350 Mag rough idle
 

2007 350 Mag MPI that is running a bit rough at idle. Full tune up just done. Plugs, wires, cap and rotor, fuel filters, oil filter, and IAC, along with manifolds and risers, flame arrestor and throttle body cleaned. No alarms, no codes thrown currently. My next thought is a clogged injector(s)??? Engine sounds and runs fine above 1K rpms... Anyone else have any ideas?? Thanks!

The HVS caps and rotor for these are very prone to cause problems. I really do not care what they look like as being new still or not. 5 & 7 crossfire and or many very low quality in the marketplace. Also forms corrosion under the cap very very easily even within a year.

was your HVS ever moved or rotated or pulled out.

The distributor technically here is not distributor - it is called HVS = high voltage switch.

Also what cool fuel system do you have on this app ? If it is a Bravo app then gen III cool fuel.

Did you replace iac muffler?

HVS was never touched. I believe it is the gen 111 fuel app.....

yes......

Actually last time the boat was ran in the fall (prior to the major tune up)......the constant alarm went off while cruising at roughly 55 mph. Goes off when I throttle down. Not overheating, good oil pressure, lube bottle full etc. I hoped the "major tune up" would solve the slight misfire on idle.....but no luck! So I'm still searching!!!! My only other thought is a clogged injector?????? Any other ideas?????

the very very bottom of Gen III cool fuel cell the 10 micron pad fuel filter, and install a new one in the basket especially if the basket had water in it. The cell needs to be perfectly clean and new O-Ring installed to seal the pull out very well.

Alarm possible water pressure and or water pressure sensor or its connection. Are you able to reach WOT rpms for your motor per OEM specs ?

who scanned the engine ? and with what diagnostic tool ? did you look into history of the scan ?

Any fuel pressure readings at idle taken

HVS cap and rotor condition or try new again.

Flame arrestor spotless ?

Have to go back to work, good luck

The pad filter was also changed.

Water sensor and battery is my next thought...... as I do have a dead "main battery". Might be causing a faulty alarm....

Not scanned yet...... that's my last resort! lol!

No fuel pressure tests done yet...

cap and rotor are brand new.....

Just cleaned flame arrestor...... but was very clean overall

ECM 555 continuous horn - BATTERY VOLTAGE and that can be both ways for the horn meaning to low battery voltage or even too high battery voltage. Yours is 4 sure low voltage and could even be your idle problem TO.

If you have batteries connected in series - It takes only one low or bad battery to bring the others down.

One of the worst things you can do to an PCM or ECM 555 controlled engine is keep running it on a bad battery plus you are taxing the alternator hugely. ECM's like proper steady voltage supplied at all times from start up to all day running. Just saying.

Good luck with it and buy some new batteries plus make all your connections are very clean and tight. OEM engines require NO wingnut connections for battery connections anymore. All of them are totally against it including all outboard engines as well.

Thanks BUP for your thoughts...... I'm going to try the new batteries, check all connections, and throw some fuel injector cleaner in and see what I get!!! Hopefully it solves the issues.

Post your fix when done.

Well......new battery, and ran some injector cleaner directly through the fuel filter and the regular tank....and no luck! Any other suggestions, before I bring it to get scanned later tomorrow..... this one has me stumped!!! uggg!

Double check your Plugwires, cap and rotor, I installed MSD plug wires last tune up and only noticed the rubber insulator hugging the 8 vertical terminals on the cap were to long and had pushed it's way back off the CLICK terminal.

You still have the warning horn going off ?

What spark plugs did you install - brand and number on the spark plugs ? AC delco 91- ???

did you gap your new plugs ? Some spark plugs you do not touch the gap because it can cause a miss fire. Double platinum tip spark plugs you do not touch the gap.

Well........good news it is "appears" fixed! I believe it was a combination of a partially clogged injector AND spark plug wire INSIDE the boot broke off, and was very loose on the plug. Runs just as good as the other engine now on the muffs. True test will be first run out, in a week or so. Crossed fingers!!!!
Thanks for everyone's replies.......