2003 Merc 496 Help!

[shrapnel]

AT my wits end with my 2003 282 BR with 496 Merc. Have replaced SO MANY PARTS and still have the same issue...STarts and runs great, after running for even 5 minutes when I shut down it starts idling very rough and eventually dies. It makes a loud "popping" sound while struggling to idle.. After letting it sit and cool off, it will start and idle fine again. When it does this, the voltage drops below 12v. Have replaced the following: Batteries, Isolator, 50 Amp Block Breaker, Spark Plugs, Fuel Lines, Fuel Pump, IAC twice, Have disconnected charger, amp and stereo. Any suggestions>???

 

[Bt Doctur]

when I shut down it starts idling very rough and If you mean you turn the key off and it keeps running? that means your dieseling and that needs to be corrected first. Have you tested the alt?

 

[shrapnel]

when I shut down it starts idling very rough and If you mean you turn the key off and it keeps running? that means your dieseling and that needs to be corrected first. Have you tested the alt?

No, I never said that I turned the key off. By shut down I meant come off plane and just idle.

 

[alldodge]

You need a scan tool, but check what the fuel pressure is

 

[Scott Danforth]

stop throwing parts at it, get Rinda and plug in to see what the computer is seeing for timing, injector pulse, etc.

However as AD stated, step 1 is read the fuel pressure. popping is usually running lean.

 

[QBhoy]

when I shut down it starts idling very rough and If you mean you turn the key off and it keeps running? that means your dieseling and that needs to be corrected first. Have you tested the alt?

If I am being picky...I wouldn’t say that would be under the heading of dieseling. More likely pre ignition caused by water in fuel or poor ignition etc.
Dieseling is a very more worrying and serious thing, where the engine is actually fuelled by its own oil and associated vapours...a serious serious thing that.
Sorry in advance for being pedantic