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Petrol or Diesel? Black smoke is the engine running 'Rich'. The mixture of air and fuel has too much fuel and not enough air. When was the motorhome's engine last given a major service? Clogged air filters can cause black smoke and clogged fuel filters can cause a power loss. Are there any warning lights on the Dashboard?
If a service doesn't solve this you will need to move on to other areas. Parts like the EGR valve, (Exhaust Gas Recirculation), and the injectors. The DPF, (Diesel Particulate Filter), on a diesel engine can also cause these issues.
You could get it plugged into a diagnostic system or a OBD2 scanner to check for trouble codes but this will cost you money. Ask at a few different garages as the price charged to scan the system can be VERY different between garages.
Comment below with more details about the vehicle and I'll see if I can help you more.

The colour smoke an engine produces gives a good idea of the fault: -
Black/dark grey smoke is partially burned fuel caused by the right amount of fuel being injected badly or by a small excess of fuel.

Blue/blue-grey smoke is burning engine oil.

White smoke is either steam (usually from coolant ingress) or massive amounts of unburned fuel. A few possible causes of the latter is strangled exhaust, one or more injectors stuck open or a damaged injector (broken nozzle).

If there is no coolant loss I suggest you remove the fuel injectors for testing.

no. (but the isc valves loves to stick but will not cause black smoke)
the 4.0L is one of 5 million made, it's well known,
the black smoke don't lie. it's rich and the cat seems burned up too.
as with black smoke the cat will try to catalyze all that and glow red hot. is your cat missing?>
so why not believe the code 171, its real and is catastrophic failure. there are 2 engines here, FED and California.(exhaust)
(2 different exhausts and sensors there.
as they say, fix what is OBVIOUSLY bad, 171
(find why using tools or inspections)
Fuel System Lean (Bank 1)in most cases the exhaust is cracked near B1S1 0xy sensor
this causes it to stick at 0volts, (lies) and the PCM sees that obvious lie then goes rich. (limphome rich)
if the pcm cant measure oxygen, it must now guess at fuel trim.(bad that.)
it goes rich, so you dont melt pistons running lean.
(by design)

bad front oxygen sensor (aka , up stream bank 1)
in calif cars, it can have a split exhaust on the I6 and have 3 sensors. (hope not yours, do look..)
most have 2 sensor, front and the useless behind cat sensor(B1s2)
S2 is useless for running mix, the rear is for smog test the cat.

so it rich, and now misfires. and the spark tips are black.
and it misfires to bad it can even idle, sure. (Drops)
the cause, is too rich.
the 171 means the PCM sees it stuck at 0v forEVER.

there are in fact other causes.
but these 2 are top cause.

on all 3 of my 4.0L engines
the exhaust manifold cracked on the under side.
side facing block. (i use a hose to ear to hear the putt putt puts, (with FULL PPE protection from burns from a dead cold engine.) ask how.
even the SST exh. man. did that.

or the header flange gasket is TOAST. (that too putts when bad.)

Yes this is correct, you can get important information from the colour of smoke from the exhaust:

Blue/Gray Smoke: Blue/gray exhaust smoke is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:
Valve Seals: Leaking valve seals will cause blue/gray smoke at startup because oil leaks past the seals into the cylinder after the engine shuts down.
Valve Guides: Excessive clearance between the valve stem and the valve guide allows oil to leak past the gap into the cylinder.
Piston Rings: Worn or damaged piston rings will cause blow-by resulting in blue/gray smoke.
Worn Cylinder Walls: Worn cylinder walls cause blow-by resulting in blue/gray smoke.
PCV System: A stuck closed PCV valve will cause excessive crankcase pressure resulting in blue/gray smoke.
Black Smoke: Black exhaust smoke is an indication of a rich fuel condition. These are possible causes:
Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.
Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.
Fuel Return: A restricted fuel return line will cause a rich fuel condition.
White/Gray Smoke: White exhaust smoke is an indication that coolant is burning in the combustion chamber. These are possible causes:
Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.
Engine Block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.
Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/gray smoke coming from the tailpipe.

burning oil change spark plugs and air filter

If you need further help, I’m available over the phone at https://www.6ya.com/expert/richard_b59056c0c62ecb00

ring or valve issue check that the valves are all working and not stuck open, if theyre good take the head off and remove the piston, it will probably need a piston ring and sleeve.

Too much fuel is the usual problem.
One of the injectors may be stuck open, or some other fuel leak into the engine.

youll think im crazy but change the oil and look for a oil leak, prob around the fuel filter

hello,according to service information;smoke formation or si 07.16-p-0004a (service inform) from mb ,your engine have normal function,if you want ,ask your dealer about the service inform with number 07.16-p-0004a,you can read the explanation regarding your problem,ty