Hey all,
Today I figured out an issue with my cavalier that had been bothering me for quite awhile. So first some history.
I turbocharged the car (2001 Chevy Cavalier) using the GMSC reflash for a base tune with the aid to get me running credited to Ryan from P&P. I got the car running well enough in open loop to continue tuning beyond that and get a good baseline hammered out. Soon thereafter I got my emissions notice meaning I had to reenable closed loop fueling and get my monitors to run in order to pass. I struggled getting the vehicle to run well enough to even think about driving it and after going back and forth diagnostically I settled on swapping out the aftermarket Bosch O2 sensor (primary) for a GM one from the dealer (Manufacturerd by NTK) This got the car running well enough to pass emissions but an issue that has been there since then (and actually was the reason it would not run with the bosch) was still persistant. Basically after startup, warm or cold when the car drops into closed loop my Short Term Fuel Trims begin subtracting fuel excessively (up to -22
driving A/F ratios beyond 18:1 and cycling this lean several times before beginning to cycle normally. (A/F cycles rich and lean of 14.7:1 ~10% above 4Hz @ 2000RPM) After driving, idling down for a few minutes eventually does result in a small rolling idle as the AF ratio cycles progressively richer and leaner.
Being in the Automotive program at Southern Illinois University I’m currently in an automotive emissions diagnostics class. In this particular class Im able to essentially create “bugs” on vehicles that will not necessarily be properly diagnosed by the manufacturers diagnostic procedures but can drastically affect 5 gas emissions and drivability. I decided to bring my car in yesterday to investigate my initial suspicions about what could be causing my issue. Originally my thoughts were when tuning the low end and idle VE tables I shot for A/F ratios that were too lean, therefore when closed loop fueling took control the PCM subtracted too much fuel and was running the engine too lean. I began researching this by adding 5% worth of fueling to the idle VE table and observing the logs and wideband readings afterward. I did this about three times and noticed no change in the way the vehicle acted whatsoever. However I did notice this…
If you notice the STFT is subtracting 22.7% fuel and the Wideband reflects a very lean AF ratio. The catch is that the B1O2 is still not getting much below 300mV. Interesting to say the least since the majority of the time O2’s cycle between 150-950mV on my vehicle. Which brings us to this chart courtesy of my Auto 340 class.
If you notice as we run the O2 sensor colder in its operating range both in rich and lean regions it begins to stay around its bias voltage instead of swinging to the proper rich and lean outputs. At this point it had all come together for me.
When the car was stock and also when I simply had a header on it all four primaries were firing directly at the O2 sensor which is also unheated. When the turbo went on my troubles began, so what changed besides everything when the turbo went on? Well quite simply now the exhaust exit’s the ports, through the manifold, through the turbine, and down about 12” of down pipe before the O2 sensor sees it. A huge difference when you are talking about EGT. My theory had been disproven but I now had a completely new theory that made a lot more sense. Quite simply, the O2 sensor was not getting up to near the temperature it should have been. So how do we go about testing this? Well quite simply I grabbed a spare heated O2 sensor from a GM 3.1, used test leads to wire the signal high and low wires to the stock connector, and then wired a rheostat between ignition B+ and grounded the other side of the heater circuit. I reduced the resistance on the rheostat to 0 firing the heater up in the sensor, and cranked her over watching the log for when it fell into closed loop…
Notice the STFT during initial drop into closed loop only drops to -12% or so. The AF on the wideband also only shows a maximum of about 15.7:1 AF. Perfectly acceptable since STFT during normal cycle does not drop so low.
So the lesson here is watch where your moving O2 sensors, I could have avoided a lot of headaches in diagnostics had I left the O2 a lot closer to the turbine exit.
My move to solve this issue is to #1 find out if my PCM has pin outs for an O2 sensor heater for the foremost O2 since this O2 sensor was superceded in 2002 with a heated version for the ecos. Majority of GM vehicles in 2001 however used a heated upstream sensor and the same PCM so I may have the ability and the pinouts on the PCM existing already for a heater control circuit. My second possibility is to use the heater circuit for the rearmost O2 to control the front via a relay. Third possibility is simply using a toggle switch to control the O2 heater for a preheat and to maintain temperature during closed loop operation.
Anyone else had any issues like this?
Buildin' n' Boostin for 08' - Alex Richards
SUMMARY: Use a heated O2 sensor if you have an LD9. Why they didn't come with one stock, who knows. They're great.
2001 Olds Alero (LD9)
650 whp / 543 ft-lb
@turboalero
[ion wrote: C2]SUMMARY: Use a heated O2 sensor if you have an LD9. Why they didn't come with one stock, who knows. They're great.
^X2...I installed a heated sensor in my '00 and I drop into closed loop within 15 seconds after key on from a cold start....much easier to work with.
Glad to hear you got some answers.
"Never argue with an idiot. They'll drag you down to their level, then beat you with experience!" -Anonymous
[ion wrote: C2]SUMMARY: Use a heated O2 sensor if you have an LD9. Why they didn't come with one stock, who knows. They're great.
Read my profile, I'm 2200'ed....lol
But nevertheless...
There you are...
Buildin' n' Boostin for 08' - Alex Richards
I feel both the LD9 and 2200:s with any exhaust work should have a heated O2 sensor.
FU Tuning
As for seeing if there's a pin-out on you PCM for the heated primary EGOS... it wouldn't surprise me if there's one. I remember an article on a mid-west roddin'-shop that's doing flex-fuel conversions on even OBD-I systems, and they said they simply use an unused pin on the factory box to feed the ECM inputs from the GM in-line fuel-type sensor... commonly found on '00-'02 S-trucks with "5" as 8th VIN character... mounted in the system. Since the S-trucks & J-cars use the same PCM (What I've heard...), there just may be one if the S-trucks have it from the factory.
Go beyond the "bolt-on".
No need to try and find a pin in the ECU for it. For the heater circuit jump it off the rear (heated ) O2 sensor. Also there is a kit for the one wire sensor card to add a heated sensor.
FU Tuning
yeah i have a very similar problem, car goes lean after startup for 30 seconds or so .. ECU is subtracting fuel trims but if i force the car into open loop AFRs are perfect .. and car's ok when its hot.
sounds like a heated O2 will fix the problem so i'll be wiring that up eventually - i remember reading the heated O2 howto a while back.
14.82 @ 97 mph
Jason Z24 wrote:yeah i have a very similar problem, car goes lean after startup for 30 seconds or so .. ECU is subtracting fuel trims but if i force the car into open loop AFRs are perfect .. and car's ok when its hot.
sounds like a heated O2 will fix the problem so i'll be wiring that up eventually - i remember reading the heated O2 howto a while back.
If you remember where, show us too so we can learn it.
Go beyond the "bolt-on".
If you have 2200, there is a company that makes a plug and play harness for 4-wire 02 sensor. I don't remember the name, but it is here somewhere.
>>>For Sale? Clicky!<<<
-----The orginal Mr.Goodwrench on the JBO since 11/99-----
Actually if you just pull the two pins out of the stock PCM end of the O2 connector and repin them correctly into the 4 pin connector you can save yourself a whole lot of money.
The 4 wire connector can actually be had under a Fuel pump harness repair kit...Same Metripack connector, I would recommend that you do use the existing pins in the stock 2 wire connector in the new 4 wire since the o2 breathes through the wires for the reference gas. That way you avoid any splices or joints. Repin the new connector with the two old signal high and low wires and run your heater circuit however you so choose and your good to go :-)
4wire O2 connector/PCM Side
This part is actually only 10.99 if I remember correctly, I just checked today i dont remember for sure.
Buildin' n' Boostin for 08' - Alex Richards
Alex: You got a diagram for that, please?
Go beyond the "bolt-on".
Here is the electrical diagram for the stock sensor...
This is the connector for the O2 sensor...
You will want to take the Tan and Purple wires from the stock 2 pin connector and pin them into pin cavity A and B on the 4 pin connector. If you get this fuel pump connector from Advance you will need to make sure the purple wire goes in the correct cavity as the connector out of the bag has a purple wire as well which is in the wrong cavity so pay attention to which is which. The two black wires will be your heater wires and can be pinned either way, Polarity does not matter.
4 pin fuel pump connector
Buildin' n' Boostin for 08' - Alex Richards
