Hopefully this hasn't already been answered. It's a difficult thing to find the wording to search for....

Installed the AEM UEGO wideband, logged using the datalogit. Was immediately irritated since I get ocillating AFR readings, varying by as much as 4 or 5 AFR points at each reading. A graph of the AFR literally looks like a seismograph! I thought the sensor was to blame, or the wiring, but I verified that that's not the problem today, by removing the sensor, plugging the bung, and logging. It read a very constant 5V for the free air, with no ocillation. So now I'm left with the presumption that my engine is actually doing this for some reason. I have no idea where to start. What could cause this? Anyone seen this type of behavior? I can only hypothesize that maybe an injector is acting up, maybe my ignition system is failing, or maybe there's bad compression, although I don't know that these symptoms would match any of those problems. The injectors were just cleaned and calibrated about a year ago, so I really wouldn't expect them to be bad. I also have installed brand new plugs, and I've tried running water through the system to clean it out. The PFC maps are unmodified, just the injector settings changed to match my 4 850s.

If it would help to illustrate, I can post a log of the AFR data when I get home. Otherwise, any feedback would be much appreciated!

 

Unplug the stock O2 sensor and see what happens. My hypothosis is that you are running closed loop.

-Max

 

0.4 or 4.0

just to be sure before giving advice

 

I love this forum! Nice quick answers!

I've tried all combinations of open/closed loop. While troubleshooting, I did some idle logs, starting with O2/Ign feedback on, then just one or the other on, then both off. All have the seismograph look. And during a WOT run, it should go to open loop anyway, shouldn't it?

And yes, they are as much as 4-6 full AFR points difference. For example a log might look like: 8, 13, 9, 12, 14, 9.....

Just so I know what I'm shooting for, how much variance is in a good AFR log for a 7 running correctly? Such as at idle, will it give you a series of numbers off by only a few tenths? I can understand a few bad readings, but like I say, these are constant. If it would help, I can dig out a log for illustration, or post a picture of a graph of them.

 

that sounds like a bad sensor... you should not see variation like that...

a big clue as to it being your hardware and not your car is the fact that the sensor is only good down to 9.0ish (assuming its the bosche) besides im positive you couldent idle with an afr like that

 

Weellll, the car's not running just right anyway. At seemingly random times, I'll have a horrible idle, which feels like a whole rotor isn't firing. Once I get moving, it'll go away, and it might not come back the rest of the day. I'm also fouling plugs like mad, and they're TOTALLY black. I know my fuel maps aren't perfect, but I'm not sure they're bad enough that they'd be fouling everything that bad. The average of the sensor readings is about 12.5:1 at idle, and my WOT runs seem to be high 11's and low 12's. That shouldn't be too bad, again assuming the average of all these numbers is at all a reliable thing to be looking at. Still, you could be right. Maybe it's the sensor. I just felt like maybe that wasn't the case since it seems to read free air just fine.

 

im at about 13.5-1 at idle and i never go above 11.5 at wot... my car wouldent idle below 10-1 or higher than 14-1 when i was setting it up... at either of those extremes it would stall.

 

That's good to know. I wasn't sure what the limits were. And again, how steady are your sensor readings?

You know, I may have been wrong about my initial findings. I was just using a watch in the datalogit to look at the readings, but now that I've plotted the logs, it looks like the sensor may have been acting funky during the free air readings also. I'm getting ready to post a couple pics of the plots......

 

Here is a plot of the AFRs with the UEGO sensor removed from the bung, the bung plugged, and the sensor plugged in and reading the free air. The car is running, and I'm in a garage, so I don't know if it is picking up any whiffs of the exhaust or not.

 

are you sure the ignition and compression are ok?

 

Here is a plot of the AFRs with the UEGO sensor removed from the bung, the bung plugged, and the sensor plugged in and reading the free air. The car is running, and I'm in a garage, so I don't know if it is picking up any whiffs of the exhaust or not.

 

Check your grounds. Mine are bad, and just turning on the A/C effects it or even the radio. Check your grounds or add more throughout the car just to help it out.

 

And here's one of the idle, with O2 and ignition feedback turned off...

Sorry about the dup posts...having trouble with the server right now.

The ground should be good. It goes directly from the wideband control box to the battery. Not sure about the compression or ignition at this point.

 

your sensor is fubar'd or something is not set up right

 

Yep. Something isn't connected right or there is a break.

 

Log your fuel pressure if the problem is under load. Fuel pump may be on the fritz or feed/fuel filter isn't up to par.

The sensor and circuitry of a wideband either works (and calibrates) or doesn't from experiences building the TechEdge...

Regards,
--Ashraf

 

I guess I'll try some alternate wiring tomorrow if it's not too nasty out.

Shouldn't be pump related. It's happening under load, at idle, and as confirmed today, even without having the engine started......

Yuck, I hate electrical problems......

Thanks for all the input.

 

another duplicate...

 

No luck with the alternate wiring. Tried changing the ground from going straight to the battery, to using chassis grounds, and no change. Also tried running the voltage source through a relay and straight to the battery, and no change. Dammit!

 

send the person you bought it from the logs and ask them to replace the unit....


or return it and order one of these puppies http://www.turboxs.com/txstuner.htm

 

Wow, and then when you're through you can play games on it!

Actually I'll be seeing the shop I bought it from, tomorrow. They've been trying to help me sort through this too.......Think I probably need to get on the phone and talk to AEM directly.

 

Just to follow up....

Dynotuned today, and my AFRs are both steady, and they are actually about 2 full points higher (leaner) than the average that I'm seeing on the AEM. So that rules out the engine running that way.....