Well, lately I've got HORRIBLE gas milage(normal for a bad o2 sensor), running very rich(as far as I can tell). Well, I installed an air/fuel guage yesterday and it just sits there on the richest it could possibly be. Is this because of a bad o2 sensor or another problem? I think I hooked the air/fuel meter up correctly, but I just wanted to make sure. Red wire for +, black wire for -, and the purple wire for signal.

Since I'm assuming that is right, what else could be wrong with it?

Michael

 

An rx with a non operational acv and or air pump, will give you a high reading at idle. Such as .7 to .8. If you go on a drive and put the car in fifth and cruise along, the lites should jump around and if you had a meter on the signal wire you'd see the voltage jumping on either side of stoichometer or .4v. Go to the www.autometer.com site and look under tech tips and frequently asked questions and you'll see how one of those meters is supposed to work. i.e. the flashing lites. By the way, with wide open throttle it should read around .7to .8 for a n/a rx. At least thats what I observe. EDIT: Here, try this http://autometer.com/

 

Okay, now here's a good question, why am I suposed to tap the wire for the air/fuel meter?

Michael

 

I don't understand *tap the wire for the air/fuel meter*. There might be a misunderstanding. I don't have a air/fuel meter. I elected to just use a cheap digital volt meter from Radio Shack instead. Does the same thing. I was not suggesting you tap into the wire with a volt meter if thats what that phrase meant. Do the lights flash as you drive the car?

 

I connected the purple wire to the O2 sensor wire. About 2" from the connector.

 

Your right, I ment 'where' instead of 'why'. Okay, I've tapped the wire(using wire taps, they just break the insulation and contact the wire) and all I get is the air/fuel guage pegged to rich all the time. Hmm...

Michael

 

Even when you drive the car????

 

Weird! I just posted this before I saw your post!



Since I had recenlty done the BAC fix I have a feeling I forgot to put some grounds back on the ECU. As a matter of fact, the main braided ground with ring fell off(!) and I forgot to replace it. I will try grounding the ECU better tomorrow and let you know if that was it.

N1XRR—I have the same problem and by deduction I've come to believe that the problems lies at the ECU. I just don't know electronics enough to determine if an improper ground would effect the sensor reading! Any help?

BMy Post on the O2 sensor and A/F gauge

 

Bump

 

I also think my car is running rich. I havn't hooked up an Air/fuel meter, but I have made one out of an LED and plugging the LED into the CODE checker (green plug) by the battery. I'm told that if the light is on SOLID that means running rich and if it's OFF that means running LEAN, and if it's flashing on and off that's stoich. Well I plugged it in and started my car and the light would come on constantly... I would rev to 3k and it would stay on, if I let it drop to 1k it would turn off, then give it gas again and ON... Not sure what's up

 

While the closed loop system is there only to improve economy, a failed O2 sensor should not cause "horrible" gas mileage, only a mild reduction. If the car is running as rich as you say, something may be causing that, and the O2 sensor is simply reading it. Are you getting an error code for the O2 sensor or anything else? A gas analyser at a workshop will confirm if you are actually running rich, then you can start looking for the cause.

 

Maybe I'm just going about this the wrong way. Can someone, who has successfully installed their A/F gauge, please post what and where they used their 12v switched source and their ground?

B

 

Well, I just finished regrounding the ECu—both injectors and O2—and tried the a/f gauge out again. No go. I don't get it! The only way the A/F gauge works is when I disconnect the 02 sensor from the car. As soon as I plug it in I lose my reading. Is there something about the connector or the stock wire that I'm not getting? I have the A/F gauge O2 lead spliced in about 10" before the connector (behind the intake.) Is the lead supposed to go directly to the O2 sensor? Can I ask anymore questions?

B

 

Disconnect the wire b/t the o2 sensor and the ECU(PULL THE PLUG OFF THE ECU). Using your meter, see if the wire is grounded. And second, make sure the center conductor is not shorted to the shield around the center conductor. In other words make sure the center conductor is not shorted to ground. EDIT: The shield itself should be grounded.

 

I have heard before that you should not tap into the O2 sensor wire in the engine bay because it's a shielded cable. When you tap into the wire, you will almost certainly "join" the signal wire to the wire shield. This is definitely not what you should do with shielded cable. You should connect A/F meters to the ECU end of the wire, which isn't shielded. I've never been able to absolutely confirm this, but if you know a little about shielded communication cable, it does make some sense, and no one's flamed me when I've suggested it before! This may your problem, but I can't be sure.
BTW, what exactly did you do when you "regrounded the ECU—both injectors and O2"?

 

Hailers, you ALWAYS manage to post just before me!
That's good info, rxse7en, do what he suggests.

 

What time of the day is it in NEW ZEALAND right now, please?

 

I had recently replaced the O2 sensor with a generic Bosch model. No shielded cable.

I just went out and checked my voltage at 2D at idle and I was getting a negative volt reading. The O2 wire in the wiring harness is not conducting! I just bypassed the wiring harness and now I get a correct reading at 2D! Even the A/F gauge works correctly now.

NZ—I regrounded 3G, 3A, 2R and 2C. And, I know there's gobs of people in NZ, but my wife wants to know if you know a Geoffery Alexander? I had to try.

Now that I think about it, I don't remember the previous o2 sensor cable being shielded. There was only one bunch of smaller wires inside. Not two different ones.

Am I running a risk by bypassing the wiring harness?

B

 

How about this guys...

There is a wire near the back of the car that is only for ground that attached to the exhaust, but doesn't reach becuase the Racing Beat exhaust doesn't have a place for it....could that be a ground wire thats causing a problem?

 

Just some info. The shield for the shielded wire is terminated prior to reaching the ECU. Its terminated about six or so inches before terminal 2D. Its covered up and you have to work at it to find the shield. The place most likely for the shield to touch the inner conductor is at the mating point with the oxygen sensors connector. It would only take one small strand of the shield to kill the output of the 02 sensor. I don't think you'll ever miss the shield in the way you have your car set up. Just a guess.

 

12:10pm, Tuesday

 

Ah, no... sorry, man!
Glad to hear you got your problem sussed.

 

Thank you gents!

B