2004 5.0 mpi ecm555 fault pitot low power revs to 3k and pulls down to 2.2k

[Cruisingjoe]

2004 mercruiser 5.0 mpi ecm555 fault pitot on smart craft guage on port engine- no buzzer sound but has AL on main guage and fault pitot on rpm guage of port engine

Engine first revs to 3000rpm then starts to drop to 2200-2400 . Fluctuates back and fourth

Not sure if the pitot is placing engine in guardian mode

Things replaced and checked so far
Rotor and cap. 1 screw was missing from rotor (ugh)
TPS sensor checked through range
IAC ohm's good
Cleaned spark arrestor (dirty)
Oil is good
All smart craft gauges show good quality readings

What should I do.. Ugh

 

[Bt Doctur]

thinking the water pressure sensor located in the p/s cooler

 

[Cruisingjoe]

What I don't understand is if it says fault pitot (meaning water pressure sensor why do both engines say 36 psi water pressure for the port(limp mode engine) and 33 psi for the starboard side which does not have the fault code that is coming up on the smart gauges

 

[muc]

Pitot fault is a problem with the speedometer sensor, but that sensor is usually on the starboard engine.
Suggest connecting a scan tool and see what's going on.
A pitot fault only triggers guardian if there is a problem with the 5 volt reference.

 

[cdiamond]

I'd say Bt Doctur hit it

36 psi is way high

the ecm will interpret that as a problem

 

[Bt Doctur]

With all the BS on these engines I would find out the ohm`s reading for a non-alarm condition and go to a electronics store and get some resistors to put in the circuit. and just replace my impellers at the first sign of a temp rise.
I would think flow is more important then pressure

 

[Cruisingjoe]

These engines are absolutely ridiculous..

On the smart gauges does it tell you if its in guardian mode?

 

[muc]

My guess is that the symptom you have (surging) isn't related to the fault you are seeing on the smartcraft gauge. When guardian kicks in, it just reduces power output. It is very rare for it cause RPMs to fluctuate.

You should check fuel pressure under load while the problem is occurring and scan the engine to check for codes and view operating parameters.

 

[Cruisingjoe]

That's what I am thinking thankyou

 

[Cruisingjoe]

So now it's not the Fuel, TPS, IAC, injectors. Good compression. Ecm was swapped, One was leaking at idle but I think that it was stuck, going to send them out to get cleaned. No faults logged in computer and all parameters seemed good. As a merc tech swapped parts from engine to engine.. Not going into guardian mode.
Now what should I look into doing
1) never checked fuel pressure under load, could that injector force air into the fuel rail causing it to drop rpm?
2) oil pressure sending unit, can you unplug and engine will run? So I can test if that is failing at rpm?
3) does a sea ray have like a check valve in the exhaust so water cannot push back into the engine?
4) possible crank bearings? And how would I know. Turn over engine with a wrench?
5) vacuum test, maybe a intake manifold air leak?

Last but not least drive train where it couples, if there is a bend or something faulty, could it cause enough vibration to pull down the rpm? I know rotational force outward on a shaft, gear, pully, will In turn pull rpm down tremendously. Once again thankyou guys for your help!!:

 

[Cruisingjoe]

Any possible helpful suggestions?

 

[Fun Times]

Flow testing/cleaning the injectors is a good idea....Even if it isn't the problem, it's still good to have them done while looking for hard to find problems such as this.

Have you cleaned the throttle body and flame arrestor?

Question numbers,
1) You'll absolutely want to check the fuel pressure under load/under way during the event....Many things change from idle to quick engine revs while in neutral gear compared to in gear under load RPM.
Your question # 3 about a valve reminded me that some (not all) Sea Ray's use a fuel valve called a Parker Skinner Fuel Solenoid. The following link has some good info about it along with some photos of it installed. So look for that on your boat just in case. http://clubsearay.com/showthread.php/23308-Parker-Skinner-Fuel-Solenoid-Manual-Overide

2) No you can't unplug an MPI oil sending unit as you'll put the engine into a critical guardian mode that may force the engine to idle RPM. If the MPI oil sensor was a problem you should have different symptoms. Like mentioned by Muc, 'connecting up a scan tool' would also help take the guesses away with the oil sensor.
http://www.rinda.com/techmatepro/

3) Most Mercruiser engines have what is called water shutters located in the exhaust Y pipe. See item # 7 for a visual, http://www.mercruiserparts.com/Show...1681&bnbr=340&bdesc=Exhaust+System+Components

4) What has you thinking about an oil pressure problem?

5) How is the engine idle speed as it should be a pretty smooth 600 RPM.

6) Are you hearing or feeling any heavy vibrations during the event to give you an indication to consider something like this as something like this would be least likely to cause surging unless the knock sensor hears something to lower the ignition timing.

Maybe next time you're on the boat and the problem is occurring you could try posting a video of the problem as it might be somewhat helpful to see what you got going on there.