I'm trying to diagnose various things with my 2005 Mercuiser engine, including possibly excess fuel consumption. I recently got a diagnostic scanner to help with this, but I'm not used to interpreting the readings. I've attached a some plots showing Engine RPM, Coolant Temp, Manofold Absolute Pressure and IAC Duty Cycle while the engine was running.
I showed these to an auto mechanic, and he thinks there might be a bad MAP sensor or a vacuum leak. According to the Merc Service manual for the engine, the manifold pressure seen by a vacuum guage should be 15 to 21 inches at idle (I assume inches Hg). The manifold pressure is reported in absolute PSI, so it has to be converted to what a vacuum guage reads (which I don't have on hand). Another Merc manual has a plot of that (attached), and it looks like 15 to 21 in from a gauge should translate into about 7 to 4 abs PSI as reported by MAP.
In the collected data, the reading is out of this range. In the first plot at idle RPM, it's reporting about 8.6 PSI, and when I run the RPM up to 875 in the second plot, MAP reports a lower value of 8 PSI.
Finally in the third plot, which is when I first started the engine, the pressure goes from atmospheric (~15 PSI) down to 8 eventually, and the IAC Duty cycle jumps from 0 to 100%, dips a little then back to 100%
So, am I interpreting the MAP Sensor readings correctly? Out of range readings, and therefore either a bad sensor or a leak?
Does the IAC Duty cycle of 100% mean it's wide open? If so, should it be?
I showed these to an auto mechanic, and he thinks there might be a bad MAP sensor or a vacuum leak. According to the Merc Service manual for the engine, the manifold pressure seen by a vacuum guage should be 15 to 21 inches at idle (I assume inches Hg). The manifold pressure is reported in absolute PSI, so it has to be converted to what a vacuum guage reads (which I don't have on hand). Another Merc manual has a plot of that (attached), and it looks like 15 to 21 in from a gauge should translate into about 7 to 4 abs PSI as reported by MAP.
In the collected data, the reading is out of this range. In the first plot at idle RPM, it's reporting about 8.6 PSI, and when I run the RPM up to 875 in the second plot, MAP reports a lower value of 8 PSI.
Finally in the third plot, which is when I first started the engine, the pressure goes from atmospheric (~15 PSI) down to 8 eventually, and the IAC Duty cycle jumps from 0 to 100%, dips a little then back to 100%
So, am I interpreting the MAP Sensor readings correctly? Out of range readings, and therefore either a bad sensor or a leak?
Does the IAC Duty cycle of 100% mean it's wide open? If so, should it be?