Runs perfect.... until it doesn’t.

[WmWatt]

A search on "CEL codes" lead to this link to a video showing how to read them...

https://fordfestiva.com/forums/forum/maintenance/repair-help-forum/61496-video-how-to-read-obd1-codes-cel-code-17

That search would show more posts on codes should you need it.

[Sfbradburn]

About time for an update…

Festiva got put on the back burner for awhile. My 8month pregnant wife got t-boned in July, fractured her wrist but that was about it. Baby was born at the end of July as planned, and is completely healthy.

I did end up checking the code, and it threw a “15” O2 code. I traced the wiring and didn’t find anything wrong. I knew the O2 sensor was just replaced so I was hesitant to replace it. Since I wasn’t driving it long distances, I just left it for a few months and used it to hop onto town. The issue was still there.

On one trip to a buddy’s house I decided to unplug the O2 sensor. At this point I assumed it would run the exact same which would point to bad wiring or a bad O2 sensor… once unplugged, I went a whole trip without the missfire/bogging. On the way home I decided to take her on the Highway and really open her up. Absolutely no problems. I got the Festiva well over 80mph and didn’t even give a hint of running rough.

It’s been about 2 months, and the O2 sensor is still unplugged, and the Festiva is still running perfectly. I ended up taking a 2+ hour beach trip mid October to surf and drove back the same day. Ran 70mph+ both ways and didn’t have an issue. As of now I’m just going to leave it as is. My county doesn’t have emissions inspections, and it’s running so good that I don’t really won’t to mess with it. Are there any potential issues from running without an 02 sensor permanently? I’m guessing the previous owner put the wrong 02 sensor in or something.

[WmWatt]

My understanding of the O2 sensor is to detect unburnt hydrocarbons in the exaust. If there are too many the computer adjusts the air/fuel mixture to try and bring them down on earlier models. On later models I believe it also adusts other things like timing advance. What you might see is lower fuel economy. BTW if you unplug the sensor I think the check engine light should stay on. The car will run with malfunctioning emissions controls. In fact it's a design feature. You don't want the engine failing on the freeway because there are a few hydrocarbons in the exhaust. Cars are designed to run without the contols, called "fall back mode". It will get reduced fuel efficiency, pollute the atmoshpere, and won't pass an emissions test. On any Festiva when first started the car runs in fall back mode until the O2 sensor heats up and starts working. You won't be harming the car, just the environment. People here have recommended the DENSO O2 sensor.