Ok guys.. This has been going on for a long time and I haven't been able to solve it. I do not have a check engine light on.. When I pull codes on the koeo and continuous memory nothing shows up but when I do a koer test a code 41 always comes up. I have verified with a voltmeter that the o2 sensor does stay low during this test but if the truck is not in test mode it switches between rich and lean normally. I have tried a lot of things including 2 other o2 sensors. Any ideas??? BTW it is a 91 f150 2wd auto with a 5.0L.

 

Bad wiring.

 

What he said......pull the plug for the O2 pigtail apart and clean the contacts...may have a bad connection and throwing itself into closed loop.

 

If it's a bad connection or wiring issue, why would it only do it during a koer test. Besides I have already ohmed the wiring back to the computer and it checked out. I have also tried a different computer and get the same results.

 

Because there's nothing for it to read unless the engine is running. Maybe it really is running lean. Have you done a fuel pressure test?

 

I'm sorry but your post doesn't make any since!!! If I drive the car around for months and then check the koeo and continuous memory....there are no codes. If I run a koer test right after I get a code 41.

 

Was there ever a resolution found for this issue? I'm having a very similar problem:

My vehicle:
1989 Ford Bronco 5.0 (302) (stock engine)

KOEO Codes:
11 (System Pass)
Continuous memory codes:
11 (System Pass)
KOER Codes:
41 (No HEGO switching detected always lean (right side).)

What I have done:

Tested fuel Pressure (39 PSI, holds far beyond 60 seconds, drops roughly 1 PSI every 2-3 minutes)

Tested HEGO Connector ground (2.9 Ohms)

Tested HEGO Heating element & Sensor.

Cleaned the harness and tested the wiring making good contact to the sensor.




Any suggestions?

 

I just had this problem about a year ago.I checked the system twice and had a buddy check it also just to be sure I was testing it the right way.Replaced the PCM (interbal fault) and all has been good.