What a Treblinka gas chamber would have looked like, had one actually existed 
From the research I've done, diesel engines generally do not produce a lethal amount of carbon monoxide gas. The exhaust from gasoline engines, on the other hand, is quite lethal and contains much more carbon monoxide. Furthermore, the Germans used gasoline, not diesel, engines in all of their tanks and vehicles during the war. So assuming for the sake of argument that the Germans were actually conducting homicidal gassings, they surely would have used exhaust from gasoline engines. But hey, that's the way everything is with the holohoax story. The Germans, paragons of efficiency and engineering, always seem to have chosen the most inefficient (and downright impossible) methods for their "masterplan of genocide."
Yad Vashem claims that gas from a diesel engine (the "Diesel of Death") was piped into the ceiling of "death chambers", and dispensed through pipes that "looked like showerheads".
IHR on the improbability of using Diesel engine gas for "exterminations":
In recent years, the most widely-circulated story has been that Jews were gassed at Treblinka with carbon monoxide from the exhaust of a diesel engine. (note 22)
However, as American engineer Friedrich Berg has established, this story is improbable for technical reasons. (note 23) In spite of the obnoxious odor of diesel exhaust, diesel engines produce much smaller quantities of toxic carbon monoxide than ordinary gasoline motors. (note 24) It would thus be difficult efficiently to gas large numbers of people using diesel exhaust. A normal gasoline engine would be much more logical. (note 25)
It is important to keep in mind that the "evidence" now usually cited for diesel gassing at Treblinka is no more credible than the evidence that was once presented for steaming and suffocating. Apparently the steaming and suffocating stories have been dropped for the sake of credible consistency.
Solid evidence for gassings at Treblinka has proven to be very elusive. For example, it turned out that none of the witnesses in the 1951 West German "Treblinka" court case ever actually saw anyone being gassed. "The type of gas used to kill the people there [Treblinka] cannot be determined with certainty because none of the witnesses was able to witness this procedure," the judges declared in their verdict. (note 26)
At least some former Treblinka prisoners testified in postwar West German trials that they not only never saw a gas chamber, but did not even hear about gassings from others. (note 27)
Holocaust historians today are not able to agree about the number of homicidal "gas chambers" at Treblinka. Raul Hilberg maintains that there were three at first, but because they were allegedly not adequate for the job, more were built later on. There were eventually six or perhaps ten chambers, he reports. (note 28) Others have reported the existence of 13 gas chambers at Treblinka. (note 29)