502 EFI Raw Fuel Coming From Exhaust
 

I have a pair of stock 1994 502 EFI's. Total hours: 532. Hours on engines since rebuild: 80. I've had some issues with these motors in the past. All seemed to be fuel related. Evil VST's. I blamed everything bad that ever happened to me (on and off the boat) on the Fn VST's. So this winter's project was to remove the VST's and go Aeromotive. Eddie Young did the fuel rails for me. Opened up #7 and set them up to feed from both ends. After 10 micron filter, AN10 split to two AN6 feeding the rail. AN6 out of the rail to Aeromotive regulator. From Regulator 3/8 return line to the tank via fill hose bung. Regulators are set at 37psi and drop to about 33-34psi idling.

Port motor starts, idles, and runs flawlessly. If it wasn't for the gas slick behind me along with the smell of gasoline I would never suspect anything was wrong.

Next step was to look at distributor cap and rotor. My Ah-Ha moment. Pulled the wires off and the post for #2 had carbon on it. Put the wire back on and sure enough it was loose. So new cap, rotor, wires, and plugs and I know I've got this fixed- Nope. Fire it up and within 2 to 5 seconds I'm doing my best BP impression.

Now I'm thinking it must be MAP sensor. I have a parts donor sitting right there so I swap MAP sensors. Fire the motor up (again cold) and you guessed it- no change. Fire up Starboard side and no gas slick.

Ran about an hour and pulled the plugs. All are dark brown to black.

I got a hold of a scan tool today and here are the numbers:

Coolant Temp 154F (New Mercruiser 160 T'stats just installed)
Map Volts 3.27
Manifold Pressure 21.4
Baro Volts 4.93
IAC Position 82
Base IAC position 80
Injector On Time 3.8
Injector On Time Crnk 9.6
Fuel Flow Rate 2.1

These readings were taken immediately after a ten minute run at 4200rpm. Then did a quick WOT run with both motors hitting 5200rpm and temp on scanner dropped to 151.

Suggestions on what to try next?

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MAP is over 3 volts

Map specs should be 1 to 2 V MAX at idle and 4 to 5 MAX at WOT.

My bad I see your scan was at 4200 rpm BUT NOT sure so

I am asking is this scan taken at Idle or from freeze frame at 4200 rpms.

If this scan was taken at idle your MAP Voltage is to high.

You need to find out why. Bad MAP or incorrect MAP inputs to the ECM will cause very rich fuel conditions.