well i yanked off my egr valve again and found that the plenum was all pluged with carbon so now thats working . one thing i have found is when i am doing my koer test i am monitering my 02 voltage at the same time and as soon as i push the test button the voltage spikes from .34 ish too 1.2 ish thats before the engine even revs up. i went for a good drive toniht got home did a koeo test 11 10 11 so everything is ok i then did a koer test and got a code 41. possibe i have some interference voltage?

 

so i found out that my canister purge valve was not working it has been letting air pass through all the time probly causing my problem . anyways now i can drive as long as i want come back pull codes and i get 11 10 11 so its all good. only thing is when i do a koer the code 41 comes right back i can still watch the voltage spike as soon as i start that test. i dont understand why this is happening.

 

There have been instances where the O2 heater voltage does bleed through to the signal output. A high resistance connection due to a faulty heater element or contamination can allow this happen. You may not see it in normal operation because the PCM is running in open loop at start up. At least that is my interpretation of how the circuit works.

 

ok so i went for a 2 hour drive and just when i thought i had it figured out the check engine light comes on pull codes and i get a 42 rich 10 seperater code and 41 the dam lean code. stupid thing dosent know what it wants ...

 

Just wondering if you ever figured it out? Im havin the same freakin code haunt me right now and ive done damned near everything to get rid of it lol. Lemme know where your at with this!
Matt

 

So did either of you guys find the solution to this? I've been having quite a fight with it myself.

Situation:

1989 Ford Bronco 5.0L (302) Stock motor
KOEO codes: 11, 11

KOER codes: 41

What I have tested/tried:

Confirmed that the ground is less than 3 Ohms (Presently .02Ohms) (HEGO)
Confirmed that the heating element is good. (HEGO)
Confirmed that the fuel pressure holds.
Confirmed the EGR is functional
Checked for Vacuum leaks (Engine runs fine.)

This has been driving me up the wall for weeks. Any insight would be appreciated.

 

What is the fuel pressure at idle w/vacuum hose on the FPR? What is it w/vacuum hose off the FPR? What is the fuel pressure under load?

How old is the O2 sensor? Is it covered in dirt/oil/etc.?

Are there ANY leaks in the exhaust system ahead of the O2 sensor? A tiny leak can trigger a lean code.

 

Thank you for replying so soon. My results are as follows:


At idle with the FPR attached:

36PSI

At idle with the FPR disconnected:

42PSI

The O2 sensor is brand new and I've compared the resistance against the manufacturer's specs and other new O2 sensors.

What I meant in the last post by "Fuel pressure holds" is that the system held pressure for well over 60 seconds. It drops at about 1PSI every 3 minutes or so.

 

FYI.. The most likely source of air leaks upstream of the O2 sensor is in the Thermactor(air injection) system. On 1/2 ton trucks there is a tube across the back of the engine connecting ports on the back of the cylinder heads that are internally connected to the exhaust ports. This tube is connected to the air pump via a series of valves and tubing, and this tube and the check valve attached to it are metal and prone to rust and cracking. When this happens you may hear what sounds like a small exhaust leak but the bigger problem is that this will also let some fresh air into the exhaust upstream of the O2 sensor which will cause all sorts of problems for the computer to maintain the correct air/fuel ratio.

 

I could not find any leaks in the primary exhaust areas, but I haven't checked the AIR system. I'll check that when I have a moment.