Starts and Shuts Down when warmed Up

6

67vetteal

New Member
Aug 2, 2008
133
Long island
Boat Info
1997 250 Sundancer
Engines
454 Mercruiser
Driving me Nuts!! 97, 7.4, Throttle Body EFI. Starts up cold just fine and runs like a champ. Stop for lunch etc. and it starts and immediately dies. After multiple attempts it will start and run just fine!:smt021 I've changed out the Idle Air Control, Electronic Coolant Sensor and Fuel Filter. Anyone else have this season ruining type problem. (I've searched the archives to no avail). Thanks, Al W.:huh:
 
I'm troubleshooting a similar problem for a friend with 8.2's. They're fine with a cold start and run strong, but once warm, both engines are prone to stalling from what appears to be a normal idle.

A dock neighbor has suggested that the bowl in the electric fuel pump (square pump on top of engine, not the dreaded belt-driven mechanical pump) has vanished fuel in it.

I haven't opened it up to check that yet, but it doesn't appear to be a difficult job.

The 8.2's have fresh fuel and new filt/seps, but we haven't tried the Idle Air Control valve.
 
I had a 97 400 DA. When the ambiant temp was above 85 degrees one of the engines would vapor lock only after the conditions you described. Mercruiser knew the problem(insuffient fuel pressure,first year of production) and fixed it late in the model year run. Because I live in Ohio, It was not a major issue (not many days over 85). The solution was to run the blowers after shut down or to crack the engine hatch open. Sounds crazy but it worked. I guess the question would be if your situation is temperature related.
 
I agree it could be vapor lock. To prevent this, try letting the engine idle for several more minutes before shutting it down. On mine the engine temperature will drop about 5 degrees when I do this.
 
I had a 97 370DA with 7.4 Horizons. They were also prone to vapor lock on hot days. Never fixed the issue, just learned to live with it. As stated in prior posts, running blowers and colling down motors before shutting the off helped.
 
Great ressponse and Thanks! I've owned this boat for five years and never experienced this problem before. Fuel is last years and I store in an Aluminum Tank full over the winter. I'm starting to wonder if the "Ethanol" Demon is biting me? Ethanol is such a Scam! I'll be sticking to finding a solution and will continue to post my Saga. Thanks to all and any suggestions are welcome! Al W.
 
Friend of had a similiar problem ever since last season and finally figured it out. His would run for 30-45minutes and then begin to, and eventually just die. Took awhile to restart.

His big clue came when in this condition where it was beginning to miss, he adjusted trim. The engine nearly died. Seems the trim motor was robbing the engine from generating a spark. So in the end, it was the electronic control module inside the distributor that needed replaced (after replacing battery cables, checking ground and a new coil). That sure was a tough one to figure out...
 
It is strange that after multiple attempts it will eventually start and run fine. Do you adjust the throttle at all while trying to start? Has the throttle position sensor been checked? You should have a specific ohm reading depending on how far the throttle plates are open. Not sure but this could be affected by heat but might be worth checking. I would check and clean all connectors near the throttle body - injectors, TPS, IAC - could be something simple like condensation or corrosion. It's also possible that you are encountering fuel issues - I would run the fuel down as low as possible before refueling again. With these new formulations the recommendation appears to be to only purchase what you can use in 2-3 months to avoid problems.
 
Here's an update. There are so many "possibles" to be considered and I'm not prone to "Paralysis by Analysis" that I'm taking an approach of conclusion by elimination. Sooo, Sat. AM, a buddy of mine who is a great boat mechanic will be putting his Laptop on my boat and we will Scan the Electronics system.
I'll deal with the results appropriately and continue on. I'll update my posts at that time for the Archives. All too often we don't get the answers only the questions! Al W.:thumbsup:
 
Last edited:
I would chase down the ignition system - Dist Cap, Rotor, Wires, and maybe plugs.
 
Hampton said:
I would chase down the ignition system - Dist Cap, Rotor, Wires, and maybe plugs.
Click to expand...

Last year I pulled the engine to install new Risers, Exhaust Manifolds and of course new Ignition service parts. I've only put 20 or so hours, (all good) on it since. This problem is always predictable and doesn't change. I'd consider your line of thought but she starts quickly and runs strong with no observable weakness. I'm really thinking Vapor Lock due to
poor fuel quality seeing as the Gas is last Septembers. We'll see! Al W.:huh::smt089:smt100:smt009:smt024
 
67vetteal said:
I'm really thinking Vapor Lock due to
poor fuel quality seeing as the Gas is last Septembers. We'll see! Al W.:huh::smt089:smt100:smt009:smt024
Click to expand...

Could be, but with fuel injection, vapor lock is a lot less common of a problem. Unless your fuel pressure is dropping too low? Maybe fuel pump? :huh:
 
67vetteal said:
Driving me Nuts!! 97, 7.4, Throttle Body EFI. Starts up cold just fine and runs like a champ. Stop for lunch etc. and it starts and immediately dies. After multiple attempts it will start and run just fine!:smt021 I've changed out the Idle Air Control, Electronic Coolant Sensor and Fuel Filter. Anyone else have this season ruining type problem. (I've searched the archives to no avail). Thanks, Al W.:huh:
Click to expand...

Al, If it is vapor lock and you are using Premium grade fuel you may find some relief in using 89 octane. The Premium has a lower boiling point which would increase the occurence of vapor lock. Mike
 
You can also insulate the fuel lines with some high temperature cloth tape. This may prevent vapor lock if you determine that is the cause.

Doug
 
Here's the latest! Took our boat to my favorite mechanic for a Code Scan and some professional advice. The Scan produced no codes. (Good news). Then we discussed the symptoms at length. He explained Fuel Thermal Layering to me. The Alcohol, (Ethanol), absorbs water over the storage period of the winter. Being Vented our systems are open to moisture and the Ethanol absorbs this moisture. Next, the Water settles out to the bottom of the Tank as the lowest level. Then the Ethanol/Alcohol become another layer above the first one. Finally, the remainder which is a poor grade of Gasoline floats above this all. He believes this is the Root of my problem.
Now the potential cure. I'll be adding Stabile for Ethanol
as per the directions. Also Marvel Mystery Oil, 1/2 Oz. per Gal..
And, Octane boost due to the degeneration of the Fuel during the 10 Months of storage. He informed me that among the many other problems Ethabol blend is producing, it also Etches Aluminum!!!:smt013 I'll then run all this Fuel out and put fresh Gas in the boat. At that point I'll know if this has cured my problems.
Early on in this Thread, Hampton suggested I service the normal Ignition items. Good advice as it turns out. The Distributor on my engine is a mess. I did not know that the Internals of my Distributor should be changed out periodically as a service PM. I'll be doing this work myself so it's not as if I was getting uneeded work done. When all is done I'll report some more if someone requests it. Al W.
 
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