Well first how off was the thermo? Secondly you are probably fine if the outside of the meat was at 140 before 4 hrs. If you injected it should have been 140 internal at or under 4 hrs. Since I can't know what and when I can not make the decision for you as to the safety concern. I will say that if you run it to over 200 F in the house oven you most likely are ok but you have to make the decision based on the info I do not have. Error on the side of safety making this decision.
It was off by about 20-25 degrees. I did not have a thermometer in the brisket to start with. I checked it at about 5 hours and it was at 140 internal. I did inject it. It is funny I foiled it and moved it into the oven about 1 1/2 hours ago. They have already gone from 158 to 192. Not really sure what is going on.