Black smoke

[Anthony LA0621]

Have a 2003 Mercruiser MCM 350 MAG MPI engine serial #OM627617 Engine starts and idles fines, but smells from exhaust and you can see some black smoke. When I accelarate and get to about half throttle the engine power dies - it doesn't stall it just seems to limit power.

I replaced cap, rotor, plugs, inline fuel filter, water separator in the begininng of the season beacuse I had a hard time starting. Cap and rotor were in bad condition from moisture and corrosion. The plugs were black from carbon.

Is there a way to get diagnosis codes without expensive diagnosis tools?

 

[maxxman04]

Re: Black smoke

not sure about the diagnosis without scanner, but it sounds a bit like a bad fuel pressure regulator. black smoke usually indicates too much gas. being fuel injected, fuel delivery is via electric pump thru fuel pressure regulator before it gets to motor. check for proper fuel pressure coming out of pump, and coming out of regulator. manual for your setup should tell you exactly how, or check the "ADULTS ONLY" sticky.

 

[kyler]

Re: Black smoke

im pretty sure you would have to have some sort of code reader to get any dtcs out of it

 

[maxxman04]

Re: Black smoke

in the automotive world, anything '95 and newer uses the OBDII system, which REQUIRES the use of a code scanner. any attempt to get codes without a scanner will fry the computer.

 

[Anthony LA0621]

Re: Black smoke

Where is the fuel pressure regulator and is it adjustable. If I connect a guage to the factory gauge port connection on the engine does this tell me the pressure after or before the regulator? Also what is the fuel pressure connection size, is it a standard size for all fuel gauges?

 

[Anthony LA0621]

Re: Black smoke

I get that the dark exhaust and smell of it is too much fuel, and that it can be caused by over-pressure from the regulator not releasing enough to keep the fuel train at the correct psi - but why would the engine start and idle so well and then bogg down under a load? Is the engine management system limiting the rpm's? If so, what is it looking at to determine this?

 

[maxxman04]

Re: Black smoke

an idling motor is under no load, no strain, so even if there is too much fuel coming in, it will still idle seemingly ok. the regulator could be malfunctioning only above idle as well. fuel injection systems are hard to beat for throttle response, economy, and power, but can be a little tricky to diagnose problems. to fully understand the workings, a quick google search can be done, to find a site that will go into detail the inner workings of your particular system. my thought on the regulator being bad is just that, a thought. it could be something else. good luck

 

[Anthony LA0621]

Re: Black smoke

Thank you, I going to do some tests in a little while. I can't seem to find what the pressure should be. Is the pressure standard or does it vary? From what I've found it doesn't look as if the regulator is adjustable. Last year I replaced the cool fuel pump, and I don't remember if the regulator was part of the repair.

The manual I have has good info on removal & installation of components, but unless you have the scan tool it is not very helpful on testing components. Where can I find info like what the fuel pressure should be on the fuel rail, or how to test the MAP sensor, or throttle position sensor?

 

[maxxman04]

Re: Black smoke

not certain about downloadable manuals online. hopefully someone else can help here. i had another thought tho. when you replaced the cap/rotor/plugs, did you check the timing? might do that real quick to make sure it's good. your problem does sound like your timing could be a bit retarded. check that real quick before tearing anything apart.

 

[maxxman04]

Re: Black smoke

there is a "how to test your fuel system" in the "ADULTS ONLY" sticky at the top of the forum that might be of help. if nothing else, give a few ideas.

 

[Anthony LA0621]

Re: Black smoke

As for the "Adults Only" very good reading but unless I missed something it only dealt with the boat side of the fuel. Anyway, my service manual mentioned a test of the fuel regulator, where you run engine and watch the fuel pressure then create 10" of vacuum and the pressure should reduce by about 5psi, but the vauum I'm getting with the engine idling is 17", so I'm abit confused. And the pressure at the fuel train stays petty steady - around 40psi? Does any of this sound OFF?

 

[Anthony LA0621]

Re: Black smoke

Ok here's what I've found so far.

The fuel pressure on the fuel train varies between 35 and 45 psi for the most part, based on the engine vacuum. Ruled out it being a regulator at this point. Tested throtle position sensor and egine coolant sensor and they checked out good. Was unable to determine how to test MAP sensor, but I took the boat on the water and found that with the MAP sensor un plugged the boat has has full power at any range, although there is an audible alarm, which is expected according to the manual. However with the MAP sensor plugged in the engine will only rev to 1600 rpm before it begins to cut-out. As soon as I reach 1600 rpm the engine reduces in power and rpm, the vacuum reduces (which makes sense since the throttle valve is opening and engine is slowing), The fuel pressure begins to increase (I assume since the engine vacuum is reduced which is what happens during accellaration), but the fuel management system is sensing a problem and powers down the engine to protect it. Does this sound correct?

 

[turfguy1969]

Re: Black smoke

i have the same type of issue at idle-black smoke etc. Did you check timing or the idle air control sensor?

 

[rbh]

Re: Black smoke

grey smoke is fuel, black smoke is oil. were all plugs fouled?
grey soot or black oil fouled?
rob

 

[Glastron_V210]

Re: Black smoke

On a car MPI system the fuel pressure you quoted is bang on. This also indicates you don't have a fuel return line blockage which is another cause of high fuel pressure/richness.

The map sensor outputs a 0-5 volt signal based on the vaccuum it reads. Test it with a vaccuum pump to verify the operation. Go key on and splice into the wires. You will have +5 volts on one wire, 0 volts on the other, and a 0-5 signal based on vaccuum on the third.

The IAC is not a sensor, it is a small valve operated by a stepper motor and is not likely your problem. It controlls the idle air to keep the idle rpm in range.

So what is the problem? I'd say stuck injector, but it idles fine so not likely. I'd still check though. Use an automotive stethescope on the injector heads...is there an audible clicking from each of them...if not, it's stuck. When you rev up they should click faster.

I think you're on the right track with the map sensor. Without the map, I suspect the ecm will try to run on a rpm vs. tps fuel map. This is not great, but is close enough to seem like full power. Test/replace the map. For a car they are only about $40, so for a boat they ought to be about $300 ha ha.



Chay

 

[bigskiohio]

Re: Black smoke

i thought white smoke oi,l black running rich?

 

[QC]

Re: Black smoke

BLUE smoke = oil . . . black too much fuel for available air . . . MAP sensor tells engine how much air "pressure" is available . . .

 

[turfguy1969]

Re: Black smoke

Ok, so if black smoke is too rich fuel mixture, couldn't the timing be off enough where the cylinders are out of synch, and fuel passes those strokes and is burned as black smoke? If timing were way out of whack, wouldn't you get that upper rpm missing/hesitation?