4.3LX Gen+ Cold Start problem

[canyonken]

1996 Searay 175XL with the Mercruiser 4.3LX Gen+ Serial OF803642 with 2 barrel carb. I am pretty sure it has Thunderbolt IV ignition. All plugs look great. The engine will start right up on first try in the morning. Engine dies after 5 to 8 seconds of fast idle. Engine will not start after this no matter how you try throttle position or pump throttle. Engine will start and backfire, etc. using starting fluid. After 5 trys of starting fluid the engine will finally start and idle like a champ. No more problems all day after that. Once engine is warm you can start and stop engine all day long. The engine runs great, idles great. It just won't start cold without playing the starter fluid game. What could cause this?
Thanks,
Ken

 

[Uraijit]

Re: 4.3LX Gen+ Cold Start problem

Is your choke working properly?

 

[canyonken]

Re: 4.3LX Gen+ Cold Start problem

I have an electric choke. Is the choke only a factor during cold starts or is it used during warm starts as well?

 

[Don S]

Re: 4.3LX Gen+ Cold Start problem

You aren't just trying to start it in neutral like you would an EFI car are you?
Carbs and chokes take some operators help to start and run.

 

[Maclin]

Re: 4.3LX Gen+ Cold Start problem

But CanyonKen, is it (the choke) working properly?

• When the engine is cold is the choke plate closed?
• Does it pull open slightly when the engine starts and then open very slowly over the course of 3 minutes or so?

On automotive based I/O engines the term "electric choke" refers to the method used to heat the choke coil and pull the choke open. It does not refer to how the choke is activated or "turned on".

 

[Maclin]

Re: 4.3LX Gen+ Cold Start problem

And to Don S's point, before starting the cold engine you should move the throttle lever forward all the way a couple of times to prime the intake with fuel then move it back to just above idle to start it.

 

[Uraijit]

Re: 4.3LX Gen+ Cold Start problem

I have an electric choke. Is the choke only a factor during cold starts or is it used during warm starts as well?

The question remains, is the choke WORKING? Yes the choke will be closed to richen the mixture during cold starts. It will be open once the engine is warm. Warm starts are less finicky anyway, but the choke plates should be closed at startup, and open when warm. Sounds to me like they're staying at least partially open, all the time.

Check to see if it's working or not.

 

[canyonken]

Re: 4.3LX Gen+ Cold Start problem

Update.
I will have to watch carefully the next time I cold start it to observe the choke plate movements.
Today the boat has been sitting for two days. I pumped the throttle three times and fired it up. It starts perfectly and runs great for 5 seconds. The engine dies fast with no sputtering. THIS TIME I pumped the throttle between 20 and 30 times until I could smell gas with my nose right up at the carb. (flame arrestor off). I tried starting a second time and it fired right up and ran with no issues at all. I did not use starting fluid. It appears to me that the gas in the fuel line is draining back into the tank over night. Is this possible? Did my pumping it 25 times re-prime the fuel line and eliminate the earlier problem ???

I took off the aluminum 90 degree fitting at the top of the gas tank where the fuel line connects. It seem clogged or worn out. I will replace this fiting tomorrow or the next day. Let you know what happens.
thanks so far
Ken

 

[Maclin]

Re: 4.3LX Gen+ Cold Start problem

When it dies just crank it with no throttle pumping for 5-10 seconds and stop, then pump the throttle a couple of times then crank again. Repeat the 5-10 second crank cycle with a short 10-15 second wait in between. I bet by the third cycle it will stay running.

 

[tcarden]

Re: 4.3LX Gen+ Cold Start problem

I had same problem with my 1997 4.3. FUel pump was the culprit. I read posts for days to troubleshoot and bit the bullet on a new pump. Expensive but completely solved problem. Fires right up and runs and cranks all day.

Good luck on it.

 

[canyonken]

Re: 4.3LX Gen+ Cold Start problem

Would the engine run at all if the electric fuel pump was broken ?
The boat runs perfectly all day long once you get through the cold start.

 

[tcarden]

Re: 4.3LX Gen+ Cold Start problem

I wondered the same thing but it cured my problem which was exactley like yours. It will get progressively worse. Ran fine throughout the day and cranked with just a turn of the key when warm. I suspect that the fuel pump was leaking down and that when I went to start it cold it would either flood right away with what was in the carb. (accelerator pump seemed to be working fine) or there just wasn't enough pressure. I really don't know. However, I've had it out twice since and each time the cold start was completely different and the warm starts were the same. Go figure.

 

[Maclin]

Re: 4.3LX Gen+ Cold Start problem

If you suspect the fuel pump then test it, you can search thru the threads to find a trouble shooting guide, also fuel pump test gauge and rigging.

Basically it is a vacuum test, where you plumb in a vacuum gauge between the tank and the filter to see how good the fuel pump sucks there.

To answer your question "Would the engine run at all if the electric fuel pump was broken" my answer is "Only if the fuel tank is about 4 feet above the boat" for full gravity feed effect. Even then the fuel pump may block it enough to starve the carb out. Ok, better anwser is "No."

If it is just the first start after a day or longer layup then it sounds like the carb is draining and a new fuel pump will not help as the problem is in the carb. If there is a high enough fuel level in the carb bowl it will start and probably stay running. If there is only fuel in the accelerator pump circuit then it will start only because you pumped the throttle and then die out until there is fuel in the bowl.

Proceed as you wish, but I highly recommend that you test the fuel pump before you decide to replace it.

 

[canyonken]

Re: 4.3LX Gen+ Cold Start problem

New electric fuel pump, a carb rebuild and the timing reset, new plugs, cap, rotor and plug wires. Verified there where no vacuum leaks - engine runs awesome now, starts easily all the time.