Absolutely frustrated with this Mercruiser engine

Hoplite808 said:
Video showing the engine being throttled up from idle to 100% but engine only reaching 2000 RPMs.
https://youtube.com/shorts/UmVP4abRU6s?feature=share
https://youtube.com/shorts/UmVP4abRU6s?feature=share
Click to expand...


Well, that means it is a mechanical issue. As much as I was hoping for an electrical fix.....that is not the problem this engine has. The video shows the problem with the engine making power. The engine seems to be consistently low on compression in at least two cylinders robbing it of making any HP or torque above 2,000 rpm. Based on the weight of his boat.....I would speculate that the engine is only generating 100 hp and 100 ft lbs of torque....consistently .....which is why the peak rpm is so close in each run.

I agree that a more in depth compression and leak down test is in order. The water intrusion the engine suffered probably did more damage than was originally thought.

Frankly, I would enjoy the boat for a while and save your money for a quality long-block.
I wish I had a better suggestion.

gm74.gif
 
Try unplugging the map sensor. It should default to table driven values. Barometric pressure is calculated by the MAP sensor at key on but before engine start. At idle the MAP pressure should be low (0-10 ish) and climb as load is demanded. Watch the MAP value from key on, through the RPM range with and without load. When in neutral I wouldn’t expect you to hit the value of barometric pressure. With load this should climb. Neither ECM is reporting power reduction mode so I don’t believe the ECM is turning off half of your injectors.
 
Well, the one thing we know is still wrong, is the statement that the fuel pressure is "37 psi throughout the entire throttle range". This has never been resolved, either logically nor physically.

Either the measurement/observation was wrong, or there is a problem with the pressure regulation/supply.

The OP replaced both the mechanical and electrical fuel pumps because of low fuel pressure. Boatloads of folks thought that just dirty fuel injectors could have caused the loss of power, yet somehow don't think that a loss of fuel pressure could do the same thing. That has me confused. Either the fuel pressure should be ~30 at idle and increase to 37PSI at full load, or it should be 37 at idle and increase to ~44PSI at full load.

The OP could resolve this issue by just hooking up a pressure gauge again and retesting. Either it confirms his earlier statement (and indicates a problem in the fuel pressure system) or it shows that fuel pressure really does follow/track manifold pressure. If it does follow/track manifold pressure, then the next question would be "is ~37PSI the correct full load pressure?"
 
Hoplite808 said:
OEM props are on it. I verified this when I had the outdrive replaced.
Click to expand...
Changing the prop is just a troubleshooting step. See if you can get a lower pitch prop to test with (and maybe just keep for a future spare) .
 
I hear you stee. But would love to find the cause
 
techmitch said:
I tried to tell him what the problem was back at post 19 back in February.
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Well... I jumped into this late. I didn't see those compression numbers. All the good running big block Mercs I ever tested were all above 140. 120 would concern me.

Because it's easy, I would still do a few things like disconnect the tach, change the prop to see if it makes a difference, and check the Y pipe for a flapper that has come free and lodged itself downstream.

But that 120psi is pretty low in my limited experience.
 
After 447 posts, I seriously feel bad for OP. I really do, cannot imagine what he going through.
That said, I love my old fashioned 7.4 Quadrajet, mechanical fuel pump, distributor and all that.
Tomorrow i am opening the hatch and giving it a big wet sloppy kiss! Then spend 5 minutes turning the key, pumping the throttle, and holding it at 1500 rpm til warm up before I move it.
 
I think it’s time to throw in the towel and just sell it for whatever I can get for it. Let someone else have a good deal and I eat the price of all the work I’ve put into it and they can just repower it worst case scenario.
 
As the last ditch effort I don't want to see you get rid of your boat I want to see you enjoying your boat is there anybody on that island that you can get to come and take a look at that boat , an mercruiser mechanic I just want to see you get this solved and have some fun
 
Pirate Lady said:
Thats a heavy a salt environment. What is that ? a couple days a year as opposed to sitting in it daily for 9 months? Of course its the same thing, of course. How did I miss that?
Click to expand...


Yes, but now there are plenty of decades old injected motors running perfectly, and virtually all failures are easy to diagnose and most of those are not that expensive to fix.

But I get your point. My father is running a pair of nearly 40 year old 350 inch mercs that run perfectly.
 
Tri County Trail said:
When was this? Possible wrong ratio or incorrect labeled.
Click to expand...

Verified it when I hauled it out last year and double checked the serial numbers on both props when I replaced the entire leg with a new one. I know the gear ratio is correct in the leg because the certified Mercruiser mechanic I hired to do it verified it.
 
Hope, I know what you're saying about sell it and let someone figure it out or maybe repower but you've done all that it's got to be something that we're all just missing and I don't know how that's possible with everything you've gone through I really don't understand it I wish I could help you with this I really do
 
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