Hello long time reader first time poster.

Ok so I have a 97 ford ranger v6 4.0 L w/ 120,000 miles. 3 months ago engine light came on, according to my scanner I got at o2 sensor error driver side. First I replaced o2 sensor, scanned it again, in no longer said o2 sensor error for driver side but for passenger side, so I replaced that one too, just to make this short same thing happened again on the 3rd o2 sensor. So I checked the voltage and they are in the required voltage range. So I started to look elsewhere for the cause of the lean errors. I found a couple cracked hoses and replaced those cleaned the MAF sensor, replaced the EGR valve, and the PCV valve. None of that worked and to make things worst I was getting o2 errors on all 3 sensors at once. So I decided to do something I never have done and take apart the engine and replaced every gasket I could, the upper manifold gasket the fuel rail gasket, the lower manifold gasket and both valve cover gaskets. After all this I still got an error but just for the o2 sensor on the driver side.

So since I tried all that I thought I could do, and I do not have time anymore to fix it at my leisure, so I took into the ford dealership. 4 days later they told me that my o2 sensors work fine, and then they said it could be a short, so they checked the electrical and said everything is grounded correctly. So according to the book now they think it’s the PCM. They can’t get original OEM parts for my truck so I have to use a 3rd party PCM. There price is $450 just for the part. Since I’m out of ideas I have to try and see if a new PCM fixes the problem. At least they said I could bring in a PCM myself and not use there’s.

Now I never considered the PCM or thought about it, I know little about them except they need to be programmed and I can’t find very many of them. The part number he gave me for the OEM PCM is “F7PZ-12A650-ACA”. I can’t find that number online so I think it’s wrong or the number has changed for later models. I have found some PCM modules on the Rock Auto website but still dont know which one to get. I have also found one made by “Jet Performance”. If anyone has a recommendation on another PCM id appreciate it.

Thanks for any help.

 

The Ford Dealership said that they couldn't find a new PCM. Unbelivable.

 

Not an oem one. They also said there is no warranty for anything they do with the pcm labor or parts. Becuase it is a 3rd party device.

 

check the wiring form the PCM to the o2 sensor and insure it is good no bad (melted or chaffed) or shorted wires.

 

Does sound like the pcm, although the O2 sensors may have their own ground wire to the pcm. That's another thing worth checking.

If you have access to a GOOD scanner, they can show you a graph of what the pcm thinks that the O2 sensors are doing. Auto techs commonly observe scanners while driving around. (Of course they always have 2 people in the car )

You could also take a chance on a junkyard pcm or price some remans. When I got one for my mopar at a junkyard, they said that "we take them out of cars with engines that are running". Meaning that it was probably from one that had been in an accident.

Remans also seem to be available -- although, I think that generally means retested. From what I've read ( I've never done it on a Ford), the pcms aren't that hard to change. Hopefully some knowledgeable person will weigh in on that.

 

I'm assuming "remans" is a brand of PCM? Can someone point me to where i can find one. Google isn't helping any.

Never thought about a junkyard, don't know if there are any in orange county, but probably there are some in la county.

As for the electrical the ford guy told me he checked all the electrical from the o2 sensors to the harness, and found no ground short. I hope hes telling the truth it took him 3 days to tell me there was no short. Would that process also include checking for shorts from the PCM to just the o2 sensors?

I don't know if my scanner does monitor o2 sensors while driving, ill have to check.

Anyone here of "A-1 Cardone" brand of PCM at RockAuto.com? Just $179.00.

Thanks

 

I have found very few bad ECM's i would exhaust all other avenues of diagnostics before I would buy a ECM. They don't let you return those if it doesn't fix the problem. I would definitely see what a scanner says about that sensors output. I would probably try swapping the sides with the affected o2 sensors and see if the problem moves or not.