6.2L black smoke and gas in water
 

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.http://www.qrtd.info/12.jpg

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

I'm betting your fuel psi regulator is bad. It should max at 43psi.

X-2 what griff said also the erratic guage indicates a bad regulator

How do I diagnose which regulator to replace? The one on the fuel rail or the cool fuel regulator?

Before you start throwing money towards parts, remove the plastic cover from the cool fuel exchanger assembly. Remove the two screws that's holding the fuel pressure regulator[ controls excess fuel return to the water separator] on the copper exchanger and discard the s/s filter that sits under the regulator.What it seems in your youtube video ,your pressure spikes up [ hence the black smoke ] too high when throttle applied, dumping excess fuel through one or more injectors. If you have twins, you can start swapping the regulators at the top of intake first before diving into the cool fuel system below.

Makes sense, I will give it a try. What does discarding the filter do?

You must disconnect the vacuum line to the regulator to get an accurate reading. The gauge is fluctuating because of the varying vacuum as you rev the engine. The regulator is passing the most fuel at idle. If the regulator was the issue it would be most prevalent at idle. Also, the regulator on the cool fuel is what controls pressure. The one on the fuel rail just acts as a damper.

Bob Lloyd
Full Throttle Marine

Thanks for the info Bob, do I need to pull both vacuum lines or is the cool fuel vacuum enough to get an accurate reading? I didn't record it, but when I pulled the cool fuel vacuum line the fuel pressure didn't change. Anything else I should be trouble shooting?

I had the same problem with my port engine as you've described. Black discharge through the exhaust with SmartCraft warning message; 'Throttle back' over 3500rpm. My Rinda scanner had the same message when I checked. Found that the tiny s/s filter [ about 1/4 " in dia ] got contaminated, blocking fuel return and higher than normal [ 70 psi on the Schrader valve] pressure readings over 3500 rpm. After tossing the filter, problem solved. Merc has a redundant system I guess. There's a filter before the low pressure pump, delivering fuel through the water separator/filter, another small s/s filter in the high pressure pump inlet as well. Got single tank feeding both engines. Idle was smooth at 600 rpm for both at all time even when I had the issue. Like Bob mentioned ,the regulator on the cool system controlling the fuel pressure between 39-43 PSI. It's a b,,,tch to get to them with twin engines cramped into the engine bay,especially on the starboard one.

http://www3.telus.net/spectrasonly/Twin%20377's

What is the serial number on your engine? Some of the earlier 6.2L ran different regulators and lower fuel pressure. Maybe someone replaced it with the wrong one. Compare the fuel pressure reading with your other engine. Is your fuel pump under the engine or the module on the side? You need to unplug the hose running to the regulator at the fuel pump.

She is 0w063672. What is the spec for that serial?

I am not actually sure where the fuel pump is, I need to look around a little more to find that out. Sounds like I got another good list of troubleshooting to do this weekend.

Look under the left exhaust manifold. If you see a black snap on plastic cover, you have the 03 or newer model .The high pressure pump is behind the black cover. The low pressure pump is next to the water separator front of the right exhaust manifold.

According to the S/N, you have the late model GenIII fuel module(assuming it is a Bravo drive). It is located on the starboard side of the engine, lower front. The vacuum hose goes into the regulator mounted on the top. There have been a few problems with paint under the regulator getting sucked up and stopping up the screen. It is very easy to remove the regulator. Just 2 screws and pry it up. Make sure there's no loose paint. If it's a twin engine boat just swap regulators.

Bob

Okay great, thanks I will try all of this on Saturday. This is my first time messing with the fuel system. Any tips on doing this safely without getting gas everywhere?

It's a returnless sytem, so you have to relieve the pressure in the rails. Do it in a well ventilated [ outdoors preferred ] area, rap some rags around the Schrader valve while pressing on thevalve with a small screwdriver. Do same when swapping the regulators over, with rags underneath catching some spill.
If your symptom switched to the other engine , you'll know to replace the regulator.

You guys rock. Thanks so much for the help. I pulled off both filters then swapped the regulators. For the first time since buying the boat both engines are sounding identical when they run. No more smoke.