Troubles with mercruiser 5.0 and alpha one

[skennelly]

Good Morning,

I'm new to the board and a new boat owner. I purchased a used 1993 Crownline 18.2 foot with a Mercruiser 5.0 V8 and Alpha One drive. I've taken it out 4 times so far and it was very smooth and no problems at all.

This past weekend I was out and I had some problems that I would like to see if anyone has input on.

1. When cruising below 3000 rpm things seemed to be sluggish the speedometer was not working. When I throttled up to just above 3000 rpm there is a very brief hesitation like the motor is going to die and then the power comes back and the boat begins to plane out and everything is fine also the speedometer begins working again. Once this happens I can lower the throttle to under 3000 rpm and cruise like normal.

2. The only variable I can think of that is different than my previous outings is that when I first got the boat I filled up with 87 octane gas. I had to fill up before going out this past weekend and I accidentily put 89 octane gas in the boat. I don't think that should be too much of a problem though???? Perhaps I'm wrong on that.

I was going to plan on doing a tune up. New plugs, wires, check outdrive oil levels ect....

Any ideas would be appreciated.

Thanks

 

[QC]

Re: Troubles with mercruiser 5.0 and alpha one

Well I don't see how the speedometer would be related unless there is some crap hanging on your drive. If you have what most Merc powered boats have, it is actually a simple pressure gauge. The water going into a little hole in the front of the drive "squeezes" air in a tube that runs all the way to your gauge. The faster you go the pressure rises and indicates speed. Generally not very accurate or reliable as a little POS in that tube basically stops all action. If that hesitation happens before it jumps on plane (as you described) then the speedo is just not very interested in low speeds (they're all that way).

You should look into all of your tune-up stuff that you describe. The 89 octane had nothing to do with it unless it was simply bad fuel anyway. You can run 93 with no issues all day long, or 87 as long as it doesn't knock . . .

 

[John_S]

Re: Troubles with mercruiser 5.0 and alpha one

I am assuming carbed, but which one? 2 barrel or 4? And I think you are close enough for transition years of Q-jet to Weber, so we need to know which. or take the flame arrestor off, and snap us a nice picture.

Also, please confirm the slugishness is felt in the boat, or just a speedo anomaly.

 

[skennelly]

Re: Troubles with mercruiser 5.0 and alpha one

I'll have to investigate what type of carb I have and I'll post a pic if I need to.

To me the sluggishness is felt in the boat and overall performance wise. The speedo problem just happened to occur at the same time so I thought it would be good to mention. I know the speedo is not big deal and not very accurate anyways

It just seemed funny that after the boat hesitates and then finally gets on plane the speedo starts to work again and if I drop the boat back down to a slower cruising speed the speedo continues to work.

The hesitation only occurs when I am powering up say from coming out of a no wake zone or dead stop.

The other thing to mention is that the lake had more sea weed in it than normal so perhaps that has something to do with everything, although I don't see any visible sea weed caught anywhere.

Otherwise the boat idles and starts perfectly.

Thanks.

 

[Bondo]

Re: Troubles with mercruiser 5.0 and alpha one

When cruising below 3000 rpm things seemed to be sluggish.To me the sluggishness is felt in the boat and overall performance wise.

Probably because it's trying to Climb a Mountain, just before it breaks over onto Plane.........
Once On Plane,.....

Once this happens I can lower the throttle to under 3000 rpm and cruise like normal.

Sounds like a Normal Planing Hull to Me........

 

[Frederick R. Dent III]

Re: Troubles with mercruiser 5.0 and alpha one

I have a Mercruiser 5.0 L alpha one I/O V-8. SN OF280196.
The engine starts fine. After about 40 minutes of cruising at 1000-1200 rpm, the engine momentarily runs rough and then stops. Repeated cranking of the starter on both batteries has no effect. The engine does not even try to start. DEAD!. When I wait several hours and the engine cools down, the engine starts on the first crank and runs great. The next time out, the scene repeats itself. Engine failure occurs after 40 min of low rpm. getting tired of being towed to shore.
Within the past year, have changed out plugs, rotor, and cap. (Not the coil).
Four weeks ago, replaced the shift cable. Is there any connection there?
Is heat somehow causing a short in the coil?

Frederick R. Dent III

 

[John_S]

Re: Troubles with mercruiser 5.0 and alpha one

Fredrick,

Welcome to iBoats. You should start a seperate thread on your issue, which sounds very different from this thread. It sounds like you are chasing electrical. Did you varify there was no spark? or that the carb still had gas? ie you pushed the throttle a couple of times and got good streams from the accel pump nozzles?

 

[CharlieB]

Re: Troubles with mercruiser 5.0 and alpha one

skennelly

With the engine OFF, remove the spark arrester from the carb, disconnect the throttle linkage, if the choke plate is closed, hold it open, rotate the throttle arm on the carb to WOT while observing the accelerator pump shot. Is it working? A good strong psst or a wimpy dribble?

The age of the boat and symptoms are similar to a failing accelerator pump. A lack of fuel during throttle opening. Alcohol in our fuels shorten the life of the accel pump, it may be time to go thru your carb.

 

[Bondo]

Re: Troubles with mercruiser 5.0 and alpha one

September 10th, 2007, 04:05 PM

Ayuh,.....

I kinda think ole skennelly didn't bother coming back,+ probably ain't goin' too.....

He's posted twice, a Year ago,......

Great post though Charlie,....

 

[Frederick R. Dent III]

Re: Troubles with mercruiser 5.0 and alpha one

Thanks to all. The opinion is a carb versus an electrical problem. Will take a shot at your ideas.

 

[alex3012red]

Re: Troubles with mercruiser 5.0 and alpha one

have same engine had same problem it was time to rebuilt carb, now it's running great.

 

[Don S]

Re: Troubles with mercruiser 5.0 and alpha one

OLD Thread