99 MerCruiser 454 L29 in Carver 406 - Failed to stay running then OK

[kgarguilo]

All, I was out for the last few days on the water and while under anchor in a cove for a few hours in the HOT (over 90 degrees F) Georgia sun as we were getting ready to leave, my Starboard engine started, but would not stay running. Before I could put her in gear, she would stop. After I pushed forward with only the port engine for about a 1/4 mile, I tried it again and the starboard engine started and stayed running and we went onto the next destination - fireworks show. We docked for about 6 hours with the Kohler Gen running the entire time. When it was time to leave, same thing the starboard engine would not stay running. This time I tried diverting the Starbard engine from the aft tank to the Starboard tank and no change, so I changed the fuel back to the aft tank. After pushing off with one engine around hundreds of other boats inm the dark (yikes) we got past the no wake area (about 1/4 mile) and I pushed the port engine to 2600 rpm to limp back to our dock and then I tried starting the Starboard engine again and it started, I put it in gear and ran back to the dock under full power at 3600 RPM with both engines. This was about a 27ish minute run at 3600 rpms. I then docked in and out of gear no issues.

Info:

Mercruiser 7.4L MPI MIE V-8 gasoline naturally aspirated engine - 330hp SN- 0L303931 & 34
Velvet Drive Transmissions, Model 20-01-005 direct drive - 2.455:1 ratio

Other Info:

Both Engines were drawing from aft tank
Aft tank 7/8 full
Gen running on Port tank 3/4 full
Starboard tank not being used and is 1/2+ full
On 6/16 Took on 135 gallons of fuel between all three tanks

Aft 53 gallons of 145 gallons
Port 39 gallons of 99 gallons
Starboard 43 gallons of 99 gallons

Maintenance:

Fuel filters were changed about 20 hours ago (also did impellers/ Oil change / Fluids check)

I found one other thread in the forum, but it does not really apply to this issue which is why I started a new topic. Hope everyone had a great Independence Day weekend in America.

As always, thanks for any and all input.

[bud37]

Well written......This is one of those situations where it would be wise to have someone do a diagnostic scan to see what is up, codes in memory etc.. Trouble is all could be well then go bad after. Also this will depend on whether you want to throw parts at it in the hopes you hit home.....there are some obvious guesses...but.

In the meantime, check your battery voltages/connections , grounds and harness connectors......good luck.

[km1125]

Wonder if the "cool fuel" module wasn't doing its job keeping the fuel cool?? Does that engine have one of those modules?

[Viper]

Sounds like a typical Merc 7.4L MPI not wanting to stay running. How long after starting her are you putting it into gear? Check your throttle body and make sure everything is clean. Check to see if there is a small sponge filter in there on the side for the IAC passage. If there is, is it really dirty? Low battery voltage will also cause this symptom as will dirty or faulty injectors. There are a number of things that can contribute to this; anything from ignition to fuel related.

Do you have an emergency start switch at the helm? Does this happen regardless of what engine you try starting first?

I agree with checking for fault codes, it will also offer the opportunity to check other things like whether the IAC is working properly, and the data from other sensors that could be causing or contributing to the issue, etc. I believe yours is probably a MEFI 3 so there should be a fair bit of data to help diagnose the problem. Hopefully it's held a fault that will help steer you in the right direction.

km, pretty sure it should be a Cool Fuel II module for this vintage. That in of itself has components that can cause intermittent issues; fuel pump, regulator, regulator filter screen (very fine and tiny), vacuum hose, etc. AND of course it's a b$$ch to get at.

[kgarguilo]

Bud Thanks for the response.

Well written......This is one of those situations where it would be wise to have someone do a diagnostic scan to see what is up, codes in memory etc.. Trouble is all could be well then go bad after. Also this will depend on whether you want to throw parts at it in the hopes you hit home.....there are some obvious guesses...but.

In the meantime, check your battery voltages/connections , grounds and harness connectors......good luck.

Thank you for the kind words, My battery voltage was 12.4 I should have written that in my original submission. I looked at it as I thought of that first. I will see if I can get a person out to throw the computer on it. I see two other responses I will respond to next.

[kgarguilo]

km1125 thanks for the response

"Wonder if the "cool fuel" module wasn't doing its job keeping the fuel cool?? Does that engine have one of those modules?"

While it does have a fuel cooler module, it relies on water going through the engine from seawater which appears to do nothing until the engine is running, and has water passing through it, I think. btw the sea water strainers were cleaned less that 30 days ago and they were clean already. Thanks for helping.

[kgarguilo]

Viper thanks for the help

Sounds like a typical Merc 7.4L MPI not wanting to stay running. How long after starting her are you putting it into gear? Check your throttle body and make sure everything is clean.

I generally wait until I see movement on the temp gauge to put into gear. In this case it was still warm as we were only anchored in the cove a short time maybe 2 hours. The engine would die before I could shift into gear, so the gear was not at issue.

Check to see if there is a small sponge filter in there on the side for the IAC passage. If there is, is it really dirty?

I will look at this tomorrow afternoon, good idea.

Low battery voltage

12.4 Volts at starting

will also cause this symptom as will dirty or faulty injectors. There are a number of things that can contribute to this; anything from ignition to fuel related.

Guess this may be the next step with the computer.

Do you have an emergency start switch at the helm? Does this happen regardless of what engine you try starting first?

No Emergency start switch at helm only a key for each engine. Only happened on the starboard engine both times and I always start that engine first.

I agree with checking for fault codes, it will also offer the opportunity to check other things like whether the IAC is working properly, and the data from other sensors that could be causing or contributing to the issue, etc. I believe yours is probably a MEFI 3 so there should be a fair bit of data to help diagnose the problem. Hopefully it's held a fault that will help steer you in the right direction.

Yes this is a MEFI 3 and I am also looking at the Fox Marine MEFI 3 NMEA 2000 interface for both engines already. I will likely see if a local tech can throw a computer on it and see the data, thanks.

Wow great help and ideas, thanks so much to all.

[Viper]

Try starting the port engine first then the starboard engine. The thought is that if it's a voltage issue, the port engine can bring the voltage up before you start the starboard engine if the boat is wired the usual way. Have you ever had this issue before, and has the port engine ever acted this way?

How and where did you get the 12.4 volts from? When I refer to low voltage, I'm talking about key areas on the engine, not what your gauge at the helm is saying, can't go by that. I want to know what the computer is getting while she's cranking over and trying to stay running for example, voltage at the fuel pump, etc.

There are a number of things to check in both electrical and fuel delivery but let's see what the computer data reveals and go from there. It could be that the engine is fine and the problem lies outside the engine like a temperamental anti-siphon valve.

Do you still have the black plastic cover over the fuel filter/water separator? I doubt this is the issue here but most people aren't aware of its importance.

Last time ignition tune up done?

BTW, your original post is the way to pose an enquiry. Providing as much data as possible up front really helps narrow things down.

[kgarguilo]

Viper » July 6th, 2023, 6:33 am

Try starting the port engine first then the starboard engine. The thought is that if it's a voltage issue, the port engine can bring the voltage up before you start the starboard engine if the boat is wired the usual way. Have you ever had this issue before, and has the port engine ever acted this way?

Only had the boat for 8 months now and she has always started quickly and stayed running.
Also, as per the Carver manual I alternate the p[rimary battery on each outing by using the battery selector switch once the day is done and I get ready for my next day trip out, I change the battery to "1 or 2" Not ALL

How and where did you get the 12.4 volts from?

From the Garmin 8612 that obtains its power from the battery bank distribution panel under the salon stairs

There are a number of things to check in both electrical and fuel delivery but let's see what the computer data reveals and go from there. It could be that the engine is fine and the problem lies outside the engine like a temperamental anti-siphon valve.

Understood and the anti siphon is interesting thought as it sounded like she was starving for gas as she went down to 0 rpm.

Do you still have the black plastic cover over the fuel filter/water separator?

Actually the covers were not on the boat when I bought her.

Last time ignition tune up done?

Once of those boats that had owner after owner that kept no detailed records of any type of work.

Also, Thank you for the kind words on my post, I do try to be detailed and not waste people's valuable time.

[Viper]

So if there are no maintenance records from the previous owner, then you must perform the regular maint stuff so you have a benchmarked time for when they were last done; all fluids, tune-ups, filters, impellers, etc.

Voltages need to be taken at the engine, not at helm accessories or gauges.

The fuel filter cover assembly on your engines is designed to help reduce the amount of radiant heat directly on the filter in hopes of minimizing vapour lock. Again, I don't think this is the issue here but worth noting for others with the same system for future reference.