I don’t watch much TV but the other night I forced myself to sit through an episode of DIY Automotive after my wife’s show went off.
I’ve seen bits and pieces of it before and was not impressed.
The two hosts, a man and woman, take fairly lame questions and provide even lamer answers IMHO.
The diesel problem was this, and of course, none of us will ever know the truth behind it.
The caller has a turbocharged Volvo diesel that was running fine until it abruptly started running bad, belching black smoke, and rattling bad.
A secondary problem was that the vehicle owner now notices a blue smoke on startup, but black smoke and all the rest when running.
The 2 hosts always bring in an “outside expert” and in this case it was a gentleman who teaches the diesel courses at a technical school.
He says the blue smoke is bad turbocharger seals and the black smoke is a “bad air filter”. Both hosts (both allegedly ASE certified also) wholeheartedly agree with this diagnosis and agree the diesel (which needs a LOT of air?) is suffocating do death.
My opinion is that the blue smoke COULD be valve seals and may have been present all along. The black smoke would more than likely be an injector problem.
Just wondering what anyone else thinks; especially of the “bad air filter” diagnosis.
My opinion is that diagnosis is from the Twilight Zone. Have fun with it.
Typo. Do - to.
Here are the previous replies:
http://community.cartalk.com/posts/list/554809.page
As I said, I agree the clogged air filter is very unlikely. Valve seals are possible (for the blue smoke), but they have much less effect on diesels because of the lack of intake vacuum. Bad turbo seals will give you a blue smoke, but wouldn’t explain the rest. Black smoke indicates too much fuel and the “rattling” indicates bad combustion in at least one cylinder. I agree that one bad injector could do that. Also in my case, a timing chain jumped one tooth and really messed up both the injection and cam timing; the engine continued to run with very low power and LOTS of very black smoke. I guess it’s also possible that he dropped a valve or broke a ring so one cylinder was running without compression. That’s all I have.
I must be getting old. Had this one minimized and forgot I even posted something about it previously. I humbly apologize for cluttering. 
my diesel experience is NOT on cars, but… black smoke is usually injector related.
the initial blue smoke sounds like a couple of things; bad rings, valves, turbo, or blower. because i am not sure of the volvo diesel, i cant guess further on that.
as you mention about NOT knowing the rest of the story, there are so many variables it is impossible to get a correct diagnosis over the tube (or the net).
the only thing that IS troubling is the “rattle.”
i would suspect a bad/burnt valve being the culprit for the rattle. a bad exhaust valve may also be the whole problem (allowing for a poorly sealed compression, and ignition stroke, then dumping lots of unburned fuel out the exhaust.)
Is it possible that the “rattle” was an injector knock, those can sound pretty nasty?
Almost all of my diesel experience is with VWs (Bosch) and the first thing I thought of was an injector going on the fritz.
A faulty injector will belch black smoke and cause a serious engine knock. The ones I’ve heard sound like the mother of all rod bearing knocks and were easily confirmed by simply loosening the injector fuel lines one at a time while the vehicle was idling.
When the faulty injector line is loosened the knock goes away.
I was amazed that considering the complaint, and the fact the problem appeared instantly, these people (and especially the diesel professor) would blame a dirty air cleaner. It’s not likely at all an air filter is going to go bad at the flip of a switch.
They’ve had a few other oddities on there also such as the guy who says his A/C squeals when it is turned on. The male host told him his compressor was obviously seizing up and turn it over to the pros. One would think check the belt and the cooling fan operation as a first step.
Another was installing a GM starter on a Ford truck. Guess they thought no one would spot that. 
The clogged air filter could be from the twilight zone. We put our hands over the intake on a running diesel engine and the RPM went up in a hurry but we didn’t get black smoke by doing it. Black smoke is from too much fuel and I don’t work on diesel engines. Blue smoke could be from turbocharger seals but it only happens on startup. Some of the teachers don’t know a heck of a lot because a shop teacher might not be a mechanic who was successful at fixing things. They didn’t teach a heck of a lot when I was in four years of trade school. Not in auto shop anyway. One of our instructors was way more interested in the 22 year old seniors and made fun of the first try students.
I admire their ability to make a living doing that. How do I too get a TV show???
Black smoke is carbon, there because there’s insuffucuent oxygen for the carbon to bond to and create CO2 after the hydrocarbon molecule split…the smoke also has lots of CO/ Many would simply call this “running really rich”. Possible causes include but are not limited to faulty injectors or severe restriction in the air passage. I wonder could a diesel run too cool for complete combustion and thus be pumping out black smoke (I’m not a diesel guy)??? That would add another possible cause…
The blue smoke…yeah, oil being drawn in due to bad turbo seals is possible, but I agree that it could also be coming on past the vavlve seals.