Mercrusier 350 MAG MPI - RPM issue under a load

[nola mike]

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.

That doesn't make sense to me. Map temp should be exactly the same temp as what it is measuring, plus maybe a bit because of increased under cowling temps. Some auto pcms will lower fuel charge to account for lower air density at higher temps, though I think that that's more heavily weighted in systems relying on MAFs. And does the boat still have more power with the map disconnected? And it acts the same with both the 6.2 and 5.7 pcms, right

 

[wbas1]

That doesn't make sense to me. Map temp should be exactly the same temp as what it is measuring, plus maybe a bit because of increased under cowling temps. Some auto pcms will lower fuel charge to account for lower air density at higher temps, though I think that that's more heavily weighted in systems relying on MAFs. And does the boat still have more power with the map disconnected? And it acts the same with both the 6.2 and 5.7 pcms, right

The boat still had more power with the TMAP disconnected. When I had the 6.2 ECM on the boat and disconnected the TMAP it had more power all the time. Now I have the 5.7 ECM and when I disconnect the TMAP, most of the times it has more power but I have noticed that other times it POPs alot. Since I have the 5.7 ECM on, I have the acceleration at idle where before with the 6.2 ECM I did not. It had hesitation.

 

[nola mike]

The boat still had more power with the TMAP disconnected. When I had the 6.2 ECM on the boat and disconnected the TMAP it had more power all the time. Now I have the 5.7 ECM and when I disconnect the TMAP, most of the times it has more power but I have noticed that other times it POPs alot. Since I have the 5.7 ECM on, I have the acceleration at idle where before with the 6.2 ECM I did not. It had hesitation.

If you're positive that this follows Pcms and it's reproducible when you disconnect the map, then this has to be an information problem to the PCM, right? But you need to be sure that it's reproducible (most of the time... Other times makes it seem like it's not) What's wot rpm when it's running well? Difference between the 2 PCMs?

 

[wbas1]

If you're positive that this follows Pcms and it's reproducible when you disconnect the map, then this has to be an information problem to the PCM, right? But you need to be sure that it's reproducible (most of the time... Other times makes it seem like it's not) What's wot rpm when it's running well? Difference between the 2 PCMs?

Both ECM's let me get to about 4k with the TMAP pulled. I reproduced it with the mechanic on the boat. The 5.7 ECM makes the motor run better and according to Mercury, they did not recommend putting the 6.2 ECM back on.
I am coming to the conclusion it is a communication issue to the ECM.

 

[alldodge]

I remember that the boat use to go on plane with previous motor but;

it weights 6000 dry and loaded at least 7000 (fuel, gear people)

Example: MY old Rinker 4800 dry with 454 B1 had no issue coming up. Same boat with 350 B3 had trouble.

My 9000 dry cruiser with 415hp 502 B3 2:0 ratio 22Pitch had trouble getting up. Repowered with 530hp and changed ratio to 1:81 22P and it had trouble. Changed back to 2:0 and had to go up to 26P and it does ok

 

[wbas1]

I remember that the boat use to go on plane with previous motor but;

it weights 6000 dry and loaded at least 7000 (fuel, gear people)

Example: MY old Rinker 4800 dry with 454 B1 had no issue coming up. Same boat with 350 B3 had trouble.

My 9000 dry cruiser with 415hp 502 B3 2:0 ratio 22Pitch had trouble getting up. Repowered with 530hp and changed ratio to 1:81 22P and it had trouble. Changed back to 2:0 and had to go up to 26P and it does ok

Yes, according to the previous owner the boat was able to plan. I have a callout to him for some more detail.

 

[itsathepete]

Your pic shows throttle position sensor at 0% but throttle position voltage at 0.6V
TPS should read some % at idle I would think. Does the ECM use TPS voltage or position? Did you get a chance to check TPS reading at different throttle amounts?

 

[wbas1]

Your pic shows throttle position sensor at 0% but throttle position voltage at 0.6V
TPS should read some % at idle I would think. Does the ECM use TPS voltage or position? Did you get a chance to check TPS reading at different throttle amounts?

When I move the throttle to WOT the TPS voltage shows 4.3 volts. The ECM uses TPS volt readings from what I have learned

 

[alldodge]

Its working correctly

 

[nola mike]

Your pic shows throttle position sensor at 0% but throttle position voltage at 0.6V
TPS should read some % at idle I would think. Does the ECM use TPS voltage or position? Did you get a chance to check TPS reading at different throttle amounts?

Most/all 5v sensors don't operate at 0 or 5v (so somewhere in between) so that the PCM can tell if there's a disconnection/short in the circuit

 

[wbas1]

Most/all 5v sensors don't operate at 0 or 5v (so somewhere in between) so that the PCM can tell if there's a disconnection/short in the circuit

Not sure what you are trying to say?

 

[nola mike]

Not sure what you are trying to say?

Just that you wouldn't expect a reading of 0 or 5v on the TPS even if all the way open/closed

 

[itsathepete]

Just that you wouldn't expect a reading of 0 or 5v on the TPS even if all the way open/closed

I was just wondering if it read voltage or TPS%. Trying to isolate variables. Thanks

 

[wbas1]

I was just wondering if it read voltage or TPS%. Trying to isolate variables. Thanks

I will check it today and let you know.

 

[alldodge]

While it should read closer to 0.6V at idle, your not having any issues at idle.

 

[wbas1]

I was just wondering if it read voltage or TPS%. Trying to isolate variables. Thanks

The voltage with key on is .05V on the TPS

 

[wbas1]

While it should read closer to 0.6V at idle, your not having any issues at idle.

correct!

 

[wbas1]

Is there anyway to tell if the injectors are supplying enough fuel. I have tested the injectors and they are all working and seem to be supplying the same amount of fuel. I tested each one and when I send 50 pulses every 7ms they all drop about 7 to 10psi. I know that the difference between all injectors should only be about 1.5psi so 2 of them seem to be rich. In my case that would be a good thing. I am just not sure how to tell if the injectors are just not supplying enough fuel.
I know I have enough volume because when I disconnected the fuel supply to the rail and turned the key on to prime the system, it filled a small jar up.
It was like pouring gas from a 5 gallon container.
I am going to test again tomorrow because mercury says that I should use a pulse setting on my tester that drops the fuel pressure to at least half. The pulse I used did not drop the pressure enough.

 

[alldodge]

Is there anyway to tell if the injectors are supplying enough fuel. I have tested the injectors and they are all working and seem to be supplying the same amount of fuel. I tested each one and when I send 50 pulses every 7ms they all drop about 7 to 10psi. I know that the difference between all injectors should only be about 1.5psi so 2 of them seem to be rich. In my case that would be a good thing. I am just not sure how to tell if the injectors are just not supplying enough fuel.
I know I have enough volume because when I disconnected the fuel supply to the rail and turned the key on to prime the system, it filled a small jar up.
It was like pouring gas from a 5 gallon container.
I am going to test again tomorrow because mercury says that I should use a pulse setting on my tester that drops the fuel pressure to at least half. The pulse I used did not drop the pressure enough.

Unless you "really" know what your seeing and the test methods, you do not know what your seeing

Have a look at this thread and see if you can tell what Smitty is trying to convey
https://www.offshoreonly.com/forums...ctor-test-vs-another-claimed-replacement.html

 

[alldodge]

And more fuel doesn't necessarily mean more power