Help engine died after short WOT run

[rpuchowicz]

Went for a shakedown test and everything went smooth until running it at WOT for less than 1 min. It seemed to run fine at WOT but when I throttled downed it stalled and would not start. After 30 min cool-down it started fine. We did not run it any more because I noticed that the temps were a high after the WOT run ? 170-180.

The engine is a 1987 mercruiser 305 with an alpha 1 outdrive. The fuel pump is new and so is the TB4 cap, rotor, and ignition sensor. Plug wires all look good to. Plugs are also new. The carb was also recently rebuilt. Compression is good.

I don?t think that it is a vapor lock problem as the accelerator pump was still squirting fuel after the engine died. Nor was there a choke malfunction. By the time I got around to checking for spark the engine was up and running again.

Because the engine seemed to running a bit hot I tore into the impeller when we got back from the launch. Although the impeller looked well-worn it had not fallen apart.

[URL=http://img183.imageshack.us/my.php?image=impellerxm8.jpg] [/URL][URL=http://img183.imageshack.us/my.php?image=impellerhousingsg6.jpg] [/URL]

My first question is whether a worn-out but still intact impeller could cause overheating?

My second question is whether on overheating engine will suddenly cut out? Is there any overheating protection built into the ignition system that would cause and engine shutdown?

As I inspected the lower unit further I noticed something unusual blocking the exhaust passage.



Some rodent built a nest down there out of what seems to be sofa cushion material.
Would this cause an engine to overheat? Would it cause the engine to shut down at high RPM?

Any help would be greatly appreciated? Thanks.

 

[ne7800]

Re: Help engine died after short WOT run

if it was me i would be looking at the coil it could has overheated

 

[Bondo]

Re: Help engine died after short WOT run

Ayuh,.... Welcome Aboard,....

Clicking on your pictures for a closer look,.... Sucks.....
Talk about Bull$h!te pop-ups,..??..?? Danm near locked up my 'puter before I got it Closed....

My first question is whether a worn-out but still intact impeller could cause overheating?

Combined with the major exhaust restriction,... I'm sure they are contributing factors...

My second question is whether on overheating engine will suddenly cut out? Is there any overheating protection built into the ignition system that would cause and engine shutdown?

Nope,.... It's not designed that way,....
But,...
You might have part of it heatsoaking,+ killing the motor....

Don has a diagnostic tree around here somewhere for finding the faults in the T-Bolt IV systems,....
Somebody might have it linked for you....

And,....
Find another server to host your pictures,.... That 1 really Sucks.....

 

[FreeBeeTony]

Re: Help engine died after short WOT run

how did that stuff get in the exhaust passage?

 

[drrm123]

Re: Help engine died after short WOT run

image came up ok for me, if that's nest was in the exhaust system it would cause a restriction and cause engine to run hotter and possibly cut off, what you never put a potato in someones exhaust pipe before?

 

[rpuchowicz]

Re: Help engine died after short WOT run

how did that stuff get in the exhaust passage?

The outdrive was sitting outside under a tarp for most of the summer. I can only guess that a chipmunk or a mouse decided to make a home in there. I?m pretty surprised that it did not blow out at WOT.

From what I can gather it looks like the overheating problem and the engine dieing problem are probably unrelated. I think that the stalling problem is caused by a bad coil. Since everything checks out on the Thunderbolt 4 troubleshooting chart, my guess is that when the coil heats up under sustained high RPM's it fails and when it cools down it begins to work. I hope I am right because I have not been able to cause it to fail while running on the trailer. I guess I will just stay close to the launch next time out.

 

[Bondo]

Re: Help engine died after short WOT run

my guess is that when the coil heats up under sustained high RPM's it fails and when it cools down it begins to work.

Ayuh,... I can see a Cause,+ Effect an Overheat might have going on Your theory,.....
A weak Coil bolted to an overheating motor will get Hotter, Faster....

Originally Posted by FreeBeeTony
how did that stuff get in the exhaust passage?

I can only guess that a mouse decided to make a home in there.

'ell,.... I bet that alone is worth 20hp right there.... Loss of course...

That boat's gonna Fly when you get her patched up..........

 

[180shabah]

Re: Help engine died after short WOT run

I guess I will just stay close to the launch next time out.

I wish more people thought like this...Any new piece of equipment is unreliable until you are SURE otherwise.


Most of the time you hear....we had a problem so we replaced some stuff, filled the tank with premium and added liquid fire 4000 Octane Booster. The we took it for a ride and 20 miles down river it just died again. Just like last time......

You are playing it right staying close to home until you get all the bugs worked out. If it does quit again, you need to do some testing immediately. Check for fuel(which you said was present last time, so probably good) and spark. Have your specs with you(in your head or on paper) and test the coil with a meter.