Black Smoke on Heavy Acceleration

richard5933 · July 26, 2020, 01:24:36 PM

Somewhat of a new issue - thought I've seen this since the Jake Brakes were installed, but today I definitely saw it. Black smoke on heavy acceleration, in both 1st and 2nd gears. Cleared up pretty soon after getting moving, but it is something that I don't think should be there on an engine with only 53,000 original miles and which has been babied its whole life.

When the Jakes were installed the tech ran the rack and did a tune up. Otherwise not much has been done to the bus that would have any impact on the smoking. Engine idles smoothly and I have noticed no performance issues at all. Oil consumption is normal, oil level is holding pretty steady, coolant level is steady, and there are no problems with oil spotting on the back of the bus.

Any thoughts on what might be the cause? Could it be something not be set correctly when the tune up was done? Could there be an issue with the Jakes causing it?

buswarrior · July 26, 2020, 01:31:25 PM

Check the air cleaner and piping for obstruction?

Black smoke is either too much fuel, or not enough air.

Happy coaching!
Buswarrior

DoubleEagle · July 26, 2020, 01:43:04 PM

Fuel modulator not set right?

richard5933 · July 26, 2020, 01:56:32 PM

Quote from: DoubleEagle on July 26, 2020, 01:43:04 PM
Fuel modulator not set right?

Fuel modulator? Not sure what this is - sounds like something electronic, which my bus wouldn't have.

Quote from: buswarrior on July 26, 2020, 01:31:25 PM
Check the air cleaner and piping for obstruction?

Black smoke is either too much fuel, or not enough air.

Happy coaching!
Buswarrior

Definitely something to check. It's still the oil bath air cleaner, so I'll drop it down and take a look.

chessie4905 · July 26, 2020, 02:06:11 PM

what size injectors? Did it have more power after Jake install?

richard5933 · July 26, 2020, 02:36:57 PM

Quote from: chessie4905 on July 26, 2020, 02:06:11 PM
what size injectors? Did it have more power after Jake install?

Not sure the size - injectors were not changed during Jake install, so they are still the OEM (I assume).

Power was about the same before/after the Jake install. The engine did seem a bit smoother after the tune up. I wouldn't say that it had more power, but perhaps it was smoother through the power curve. The bus has always pulled well and had plenty of power.

richard5933 · July 26, 2020, 02:37:57 PM

I did just check the air cleaner and intake. Only a very slight amount of sediment in the bottom of the oil pan, and all the screens were glistening with clean looking oil. No visible obstructions in the intake tubes or screens.

luvrbus · July 26, 2020, 05:05:21 PM

Could be the tank the fuel has to much bio diesel,a lot of things can cause the N/A engines to blow black smoke even dirty fuel filters

DoubleEagle · July 27, 2020, 08:14:47 AM

Quote from: richard5933 on July 26, 2020, 01:56:32 PM
Fuel modulator? Not sure what this is - sounds like something electronic, which my bus wouldn't have.

The old term is Throttle Delay Cylinder or Mechanism. It's not electronic. Adjusting it is part of the "Tune Up". It controls excessive fuel delivery to reduce smoke. To quote the manual: "The throttle delay mechanism is installed between the No. 1 and No. 2 cylinders on the right-bank cylinder head. ... When the engine is accelerated, movement of the injector racks toward the full fuel position is momentarily retarded or delayed while the piston expels the oil from the cylinder through an orifice". My experience has been that if it is not working correctly, you can blow a lot of black smoke at lower speeds.

edvanland · July 27, 2020, 08:24:20 AM

I have a 8V92 on a MCI7 mine would do the same thing, I then took the muffler off and put a resonator in its place what a difference. Very little black smoke when I start out to fast, cooler, and sounds better. You would be surprised how much the muffler chokes the exhaust down, I was. That's what I and several other people I know. Worked for us so its something you might want to consider. Good Luck.

luvrbus · July 27, 2020, 08:30:28 AM

You don't see many delays on on the 8v71 N/A engines they were big on the transit model but not a high way coach,if the air gap is off on the governor they will roll black smoke,and when the fuel pressure is low they put out black smoke lot of things can make one smoke under acceleration some a easy fix and some major

luvrbus · July 27, 2020, 08:32:29 AM

Quote from: edvanland on July 27, 2020, 08:24:20 AM
I have a 8V92 on a MCI7 mine would do the same thing, I then took the muffler off and put a resonator in its place what a difference. Very little black smoke when I start out to fast, cooler, and sounds better. You would be surprised how much the muffler chokes the exhaust down, I was. That's what I and several other people I know. Worked for us so its something you might want to consider. Good Luck.

He doesn't want to remove a muffler from a 8v71 N/A engine those are loud