EC-439 for my '04 coupe:

It does mention that under 'normal conditions' it is not used, but there are no specifics given about exactly what an abnormal condition is. I have confirmed in my logs by extensive trial and error testing, that they are in fact used, so the 'abnormal condition', whatever it is, doesn't include CEL's. It wouldn't surprise me if any type of major modification (test pipe, HFC, or even injectors/tune mods) could trigger such condition.

 

Never knew that. I removed mine from the beginning due to test pipes and i never had a problem. Does your 04 have the widebands? I wonder if that might be the difference as i'm non-wideband.

i'd be curious what they define as "shifted" for the sensor 1's to cause the sensor 2's to take over.

I would have never guessed them to be used since the a/f will be altered after the catalyst. I assumed it would be a wild inaccurate interpretation of actual cylinder a/f.

 

I have widebands. I outlined it in another thread... but basically when I used non foulers I had issues with the A/F wandering rich from time to time, while at the same time logs indicating the ECU is overcorrecting by adding fuel. Not all the time, mainly during long freeway drives. the only explanation could be an 'overly lean' reading on the lower o2's...and over time I finally got a 'lean' code for both banks.

By removing the nonfoulers the condition never returned, and corrections are now normal 100% of the time. It could even be the case the ECU is no longer using the lower o2's, and only started using them previously due to the 'tricked' reading.

I suspect that if you completely remove the lower o2's the ECU will not use them. But any attempts at 'tricking' them ended up in ****ed up closed loop operations for me.

 

ah, i could see that being an issue.

again since you are a wideband car verses my non there might be a difference in the jobs of the rears. I had non-foulers with no issues at all before i removed them.

 

Were you monitoring with a/m wideband the whole time you had the nonfoulers on? I wonder how close to target stock narrowbands can even get being how slow and inaccurate they are. What was 'normal' for you might have been what I was seeing as an issue.

 

yes, i had a wideband from day 1 with FI. My idle and cruise a/f was dead on when i was vortech running the ss box and non-foulers on my rear. It would barely fluctuate .1 a/f at idle.

 

Update -

I did about another 200 miles and the lean spot appears to have gone. The car drives much smoother now when part throttle accelerating and in general really, so its looking good.


One thing I have noticed though, since changing the o2 sensor, it seems to be running richer at WOT. It was tuned to run around 11.8 AFR towards redline but since changing the o2 sensor it now runs around 11.2 AFR.

I thought the o2 sensors wouldn't have any effect at WOT because of it being in open loop?? Or do the long term fuel trims still have an effect on things when in open loop?

 

You are correct that o2 sensors will have no effect on open loop. Also, the fuel trims do not apply to o2 sensors either. Long and short fuel trims are only applied to closed loop fueling.

It's hard to say what could have changed it. Barometric pressure, air density, temperature. Those will all change fueling. The ethanol content of your gas will also change it. Some pumps use 5%, some all the way up to 15%. That will change the density of the fuel will can slightly affect your a/f ratio. I wouldn't worry about it going down to 11.2. Just ride it out and see what it does. It should start to lean out as the weather gets colder.

 

Ah, that makes sense then, as it was an unusually hot week for us in the UK. I'm away working for a couple of weeks now so will see how it goes when I get back and the weather is cooler. Really looking forward to being able to drive it properly without having to worry about possible damage from running lean. Think I'll treat myself to a day on the track.

Thanks alot for your help

 

Well, the o2 sensor hasn't cure the problem. Well it did until I changed it again. I don't know if you remember but I put a 2nd hand sensor in and it seemed to cure the problem. It appeared to run perfect for about 300ish miles. I then decided to replace both the front o2 sensors with brand new ones to be sure (wish I hadn't now) and reset the ecu. Sure enough after about 60 - 100 miles it was back again and has been ever since.
I was pretty frustrated so thought I'd get xmas out the way before I thought about it again.


So as it is now, on startup (whether engine warm or cold) it fires up fine, Afrs @ 14.7 ish then after a second or two it gradually starts to lean out all the way off the scale, over the course of about 5 seconds, until it runs rough and is about to stall then it suddenly drops back to 14ish afr and runs smooth.

Once driving the lean/flat spot (mid to high 16's afr and it hesitates) happens between 3 and 3.5k when part throttle accelerating in vacuum between 0 and 10 inHg. When accelerating with positive boost it doesn't do it, and likewise at very gentle acceleration -10to -20 inHg its also fine.

My next move was to Remap with one of the new Airflow Meters just to eliminate that, but I'm not holding my breath.

I'm also wondering if there could be a problem with the O2 sensor wiring on the car as it drove so well until I disturbed it by replacing the sensors again.



I really wanted to track it this month. Do you think it could do any damage if I did? I can pretty much drive round it now by keeping +ve boost when accelerating, but when it does run lean its not under much load due to being in vac ?

 

Exhaust leak and/or clogged cats..

 

Mmmm, I have decats, but I suppose an exhaust manifold leak, could be a possibility. How would it cause these symptoms?


I assume a smoke test is the way to go to detect this? I'm yet to find someone that does this.

 

Update for anyone interested - All sorted!!

Went back to the tuner a couple of months ago and fitted a MafGT in place of the PMAS and another remap.

I have since done around a 1000 miles and a day on circuit and its as smooth as silk.


Tuner is not 100% convinced that it was the Maf, but more likely the transition between closed and open loop that was causing the issue. The car pretty much runs open loop now during any level of acceleration and this has cured the lean spot.
Only downside is I'm using a little more fuel (down about 4 MPG on average) but I can live with that!
Also got a little more power out of while he was there.

 

I had been tuning a 7 psi turboed revup engine with a stock MAF and encountered a similar problem to yours.

I found out that although the TARGET AFR table was set to richer then stoich in this area the ECU would (under certain parth throtte conditions) first go into open loop but then switch back to closed loop for a few hundert rpm and then back to open loop again. I was only able to band aid the problem by adding a lot of fuel into the fuel compensation table for this specific "spot". It was eventually cured when the car received a different MAF (PMAS).