I need desperate help with my bronco II. I have a code 41, and have done everything I can think of to track the problem down.<O</O</O
1. Replaced Oxygen Sensor, 2. Replaced Fuel filter, 3. Checked Fuel Pressure, MAP, FPR, 6. Vacuum lines & Leaks, 7. Borrowed Break out box: Checked ECM, Injector Bank I and Bank II, resistance of each Injector, Injector Driver Signal. 8. Checked external Source for fuel pressure problem.
Other observations: Bronco starts good, runs good until warmed up. Hesitates, after warmed up, while accelerating until approximately 3000 rpms and starts to pull strong. (???) I understand that at WOT the ECM overrides (term?) the O2 Sensor, but what is causing the Bronco to run lean. Things I have not checked yet
1. clogged Catalytic Converter
2. TPS?
3. IAC?
Please advise<O></O>

 

1st question: is it a CM 41 or a KOER 41 or both? Did you clear CM/KAM after changing the O2 sensor? Can you determine if the engine is in fact running lean as reported by the O2 sensor or is it really running rich?

 

I cleared the codes after every step. I am not sure about the CM, but I know it shows up during KOEO test. I will check tomorrow and see if it show up in CM.

 

CM codes are the second set of codes output during the KOEO test. Does it give you a pass (11) code for the first set of codes from the KOEO test? I'm also guessing that means you haven't tried the KOER test. Because KOER codes represent hard faults, it is often easier to diagnose from the KOER test.

 

Ok, I cleared all codes again today and start from scratch. Warmed engine up for 10 (+) minutes @ 2000 rpms. Shut engine off and using jumper wire between self test connector and self test input (STI) started to pull codes, and here are the results:
KOEO - 11 / 11
Continuous Memory - 41 / 41
KOER - 41 /41

please advise

 

Now that's how I like to see someone report the results of the self-tests.

Is it actually running lean as indicated by the O2 sensor or is it really running rich? Sometimes the best way to see what's going on inside the engine is to pull the spark plugs and see their condition.

Have you put a voltmeter on the O2 sensor signal wire? What do you get?

Any exhaust leaks? An exhaust leak upstream of the sensor can allow excess O2 into the exhaust stream and make the sensor think the engine is running lean. Misfires can do the same thing.

Have you checked the state of your grounds? O2 sensor signal is less than 1V. A bad ground can insert enough error into what the computer sees to cause problems.

 

mrshorty before I go on, thanks so much for your time and advise .....

1. I checked sparkplug #6 (looks ok, maybe a little carbon build up on the base)

I also checked the O2 sensor and harness with a voltmeter, removed the O2 sensor from the vehicle and checked with the voltmeter while using a propane torch (based off of a troubleshooting guide I have) all seems normal/OK.

I am going check under the Bronco to get a good visual / audible on the exhaust, and check for leaks up-stream from the O2 sensor and provide results here.

Please advise on how to best check the ground

 

I decided to rule out the TPS. Used breakout box and measured between pin 47 & 46 ( .96 volts TB closed, and 4.36 WOT), so appears to be ok.

 

The best way to check a ground is to measure the voltage drop across the wire.

 

I am following the alldatadiy troubleshooting guide, but got stuck at checking the O2 sensor. It has good signal, but because it has 4 wires vs 3 wires the steps don't match the troubleshooting sequence and it is setting me back. This Bronco is getting me so frustrated. I do enjoy the experienced and I am determined not to retire this vehicle.
Anyway, back to troubleshooting; Am I checking the ground around the O2 sensor, ECM, or the whole engine bay? Please give me a starting point. Where would you start?

 

I need help troubleshooting a 4 wire O2 Sensor. I did an internet search and got conflicting information:

Black wire1: Heater element neg
Black wire2: Heater element 12 VDC
Gray: High output signal (ECM)
White: Low output signal (ECM

or

Black wire1: Heater element neg
Black wire2: Heater element 12 VDC
Gray: O2 ground
White: O2 signal

Please advise, I need to know to properly troubleshoot the my O2 sensor & harness

 

My wiring diagram isn't very good, and doesn't have the same colors. But it shows a Gray/Yellow wire as heater power and Black/green as heater ground. That black/green is the same as the computer ground, and also comes off of pins 40 and 60 of the computer.
I don't show colors for the other two, but the signal+ wire goes to pin 29 and the signal- wire goes to pin 49.

 

I think part of the troubleshooting problem was that this bronco II was built in late 89. I have a buddy who also has an 89 and his HEGO connector only has three wires, and mine has 4 wires. As mentioned:

black / green - HEGO Heater (-)
gray / yellow - HEGO Heater (+)
green / purple - HEGO Signal

on mine:
orange - HEGO (-)

On my buddy's bronco II the orange wire is grounded to the back of the engine. I decided to cut the wire and ground it to the engine. I cleared all codes and ran the truck, no engine check has come on yet. I going to pull codes anyway to ensure all is well. I will provide feedback later.