4.3L EFI power loss (at altitude)

[ILOVEBEER]

Hey guys I just took my boat up to the lake (4900' MSL) and it was a DOG!! I know that this happens at altitude but I guess I just wasn't prepared for the severity.<br /><br />First off, when I would go WOT, the boat wouldn't get on plane unless everyone (6-8 people) would move forward. <br /><br />Also, I had to "pump" the throttle to make max power. With the throttle in max, the engine would make less power than if I pulled the throttle back an inch. Then the engine would start to back off and I would have to move the throttle back to max to increase power. The engine is EFI so I don't understand this. Every morning when I start it, it does it's little automatic mixture setting doo-dah.<br /><br />A freind of mine suggested a different prop for the high altitude lakes. What do you suggest? Is there another way (besides turbo or supercharging) to get the engine tomake more power at altitude?<br /><br />Thanks<br /><br />-Beer

 

[tommays]

Re: 4.3L EFI power loss (at altitude)

They all make LESS power at altitude a smaller prop would be the easy cure<br /><br /><br />This make the assumption that the boat runs well at normal altitude AND is up to date on its service <br /><br /><br />tommays

 

[bruceb58]

Re: 4.3L EFI power loss (at altitude)

5 percent power loss per 1000 feet due to decrease in oxygen.

 

[ILOVEBEER]

Re: 4.3L EFI power loss (at altitude)

I know that it will lose power and why it will lose power. <br /><br />

Originally posted by ILOVEBEER:<br /> I know that this happens at altitude but I guess I just wasn't prepared for the severity.<br />

I hate to repost but I don't think I got my point across.<br /><br />What I don't know is why this is happening (it is EFI):<br /><br />"Also, I had to "pump" the throttle to make max power. With the throttle in max, the engine would make less power than if I pulled the throttle back an inch. Then the engine would start to back off and I would have to move the throttle back to max to increase power."<br /><br />...and this,<br /><br />A friend of mine suggested a different prop for the high altitude lakes. What do you suggest? Is there another way (besides turbo or supercharging) to get the engine tomake more power at altitude?<br /><br />Thanks for your help.

 

[tommays]

Re: 4.3L EFI power loss (at altitude)

I cant really say BUT if your over proped its not gonna run right<br /><br />And it sounds like you have a HUGE load on the boat<br /><br /><br />tommays

 

[ron7000]

Re: 4.3L EFI power loss (at altitude)

I don't know much about the marine (merc?) EFI's so this is just a guess- unless they have O2 sensors there is no way the ECU knows what the air-fuel ratio is and all it's going off of is a preprogrammed map. So at higher altitude you're running super rich and the only way to correct it is reprogram the ECU with a leaner fuel table for that altitude or bolt on a carb jetted correctly.<br />I don't see how any prop change will help, at an open throttle setting the ECU will still want to dump the same amount of fuel and the mixture will still be super rich.<br />I would inquire at a dealer and see if there are different efi engine models sold as high-altitude. I doubt they do any mixture calibration, maybe a little based off manifold vacuum to give good idle quality but that's only relevant at idle.

 

[ron7000]

Re: 4.3L EFI power loss (at altitude)

also know that running at high altitude you are running really rich, and as a result will have more fuel in the oil than you normally would. Oil diluted with fuel has less viscosity and means increased wear and sludge/varnish so beware. You may be doing more harm than you know, the longer you run it like that the sooner and more often you will need to change your oil.<br /><br />I wonder if, what I said about the EFI is true, is if you can knock down your fuel pressure to the efi system that may lean it out to correct the AF ratio. Might be a cheap fix opposed to having the ECM reprogrammed, but it wouldn't suprise me if all they do is turn down the fuel pressure to compensate for high altitude. Look to see if your fuel pump is adjustable, just a thought.

 

[bruceb58]

Re: 4.3L EFI power loss (at altitude)

If the EFI has a mass airflow sensor it can sense that it is at higher altitude that way so it is compensatining for the altitude.<br /><br />I hate to repost this but maybe I didn't get my point across:<br /><br />5 percent power loss per 1000 feet due to decrease in oxygen.<br /><br />There is nothing you can do that is cost effective to make up for the lost power.<br /><br />EFI or Carb, your boat will have less power. The EFI is able to compensate to adjust the mixture for the decreased oxygen but that is it.<br /><br />Your engine has less power at that altitude so you need a different prop. Just like your car has less power at high altitude and you shift to a lower gear, you have to do the same with your boat and do the equivalent.<br /><br />On my old boat, I had a set of props for high altitude and a set for low. By set I mean one on the boat and one spare.

 

[rodbolt]

Re: 4.3L EFI power loss (at altitude)

most the merc V6 EFI motors I see are speed density systems not mass air flow systems, make sure your MAP sensor is working correctly and select a smaller prop. once over propped,and 8 folks with a tiny motor it doesnt take long, will cause excessive spark advance then power reduction as the ECU detects the knock and retards timing and makes a rich fuel mix richer.<br /> so far we dont have O2 sensors on marine EFI fourstrokes.<br /> most 4 stroke EFI setups have a barometric pressure as well as a manifold pressure sensors to detect changes in air pressure and adjust fuel mapping as required.<br /> however all the sensors in the world cannot compensate for inccorect gear ratios and prop sizes for the particular altitude you wish to run. you can contact mercury marines technical assist for gear ratio and prop reccomendations for running your weight load and engine at that altitude.

 

[ILOVEBEER]

Re: 4.3L EFI power loss (at altitude)

Thanks guys. So as for the power issue, there is nothing that is cost effective to overcome that. It sounds like I need to get a different prop or kick some people out <br /><br />Thanks<br /><br />P.S. Smart tabs too!!