engine code help needed

[kned33]

I have a 1991 Festiva GL. Yesterday, the car would hiccup then run okay for a while then it actually stalled, started up easily. But most of the way home it would briefly die then start going. There were a couple mile stretches where it would be okay then it would resume running eratically. (I have noticed that at times it is hard to start.) I ran the engine code 1 flash followed by five flashes. What does the code mean. My shop manual is useless when to engine codes. Ironically my festy just passed Calif. smog three days ago.

[jglutz]

Code 15 = Oxygen Sensor
Check the wiring/connector first...if all in tack...time for a new one.

[kned33]

Code 15 = Oxygen Sensor
Check the wiring/connector first...if all in tack...time for a new one.

Thanks, I will do that. By the way it ran fine today. Can oxygen sensors create intermitent problems when going out?

[jglutz]

Yep; that why I said to be sure and check the wiring.

[FB71]

one problem with this scenario...

when the PCM identifies a fault, it sets a DTC. As soon as the DTC is set, the PCM goes into FMEM (Failure Mode Effects Management). This causes the PCM to ignore the actual value of the sensor, and plug in a "known good" value.

[jglutz]

^^Jim, i thought about that...FMEM (limp mode)...I think other than start up...the PCM does not time out the same for the CEL and FMEM...eg...if the wire broke....CEL comes on after 5 seconds....FMEM would come on after 60 seconds. In kned33's situation...maybe the O2 sensor circuit restored itself before FMEM kicked in but the CEL had already been set.

[kned33]

Jim, are you saying the oxygen sensor is in a sense being by-passed. I don't know what you mean by DTC nor do I know what the PCM is.

Skate - what is CEL.

Betwen the two of you what exactly are you talking about. I'm your average front yard mechanic so I need you to speak in terms I can understand. Though I am greatful for the input.

[FB71]

DTC = Diagnostic Trouble Code
PCM = Powertrain Control Module (engine computer)
CEL = Check Engine Lamp. Ford calls it a MIL = Malfunction Indicator Lamp

Joe, as soon as the PCM recognizes a fault worth a DTC, it immediately switches to FMEM, no delay.

More than likely, the O2 is not fully out of range when the issue occurs, and the PCM tries to compensate (changes fuel trim rich or lean). This is the period of symptom presence. Once the PCM determines the O2 is non-responsive, it sets a DTC and switches to FMEM, which plugs-in known good numbers for the O2 and long and short term fuel trims.

[kned33]

Jim,

So FMEM compensates for an oxygen sensor that is going out? Or has gone out? Or is simply none responsive do to a bad connection?

[FB71]

FMEM is a software strategy that causes the PCM to ignore a sensor that has been identified as faulty, and fills in a value it would normally expect to see, based on other parameters. The O2 could be flat (no longer responding to changes in oxygen content in the exhaust), it could be seeing an air leak in the exhaust manifold, making it read lean all the time, or there could be an electrical fault. Usually, an electrical fault will immediately trip a code, the MIL, and send it into FMEM without missing a beat. The fact that you a period of poor running, followed by a recovery and a MIL, tells me the sensor is either faulty, or you have a crack in you exhaust manifold / blown exh man gasket.

[kned33]

Jim, Thanks for info. If I had a crack in the exhaust manifold wouldn't I see an exhaust leak there? Likewise with a blown gasket? I have a troubleshooting manual for electrical components. I'll if it says anything about the o2 sensor.

[FB71]

Yes, usually you would hear/see a cracked manifold (provided you removed the heat shiel from it) and/or exh man gasket. Its also unlikely its either one of those two concerns, but not impossible. Most likely, the O2 sensor is just flat.

[kned33]

Yes, usually you would hear/see a cracked manifold (provided you removed the heat shiel from it) and/or exh man gasket. Its also unlikely its either one of those two concerns, but not impossible. Most likely, the O2 sensor is just flat.

Jim,

I just checked prices of o2 sensors. :evil: Autozone wants 173 dollars for a made for festiva sensor. They have a universal for around twenty but it is one wire. An Ebay store has a universal 4 wire for 25 plus shipping. Does it matter what kind I get. I prefer not to spend close to 200 for a sensor if I don't have to.

[FB71]

try this;

http://www.partsamerica.com/productdetail.aspx?MfrCode=BOS&MfrPartNumber=11027&PartType=291&PTSet=A

that's all you need.

[kned33]

Thanks Jim,

THere is a Kragen's nearby. I gather I will have to use a shrink wrap connector.