Mercurser 5.7EFI Problems

[trx450always]

So we have a 2001 sea ray 210 bowrider with the mercurser 5.7 L EFI. It runs awsome, and everything is great, but every year we go to lake powell, and ONLY after the boat sits for 10-15 minutes, you start it up and then take off, the boat sputters, and tries to die. If you can milk the boat along for a minute, then it will slowly get up and go again. If it stalls, you need to go WOT in neutral and start it. That will fix it. So we took it to the shop here, and they said it needs a whole new ECM, for 2100 dollars!!!! the engine only has 125 hours on it, and it only seems to do this at lake powell at 400ft elevation. The problem has gotten worse over the years, it happened 8 times this year. Only happened 2 last year. Is this a common problem, an what is the best way to fix this.
Thanks,
Sam

[stonebreaker]

$2100 for a computer is a ripoff. You can buy an entire aftermarket fuel injection system for that much, manifold and injectors included. Get the part number off your engine computer and go to www.gmpartsdirect.com and enter it for a price on the computer. I got the part number for the MEFI-5 engine controller from here and GMPartsDirect gave me a price of $227.

As far as the problem goes, what's different about lake powell? Is it at a different altitude from where you normally go? What about fuel octane? Have you hooked up a diagnostic to the computer and pulled the error codes? What about logging the engine parameters when the engine is acting up?

[trx450always]

Originally Posted by stonebreaker

$2100 for a computer is a ripoff. You can buy an entire aftermarket fuel injection system for that much, manifold and injectors included. Get the part number off your engine computer and go to www.gmpartsdirect.com and enter it for a price on the computer. I got the part number for the MEFI-5 engine controller from here and GMPartsDirect gave me a price of $227.

As far as the problem goes, what's different about lake powell? Is it at a different altitude from where you normally go? What about fuel octane? Have you hooked up a diagnostic to the computer and pulled the error codes? What about logging the engine parameters when the engine is acting up?

Yes, we normally run it at sea level, and lake powell is at 4000 feet. The tech said they couldn;t pull any codes, but we did turn off the battery before the trip to the dealer if that matters. The only thing that worries me is that the problem has gotten worse since 2004 when it started this. I believe there is a bad sensor somewhere. Would it be possible to go to a MPI system with this motor? Octane and all varibles are the same otherwise. Engine runs great. But this problem is a pain!

[stonebreaker]

Well, disconnecting the battery is a bad thing in this case - it deletes the error codes from the computer's memory, so your mechanic can't check for any failing sensors.

Second, my first guess would be to test the MAP sensor - the manifold absolute pressure sensor. It may not be completely bad - it may pass the startup test but may not read the manifold pressure correctly. I had a couple of O2 sensors on my car do that. Makes it tough to track down the problem. Borrow or buy a spare and test the boat next time you go to the lake. Does it have O2 sensors?

What's MPI? Do you mean MPFI (multipoint fuel injection)? Is it a TBI system now? THAT can get expensive - an MPFI system is around $2000 to $2500 in parts alone, then you have to either install it yourself or pay someone to do it; then you have to have the computer programmed, which usually costs an additional $200 to $500. Unless you're planning on hotrodding the engine, I don't think you would really see much advantage from it. Maybe a little better fuel consumption, but not a whole lot.

[gonzo]

I could be a vapor lock. The high altitude will make it worse. Something as simple as a clogged filter can do that.

[Verytricky]

I had a 'flat spot' with my Volvo 5.7

The cure was in the way the distributor was set. It was incorrectly adjusted - the ECU works around this problem, but has to 'think' more when it is wrongly set up.