MEFI 2 system and I have the Merc manual for it. Service Manual Number 23 page 5D-24 has the normal specs at warm engine idle. My engine runs very rich at idle. Using a Rinda, my injector pulse time is 4.5ms versus a book value of 2-3ms. Coolent temp is 163 degrees. Baro volts are 4.62 vs book of 3-5 volts. Manifold pressure is 15.3 and I cannot find a value for that in the book. MAP volts are 2.25. Vs book of 1-3 volts. TPS is zero degrees and .64 volts vs book of .4 to .8 volts. As I understand it, MEFI 2 primarily uses engine load (MAP) and RPM to determine fuel injector pulse time. Seems my other specs all fall within book. Any ideas why Im running such long pulse times?

Need Articfriends to come in, but lean toward a MAP issue. Volts are higher which in turn causes longer pulse. My old build MEFI-1 was doing similar

That said the ECM will change the pulse width to keep the motor running when rpm's go lower. We would not see it go lower because the ECM will changed faster then we can see.

What are the readings when placed in based timing mode?

Just ran it in Base Timing Mode with the following data: Coolant Temp 158, Manifold Air Temp 96, TPS .64 volts, Throttle zero percent, MAP Volts. 1.35, Manifold Pressure 10.7hg, Baro Volts 4.66, Spark Advance 8.1, IAC Position 126, Base IAC 125, IAC Follower Zero, Injector On Time 3.3 to 3.7, Fuel Flow 3.3gph. Thanks for the help.

With the IAC being over 100 (it should be 40 or so) leads me to believe its stuck or maybe trying to lean things out.

Whats the fuel pressure

Fuel pressure is 38psi.

PM Smitty (articfriends) see what he thinks

Wonder if someone sent the ECM off to reprogram, it might be messed up. Unfortunately it and look on the back to see if there is a new sticker or label

I'd start with getting that MAP in the proper range and making sure the TPS is in line also. Check your IAT sensor value and base timing as well. Do all EXCEPT the base timing in regular mode. If you replace the IAC Mercruiser ONLY!! Aftermarkets have been frying ECM IAC drivers as of late, which may be your issue as well.

PROBLEM SOLVED. Replaced MAP sensor with OEM part and my MAP voltage and injector on time dropped on half and back to specs. No longer runs super rich at idle. FYI, and everyone probably already knows, but the Quicksilver upper intake manifold gaskets I got were still packaged in the GM bag with a Quicksilver label above the GM part number. I paid 80 bucks for the Quicksilver part that is 20 bucks from GM. When I get my injectors flow tested this winter, I will just use the GM gaskets next time. Thanks everyone for your help.

Thanks for coming back with the answer