5.0 EFI Bogging/Stalling at Idle

[Flynny]

I'm looking into purchasing a 2001 Sea Ray 240 Sundancer with a Mercruiser 5.0 EFI. The boat itself is in great shape and I'm ready to pull the trigger, but there's something going on with the engine. The owner blew the head gasket in the original engine last season, so he put in a new longblock, new oil pan, transferred over the 2-year old risers and manifolds, and transferred the original intake. He put about 30 hours on it after this rebuild.

The engine starts up and idles fine. It picks up great and returns to idle perfectly, as long as you don't pick it up past about 3000RPM. If you bring it up to 2700-3000RPM, let it run there for a minute, and then bring it back to idle, it drops well below normal idle speed, almost stalls, picks itself back up to 1500ish, nearly stalls again, jumps back up, and then stalls. I can prevent this by manually giving it more throttle, but it's really not an issue I want to deal with on the water. When it gets near stalling, you can hear an air "whoosing" sound, like a valve opens trying to pull in extra air.

So far I've confirmed it's not a fuel issue by replacing the water separator and running off an external tank. The fuel looked good, but I wanted to rule it out as an issue anyway.

I've read many posts about bad Idle Air Controllers (IACs), but I'm not sure if that's the issue here, because it will idle just fine if you slowly bring the throttle back, or don't rev it as high. Then again, it is original, maybe it's sticky?

The current owner has other interested buyers, so he's not interested in trying to fix it himself. I'm just wondering if this sounds like a simple issue, or if there could be something seriously wrong with the rebuild. The owner said this never happened on the water last season.

 

[1fastjetboat]

IAC most possible cause. But could be something else if you buy boat it will not hurt to replace in that year boat they run about $90.00 last time I did one. Remember that boat is 15 years old. If you feel comfortable with price than bring it home. Don't be to trusting in what people tail you when they are trying to sale you something. Make sure he has supporting documents for engine replacement.

 

[alldodge]

Things that make me go hummmm
Engine blew a head gasket and he replaced with new long block.
Reving to 3K rpm causes the engine to hunt for idle

There is more to the story and you haven't taken it for a ride yet. First no ride, no buy. Don't see someone replacing the motor for a head gasket. My thought is there may still be a head gasket or other issue.

He has other buys (so he says) let one of them buy it.

 

[1fastjetboat]

Remember there will always be more boats for sale. Try not to buy someone else's headache . Like alldodge said with boats you really need to drive them. I know it can be a pain sometimes if water is not close by but you can have a boat that runs perfect on muffs and will not perform on water. I'm a mechanic and do all my own work so it's not to bad for me if price is good but if you have to pay a shop you really need to be careful in what you buy. Money talks, if the other buyers wanted to buy the boat it would be gone. Good Luck

 

[Calae 2000]

Hmm interesting subject. I just bought a 94 Thompson 20 ft open bow with a 5.0 Mercrusier. I started it for the first time yesterday since purchasing it back in Jan. Started it on muffs. It fired up and was running fine on fast idle. After the temp came up near 150 degree it started running rough at slow idle and finally stalled out. I took out the little inline carb housing fuel filter and was pretty dirty. Looked like fine sand in it. Its one of those little cleanable type filters. Oh and its a 4 barrel Quadrajet. So I am gonna replace the fuel separator filter to and hope that takes care of it. Who knows it may need a carb rebuild kit to? But I like to always start with the simpliest and cheapest fixes first. Any thoughts on the subject are appreciated, thanks....

 

[Flynny]

Hmm interesting subject. I just bought a 94 Thompson 20 ft open bow with a 5.0 Mercrusier. I started it for the first time yesterday since purchasing it back in Jan. Started it on muffs. It fired up and was running fine on fast idle. After the temp came up near 150 degree it started running rough at slow idle and finally stalled out. I took out the little inline carb housing fuel filter and was pretty dirty. Looked like fine sand in it. Its one of those little cleanable type filters. Oh and its a 4 barrel Quadrajet. So I am gonna replace the fuel separator filter to and hope that takes care of it. Who knows it may need a carb rebuild kit to? But I like to always start with the simpliest and cheapest fixes first. Any thoughts on the subject are appreciated, thanks....

I seem to recall reading about a lot of different people having this exact same problem when I was researching this issue. You should google this problem, there are a lot of forum posts out there about it. The difference is that yours is a carbureted engine, while this one was EFI fuel injected. Two different animals.

By the way, final update on this, took all of your advice and passed on this boat. The owner just was not working with us on this engine issue. Onto the next one!