I have a 1996 Mercruiser 454 Mag/MP motor throwing a code 33 for a map sensor. I have replaced the map sensor and have checked out the rest of the circuits. But I still have the code and cannot find out how to clear it without using a scan tool. The Mercruiser tech support had told me that if the code does not get cleared, then the computer still thinks that it has a problem and will try and compensate for the issue. The motor seems to be running rich. Has anyone else had this problem? And does anyone know how to clear it without the tool? I have checked just about everything possible that I can think of, and everything checked out good.

http://www.offshoreonly.com/forums/s...d.php?t=103342


Build this and once you got the engine in service mode go 100% throttle and back should clear the codes......
LF

That is ofcourse with the key on, correct.

Correct. I have had a similar problem and I am curious to know if you got rid of the code by changing the MAP. What was your problem, other than the ECM throwing a code? Did the engine run rich?

Does all the different ecm`s use the same code`s? And if so does anybody got a list they could post?

Buy the Merc scan tool.

$395.00

http://216.230.203.183/marine/mtspec.htm

Best money I ever spent. Shows you the codes and allows you to clear them, plus much more.

Yeah, you just need a paperclip in the "A" and "B" terminals of the Data Link Connector, and advance the throttle to 100% and back, then remove paperclip before turning off ignition.

Dave

Cleared codes last night, code came back. The map sensor circuits checked out fine. I put a automotive gm map sensor on. Is the Merc map sensor different or something? The motor acts like it is running rich, the plugs are all black and I am getting alot of black on the transom. The other issue I'm not sure of is at idle the fuel pressure is about 30psi. Does that seem to low. I have gone thru the VST tank and all seems ok.

The MAP sensor is as far as I know the same. It should be a 1 bar sensor, GM type. My manual says that the fuelpressure should be 37 psi with the vacuum hose removed. Did you remove the vacuum hose when measuring 30 psi?

Yes I removed the vac at the regulator, and it jumped up to 36psi.