5.0 amercruiser mpi has alarm and low power

wpowell323

Petty Officer 3rd Class
Joined
Mar 29, 2009
Messages
75
I am getting the 2 beeps per minute alarm and the boat will go into guardian and reduce to 90%, but the actual power the boat normally has is also off. I has a hard time planing and takes forever to reach 4000 Rpms.

I changed the IAC and nothing changed. I changed the pitot sensor and nothing changed. The tps is in volt range on the DDT, the map sensor reads 18.0 at 4000 RPMS. I know checking this motor with the DDT is not ideal, but that is all i have access to. With the loss of power I am thinking it would be one of these things, but they all seem to be in spec. Looking for some insight before i just go buying parts.

the motor is a 5.0 mpi serial number OM692020
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 5.0 amercruiser mpi has alarm and low power

What trouble codes are being set? Among MANY other things it could be the water pressure sensor... Just throwing parts at it is only going to cost you money... You need to know the trouble codes...
 

wpowell323

Petty Officer 3rd Class
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Mar 29, 2009
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Re: 5.0 amercruiser mpi has alarm and low power

no codes show up on the DDT and i don't have access to a CDS. the only thing i see in the ddt is the block PSI seems low. It is about 5-6 psi at 3500 rpm's. I replaced the MAP, TPS and Pitot with no change. Luckily i have another boat with basically the same motor to rob parts off of, so it hasn;t cost me anything so far. Guess i am going to try the cam position and the oil pressure switch. Those are the only 2 things I see in the mercruiser manual that are left that will cause 2 beeps and 90% power. Any thought or tips or suggestions would be greatly appreciated.
 

Fun Times

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Re: 5.0 amercruiser mpi has alarm and low power

the only thing i see in the ddt is the block PSI seems low. It is about 5-6 psi at 3500 rpm's.Those are the only 2 things I see in the mercruiser manual that are left that will cause 2 beeps and 90% power. Any thought or tips or suggestions would be greatly appreciated.
Low water PSI can cause this as well, You'll want to get the water psi back up first.;)

There is a sensor on the power steering cooler near the rear of the engine.

Merc part number 8818793 has superseded to 8M6000623, SENSOR, Power Steering.
 

Don S

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Re: 5.0 amercruiser mpi has alarm and low power

Here is a worksheet that may help us find your problem. Print it out, take your boat out with the DDT connected and fill in the information. Then scan it and post your results.

The second form shows how to get to the fault codes, and fault history. Need that info as well.
 

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wpowell323

Petty Officer 3rd Class
Joined
Mar 29, 2009
Messages
75
Re: 5.0 amercruiser mpi has alarm and low power

i will try the chart and the DDT trouble shooting. Any idea how to get block PSI up? i switched the water pressure sensor on the cooler tube hoping it was just a bad sensor, but the numbers are still low. I have seen other people post that putting a ground wire on that sensor sometime helps with getting an accurate reading. Have you ever heard of this? The sea water pump is new and everything seems to flow properly. Are there any obvious causes for low block PSI? would 5 pounds at WOT throttle cause it to go into guardian despite themotor is running at 160 or below? I get an alarm as soon as i take off and i notcied the last time I was out one of the codes was low block psi and it read only 1.9 lbs at Idle, but it did not show a fault at higher speeds desite the reading we only around 5 psi. The only other thing i have noticed is the oil pressure seems high on the DDT. At what point would the guardian activate for high oil pressure? maybe the oil pressure sensor is sending a faulty reading to the computer?
 

Don S

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Re: 5.0 amercruiser mpi has alarm and low power

That water pressure may not be your problem. You don't have an overheat do you?
High oil pressure is also not your problem.
 

muc

"Retired" Association of Marine Technicians...
Joined
Jul 7, 2004
Messages
2,064
Re: 5.0 amercruiser mpi has alarm and low power

I see that Don S posted a nice flow chart for the DDT

I think you need to spend more time with the DDT, it will give you the info you need.
When no faults show up you need to look at history --- what does it say?

Long time since I used a DDT but I think you go to.
History than
Fault History than
Fault Seconds

This area will most often tell how long and why the engine was in guardian.
Or you need to watch the DDT in Data Monitor while the problem is happening.
 

Don S

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Re: 5.0 amercruiser mpi has alarm and low power

Have you checked your impeller and raw water pump lately? If the pump is weak, you won't have good pressure. Those impellers should be replaced at least every other year.


From the manual.

The seawater pump sensor measures water inlet pressure or water block pressure. It is
located at the seawater pump inlet hose. Normal pressure ranges are 7-34 kPa (1-5 psi) at
idle and 48-117 kPa (7-17 psi) atWOT. To check if sensor is within range, the diagnostic tool
reading with key ON should be approximately 0.
A malfunction of the seawater pump sensor will set the fault of Seapump CKT Hi, Seapump
CKT Lo or Seapump PSI Lo.
 
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