I just joined the Forum. Thank you.
Have twin 377, 320 horsepower engines

Took the boat out this morning and when I powered up it went into Guardian mode. Oil pressure and water temperature sending gauges are normal. Water PSI is at 15. Scan the engines and there are no fault codes. Check the engines switches at the shifter mechanism. Both are good.

Any ideas? Thanks Terrie...

how do you know you are in guardian mode ? water psi at 15 ? at what rpm ? - if that is 15 psi at idle then you have a problem.

No fault codes can be IAC alot of the times. You have the find the issues that knocks out the IAC. alot of times its lack of maintenance that causes IAC failure and if ran too long with IAC issue it can knock out the ECM / PCM - IAC circuit side of the ECM / PCM - I know cause I have a PCM in as we speak that The IAC circuit in the PCM is gone.

Thank you for your time in the reply. When throwing up I reach 4000 RPM and then went to throttle back the 3500 me alarm came on. I started to lose power. Brought back to idle and the alarm went off.
Both engines seem to run fine at 1000 RPM.
While I was throttling up, the sea pressure went to 15 psi before the alarm went on.

The IAC on the starboard engine was changed out because it was surging. The change out seem to fix that problem

Like throwing darts without a scanner. You need to borrow or buy one from Rinda Technologies Inc. Marine and Industrial Engine Diagnostic Tools or the like.

Sydwayz, if you read the introduction, you would see the engines were scanned and revealed no faults.

Yes I seen it but he missed it. Honest mistake about what was missed from first post.

I still stand behind my post. And how did you verify that you were in Guardian Mode ? it is done using the scan tool with that said can you verify that end of it ?

And I will say IAC but search how to do the proper install

BUP, how we know it went into Guardian mode is because the Stbd engine lost power. As we said yesterday the scanner revealed no fault. BUT TODAY hooking the scanner up, it revealed fault 326 - Guardian manifold temperature (to hot) and fault 9 Guardian active. Not sure why the scanner didn't pick up yesterday's fault.

Now we installed new manifolds and risers on both engines along with thermostats. No problem with the port engine. Yesterday was the maiden voyage with the new manifolds. The temperature gauge reads 165°F on both engines. Today we removed the check valve on the bottom of the starboard engine, port side manifold thinking that there was debris blocking the check valve. Nothing wrong with the check valve.

From scanner,
Stbd ECT........ 160°
Port EMCT......225°
Stbd EMCT.....225°

When we were running at 3500 RPM for about 1 minute yesterday, the water pressure was 15 psi taken off smart craft. Again no warning from smartcraft until this morning. Very Weird.

being that we have 15 lb PSI water, I'm rolling out impeller. I'm stumped now

where is your location ? and Guardian can be found so easily on a scan thru available power % If avalable power is anything less than 100 percent --- ONE is in GUARDIAN MODE. The lesson for today and good tip to follow. If one reads on the scan and its showing 100 % availible power --- ONE IS NOT IN GUARDIAN MODE.

You are located ?

The Rinda scanner and the like are not only used for scanning stored codes. You can read active data. You can reset the Guardian mode, and then run the engine watching the live data, to see where the anomaly may arise, and how/when it goes into Guardian mode. I didn't miss it. All I was stating that you can't just scan it once. It's a troubleshooting tool.