1984 6.2L Smoking

My father in law has a 1984 Chevy Silverado with a 6.2L Diesel. The truck has a couple hundred thousand miles but has always ran good. Recently it has started smoking. It puts out alot of black smoke under acceleration only after the engine warms up. Not when it's cold. He is a diesel mechanic for tractor trailers but hasn't come up with this cause. He has replaced the injectors, the truck seems to have more power but still smokes alot once it warms up. I'm hoping this means something specific to someone because he's baffled and about ready to sell the truck.
Thanks for any help.

Welcome aboard!

How does it sound? More rattle? Less?

Could be a plugged air filter. Black smoke is too much fuel for the available air. Another possibility is some part of the intake plumbing (like the baffle or plastic pipe connection) has collapsed internally. If it still has the air intake grill next to the radiator, check it for a bird/mouse nest (or the bird/mouse), or something else blocking it (like a plastic shopping bag).

Black smoke will usually rule out fuel quality and fuel supply. Poor fuel will almost always cause white smoke, and a plugged filter or failed/failing lift pump will drop power significantly.

Also, if there are a lot of miles on the injection pump (or a poor rebuild), it could be due for replacement. Less likely if the power is good, but if the pump is original, count on it.

No changes in noise of engine, no drop in power, in fact power a little better with new injectors. Tried running with air cleaner disconnected with no change, so I don't think there is a blockage there. Has a new fuel filter. Realized yesterday that when I changed oil last (600 miles ago) It looks like I may have put an extra quart or so in (5 quart jug that I thought was 4 quart jug). I'm going to drain it back down to see if it was that. The smoking came on suddenly not gradually.

One extra qt. won't do it. They will take between 6 and 8 qts and not know the difference. If it is excessively overfilled, the excess can get pushed/sucked through the CDR and into the intake at higher RPM's, and moreso as it warms up (oil viscosity drops and is more volatile). Although possible, I don't think it is likely.

Is the truck a 1/2 ton, with EGR (vacuum actuator in the intake plenum)? Curious problem you have....Usually when things go wrong on a N/A 6.2, we see white smoke, less power, and/or a change in the sound, and starting problems. What's the history of the injection pump? How is the throttle transition from idle to governor (in neutral or P)? Smooth, or uncontrollable?

At this time, the only failure I can see is the injection pump. While it may be mechanically sound, evidenced by the lack of power loss or change in sound, the fuel volume limiter may have failed. If so, many times this can be remedied w/o pump removal. It may need adjusting and nothing further. A time consuming process, for what it is, but simple. It requires removal of the top cover on the pump, and an adjustment of a screw. This should not be attempted by a first-timer without detailed instructions. It is the same process used when a turbo is installed, and the pump turned up. There are other possibilities of failure, but they require pump replacement, and are less likely with the symptoms you have, and lacking the symptoms you don't.

Give this thread a little time. Others may have a better idea. If you continue to drive it, try to prevent the heavy smoke with less throttle. Keep in mind, increased black smoke is increased EGT (Exhaust Gas Temp). The piston crowns are bare aluminum, and they don't like excessive heat.

Howdy and welcome

I would have a look see inside the air cleaner assembly on top of the intake.
If there is an EGR pod in there I am suspect this. (Little toad stool looking thing about 4" across right in the center of the intake opening)

If the EGR is activating under power these things will hose out a cloud of black smoke that will kill all the skeeeters for 10 miles.

Make sure this is not an issue. You can "temporarily" block off the egr with a plate to test this.

Many tests do last a long time though :D

The EGR valve itself can fail and stick open or the solenoid that run its can have issues.

The rigs that use the EGR also have a flap in the LH exhaust manifold outlet (EPR or exhaust pressure regulator) if this is stuck closed the engines breathing ability is greatly compromised and can cause problems.

Check these things out.

The vacuum controls for the EGR and EPR are on the LH Valve cover towards the rear.

With the amount of miles you are talking about this very well could be the issue.

As Maverick mentioned the usual failure we see is white smoke and low power with these.

Let us know what you find

Robyn