking a fuel pump issue. They think their fuel pressure gauge which is glycerin filled is too slow to show the drop in pressure. They have to order one to do a swap test.

Re: strange stalling issue (Mercruiser mechanics are stumped)

tezaks said:

They now are thinking a fuel pump issue. They think their fuel pressure gauge which is glycerin filled is too slow to show the drop in pressure. They have to order one to do a swap test.

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Was this issue ever resolved? If so, please share the fix. Thanks.

Re: strange stalling issue (Mercruiser mechanics are stumped)

woodyw said:

Was this issue ever resolved? If so, please share the fix. Thanks.

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If you have a similar problem, please start your own thread. The red banner at the bottom of the screen while you were posting that also said the same thing....

Re: strange stalling issue (Mercruiser mechanics are stumped)

achris said:

If you have a similar problem, please start your own thread. The red banner at the bottom of the screen while you were posting that also said the same thing....

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Chris, what is the problem with this guy asking if the problem was resolved? And no, I don't have a like problem, but some people like to hear as Paul Harvey would say " The Rest of the Story"

Re: strange stalling issue (Mercruiser mechanics are stumped)

ouachitaman said:

Chris, what is the problem with this guy asking if the problem was resolved? And no, I don't have a like problem, but some people like to hear as Paul Harvey would say " The Rest of the Story"

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Ayuh,.... Because, like many posters, the OP has never been back,....