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Old 03-29-2013, 08:51 AM
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JimN JimN is offline
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Join Date: Jul 2004
Posts: 13,169
Originally Posted by Mark rsa2au View Post
Ok Still stumped.... Engine has a huge misfire / backfire at anything above 4100rpm, and on occasion limits revs to 2500 - shut down restart and rev limit gone.
Today had Code 22 (TPS reading low) and 44 (O2 sensor reading lean but this boat has no O2 sensor).

So far have replaced the Idle motor, the TPS, the MAP sensor, the Spark plugs, the spark leads, distributer & rotor. Tested Temp sensor ok, fresh fuel, New injectors. Also timing 10deg BTDC @1000rpm in diagnostic mode. Fuel pressure arround 29 - 31psi.

Checked earth from sensors to ECM and all good, but earth wire at sensors to rear earth connection shows 0.7 - 1.1 ohms difference. Is this ok and if not what would cause it?

Checked water pump, trans cooler, and calibrated temp sensor for the engine warning light. The check light comes on and goes off when I dissconnect this temp sensor. Calibrated to 95degrees C (203F) and it comes on after a hard run but the dash temp shows 160F and this sender is in the same water channel is it not?

JimN there are many Mastercrafts (also Malibu- made locally, Nautique, Supra, Mobius,etc) over here, its just the dealer will not support boats not imported by them - even though this boat was imported before 2004 when MC officialy started in OZ.

Not sure where to go next.... any suggestions other then a match?
The 1.1 Ohms is high. Get the resistors and substitute them for the ECT, as I posted. If the check engine light goes off when you disconnect it, it has a problem (or, the plug/wires on its harness). The sensor going to the gauge has nothing to do with what's going to the ECM.

44 may be IC module- contact Mastercraft or Indmar and ask them about it- my manual isn't here at the moment, so I can't check this.

Disconnect the battery, let it sit for a few minutes and remove the plugs from the ECM. Open the plastic shell and look for the black wires and measure from the ECM plug to the battery posts, not the terminals. The resistance between the terminal and post can be enough to cause problems.

Here's a manual for MEFI 4, but it's not exactly for your engine. The pin out,, diagrams and diagnostics are basically the same. You'll notice that the MAP sensor is different (the one in the link is like the one on the LTR. MCX and some of the others that aren't TBI).
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