Mercrusier 350 MAG MPI - RPM issue under a load

[alldodge]

Those screen shots are F'd up
The first one shows
coolant temp 145*
Manifold air temp 127*

 

[wbas1]

Those screen shots are F'd up
The first one shows
coolant temp 145*
Manifold air temp 127*

yeah I was just looking at that also. I saw him take the screen shot while the boat was at idle. I guess another well qualified mechanic. OMG!!

 

[wbas1]

Those screen shots are F'd up
The first one shows
coolant temp 145*
Manifold air temp 127*

should they at least be close if not the same?

 

[alldodge]

Actually the 145* may not be bad but there is no way the air temp is 127*

 

[wbas1]

Actually the 145* may not be bad but there is no way the air temp is 127*

why not, it is hot in NY. LOL it is a dry heat.

 

[alldodge]

ok NY Dry
AZ road rash

 

[wbas1]

ok NY Dry
AZ road rash

Just so I know, what would be a correct temp for the manifold air temp?

 

[alldodge]

Should be real close to outside air temp. So at 127 I would be looking for the guy with horns

 

[wbas1]

Should be real close to outside air temp. So at 127 I would be looking for the guy with horns

I needed that good laugh.

Should be real close to outside air temp. So at 127 I would be looking for the guy with horns

would this be the map sensor giving this reading or another sensor?

 

[alldodge]

Yes but its a MAPT which is a manifold air pressure and temp

 

[wbas1]

Yes but its a MAPT which is a manifold air pressure and temp

Just so you know, those readings where taken after we took the boat for a ride. Not sure if that makes a difference.

 

[alldodge]

Pic shows it was idling, so air was being sucked in, right?

 

[wbas1]

Pic shows it was idling, so air was being sucked in, right?

Correct.

 

[wbas1]

i just spoke with my mechanic about the reading on the TMAP and he said that is a normal reading. He said it is accounting for the air intake temp & the block temp.

 

[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

View attachment 366203

what does RTN 5V mean in the diagram?

 

[alldodge]

The 5V return is the ground side of the ECM reference voltage. Battery ground and 5V return are not the exact same

 

[wbas1]

The 5V return is the ground side of the ECM reference voltage. Battery ground and 5V return are not the exact same

do you think I should check the fuel system to confirm that nothing is being blocked? I was going to have someone test the injectors. i was thinking to start at the injectors and work my way back to the tank.

 

[alldodge]

I thought you already tested fuel pressure and it was correct and stayed there thru the full RPM range.

Having injectors cleaned and flow tested is never a bad thing other then the cost of having it done. If this is done you want it done by a place that does marine injectors and not autos. Marine run at and above 50% most the time, and autos rarely run up to 50%

 

[wbas1]

I thought you already tested fuel pressure and it was correct and stayed there thru the full RPM range.

Having injectors cleaned and flow tested is never a bad thing other then the cost of having it done. If this is done you want it done by a place that does marine injectors and not autos. Marine run at and above 50% most the time, and autos rarely run up to 50%

Yes the fuel pressure stays at 40 pounds at idle end at wide-open throttle. I am pretty much grasping at straws right now

 

[alldodge]

I'm right there with you

There is a guy on OSO goes by Articfriends (Smitty) that is probably one of the best at testing injectors