Bryan,

As I have been going through this same situation on the dyno, Engine going into "Safe" mode, the following items need to be checked:

1. Water temperature and temperature sender - Front of manifold

2. Oil Pressure and oil pressure sender. Near oil filter boss
on block

3. Knock sensor - Lower side of block, usually center of block

4. MAP Sensor - Rear of Manifold Plenum

A scan tool would be of great assistance, however, I am stil trying to trouble shoot my problem as the scan tool did not show any faults or codes.

I have a nice mechanical gauge on the end of my fuel rail and it reads 32 PSI at idle and 53 PSI at high RPM. I am running a supercharger, but the ECM is going into "safe" mode for some reason. Maybe we have the same problem. Check the above and post your results, hopefully someone will have a solution.

On 1 through 4, all look good, no codes, each sensor checked out on the voltage readings. A knock sensor is impossible to buy locally, I will have one Saturday, mine does look a bit beat, plus installation torque is key on them at 16 to 20 pounds per the manual.

I spoke to a master mech today who has done maitenance on my boat and he was surprised by this issue, he said the 4 ways it will go to Gaurdian/safe mode (OM series MEFI3 motors) can be eliminated by unplugging each one, one by one, all will be on a stripped wire. He said BE GLAD it is not a 1998 or late 1999 model, I might not have been so lucky!

For me, new water separator today, the winter was not good to the old one, full of crud, I also changed drive fluid today, why not at this point, I plan to take our mechanic on a boat ride Saturday, wish us luck.
This guy we are using now is Merc Cert but new to us, if we are not fixed Saturday she will go in the shop while I am gone for two weeks with our regular guy.

I would still like to see that manual page on the safe mode, email it to me.....

Tell us more about the set up and dyno????????

WHAT exhaust you running?

Thanks...
Bryan

What is the issue with 1998 and newer? Why would they be more of a problem?

Not sure why he mad that comment, maybe because they had different ECU's before 1999, I am surely the wrong person to ask. I was busy trying to gather applicable info to my situation.

There is always tomorrow!
Bryan

Any update? I'm heading to the dyno with a reptrgrammed ECM and a stock 454 ECM to try them both. I hate to say it, but I hope its the ECM, though more expensive, at least I'll have the problem fixed.

How was your ride with the mechanic, hopefully yours is something simple.

Let me know.

Kirk

No, waiting on the mechanic to boat test on the water, we will also install a new knock sensor, I will have data this evening.
Good Luck on the dyno.
Bryan

Guys, I remember back last summer someone had a similiar problem on OSO with a twin engine boat, and he found that by having the both battery switch that separates the batteries has to be on 1 for one engine and on 2 for the other engine. I don't remember the details but if the switch was turned on both, there was a feedback which affected the engines and lowered the rpm at top end. Wish I could find the thread.

Well, water test sucked, every sensor on the motor is in tolerance, we did find a few pins pushed back on the ECU connections, we are now leaning toward the ECU.
We splash again in the morning with a new ECU and extra sensors and a merc dash unit that will plug into my dash harness to take my dash out of the loop, pretty neat.
Fuel pressure was 42 on top and strong, did not leak down when key was shut off either.
Timing was advancing correctly.
Compression remained good.

What keyed us on the wiring harness was when we moved the merc comp to the other side of the engine bay the motor returned to normal.

My motor is NOT going into the safe/limp mode. She just runs lik **** at 3500 rpm to 4000 and put the motor in some funky mode.

He said IAT normally has a number close to something, and when the condition arrises IAC shoots sky high.

More tomorrow. Bryan

Sounds like you have the right tools and mechanic looking at your engine.

I just returned from the dyno, tried the new ECM, same results.
Tried the new 2 bar MAP sensor, same results. Unplugged the knock sensor, same results.

Engine runs up to any RPM you like and when you hold it there for 20+ seconds, the motor starts seems to lose power and then you can watch the EGTs decrease dramatically. Bring the throttle back to idle and it clears up and is ready for another run.

Is there anything mechanically that could be causing this? I've been advised to do a pressure test on the block to verify that at high RPM, the higher water pressure isn't leaking into the cylinders.

Since I'm now grasping at straws is there anything else that would potentially cause this? Anything you can come up with I will check, this really sucks!

Man, we do sound to have a similar issue, my deal was she ran fine before winter so we doubt anything big internally. The mechanic explained that you should hold the wires to plug the ECU in vice the plug, and he called it, several pins pushed back, which he corrected.

I do think it is something simple, if we can just find it.
I am now HOPING that the ECU is bad, just so it will be fixed.

Funny, he said today this problem is now "personal."
We launch again at 8am on Easter, I hate to miss church but that is life. Boating is our weekly family pastime and very important to the whole family.

Keep us posted on your data and I will too.
I did not mean to take over this thread it just worked out that way.

What is your IAC and IAT numbers, my IAC was haywire at 18, the new is 0 and she will start fine and idle smooth.

Bryan