Mercrusier 350 MAG MPI - RPM issue under a load

[wbas1]

Well I have someone coming down tomorrow AM to look at the boat. I am going to take some readings on all the sensors to see if they acting up or not. More to follow.

 

[wbas1]

I think I am having a lean fuel issue so my question is this. What tells my motor and computer that I am under a load and need more fuel.

 

[nola mike]

I think I am having a lean fuel issue so my question is this. What tells my motor and computer that I am under a load and need more fuel.

MAP sensor when warm, ECT sensor has effect until it warms up. PCM probably takes RPM into account as well, I don't think there's a TPS sensor on there; if so that would have an effect as well.

 

[alldodge]

MAP, TPS, Temp and RPM
MAP increases pressure as the throttle opens and vacuum is reduced
TPS how far open it is
Temp tells if its cold and needs more fuel or warmed up and needs a tad less
RPM how often injectors fire

Fuel tables are setup inside the ECM so as things change the fuel tables are used by the ECM to fire injector and for how long

 

[wbas1]

MAP sensor when warm, ECT sensor has effect until it warms up. PCM probably takes RPM into account as well, I don't think there's a TPS sensor on there; if so that would have an effect as well.

I have a TPS and MAPT. What is the ECT and PCM.

 

[nola mike]

MAP, TPS, Temp and RPM
MAP increases pressure as the throttle opens and vacuum is reduced
TPS how far open it is
Temp tells if its cold and needs more fuel or warmed up and needs a tad less
RPM how often injectors fire

Fuel tables are setup inside the ECM so as things change the fuel tables are used by the ECM to fire injector and for how long

My mistake on the TPS. Has OP checked fuel pressure?

 

[wbas1]

MAP, TPS, Temp and RPM
MAP increases pressure as the throttle opens and vacuum is reduced
TPS how far open it is
Temp tells if its cold and needs more fuel or warmed up and needs a tad less
RPM how often injectors fire

Fuel tables are setup inside the ECM so as things change the fuel tables are used by the ECM to fire injector and for how long

I replaced all of them. Temp, MAP and tps.

 

[nola mike]

I have a TPS and MAPT. What is the ECT and PCM.

ECT = Engine Coolant temp
PCM = Powertrain Control Module = ECM + ECU in this context

 

[nola mike]

I replaced all of them. Temp, MAP and tps.

Replacing things without testing them doesn't tell you that the system is working. Did you check the wiring and the output of each sensor before / after replacement? The diacom makes it easy to see if the sensors are actually sensing... I think it's pointless for you to keep throwing parts at it hoping that you'll get lucky. You could have bought the software easily by now with the $$ you've thrown away.

 

[wbas1]

Replacing things without testing them doesn't tell you that the system is working. Did you check the wiring and the output of each sensor before / after replacement? The diacom makes it easy to see if the sensors are actually sensing... I think it's pointless for you to keep throwing parts at it hoping that you'll get lucky. You could have bought the software easily by now with the $$ you've thrown away.

You are 100% correct. I am still trying to get someone to look at the boat.

 

[wbas1]

ok - I would think all those sensors are working because I can rev it up 4K in neutral without any issues

 

[alldodge]

Reving doesn't mean anything other then the motor can rev that high

We keep coming back to the MAP
What is the part number of the MAP?
When you say your unplugging the MAP, is that electrical connector correct?

Have we checked the 5V reference at the MAP, Gray wire to Blk/Pink to see if its exactly 5V

 

[wbas1]

Reving doesn't mean anything other then the motor can rev that high

We keep coming back to the MAP
What is the part number of the MAP?
When you say your unplugging the MAP, is that electrical connector correct?

Have we checked the 5V reference at the MAP, Gray wire to Blk/Pink to see if its exactly 5V

I will double check over the weekend. I have done so many tests I forget. If I am correct I get very close to the 5v

 

[wbas1]

alldodge - I cannot thank you enough for hanging in there with me. We will get to the bottom of this.

 

[wbas1]

This is what I have on the boat right now for the map.

RPS MAP Sensor TMAP 4.3 5.0 5.7 Mercruiser 885165 Volvo Penta 4.3 6.0 5.7 gi gxi 3859020 3858987​

 

[alldodge]

That's the right one

Measure this while running
MAP pin 1 and 3 to see what the Temp volts show
MAP pin 1 and 4 to see what the Pressure volts are

At WOT 1 to 4 should show 4.5 or so volts, and idle should be 0.5V

Also check TPS pin B and C to see position
Same voltage readings for TPS as MAP
EDIT: TPS can be checked with motor not running just ignition ON

 

[wbas1]

That's the right one

Measure this while running
MAP pin 1 and 3 to see what the Temp volts show
MAP pin 1 and 4 to see what the Pressure volts are

At WOT 1 to 4 should show 4.5 or so volts, and idle should be 0.5V

Also check TPS pin B and C to see position
Same voltage readings for TPS as MAP
EDIT: TPS can be checked with motor not running just ignition ON

When testing the MAP at WOT, should I be in neutral?

 

[alldodge]

When testing the MAP at WOT, should I be in neutral?

No, Need to see what its doing under load

 

[wbas1]

That's the right one

Measure this while running
MAP pin 1 and 3 to see what the Temp volts show
MAP pin 1 and 4 to see what the Pressure volts are

At WOT 1 to 4 should show 4.5 or so volts, and idle should be 0.5V

Also check TPS pin B and C to see position
Same voltage readings for TPS as MAP
EDIT: TPS can be checked with motor not running just ignition ON

Here are a few updates while in gear at idle. I could not get out today due to the wind.

MAP
Pins 1 and 3 = 5 volts at 1k
Pins 1 and 4 = 1.5 volts at 1k

TPS - key on not running
B and C = .6 volts at closed throttle
B and C = 3.9 Volts at WOT

 

[alldodge]

The TPS should be 4.5V at WOT. Disconnect the linkage and see if you can get it to increase. If it will go up to 4.5V then check into the throttle linkage as to why its not moving that far