Ford Explorer Carbon Monoxide Problem/Experiment/Theory
I just bought a 2017 Explorer two weeks before this story went national.
Here is a possible way exhaust can be going into the cabin.
3 factors must be present simultaneously for this to happen.
1, there must be an exhaust leak between the engine and the catalytic converter. The Cat removes the CO from the exhaust.....if you start your car and warm it up, after about 5-10 minutes, you can put a CO detector directly into the exhaust stream at the back of your car and it will read zero parts per million. However, this isn't the case if there is an exhaust leak before the exhaust reaches the Cat.
2. Your HVAC must be in "recirculate" mode. Putting the system in recirculate mode creates a low pressure system inside your vehicle relative to the pressure outside the vehicle. This means any small leaks in the vehicle cabin (no vehicle cabin is totally "air tight") will start sucking small amounts of air in from the outside....like a vacuum. Higher pressure will go toward the low pressure area.
3. The exhaust leak must by located near one of the air leaks in the cabin.
Essentially, the vehicle in recirculate mode is vacuuming up the exhaust that is coming out of an exhaust leak near a cabin leak. Smelling the exhaust when pulling a hill or when the engine is under load makes sense since combustion inside the engine isn't perfectly equal when at cruising speed, pulling a hill, or in stop and go traffic. However, since you can't smell CO, chances are the CO is coming in the cabin in small amounts no matter what type of driving you are doing.
I am taking my new explorer on a 3 plus hour trip one way this weekend. I have a data logging CO detector with me, so I will be able to experiment going there and back. I already have some baseline data from my other car, so it will be interesting to see what happens. In the meantime, if my car ends up getting exhaust into the cabin, I will not use my recirculate mode for my HVAC until Ford figures out what to do. If you have already been to Ford and they have replaced parts, in my opinion, if they have not replaced any parts forward of the catalytic converter, then it was all for nil. If they eliminate the exhaust leak, the option goes away. If they are able to seal the cabin completely, the problem will go away, but it is a band aid since the exhaust leak still has the potential to get in if the cabin air leak fix fails at all. Problem 1 for them is figuring out the source of the exhaust leak in the first place. If they find that, then they can properly fix the problem.
Again, the above is only a theory, but it makes the most sense given other things I have heard. I suppose it is possible that the exhaust is coming into the car to the rear of the CAT, but that would mean there are a lot of defective Cats on the vehicles.....unlikely in my mind. I will post the results of my trip next week.
