Hi,

So a bit of background to try help me find the issue.

boat a 2008 fountain 38 ec
2x 496HO with bravo 3X
cable shifters

So i bought a boat 12 months ago with out much history, except it had 2 new 3x drives. I decided to do some preventive maintence, i did the manifolds, annodes, and replaced the drip tray thing between the manifold. Afterwards there was a bit of difference in the performance of each engine(Rev wise with same throttle position). so i changed the sparks plugs, and fuel filters. ( no idea when last were done) they are running much better and even. I also had the double beep on one engine and code was for the IAC, i changed both of them and that was solved. now a new issue.

It now moves well up to about 4500 rpm, then the port engine has a constant alarm, and gives me 3 codes, one overspeed, one engine power limited, the other critical voltage., 133- legacy sensor supply A. This is only on the port engine. If i move port engine to idle, the alarm goes, and then i can power back up to around 4500 with out issue.

First question what is this sensor, and should i try replacing it, or is it likely something else is wrong? I sent a mechanic to scan it, but he gave me the same faults as what the smart craft gave me. he didnt really indicate any issue as at idle it is fine, and he didnt take it for a sea trial. suggested maybe some fuel additive, which i have used with no detectable difference, after one tank used and refilled.

I ve also changed all the circuit breakers, has new batteries, new belts, and will likely do the raw water pumps after the summer here. Pressure and temps are good. and it moves well up to 4500.

How are the grounds, are they all corrosion free, greased and tight?

Also, just because you have new batteries doesnt mean there wasnt a draw and draining it down. Check the voltage with a tester. Once they go below 12 volts my 496's do some crazy schit.

What additive did you use? Last year I chased a bad fuel issue and ran Starbrite fuel enzyme and Lucas fuel injector cleaner with great results. There is a lot of fuel in the fuel rail and system, it takes a while to use all the residual.

Probably wouldnt hurt to touch base with BUP and have the injectors cleaned too.

I believe the code 133 is referring to the 5 volt sensor supply, It can get tricky to find which sensor is the problem. They are all connected to the same 5 volt reference supply so it could be an unrelated sensor coursing the volt drop.

If you are close to the Dallas Texas area I am in town for the next 2 weeks, code 133 is not singling out one sensor. Its the 5 V reference power Low -- excessive current draw on the 5 Volt circuit --

Watch out what you do here because you can spike back to the PCM and hurt the PCM internally. The 496 PCM 555 really hates incorrect voltage and extremely HATES VOLTAGE spikes. The same goes for ECM 555. I am just giving you heads up here to help.

I have said a bunch and even up here. TIP for whomever about -----

Guardian MODE

the best thing one can do with this = low rpms nor can not achieve full WOT RPMS is scan the engine and LOOK AT AVAILABLE POWER %. If available power is showing 100 % = THEN ONE IS NOT in GUARDIAN MODE. - if available power is showing anything less than 100 % guess what ONE IS IN GUARDIAN MODE.

From the scan testing thru out RPMS -- with that said if you have 100 % available power showing and you have NO FAULT CODES - all parameters are within in spec but still can not reach full WOT RPMS.

FUEL pressure testing
compression testing
spark plugs and other ignition related parts check out and or changed if bad

if all that tests good even with new parts changed, then 9 out of 10 times I am going to the FUEL INJECTORS --- ESPECIALLY for all 496 apps and or all apps that have the GEN 3 cool fuel system and the Volvo Penta -- Carter cool fuel system. .

This post is directed for all MPI / tbi marine engines and the ecm s that display available power from the scan

Available power % in a scan is a good indicator to be monitoring at the very least a couple of times per year or when WOT rpms is lower than spec.

I charged up the batteries with the shore power, i will recheck the earths, but maybe wrongly assumed if an earth issue it would be on both engines? Will start with this,

Unfortunately i am about 16000miles away in Auckland New Zealand otherwise i would take you up on your offer. Point heard about the PCM, I guess i start with the earths and work back. for me its strange it doesnt have a voltage issue below the 4500k rpm.

Batteries have nothing to with what your getting, your system has a 5 volt reference power supply to the sensors, the sensor maybe a pull up or pull down in voltage. The varying voltage is then sent back to the PCM, somewhere in your system you have a sensor going bad for what ever reason it's pulling voltage from the 5 volt reference supply (probably a short) it could be the trim sensor shorting and pulling the 5 volt away from the other sensors.

Thanks Camalot.

As there is a few sensors, any most likely ones i can start with? Would a scan during actual time indicate which sensor? I could take the mechanic for a ride while he is plugged in, if that will help isolate the sensor going bad.

Seawater pressure
CPS Crankshaft position sensor
Paddle wheel sea water temp
TMAP Temp Manifold Air Pressure
TPS Throttle position sensor
Oil pressure sensor