Mercruiser 7.4 LX MPI EFI problem

Too late now but the correct method to figure this out would have been to chuck up some air to that cylinder with the rockers off and hear where the air is leaking. Pressure test the cooling system. Both tests would have been easy and telling.
 
scoflaw said:
Too late now but the correct method to figure this out would have been to chuck up some air to that cylinder with the rockers off and hear where the air is leaking. Pressure test the cooling system. Both tests would have been easy and telling.
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As I stated earlier I used a leak down tester to try and do exactly that. I couldn’t hear air in the exhaust or the intake. It’s raw water cooled not a closed system so I’m not sure how one would pressure test the cooling system on this engine.
 
Pressure testing that system is easily done but your past that point now. With a large volume of air put to that cylinder how is it possible you couldn't hear anything? Maybe it was exiting thru the water system. Were those heads checked for cracks?
 
@scoflaw I don’t know what to tell you other than I couldn’t hear where the air I pushed into the cylinder was coming out which is why the head had to come back off and go back to the machine shop for testing. With both rocker arms loose I blew the 120 psi from my compressor into it and according to the gauge on the leak down tester 0 psi would hold. When I compression tested it before the first time I pulled it there was 150 psi in that cylinder and the #5 cylinder was the bad one due to seized valves. I’m still waiting to hear from the machinist on his findings.
 
Ok, the machinist finally got back to me. The vacuum test on the valves found the exhaust valve failing to seat. Not sure how it got screwed up but he is fixing it now and hopefully I'll get it back by next week and can reinstall everything and get it running right once again.
 
Hope he's at least ponying up for the new gasket set, too.
 
Ok, I got the head back from the shop on Wednesday. Been working on it all day and finally got it all back together. It took a hot minute since I was by my lonesome to get the timing set but it seems to be running reasonably well and on all 8 cylinders now but on some really old stale gas. Hopefully I can make some time this weekend to take it out for a sea trial to test my work if not next weekend I should be able to.
 
You need to get that old stale gas out of the equation. It can cause all sorts of other problems along with the poor performance.
 
Thornton69 said:
You need to get that old stale gas out of the equation. It can cause all sorts of other problems along with the poor performance.
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Gotta use it up to get rid of it unfortunately. About 50 gallons in the tank and no way to dispose of it legally here. I’ve put some additives in the tank and once I get it down below 1/4 tank I’ll fill it with fresh fuel.
 
You don't have bulk plants out there? They all take it here for a fee. That fee is much less than a repair bill on a damaged engine. I would not burn off that kind of volume in my boat. Maybe the wife's car though.
 
Thornton69 said:
You don't have bulk plants out there? They all take it here for a fee. That fee is much less than a repair bill on a damaged engine. I would not burn off that kind of volume in my boat. Maybe the wife's car though.
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I’ve called everyone I can think of here. No one will take it. Just not going to push the engine hard until it’s burned off.
 
I have used 10% kerosene with old fuel with great success. If you check some of the fuel additives that claim to increase octane the label indicates the contents are kerosene… Even some the injector cleaners on the self contain kerosene.
 
Update:

Finally had time to try and take her out for a sea trial after my engine repairs. Engine ran well but the temperature gauge was reading high but the engine didn’t seem to be overheating. Got in the compartment and nothing was overly hot. Was able to put my hand on the risers without burning them so I’m thinking either the temperature sender has failed or the circulation pump which looks a bit crusty is giving up and creating a high reading on the sender. Cheap and easy enough to just swap them both out I think to be sure. The real fun started about half way out the channel when I’m guessing the gimbal bearing and/or the whole outdrive failed in some way and the whole boat began to shudder something horrible. Was able to limp back to the slip as long as I kept the RPM’s under 1300. Got ahold of the only mercruiser mechanic in my area today and the outdrive he related was previously available is now damaged beyond use. He thinks he may be able to piece several sets of drives he kept for parts together and possibly make a good Bravo 3 replacement for me. If not he said he has a almost like new bravo 2 drive he could sell me. I’d rather keep the original but if the price is right I don’t know I guess the Bravo 2 will work. Anyways hopefully sometime this year I may get to actually enjoy the boat rather than be frustrated by everything breaking.
 
The B2's are a tough drive. With the price being right, I wouldn't hesitate.
And an FYI, the only different between the B2 and 3 is the lower. There is a few different gear options available in the uppers. You could compare what's in it to what you have for a closer comparison and look to replace the lower down the road if not happy with it.
When selecting a drive, I would also try to stay 2000 and newer. The older clutch assemblies in all Bravos are now obsolete and pricey to upgrade if you ever need parts for them.
 
B2 is no tougher than 1 and 3, same upper, Bravo's weak link. Spins a much larger prop, made for heavy boats with no intention of going fast. Had one on a 2000 245 weekender with a 5.0, top speed 32 mph
 
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