Hi guys. I'm getting a check engine light and my 5.0 is running like a pig. I've been getting about 8 miles to the gallon. Even with the 33 X 12.5s I run and 4:10 gearing this is bad for the truck. I've has exhaust issues with this truck since I got it. Twice I've had mushroomed valves in the 8 cyl. and I used to run through cats like there was no tomorrow. Well back to today, and I'm getting a 41 code in the continous memory. I also got a 77 code two of three times, which I don't know why. I did the dynamic response test what I thought to be the same.

Anyhow I'm wondering how to go about testing this and see if I can rectify the underlying problem and get this dog running strong again. I know I can change the O2 sensor but I want to do this right, not just change parts.

Thanks

Mike

 

Code 41 is an O2 sensor reference voltage LOW for an extended period of time during the last 40 operations of the engine. (most likely a bad O2 sensor) the O2sensor reading being off screws with a whole litany of other engine control devices. Fix this one and the rest should come back in line.

Code 77 is only generated during the KOER test. You must push the acceleartor to the floor and release it within ten seconds of the dynamic response code. Repeat the test and "goose" it within ten seconds of the code and see if 77 reappears.

 

I agree with greystreak92, just make sue the o2 sensor you buy is prefired those that are not prefired can and usually do go bad fairly quickly. It's easy to tell because when you open the box it looks discolored like its been in a vehicle already.

 

Is code 77 the only code in KOER? If you're getting 8MPG, I would assume you'd get a Code 42 as well.

 

Not necessarily. Code 41 is a LOW voltage reading from the O2 sensor. Code 42 is a HIGH voltage reading. If the O2 sensor has failed, the continuous reading will remain where ever the sensor has "stuck".

 

After posting, I thought about that possibility. (dead O2) Nice catch there, greystreak.

Makes sense....dead O2 reporting low voltage (lean condition) to EEC. In turn, EEC enriches mixture too much causing terrrible mileage.

 

Hi again guys. I don't want to sound unappreciative but I am aware that I can change the O2 sensor, but I guess I didn't explain that this happens frequently. I am wondering if there is something thats fouling the O2 sensor or theres a flow problem with the gases. And yes the problem is and has been that the engine ends up running rich and thats causing overheating of the cats and overheating the valve (especially the 8 cylinder)

I am looking through my receipts but I think the O2 sensor is only a year or two old.

Thanks

Mike

 

Mike, if you have a multimeter, you can check the O2 sensor wiring. You might have a wire intermittantly shorting out on the exhaust somewhere? Or a high resistance plug-in? You're right, an O2 sensor should last longer than a year or two; they're ususally good for at least 60-80K miles.

 

You might check your fuel pressure as well. A faulty regulator can give you too much gas ; fouling the O2, and the other symptoms you describe.

 

Old, dirty plugs and intake components also contribute to an initially "rich" mixture which may well have an effect on things too.

 

Just to play the devil's advocate here for a second, after reading his problem description and lack of success in fixing it, it sounds like one Bronco that I would dump.

 

This has been over ten years though and 150000 miles. So I should add that. I'm thinking I'll test the fuel pressure and test the O2 sensor. I'm also going to take it to a muffler shop cause I think I got a leak or two in the muffler. Is there a way to test the exhaust and air recirculation system?

I am going to tune it up this weekend. Plugs, wires, filters (oil, gas and air) rotor, cap...anyhow I guess I'll see how that resolves it.

Jbronco you have to go to the corner and sit for five minutes. Dump the Bronco? I hear you, but I been through hell and back with her so not happen'.

Thanks guys

I guess now I'll have to ask how to check the o2 sensor.

Mike

 

OK sorry, I just got out of the corner. I just figured that you would automatically know that I meant that you would buy another Bronco. But I kinow what you mean about being loyal to your ride. I used to be exactly the same way, and I still basically am, but I have a lot less tolerance for continuing problems then I did when I was younger and after a while I decide not to be loyal to a vehicle that is not being loyal to me (I don't mean to imply that about your Bronc). I went as far as to place a 'for sale' ad in the paper for my Bronco about 2 1/2 years ago when it seemed that everything that could break, did. It was right around 100K. I fixed all kinds of stuff but I was so p!ssed about all the money and honestly I did not trust the truck anymore. But something stopped me, I pulled the ad and told callers that I decided to keep it. I am glad that I did because since then it has been very dependable (knock on wood) and I've done a lot of stuff for creature comfort like a bad-a$$ stereo and other things. Since my credit went down the crapper after I was laid off from work, I have decided to keep the Bronco for the rest of my life, unless I win the lottery or something. And even then, I would keep it and make a show truck out of it.

 

There's 4 wires going to the O2 sensor... If you unplug the harness, you should see the 4 Pins:

Find the 2 Wires that goto HEGO and Ground. Plug the harness back.
With a Voltmeter, backprobe the 2 wires (HEGO, Ground).

Start the engine cold. The voltage should be .6V or higher.

Once the engine warms up to operating temp., the Voltage should drop back down between .4V-.6V.

If indeed your O2 sensor is dead, the voltage will be stuck below .4V in your situation (Code 41 LEAN).

 

Sweet thanks. I'll do that this weekend and post what I find out.

Jbronco, actually I'd been going through that same decision process and I know I can get this thing tuned and gently work her back into shape.

Thanks guys you keep me truckin down the road.

Mike

BTW I got a smog check coming up and being that I'm in Cali its always tough to pass.