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I have a 272 with 454mag mpi, it ran great the 4 times I had it out over the past 2 months, last weekend had it out and it ran fine, seemed to idle a little rough on the way in. Dropped it in this morning and it started and ran ok, seemed a little rough. Went to go out tonight and it was idling real rough, got 5 minutes off the dock (just above idle) and it started to sputter and was pouring black smoke, barely made it back to the dock and it died. I changed the fuel filter, got it started but still the same thing, ended up fouling the plugs. Put new plugs in it and it started again but tons of black smoke and running real rough, will not idle, I have to keep the rpms up for it to stay running. Any ideas???

Also, I get black smoke and running rough at all rpms, at one point, I held it at 3500 rpm for a minute or so and it smoothed out for 5 seconds then bogged down and just about died out then ran rough again.

Did you fill up with gasoline immediately before this problem occured?

Put 25 Gallons in last week (on top of a half tank) , ran for about 1 - 2 hours on that. The problem got progressively worse, I thought is idled rough and over a total running time of about 1 hour it got to where it will barely run.

Black smoke normally means you are running rich on fuel Two much fuel causes your plugs to foul and the black smoke sounds like something is stuck open dumping fuel in

Some possiblities;
Stuck injector
High fuel pressure (clogged return screen)
ECM thinks the engine is cold (bad ECT sensor)
ECM thinks the engine is under high load (high MAP or bad MAP sensor)

DId you check for trouble codes?

Great suggestions...Perfect places to start.

Will be checking codes Sunday morning, I will post up asap. Thanks for the help guys.

Showing code - Code 14 and 33 - Coolant Temp Sensor Low and MAP Sensor Voltage High. The engine was cold when I ran the test, would that cause the Coolant Temp Sensor low, or does that mean low temp or low voltage and a faulty sensor? Where is the MAP sensor?



Thanks

map sensor towards the rear, water temp sensor towards the front top. you need to get yourself the factory workshop manual for this motor ( not the aftermarket one) if you are going to do this work yourself... it tells you simply and directly how to diagnose and fix all of this stuff in less time than it took to read this.

I replaced the Coolant Temp Sensor and MAP sensor, reset the codes in the computer. Started it up and it runs the same way, shut it down and checked the codes. Both codes are back 14 and 33! What now?