350 Mag MPI chugging at higher rpms

[chopper_bob]

Hello (again),
2013 Monterrey 244FS with 350 Merc BIII. Has 155 hrs, 100 hr service done last year. Stored on lift in Jax, FL. Fuel stabilzer added before our mild winter and ran a few times during that time. Took her out yesterday, started up fine, ran fine for about 30 mins. Then she’d start chugging while at half throttle cruise and guardian mode would kick in. Back to idle, went away. Ran up again and same result, at random intervals and mid to high rpms only. In idle I can rev the motor up, couldn’t get it to happen. Temps pressures seem fine. Sounds like fuel starvation issue. Snapped a pic of my Block pressure at 1600rpm shows 130psi? Is it that high normally?
So I’m thinking fuel/water filter first. Fuel pump?
I did have a battery die over the winter, replaced it suspected a bad alternator, but it’s holding 14v while running. Could a bad alternator cause a plug not to fire???
Any other thoughts/ suggestions?
Thanks in advance!

 

[achris]

... Snapped a pic of my Block pressure at 1600rpm shows 130psi? Is it that high normally?

If 'block pressure' means water pressure, hell no! (usually maxes out at about 15psi)

..Any other thoughts/ suggestions?

Water pressure sensor in the power steering cooler. Common failure point.

Chris....

 

[Bondo]

Sounds like fuel starvation issue.
So I’m thinking fuel/water filter first.

Ayuh,...... Welcome Aboard,...... Dump the fuel filter's contents into a clear jar, 'n check for anything but clean fresh gasoline,......

 

[chopper_bob]

Thanks for replies. New filter ordered, checking what comes out of existing one this week.

l'll inspect pressure sensor, just replaced it less than 30 hours ago...

 

[alldodge]

l'll inspect pressure sensor, just replaced it less than 30 hours ago..

Maybe the senor plug became disconnected

 

[chopper_bob]

Maybe the senor plug became disconnected

Update. I checked fuel filter, cleaned flame arrestor, all fine. Turns out I think the chugging I get is the guardian mode kicking in and pulling back motor. So, it runs fine, accelerates fine, then guardian mode kick in and doesn’t give me a reason why on screen. Various rpms it kicks in randomly, but allows me to get right back on plane after idle.
So, what is causing guardian mode to kick in? Bad sensor somewhere?

I ran the poor mans test for codes using mulitimeter with continuity setting and all I get is a sold tone. (Theres a YouTube video how to do that), so no codes.

Again, my block pressure gauge shows 45-50 at idle and 150 or so up on a plane. I swapped in THREE pressure sensors, all same reading. Am going to hook up round dial pressure gauge and test it also.

Bad sensor somewhere? Bad computer?

 

[chopper_bob]

Also, what’s the normal running oil pressure range for these motors, up on a plane, I’m getting close to 70 psi, gauge maxes out at 80. 70 seems high...checked oil level, normal range.

 

[chopper_bob]

Here’s a pic of my IDLE block pressure.....

 

[Earl Cordova]

There are a lot of things that can kick in guardian mode.
I used to take mine into the dealer to read them,
but found a guy on eBay about 8 years ago selling refurbished Mercruiser code readers.
My dealer was speechless when I told him I had purchased one.

 

[chopper_bob]

Swapped three water pressure sensors in/out, same reading.

 

[Searay205]

If its a catalyst motor could be anything. Do you have access to a Rinda diagnostic tool?

 

[chopper_bob]

If its a catalyst motor could be anything. Do you have access to a Rinda diagnostic tool?

No, I’m having a mechanic come take a look and run codes. I read on other sites, that hit pressure may be restriction downstream of pump. So, I’m gonna pull tstat housing and look in there next.

 

[achris]

Even completely deadheaded, those pumps will struggle to maintain 25psi. If your reading anything higher than that, it's a gauge/sender problem.

 

[chopper_bob]

So, whats the flow of information for water pressure? Sensor sends info directly to gauge or through another part? Does the guardian mode read directly off pressure sensor or gauge? Is a faulty gauge kicking guardian mode on?

Because sounds like next step is swap gauge itself.

 

[chopper_bob]

Even completely deadheaded, those pumps will struggle to maintain 25psi. If your reading anything higher than that, it's a gauge/sender problem.

I’ve swapped THREE sending units, all read high. My gauge cycles between different sensors when selection buttons are pressed. I can read block press, trim, water temp, block temp, mpg, hrs, volts, etc all through my rpm gauge display. So, I’m not sure it’s a gauge issue.

 

[alldodge]

Need to scan the motor for codes

My thought is there is a sensor wire which is disconnected

Gray to B-21 (Ground)
Dark Blue/White to B-11 (Sense)
Black/Pink to B-1 (5V)

 

[achris]

Need to scan the motor for codes

My thought is there is a sensor wire which is disconnected

Gray to B-21 (Ground)
Dark Blue/White to B-11 (Sense)
Black/Pink to B-1 (5V)

That's where I'd be heading. I'd be checking that the ground wire for the sensor is still 'ground'. But don't get caught. Sensor ground (also called '5V ground') is NOT engine block ground. You need to open up the engine loom and find the junction of those ground wires (it's called 'splice 101').

Do you have 2 sockets on your engine computer or 3? (ie, is it an ECM555 or a PCM555?)

Chris.

 

[alldodge]

Instead of opening the harness, I would check at the to the PCM connector pins as listed

 

[chopper_bob]

That's where I'd be heading. I'd be checking that the ground wire for the sensor is still 'ground'. But don't get caught. Sensor ground (also called '5V ground') is NOT engine block ground. You need to open up the engine loom and find the junction of those ground wires (it's called 'splice 101').

Do you have 2 sockets on your engine computer or 3? (ie, is it an ECM555 or a PCM555?)

Chris.

Ill have to check on ECM or PCM. So, check the ground Gray to B-21. I have a guy coming with scanner. Thanks for replies.

 

[chopper_bob]

Now I’m thinking guardian mode is kicking in because of another reason, TRIM POSITION.. I’m gonna check both trim limit switch and trim position indicator switch, I read they can get corroded. Makes sense, chart says HI or LOW limit/continuity will enable Guardian CONSTANT horn. Worth a shot. Theyre the originals from 2013.
Moderator, I snaked off this thread title to another thread as to not be misleading with my problem. If you all want to close this thread and I’ll post my findings on my other thread which I think is more correct with my issue, guardian mode kicking in with no other indications. My apologies. Thank you all.