5.7 efi mercruiser idles high when starting then dies.

[Louis S]

I have a 5.7 efi fuel injected mercruiser that idles high when I start it then kills itself. I have checked the iac and it works properly. I recently replaced the shift interrupter but don't know if that has anything to do with it.

 

[Sttuppid]

intake air temp sensor. Is the throttle body dirty? mass airflow sensor? Check the air filter for a mouse nest. Do you have a scan tool?

 

[Louis S]

The boat doesn't have any scanner hook up

 

[Louis S]

Everything is clean and if I unplug them would it get worse or stay the same? How do I diagnose the sensor?

 

[AllDodge]

The boat doesn't have any scanner hook up

If it's a EFI it has a connector for a scanner

What is your motor serial number

This should be in the Mercruiser section

 

[Louis S]

Where would the hook up be?

 

[AllDodge]

Where would the hook up be?

It's on top the motor and normally near the ECM of thermostat. It will be black in color and have a plastic cover over the connector.

 

[jimn]

Where would the hook up be?

A better question would be "Once you find it, what will you do with it?".

You don't need codes, you need data but first, what are the year, model and serial number of the engine?

 

[jimn]

intake air temp sensor. Is the throttle body dirty? mass airflow sensor? Check the air filter for a mouse nest. Do you have a scan tool?

What makes you think it has an IAT?

 

[Louis S]

So im not saying this is symptoms for other things but a while baxk i was trying to diagnose a shifting issue and unplugged the shift interrupter and it did the identical thing its doing now. I was told to try replacing it and di but I had to do some wiring to make it work and thats when it started doing it. I didnt think I can wire it backwards so I swapped the two wires and it didn't change anything. I then ordered a shift interrupter that required no wiring and now if works fine. Thank you to everyone that helped I hope this can help someone else too.

 

[AllDodge]

Good to hear your voice and going

What I'm reading is the original interruptor switch was causing the problem with motor dying. The switch you have puts 12V to the distributor when running and removes it momentarily when shifting out of gear under load. The switch was not making connection and the reason the motor dies. Replacing the switch fixed the issue