I have read lots of 172 threads but none completely match my situation.
Why would I get a 172 after a KOER test, but have no KOEO codes or continuous memory codes? This is a 97 5.8 for those viewing on a mobil device and cant read my sig.

My only simptoms are are an occasional rough idle at stoplights and it tends to throw egr codes in the winter but none currently. Engine was fully hot for KOER.

Thanks

 

No check engine light while driving, the only time I have ever gotten the 172 was teaching myself the KOER test the other day.

The egr code that shows up in continuous in the winter is a 332 but the CEL only blips and goes away, never had a continuous CEL.

Anyone?

 

What sig?

I am viewing this on a desktop PC...no signature is showing.

 

Thats odd, my sig has all the specs of my truck, I know I cant see anyones sig or even profile picture from my safari or opera mobile browsers.

I will make sure it didnt get deleted somehow...

 

Thats odd, i switched to full site view and I can now see yours, but not mine?

 

Well there it is, apparantly it only shaws up if I post from full site view?

Anyway, how about my random 172, why would it ONLY show up on KOER? What would change to cause a lean condition that isnt there normally?

 

Partially lean system, or a bad O2 that's not switching.

 

Right, I just dont understand what is different about the KOER test from normal driving that would trigger the 172.

One thing I dont normally do is blip the throttle, but I dont know why a short trip to 3k rpm would set it off. I do the test as follows: full warm engine, jump connector, start engine, engine key code flashes, pcm tests ICV by itself, light flashes once telling me to blip throttle, blip, one flash, then it idles for a few seconds and gives me the code 172 twice in a row.

Would the blip expose a vac leak not normally present somehow?

 

One more bump, why would a KOER test throw a 172 but not normal driving?

 

My 1997 Ford Service Manual shows Code 172 is a KOER and a Continuous Memory Code. When I looked through the troubleshooting guide it never listed Code 172 as CM, only KOER. So I am a bit confused on why there is a troubleshooting procedure for a CM.

A couple of theories here...if Code 172 is KOER only that would answer why it only shows up in the KOER tests.

If there is a CM Code 172 then perhaps you have not driven it enough cycles to trigger the code. Another thought is the fuel pressure may be on the low side during no-load conditions.

The troubleshooting guide also suggested a plugged PCV valve or fuel contaminated oil can be a cause of Code 172.

 

Interesting,

The member Digicon is having a similar problem, on what I believe is my exact truck only a year older, only he is having his code 172 show up during normal driving??

I will double check the fuel pressure, PCV, and smell the oil for fuel like you suggested.

I am inclined to think its not driving too few cycles, as it was not a CM code after checking KOEO codes just prior to the KOER test.

 

If the O2 sensor has ~80-100k miles on it, that's probably the problem. They do eventually wear out.