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's summary on Treblinka mentions the Diesel of Death:
Extermination Camp, in the northeastern part of the Generalgouvernement. Located 2.5 miles from the train station of Malkinia on the main line running from Warsaw to Bialystok. Treblinka was established in early summer 1942 as part of Aktion Reinhard - the Nazis' plan to exterminate the Jews in the Generalgouvernement area. In total, approximately 870,000 people were murdered at Treblinka.
The first transports reached Treblinka on July 23, 1942; including Jews from the Warsaw Ghetto. From that day until September 21, 1942, approximately 254,000 Jews from Warsaw and 112,000 Jews from other places in the Warsaw district were murdered at Treblinka. Hundreds of thousands of Jews from the Radom and Lublin districts of the Generalgouvernement were also executed there. In all, approximately 738,000 Jews from the Generalgouvernement perished at Treblinka, as well as 107,000 Jews from the Bialystok district. Thousands of Jews from outside Poland were also brought to Treblinka; these included Jews from Slovakia, Greece, Macedonia, Thrace, and some who had previously been interned at Theresienstadt. Altogether 29,000 Jews from outside Poland were murdered at Treblinka, as were 2,000 Gypsies. The mass extermination program was in operation at Treblinka until April 1943, after which only a handful of transports arrived.
From August 1942, Treblinka was run by camp commandant SS-Obersturmfuehrer Franz Stangl, who had previously served as commander of the Sobibor extermination camp. Stangl's deputy was Kurt Franz. They were assisted by 20-30 SS Officers (who had participated in the Euthanasia Program), and 90-120 Ukrainian soldiers working as camp guards.
Treblinka was situated in a sparsely populated area that was heavily wooded - this site was chosen in order to conceal the atrocities taking place there. Treblinka contained living, reception, and extermination areas. The extermination area included a brick building that housed three gas chambers. A diesel engine was housed in an adjoining shed - this engine produced the carbon monoxide, which fueled the chambers. The gas flowed through pipes attached to the ceiling of the chambers, ending in what looked like showerheads. The Nazis arranged the gas chamber in this way in order to create the impression that the Jews were merely entering the building to take showers - not to be murdered. A hallway in the building led to each of the three gas chambers, and in each chamber was another door through which the corpses were removed. About 200 yards away lay the huge trenches where the corpses were buried.
The extermination process at Treblinka was based on experience gained by the Nazis in Belzec and Sobibor- the two other Aktion Reinhard camps. When a train made up of 50 - 60 cars, holding some 6,000 - 7,000 people, arrived at the nearby train station, 20 cars were brought into the camp, while the rest were made to wait in the station. The car doors were opened, and SS officers ordered the Jews to disembark. Next, a camp officer would announce to the new arrivals that they had reached a transit camp where they would take showers, have their clothes disinfected, and then travel on to various labor camps. After this announcement, the Jews were taken to "Deportation Square." Men and women were separated - children going with the women. The women and children were made to undress in a barrack, and the women's hair was cut. Naked, they were forced to leave the barrack and enter the "pipe"- a narrow, fenced-in, camouflaged path that led to the gas chambers. After the victims were locked into the chambers, the engine was started and poison gas poured in. Within half an hour, all inside were dead, and the next group of victims would prepare to enter. Meanwhile, the bodies were removed and taken for burial in the trenches. This last job was done by a team of Jewish prisoners, called Sonderkommando.
These prisoners were not immediately executed upon arrival at the camp - rather, they were selected carry out tasks such as cleaning the train cars, preparing the victims for their execution, dealing with the possessions and clothing of the victims and handling the dead. In the spring of 1943, the Nazis used the Sonderkommando to cremate the bodies. Most of these Jews were exterminated themselves after a few days or weeks of work, with newer arrivals taking their places.
After a while, the Nazis decided that the extermination process at Treblinka was not efficient enough. Thus, between August and October 1942 10 new gas chambers were constructed there. Furthermore, the Germans added another improvement to their extermination system - those new arrivals who were too weak to walk to the gas chambers unaided were told that they were being sent to the infirmary. They were taken to a closed-in area with a Red Cross flag adorning it; inside were SS officers and Ukrainian guards who murdered them on the spot.
Aktion 1005 - the campaign to destroy all evidence of the Nazis' murderous activities - was launched at Treblinka in March 1943, and lasted until July. After this operation was completed, Treblinka was shut down. Most of the camp structures were destroyed, the ground was plowed and planted over, and the site was turned into a farm that was given to a Ukrainian family.
Hundreds of Jews tried to escape the trains on their way to the camp, but most failed in their attempts. Others attempted to escape the camp itself, but almost all were caught and hanged. Jews from several transports offered resistance in which German and Ukrainian guards were wounded or killed. An uprising was planned when the prisoners found out that the Germans were planning to liquidate the camp, however, the uprising was suppressed and most of the 750 prisoners who tried to escape were caught.
After the war, many of the SS officers who worked at Treblinka were put on trial. Both commandant Franz Stangl and deputy commandant Kurt Franz were sentenced to life imprisonment.
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)