Another 2 questions on my 1999 4.2.

Cleared most of the errors, but consistently getting oxygen sensor bank 1 sensor 1 reading rich, it doesn’t switch between rich and lean like bank 2 unless I Rev it then it reads lean as the revs drop.

actual code is “P0172, lack of O2 sensors, sensor indicates rich, not switching correctly upstream bank 1”

Sensor 2, the downstream sensor is reading fine so is the consensus a faulty sensor?

Secondly I’ve changed the dpf sensor, but for a cheap one on Amazon, still getting readings out of range and a 401 error. However when I run the keys in engine on diagnostic the engine runs really rough when the EGR test is done so EGR is opening and closing. Is the cheap sensor the problem and I need the motor raft one? All hoses to the sensor are good and the engine is recon within the last 10,000 miles so highly unlikely any ports clogged. The sensor I changed was the original metal one and the replant is plastic but just noticed it’s half the price of the motorcraft one.

 

Trevor, you don't specify what code you are getting, but I have a '99 4.2l, and I had both the P0171 and P0174 codes (along with a couple of others). I ended up replacing both upstream 02 sensors. I also found a hole in the infamous elbow behind the throttle body, part of the pcv system, that burns a hole in itself and can cause codes, and replaced that as well. On the 4.2l, it's easy to get at. No codes since. I've attached an image of the elbow. I think it's Dorman part #46022. Best of luck.

 

hi and thanks, I’m getting a similar code P0172 but for rich not lean, and only on 1 bank, also says it “isn’t switching properly”.

Already checked that hose after Googling and it’s newish, but obviously if it had been leaking I’d likely have got the lean code anyway not the rich code.

how hard was it changing the sensors and on the passenger side did you use a sensor wrench or a normal 22mm spanner. All looks a bit tight in there.

 

I tried with a normal wrench but the sensors were both original and they were tighter than a cheapskate on a blind date arranged by his sister. I didn't want to strip the hexagons. My brother-in-law is a professional tech so I took it to him and he had to blast both sensors with his rolling torch. As I recall, we took off the wheel well lining on the passenger side to get better access and he used an 02 sensor socket attached to a medium length breaker bar. Hope yours come out easier!

 

mine has had a recon engine so hopefully got taken out, but who knows! I’ll get some heat ready!

truck is lifted a fiat bit so should have a decent view of it with the lining out.

thank you.