CC247

Port engine 2004 6.2 mpi has developed a stalling condition at any rpm except wide open. It will restart no problem no codes and when it does stall the alarm does the self test beep and the fuel pump primes like turning on the key. Replaced the iac,ecm,oil pressure, check all connections from key to relays, grounds cleaned up.and it'll run fine for miles at 3500-4500rpm then come off plane and then stall, restart, stall, restart. Would guardian mode kill an engine if it see's an issue or just pull power like limp mode?Thanks

BUP

iTrader: (9)

who scanned the engine ? no faults at all ? whoever scanned your engine did they understand all the parameters and if they were all in specs ?

Did the scan say available POWER 100 % if so NO guardian was ever active. If it said any less than 100 % available power then yes guardian could have been active.

Do you have any alarms going off while running or just before the engine stalls. If so what type of alarm ? solid horn or beeping ?

Possible the problem as for things to check / change / fix

Do you have the shift in gear switch for your app ? It was introduced right around the 2003 / 2004 timeframe. This could be very well your problem. Bad shift in gear switch or loose connection or the switch is out of adjustment

HVS is not phased correctly needs to be clocked / phased properly. Has this been removed or adjusted ? Timing is NON adjustable on all ECM & PCM 555 for Mercruiser so if that has been moved or hold down clamp loose then HVS is off phased..

Bad or corrosion HVS cap and rotor - white powered or moisture / water droplets under the HVS cap & rotor

Spark plug wire(s) arcing off the engine or around the ECM 555. .

BUP

iTrader: (9)

Follow this Mercruiser SB. And as to what I was talking about to.

http://www.marinemechanic.com/merc/d...fi-nostart.PDF

CC247

Bup, Hi, first off thank you for responding to this. The scanner I used was just a code scanner outdated rinda. I'll answer questions in order, I have no alarms while the engine is running. When I turn my key to the run position, from off, I get a single beep to let me know the alarms are active and at the same time I can hear the fuel pump prime. Then I turn to crank and engine fires. That's my normal sequence for starting. What is happening is the engine while running will cut out and then go through the alarm then prime. I can then start it or sometimes it happens fast enough that it will catch it self and keep running.If I try to duplicate it by turning the key off then on I'm not fast enough to catch it. Seems like it's losing 12volts at the key switch for 1 second. But I've watched voltage at the switch, coil, ecm relay, lanyard switch is bypassed for testing only.
I've read the service bulletin before and that'd not my symptoms. Plus my serial # OM685 is out of that date range. My engine starts easy everytime, has a new cap and rotor, replaced 2x to be sure. Engine will run right to 5k and stay there with out a hiccup. Then I come down to 3k and sometimes it'll die. Sometimes it'll take a while then act up. Last night on the hose it would died within 2 minutes of idling. Going to check the alternator now, maybe a voltage spike taking out power.

BUP

iTrader: (9)

A VERY tough problem to even understand and really to follow. I can not believe it will never happen at full throttle ? never ? If never ever then I am not convinced 100 % it is mainly a voltage connection / wire problem ONLY.


But your problem happens at every rpm and throttle setting below what - 3/4 throttle setting. and at idle running on the water hose.

I would check with a volt meter then if it is happens on the water hose battery voltage even when the engine dies because you still should have 12 to 13 volts when it stalls completely with good a strong battery and a proper charging alternator.

What is battery voltage when the engine is running and when it stalls ? Check that 1st.

I would check all battery connections follow them to starter or battery selector switch - follow all ground cables make sure it is tight and clean especially back side of the engine connections.

Make sure ORANGE wire to Alternator is tight and has a good crimped terminal and nothing looks like burned spots on the connection / wire / connector and back side of Alternator. This could be your problem but the full throttle running it never happens ???

key switch possible bad or is pig tail harness - check all wires under dash and crimped connections

Check main harness cannon plug for good connections and no corrosion in the male / female terminals

check main power relay and its circuit.

It would be hard to believe if your problem never happens at full throttle but at all other throttle settings for it to be a voltage connection / wire problem only. Just saying

Next is the HVS cap and rotor really do not follow problems under any serial # in the real world - they can go bad and cause some very poor engine running problems no matter of the year and or engine serial #. Just saying as an FYI.

CC247

Ya at wide open for a good 8-10 minutes runs great. Is the ecm capable of shutting down the engine if it sees a bad sensor? I read the other post you commented on about the same issues 6.2 mpi dies out. I've changed the cap and rotor 2x's in the past 12 hours still the same. Sorry the info I'm giving is all over the place, I know. I've pulled the wiring harness out and checked it from switch to cannon connector, all good. The alt charges 14.2 then drops 13.5 after a couple mins, then the engine rpm's drop about 200rpm for a split second then it dies, or will cough and start running ok like nothing happened. At the same time the alarm beeps once like it does when I turn the key to run, then the motor flares up to about 1200 for a second because the fuel pump is priming and the engine thinks it's starting for the first time . Whatever it is it's getting worse so I'm gonna a have someone with a laptop look at it. Again thanks for you info.

BUP

iTrader: (9)

man it almost sounds like IGNITION SPARK ARCHING off somewhere causing the problem. Not arching all the time but when it does, will cause that problem and the engine acts like nothing ever happened upon recovery. I would check spark plug wires and all related ignition related items.

Would like to know how the condition of the wiring back side of Alternator especially the orange wire and its connection.

CC247

There's not many hours on it 350 all the wires connectors are factory and clean looking. But I've pried a few suspect ones apart and they are good. I've just put a good known ignition coil/module in and going to test that tonight. Took the dist cap/rotor from other engine, but still did it. I know this is a different set up but some of the fords I work on all day have bad coils and sometimes they will fire back voltage to the pcm. ? Idk, just kinda throwing darts at this point. The alt is charging and load tested fine.

lakematdude

Since you have two engines, One at a time try swapping the crankshaft sensor, the main power relay & fuel pump relay at the top of the engine then the ECM to see if the problem moves to the other engine.

Captain YARRR

Working on exact same problem. I switched everything. Relays, IAC, ECM, CPS, coils, fuel pumps, MAP, took off flame arrestor, main harness plug on good, checked cap and rotor, Same problem all around.

I feel like the two fuel pumps on engines sound different. Put the known good fuel pump on the engine giving trouble and it just doesn't sound as strong as the other. But the voltage coming from the lead is 13V.

Running on the computer, I see that the timing is jumping around pretty crazy when it starts to die out. I see that the ignition voltage also starts to drop but I'm not sure if that's just because it's missing and dragging the alternator down. I would suspect the OP has the same situation.

One thing I did find that was responsible for the fuel pump not turning on sometimes resulting in a definite no-start: The oil switch wire had a butt connection that had pulled out and was resting on the butt connector.