4.3 mpi dies at idle struggles to get out of idle

[Str8ball]

I have read meant topics in this site about idling issues and would like to thank everyone for that.

The boat is new to me. 2007 fisher deck boat. Aluminum 2007 mercruiser 4.3 mpi

My boat is currently at the mechanic. They have done about a $1000 worth of work tuning and checking pressures etc on the motor. I tried a new IAC and that didn't work before I took it to them.

No luck. Say compression is fine and see nothing wrong with motor but say it is an electrical issue.

They say they can't get a reading from the ecm because the motor keeps recycling. I personally have had the motor above 1000 rpms and it ran fine above that. They claim it still is rough above that although their response makes me wonder if they have even tried to run it above that and then get an ecm reading.

Want to replace the harness and then the ecm after that. Obviously a lot of money for things they aren't sure are the issue. They claimed they called mercury and a rep stopped out and suggested the harness or ecm.

I asked about checking the throttle position sensor and the guy didn't know if they had done that.

I'm just looking for opinions. Mechanic claims they have been over and over everything else and are finding nothing.

 

[tpenfield]

Welcome to iBoats . . .

I see a few things.

The shop may not be the best at diagnosing and fixing an MPI engine.

Sounds like they will continue to throw parts at the engine, which you will be paying for . . . not sure what 'recycling' means in terms of the motor and why they can't get a reading from the ECM. Typically you will get a communication error, if there is a bad connection to the diagnostic port.

The ECM's are about $2K . . . not sure what the wiring harnesses go for. I would think that they would/should narrow the possibilities down before going that route.

Are they assuming you have given them a blank check?

What are your options? DIY, another shop, maybe you will get some info from additional posters, but collectively, we don't have much to go on.

Anything more that you can tell us about the history of the boat, as it may be relevant?

 

[Str8ball]

Welcome to iBoats . . .

I see a few things.

The shop may not be the best at diagnosing and fixing an MPI engine.

Sounds like they will continue to throw parts at the engine, which you will be paying for . . . not sure what 'recycling' means in terms of the motor and why they can't get a reading from the ECM. Typically you will get a communication error, if there is a bad connection to the diagnostic port.

The ECM's are about $2K . . . not sure what the wiring harnesses go for. I would think that they would/should narrow the possibilities down before going that route.

Are they assuming you have given them a blank check?

What are your options? DIY, another shop, maybe you will get some info from additional posters, but collectively, we don't have much to go on.

Anything more that you can tell us about the history of the boat, as it may be relevant?

It was a used boat bought from a dealership. Not the same one I am at.. The shop is a place that has good reviews for working on inboards.

Think they are saying it is dying before,they can get a reading. They claim they have checked everything else...spark plugs etc... Compression check. All were fine.

Mechanic keeps claiming a lot of corrosion. Which I assume he means wiring as they replaced the wires to battery etc.

I took the boat on the water when I fiest got it. Idled then for about 2 hours, after that started dying at idle and then became difficult to start. Once above 1000 rpms or so it ran well though. No stalling above that. Pulled the kids on tube etc.

I asked if the motor as sound and he said yes but its an electronics issue. Motor will die or rev up and then back down at idle. They claim it isn't running well at any rpm but answer seemed odd to me as he acted like the motor wouldn't stay running at high rpm. I've had it running steady above that three different times.

I replaced the IAC before taking it there. Didn't change. What do u need to know? Harness cost will be about 1000. They are doing that now. Then ecm if that doesnt work?

In looking at 3800 and maybe no fix?

Options are don't do ecm... Take it somewhere else if harness wasnt issue, I dont know as I'm not a mechanic. I read a lot and can do minor things based on posts here and other places that's it.