2004 4.3L Merc Alpha Starts But Stalls Out

[dkamm]

I have a 2004 Caravell 187 Bowrider with a 4.3L two barrel carb. Thunderbolt ignition.

The current issue is that when it starts, if I do not put it into neutral and give it thottle, the engine chokes out as if it is being starved of fuel.

Background:
Over the weekend took the boat out. It started and idled just fine. Made my way out of the marina through the channel and no wake at about 5 mph. Did not notice any engine or throttle issues. Once out of the channel, probably about 10 minutes at the slow speed, throttled up to get on plane. Just as I was getting on plane the boat load power. I gave it more throttle, but the engine wanted to die. I backed it off to neutral, where the engine ran, but was running rough. Tac was jumping, but all other guages reading normal (temp, oil pressure, battery). If I tried to put it into gear, it wanted to die. I eventually turned the engine off to check the engine, but could not get it started again and had to get towed in.

It is in the boat slip now. I thought it was the distributor cap as I had a similar issue a few years back with the contacts getting corroded. I replaced that. I got the engine started, but now it will not run in neutral at idle. It was summarized at the marina and has been running well the past few month. I had put a fresh half tank of gas in it before going out when it had problems and the gas was treated.

I am convinced it is a fuel system issue. From reading some other threads, I am a little confused as to where to first attack. I don't think it is the gas itself as it runs fine when I accelerate in neutral. This boat has a fuel filter/water seperator, but I am not certain when it was replaced last....but again the engine runs if I give it throttle in neutral. Could this be a symptom of a fuel pump issue? Or are there any electronics that I should test?

Any thoughts / advice?

 

[Scott06]

I have a 2004 Caravell 187 Bowrider with a 4.3L two barrel carb. Thunderbolt ignition.

The current issue is that when it starts, if I do not put it into neutral and give it thottle, the engine chokes out as if it is being starved of fuel.

Background:
Over the weekend took the boat out. It started and idled just fine. Made my way out of the marina through the channel and no wake at about 5 mph. Did not notice any engine or throttle issues. Once out of the channel, probably about 10 minutes at the slow speed, throttled up to get on plane. Just as I was getting on plane the boat load power. I gave it more throttle, but the engine wanted to die. I backed it off to neutral, where the engine ran, but was running rough. Tac was jumping, but all other guages reading normal (temp, oil pressure, battery). If I tried to put it into gear, it wanted to die. I eventually turned the engine off to check the engine, but could not get it started again and had to get towed in.

It is in the boat slip now. I thought it was the distributor cap as I had a similar issue a few years back with the contacts getting corroded. I replaced that. I got the engine started, but now it will not run in neutral at idle. It was summarized at the marina and has been running well the past few month. I had put a fresh half tank of gas in it before going out when it had problems and the gas was treated.

I am convinced it is a fuel system issue. From reading some other threads, I am a little confused as to where to first attack. I don't think it is the gas itself as it runs fine when I accelerate in neutral. This boat has a fuel filter/water seperator, but I am not certain when it was replaced last....but again the engine runs if I give it throttle in neutral. Could this be a symptom of a fuel pump issue? Or are there any electronics that I should test?

Any thoughts / advice?

Start with emptying the fuel filter look at contents for anything but fresh clean gas.

take off the flam arrestor pump the throttle and see if two good strong streams of gas shoot out of accelerator pump nozzles.

tach jumping could be a failed tach that is shorting the ignitron system would dissconnect at negative side of coil

do you have good strong spark check with spark gap tester. What do spark plugs look like

 

[dkamm]

Start with emptying the fuel filter look at contents for anything but fresh clean gas.

take off the flam arrestor pump the throttle and see if two good strong streams of gas shoot out of accelerator pump nozzles.

tach jumping could be a failed tach that is shorting the ignitron system would dissconnect at negative side of coil

do you have good strong spark check with spark gap tester. What do spark plugs look like

Thank you for the ideas. I did check the carbs when I pumped the throttle, that appears to be ok. I will have to report back on the fuel filter and spark plugs (will require me to take apart the rear bench seating) to access. Spark plugs are less than 2 months old, but have not tested the spark at the plugs themselves.

 

[dubs283]

I am convinced it is a fuel system issue. From reading some other threads, I am a little confused as to where to first attack. I don't think it is the gas itself as it runs fine when I accelerate in neutral. This boat has a fuel filter/water seperator, but I am not certain when it was replaced last....but again the engine runs if I give it throttle in neutral. Could this be a symptom of a fuel pump issue? Or are there any electronics that I should test?

If it's fuel related you should first inspect/replace the fuel filter(s). Then a fuel pump pressure and vacuum test is in order along with a carburetor operation inspection/verification.

As stated the tachometer issue can be very much related to an ignition system issue. Disconnecting the tach lead at the coil is one test, however there are multiple parts to the ignition system. Based on your descriptions I am inclined to think your issue is ignition related, not fuel. There is a comprehensive guide to the thunderbolt ignition system located in the stickies, top of forum page

 

[Scott06]

all good suggestions. One other note for the OP- you mention revving it up in neutral - this is a relatively meaningless test. It takes no power to rev up under zero load. Test on the water is the only true indication of health

You said you changed plugs is the firing order correct ? Look at the plugs either post pictures or look online at plug reading charts you can learn a lot about what' going on fuel air wise from looking at them.

 

[dkamm]

all good suggestions. One other note for the OP- you mention revving it up in neutral - this is a relatively meaningless test. It takes no power to rev up under zero load. Test on the water is the only true indication of health

You said you changed plugs is the firing order correct ? Look at the plugs either post pictures or look online at plug reading charts you can learn a lot about what' going on fuel air wise from looking at them.

Thank you. I am going to try and see if I can get to the fuel filter/spark plugs this weekend and I will report. My reasoning for giving it throttle in neutral was to see if I could keep the engine running. I realize there is no load on it, but it would start, run for a 10 to 20 seconds and stop. I figured, if I was able to give it throttle in neutral and keep it running, it must not be an electrical issue killing the engine (like a switch or sensor), but maybe a fuel issue? If it was electrical related, wouldn't it kill the engine regardless of having throttle or not? Engine performed smoothly when I gave it throttle...just when I put it back to idle it would die immediately. Regarding spark plug wires, when I changed out the distributor cap and rotor, I put the spark plug wires exactly back in the same position on the new cap as I took them off the old one...did them one by one to be sure I did not mess that up. However, I did not replace the sensor inside the distributor. Needless to say, I am going to try everyone's suggestions to rule things out.

 

[kylek92]

If it's fuel related you should first inspect/replace the fuel filter(s). Then a fuel pump pressure and vacuum test is in order along with a carburetor operation inspection/verification.

As stated the tachometer issue can be very much related to an ignition system issue. Disconnecting the tach lead at the coil is one test, however there are multiple parts to the ignition system. Based on your descriptions I am inclined to think your issue is ignition related, not fuel. There is a comprehensive guide to the thunderbolt ignition system located in the stickies, top of forum page

I'm having a similar problem with my 5.7 mercruiser. Do you have a guide or video on how to do a fuel pressure test?

 

[dkamm]

I have a update. Got to the fuel filter and it indeed was full of water. Now I had put on a new fuel filter when it went into winter storage last year, so this is a new event. Pumped out some gas to check the tank and just put it 16 oz water bottle...95% was water. Now will pump out the entire 30 gallon tank to see how much water is in there. I have kept the take mostly full when not in use, but such a large amount of water in my sample seems odd. Never have ever had this problem with this boat before...so maybe I got a tank of bad gas?

I also looked at the carberator. It does need to be cleaned, but I do not think this was my problem. The tank of water is the cause!

 

[Rick Stephens]

Leaky fill fitting, cracked vent hose, fuel sender not sealed, etc. No likely a large amount of water from a pump.

Carburetor needs kitting. Get an OEM Merc kit and tear it down.

 

[nola mike]

I have a update. Got to the fuel filter and it indeed was full of water. Now I had put on a new fuel filter when it went into winter storage last year, so this is a new event. Pumped out some gas to check the tank and just put it 16 oz water bottle...95% was water. Now will pump out the entire 30 gallon tank to see how much water is in there. I have kept the take mostly full when not in use, but such a large amount of water in my sample seems odd. Never have ever had this problem with this boat before...so maybe I got a tank of bad gas?

I also looked at the carberator. It does need to be cleaned, but I do not think this was my problem. The tank of water is the cause!

All the water will be at the bottom. Just keep taking samples from the bottom until you're only getting gas