Mercruiser 5.7 MPI Bravo barely starts and runs, smokes black

[Capnron45]

I have a 1999 Searay with a 5.7 Mercruiser MPI Magnum Bravo. Ran boat for about 40 miles doing 3100 rpm. All guages normal. Slowed boat down to fast or slow idle in a no wake zone for about 15 minutes, maybe 20 minutes. Then all of a sudden, engine just stopped. No warning. Tried to restart, will not even pop. Engine cranks just fine. Have spark so assumed fuel problem. Shot starting fluid and boat tries to start immediately. Since then I have replace numerous parts due to questionable appearance. These include fuel pump (only had 31psi), fuel/water seperator filter (did not have any water in it), TPS (when testing it was a little flukey and not smooth), Dist. Cap and rotor (highly corroded on the inside and cap had slight crack in the top), and the IAC (done on suggestion by friend). Doing something right because at least it will eventually start, but runs like crap and barely idles and smoke black like you cannot believe.
Engine always turns over well. Many times I can turn the key switch on, the fuel pump does not run. Leave key on or sometimes when I crank the engine, shut key off, and turn back on, fuel pump will start. Sometimes I can leave the key switch on and after 30 seconds or so, fuel pump will start to run. Only when I hear the fuel pump running will the engine start (with a lot of throttle). When it starts, it is exhausting black smoke, extremely rough running, and as soon as I bring the throttle to idle, it dies. Also, when it is running now, there is an alarm sounding. Alarm is just solid. Not a beep or anything. Just a straight monotone alarm. When it is running, and I try to throttle, it tries to gain RPM, but just so rough and just wants to die.
Anyone know how to check out the ECM? Or does anyone have any other ideas? I am all ears.

 

[Fun Times]

Re: Mercruiser 5.7 MPI Bravo barely starts and runs, smokes black

Hi there, welcome to iboats! This sure sounds like an ECM problem.

Of course you'll want to make sure all the power and ground cables and wire are in good shape, clean and tight as that could make the ECM do unusual things.

There is a company you can get a hold of (call them) and send in your ECM for inspection, maybe they will find something to tell you about it's condition. Here's their info. OBD Diagnostics

While the ECM is out being tested, be sure to do a cylinder compression test and most likely you will need new spark plugs as they should be fouled.

One sensor that could make the engine smoke real bad would be the MAP sensor. That was my first thought when I read smokes real bad with black before reading the rest of the story. You'll want to get yourself an OEM service manual and check it's ohms reading.

Sure hope you find something, keep us updated please and good luck.

 

[Pete104]

Re: Mercruiser 5.7 MPI Bravo barely starts and runs, smokes black

You may have thrown the right part at it but the ECM needs to be cleared of fault codes.

Dealer or somebody with a DIACOM can do this for ya. You may have gotten the issue with the IAC but the MAP sensor can act the same way. Again fault codes must be cleared with new parts or the ECM doesn't see a change.

YOU MUST get it scanned to make any progress.

I'll bet the parts people love you! Didn't ask them any questions?

 

[Capnron45]

Re: Mercruiser 5.7 MPI Bravo barely starts and runs, smokes black

The only part I changed was the IAC that I could not see or define a fault with. That was done on a suggestion by a good friend who is an excellent Mercruiser mechanic, but due to promises made to his clients, is having a hard time to come and visit me and check out this problem for me. So, to anwer your question, no the parts people do not love me. Fuel pump pressure should be around 42psi, having a corroded and cracked dist. cap is not a good thing, and changing a rusty fuel/water seperator that has not been changed in years is not a waste of money.

By using a DIACOM is this the only way you can clear the codes out of the ECM? Will disconnecting the batteries do it as well which always works on cars to clear codes ( at least with vehicles I have owned)

Thanks for the help by the way. It is appreciated.
Thanks!

You may have thrown the right part at it but the ECM needs to be cleared of fault codes.

Dealer or somebody with a DIACOM can do this for ya. You may have gotten the issue with the IAC but the MAP sensor can act the same way. Again fault codes must be cleared with new parts or the ECM doesn't see a change.

YOU MUST get it scanned to make any progress.

I'll bet the parts people love you! Didn't ask them any questions?

 

[Capnron45]

Re: Mercruiser 5.7 MPI Bravo barely starts and runs, smokes black

I have been doing a little reading in this forum, and there are apparently boats with "Check engine lights" and stuff. This boat does not have a check engine light. Would the ECM still hold codes?

The only part I changed was the IAC that I could not see or define a fault with. That was done on a suggestion by a good friend who is an excellent Mercruiser mechanic, but due to promises made to his clients, is having a hard time to come and visit me and check out this problem for me. So, to anwer your question, no the parts people do not love me. Fuel pump pressure should be around 42psi, having a corroded and cracked dist. cap is not a good thing, and changing a rusty fuel/water seperator that has not been changed in years is not a waste of money.

By using a DIACOM is this the only way you can clear the codes out of the ECM? Will disconnecting the batteries do it as well which always works on cars to clear codes ( at least with vehicles I have owned)

Thanks for the help by the way. It is appreciated.
Thanks!