MIL and running lean ?

SPoole · Post by **SPoole** » Sat Oct 11, 2008 11:36 pm

Not sure if this would be software or hardware? I was driving to work a couple days ago and my MIL came on and put me in limp mode. I did not have my laptop hooked up but I had it with me so I pulled over hooked up my laptop and when I restarted the car it was fine, so I continued on to work with no more trouble. When I was coming home that night I left my laptop hooked up and it did it again so here is a log of while it was on. The only thing I am noticing is that in the log my Overboost cut is on, but I was not even in boost when it started. Also my car seems to be idling very lean all of the sudden, my PLX reads 18-20 AFR but my comp screen wont show higher than about 17.5 AFR. Any ideas?

David974 · Post by **David974** » Sun Oct 12, 2008 3:33 am

Hi you have a problem with your wide band check connection in D14/ground and check your WB programmed analog output regards

Post by **calvin** » Sun Oct 12, 2008 3:16 pm

i'll have a look at log and cal

SPoole · Post by **SPoole** » Mon Oct 13, 2008 1:24 pm

I am not sure if it is a wideband problem... I checked my connections and everything seems ok. The reason I doubt its a wideband issue is that it only seems to be having this problem at very little to no throttle. When I give it any gas it seems to be fine but at idle and very little throttle I am seeing 18-20 AFR. The cars feels like it is running fine until the MIL comes on. Could it be a bad injector causing the lean condition at low load? Also, any ideas about why the Overboost cut is on?

SPoole · Post by **SPoole** » Mon Oct 13, 2008 2:11 pm

I just pulled my plugs to see how they looked and they are all black and wet so I know its getting loads of fuel. I let it idle and my gauge showed 19-20 AFR so my plugs should not look like that should they? Does that sound like maybe a bad gauge or O2 sensor?

Post by **calvin** » Mon Oct 13, 2008 2:33 pm

to me yes

David974 · Post by **David974** » Mon Oct 13, 2008 3:00 pm

SPoole wrote:I just pulled my plugs to see how they looked and they are all black and wet so I know its getting loads of fuel. I let it idle and my gauge showed 19-20 AFR so my plugs should not look like that should they? Does that sound like maybe a bad gauge or O2 sensor?

what i said? In my experience each time i see 3.8V on the WB input ( when D14 is used or stock sensor) while display show anther value the WB meter had a problem or NB sensor had a problem regards

Post by **calvin** » Mon Oct 13, 2008 4:51 pm

stock ecu can read till 3.8v that is about 17.5 on plx plx will read 20 or 19

stenseltizm · Post by **stenseltizm** » Mon Oct 13, 2008 6:37 pm

SPoole wrote:I just pulled my plugs to see how they looked and they are all black and wet so I know its getting loads of fuel. I let it idle and my gauge showed 19-20 AFR so my plugs should not look like that should they? Does that sound like maybe a bad gauge or O2 sensor?

does your car idle smoothly or rough and sputtering? I'm guessing the latter. If your car is dumping that much fuel to soak the plugs it's probably misfiring. O2 sensor reads unburned oxygen in the gas so a misfire will throw the reading way lean.

SPoole · Post by **SPoole** » Mon Oct 13, 2008 8:44 pm

So you think maybe pull some fuel out and see how it reacts?

SPoole · Post by **SPoole** » Mon Oct 13, 2008 9:58 pm

OK, I tried leaning it out and it started running rough so I went the other way until it started running rough and it did not seem to help. When I got so rich that it would finally read on my O2 it was stumbling alot. So I have it set where it idles the cleanest. I logged the entire time from start-up till I was done and I noticed that my AFR started out good then very quickly started getting lean until it was off the chart. But it still registers fine when I give it any amount of throttle.

SPoole · Post by **SPoole** » Mon Oct 13, 2008 11:18 pm

Here is my .cal and log file from my test tonight. Notice the AFRs climb at the beginning of the log.

Post by **Bugermass** » Tue Oct 14, 2008 12:22 am

if your o2 sensor is located too close to open air, or in a LARGE downpipe it will read lean at idle and low engine speeds.

SPoole · Post by **SPoole** » Tue Oct 14, 2008 2:23 am

It is in a large downpipe, but this issue has just started in the last couple days.

SPoole · Post by **SPoole** » Tue Oct 14, 2008 5:33 am

So I may have figured out the problem. I feel kind of stupid for not noticing it sooner, but I have a pretty large exhaust leak at the flange upstream of my O2. I am going to fix it in the morning and see if the problem goes away.