Hey everyone,

I have a 6.2L Merc that has been sooty on the transom all summer. I let it sit for about a month and when I fired it up last weekend there was black smoke with gas in the water. I have done a complete tune up and I ran some fuel treatment through it previous to this. Had a compression check, everything good, she runs really well...just a lot of black smoke and soot.

The other engine is running perfectly.

I figured I'd do some research and I came across this link:

http://forums.iboats.com/showthread.php?t=507081

That's pretty much my situation. Does this seem pretty realistic? Worth buying a fuel pressure gauge before taking it to the mechanic? Any other ideas?

You need to check fuel psi and scan the ecm so you can look at the sensor data. I have replaced IAC's and MAP sensors on these motors as well fuel pressure regulators.

Get a gauge on it, any one that does the GM schrader valve fitting will work.

When this problem started earlier in the season we replaced the IAC, fixed the stalling problem. Stayed sooty though, so for now I am assuming the system is clear. I need to figure out which one of my friends have a tester I can borrow!

Thanks guys, I'll check in to it. I guess the next question is, if pressure is off, how hard is it to replace the pressure regulator?

what is water temp, is it same as other engine, open thermostat-cold engine the efi goes into choke mode extra fuel. put gauge on fuel rail, pull pressure regulator sensor hose off, fuel pressure should go up. look at hose it should be dry, wet could be ruptured pressure regulator(engine has 2, 1 on fuel rail the other on cool fuel II module.

I have replaced IAC's and MAP sensors on these motors as well fuel pressure regulators.

when you pull vac hose off regulator, it should have vacuum on it -assuming engine is running...

Water temp is usually about the same (when both gauges decide to work). I'll try pulling the vac hose next time and see what happens.

If it is the MAP, how do I troubleshoot that? Swap with other engine or another way?

that is best way to see if problem moves with it. map sensor could be gunked up, autoparts store sells cleaner to clean sensors.

I bought a fuel pressure tester and went over to troubleshoot. I took a quick video to show what readings I am getting. What do you guys think?

http://youtu.be/ia0xFQH5kTg