Mercruiser 4.3LX 205hp, Misfires Under Load Won't Accelerate past 2200rpm

[TruDaddy]

So identified the temp sensors on the t stat housing. I removed the housing and the temp gauge read 145 still. That is not possible. Gauge or sensors?

 

[Bondo]

I already replaced the impeller. I remembered yesterday that I accidentally ran the motor with the hose off for at least 45 secs. There were barely any splines left on the impeller. I replaced everything I could with the rebuild kit and fired her up with water on. I noticed there were two decent streams of water coming out both sides of bell housing area but not the center of prop. Is this normal? I never had cause to look before.

Also, she started to overheat. Either the thermostat is shot now or there is an obstruction. Temp climbed to 155 and she did not back down. It is possible there is some shards of rubber in the system but were do I start to look? How do I back flush?

Ayuh,.... Ya gotta find All the missin' pieces,....
By back-flushin' from the t-stat housin, with the lower unit Off, that'll clear the line from the impeller, to the t-stat housin',....
If ya got P/Steerin', the in-line Cooler is a likely candidate for collectin' the bits of the old impeller,..
It's 'tween the impeller, 'n t-stat, under the motor,...

With the key "On", yer temp gauge should show the temp of the sender, 'n go to Full Hot, when ya ground out the sender wire,....

The fact that yer seein' exhausted water from the idle relief ports, insteada the prop, tells me yer shutters got burnt up, 'n fell down into the y-pipe too,....

 

[TruDaddy]

I am about to flush the system.

I have the t stat housing off right now. What is the best process for ground out test? A simple jumper wire on sender tip to engine block?

How/where do I check the shutters?

 

[TruDaddy]

Ayuh,.... Ya gotta find All the missin' pieces,....
By back-flushin' from the t-stat housin, with the lower unit Off, that'll clear the line from the impeller, to the t-stat housin',....
If ya got P/Steerin', the in-line Cooler is a likely candidate for collectin' the bits of the old impeller,..
It's 'tween the impeller, 'n t-stat, under the motor,...

With the key "On", yer temp gauge should show the temp of the sender, 'n go to Full Hot, when ya ground out the sender wire,....

The fact that yer seein' exhausted water from the idle relief ports, insteada the prop, tells me yer shutters got burnt up, 'n fell down into the y-pipe too,....

Flushed back from t stat inlet hose. The stream from the outdrive copper pipe matched the garden hose. So that is clear/clean.

I did turn key to on position and the gauge did reset. I will need to test that. Assuming the shutters are burnt and fell, would that clog create overheating do to hot water not escaping fast enough? Also, still need to understand where to find those shutters.

 

[alldodge]

Flushed back from t stat inlet hose. The stream from the outdrive copper pipe matched the garden hose. So that is clear/clean.

I did turn key to on position and the gauge did reset. I will need to test that. Assuming the shutters are burnt and fell, would that clog create overheating do to hot water not escaping fast enough? Also, still need to understand where to find those shutters.

If the shutters fell in to the exhaust pipe they will cause a restriction and will reduce the water going through the engine. The exhaust flappers are at the top of the pipe, and between the exhaust elbow and exhaust pipe. Remove the boot between the exhaust elbow (riser) and the exhaust pipe. Once the boot is removed you should see them at the top unless they broke off and fell down the pipe.

 

[TruDaddy]

Okay I found the location of the dual exhaust elbows. I used Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years! . Great resource. How do I get these bad boys off? They are free but so rigid I can slide them enough. Do I have to remove the elbow from the manifold first? If I do will I need a new gasket?

 

[alldodge]

Okay I found the location of the dual exhaust elbows. I used Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years! . Great resource. How do I get these bad boys off? They are free but so rigid I can slide them enough. Do I have to remove the elbow from the manifold first? If I do will I need a new gasket?

If there is not enough room to slide them off, then Yes remove the elbow, and Yes it would be recommended to replace with a new gasket

 

[TruDaddy]

Looks like this weekend is out of the question for boating fun. Joys of boat ownership.

 

[TruDaddy]

Update...Port side shutter is intact but starboard shutter is gone. How do I get that out of there? reach down? remove bell housing? what is the easiest way?

 

[alldodge]

Update...Port side shutter is intact but starboard shutter is gone. How do I get that out of there? reach down? remove bell housing? what is the easiest way?

Bummer, this in most cases is difficult. The flappers are non magnetic so the telescoping magnet is most cases is out. If you have a flexible grabber you might be able to get the pieces. The make them from 24 to 40 some inches. If you pull the drive you can maybe get some help but most pieces will come out through the top. Only other way is to pull the engine so the Y-pipe can be removed.

http://www.ebay.com/itm/like/130795637228?lpid=82

 

[NHGuy]

Well, it's still worth the effort to try to fish out the old bits. Get creative, maybe shove a vacuum hose down there. Or take the exhaust boot off the transom (not off the bell housing) and try to get smaller bits that way. Engine removal takes a lot to justify.

 

[TruDaddy]

Well I fished around vacuumed around and did the best possible. I even put a hose down the exhaust tube and let it go full blast. Water simply poured out of the transom holes. I also replaced the thermostat. I locked everything up nice and tight to torque specs. I refilled the fluids and put the muffs back on. She fired up and let her idle to temp. It took a couple of minutes then I decided to bring her up to 2000 rpms. The temp started to rise beyond 145 up to 160 and looked like it was climbing. I backed her off and the temp went down.

Here is my question. Before I figured out there were crossed wires I adjusted the idle timing from 4 degrees BTDC to spec of 8 degrees BTDC. I never checked it again after I fixed the wires. Is it possible that this could be overheating the engine at higher rpms? I simply am frustrated at this point. I seriously think the cooling system is working correctly. I ran the motor with the unit all the way down and water was coming from all possible places. Even when the motor was at 2000 rpms.

 

[TruDaddy]

Is it possible to have a blown head gasket? How would I check? The manual says the compression test does not tell. It does say that idling the temp is fine but 3000 rpms or more is where the problem occurs??? I read something about bubbles and a clear tube. Does anyone know about this?

 

[TruDaddy]

Bueller...Bueller...

 

[Bondo]

Is it possible to have a blown head gasket? How would I check? The manual says the compression test does not tell. It does say that idling the temp is fine but 3000 rpms or more is where the problem occurs??? I read something about bubbles and a clear tube. Does anyone know about this?

Ayuh,..... A compression test oughta point it out, a Leak-down test oughta confirm it,....

 

[TruDaddy]

I did a compression test earlier and got 180# on right side and 135 - 155# on the left side 3 cyl. My money is left side. I can't find any info on the leak down test. Can you clarify?

 

[Bondo]

I did a compression test earlier and got 180# on right side and 135 - 155# on the left side 3 cyl. My money is left side. I can't find any info on the leak down test. Can you clarify?

Ayuh,.... My compression tester has a quick-coupler, that matches my compressed air system,....
With the compression tester adapter screwd in, turn the motor to Tdc, that cylinder, 'n hold it there,...
Then apply air pressure to the cylinder,...
If ya hear air loss, find the source of the sound,...

 

[TruDaddy]

I tried that but was curious. One doesn't the compression end have a one way valve...Air coming from the cylinder? Also before connecting my compressor, I set the gauge to 25lbs. Should I set it higher to 100lbs? I ask because I didn't hear any air. How obvious is the sound if done correctly?

 

[NHGuy]

Try it in the water, maybe your water hose can't keep up with 2000 rpms of pump demand.

 

[TruDaddy]

Good point. I will try that.