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Info on the O2 Split for Turbo IS300

9K views 19 replies 5 participants last post by  braintumor 
#1 ·
This may sound obvious to some of you, but it came as a hard-learned lesson for me. So I figured I'd share this story, if nothing else just to put additional knowledge on the site and for others to contemplate.

TLDR: The ECU calculates the temperature of the Oxygen sensor while making Fuel Trim adjustments.

For nearly three years, I've run the AEM FIC-6 on my Turbo'd IS without a CEL. I accomplished this by fooling the ECU in several ways to keep it happy, and by carefully tuning while monitoring my fuel-trim data via OBD. Today's discussion will focus on a condition that has plagued my tune, but is now finally resolved.

After extensive research, I was able to fool the ECU into thinking all four oxygen sensors were present and accounted for - when I was only using one. I built an O2 simulator for the secondary (post-cat) O2's that output a "clean" signal and used high-wattage resistors to fool the heater circuits. For the primary O2's, however, I removed B1S1 and split the signal for B2S1 into B1S1 @ the ECU. This is a common mod with lots of information available on this site. This effectively ties the two banks together, so the ECU no longer gets independent feedback from B1 and B2. However, I did not split the heater circuit.

Instead, I left B2S1 heater connected to the Oxygen Sensor, and B1S1 heater connected to a high-wattage resistor that was rated within the repair manual specs. I made this decision based on my understanding of how the heater circuitry works. The heater circuits are controlled using a high-wattage pulse-width modulation circuit (PWM). This line outputs a square wave to heat the O2 sensor. Therefore, I assumed, if I were to connect the B1 heater circuit to the B2 heater circuit, I would end up with a confluence of square waves at the very least. There's a chance the current for B1 could overload the circuitry on B2 - or vice versa. By placing a stable resistance (relatively) on B1, I could sink this current and avoid overloading the heater circuits, damaging the ECU, or damaging the O2 sensor with too much current.

Herein lies my problem. By placing a stable resistance (relatively) on B1, and a temperature-fluctating resistance on B2, the ECU would drive B1 lean, and drive B2 rich. So no matter how I tuned the FIC, I would always have a ~10% variance between B1 and B2. I could marginalize the driveability impact of this by centering the variance over the 0% mark - but nonetheless, it was still there.

This is where it gets interesting: While reading up on some obscure Google eBook about Oxygen sensor theory and calculations, I learned the ECU not only controls a PWM heater signal to heat the sensor, but it also monitors how much current is consumed (or sensor resistance, see: ohms law) as an approximation of temperature. This temperature calculation is then used to interpret the O2 signal and, subsiquently, the fuel-trims.

Aha!

So I rewired both B1S1 and B2S1 heater circuits to be run off one sensor (as the original mod directs) and whala -- both B1 and B2 fuel trims are now perfrectly in-sync and FIC tuning seems more responsive. The next day I took the car on a 2hr road-trip and, just before arriving, a CEL appeared for P0032 - Heater Control Circuit High (Bank 1 Sensor 1). I cleared the code, monitors the sensor waveform and fuel-trims, and the code hasn't come back since. ** knock on wood **

Anyways -- I figured this might be useful, or at least interesting, for anyone considering the mod and just general tuning information. Or it's just a simple demonstration of how "following the directions" is important. One could theorize, that if you wanted to tune the banks independently, all you'd need to do is tweak the resistance as a crude method.
 
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#2 ·
ok so I have been dealing with this crap myself, using the fic6 as well. I have both secondary O2s in there, no sim. I have bank1 sensor1 in there with signals wired together at ecu as mod says, and the heater wires wired together at the ecu as mod says as well. Im constantly getting a heater code for bank1 sensor1. and constantly getting bank 1 and 2 lean codes. Ive tried several O2 sensors, all used, and still get the codes. have a new denso on order and will see if it changes anything.

do you have the FIC o2 voltage adjusted/tuned at all? what is your MAF clamp set to? do you have a screen shot of your settings and fuel tune?
 
#3 · (Edited)
i cant splice primary or secondary 02 heater signals on my 03 without poppin heater cels consistently. therefor cant use secondary 02 sims either. could on my old 01 but not my 03 i have all 4 sensors plugged up for heater signals spliced primary fuel signals and bank 2 main signals as i run a highflow cat so installed a secondary in there. i can run an old wire in sim for secondary signals but will never set cat monitor and also throws cat cels randomly.

ive also run a log manifold with both primary sensors in place that works well

just my adventures on it
 
#4 ·
its funny, dont have a problem with the primary signal wires spliced, but just when the heater wires are modded as per this sites how to. does the fic plug and play harness already compensate for these things perhaps with a resistor or already combining the wires?
 
#5 ·
I'll do some more driving and see if I can trip the heater code CELs further. If so, I have a feeling adding a diode may resolve the issue, but I can't say for sure without further testing.

Braintumor - I don't have the o2 map adjusted at all. I do have it set in percentage mode and the map cleared out. I've read somewhere that having 0's in the map can screw w/ the tuning, the map has to be entirely blank. But that may only be when the O2 map is in voltage mode (where a 0 would be 0v). My MAF clamp is set to 4.2v, any higher and I get driveability issues. I'll snap a photo of my maps and settings and post them up.

Polishman - I've heard issues running a log manifold and both sensors. Because the exhaust stream is mixed and the stock ECU is constantly testing the O2 sensors on each bank by making incremental fuel changes and waiting to see the results at the O2, when this occurs it ends up chasing it's tail -so to speak- and you end up with crazy whacked fuel-trims. For example, it may increase fuel on B1 +1% and expect to see it at the O2, but instead it see's 1% overall, or on the wrong sensor, so it then tries +2%, +3% and so on - until it just gets out of hand.

Overall, I will say that having your idle and vacuum only fuel map is very crucial to maintaining fuel-trims and finding that 'sweet spot.' If you're off (lean or rich) the ECU tends to over-compensate and it gets extreme pretty quick. For example, I think right now I'm about -35% at idle, if I decreased it to -40 or -45, the fuel trims will get pretty extreme trying to overcompensate and will set CEL's. It takes quite a few trial/error and many ECU resets (at least 45 min each) to fully clear the ECU maps and start over.

I'll also add, that having a good airflow to the MAF is very important too. If you don't have an air-straightner, get one.. Best $15 I ever spent. Put it about 6-12" in front of your MAF in a straight section only and it will do wonders if you're having issues.

I've also seen an FIC tune create "holes" in the stock ECU.. If you're even 5% off from the 'ideal' you can see funny things start to happen. I had a hole that would kill my off-the-line driving at 1500rpms, 10% throttle, it would peg lean and I'd lose all acceleration.. Playing w/ the FIC map and adding a bit of fuel corrected this.
 
#6 ·
I don't use nor recommend the fic, I tried my hand on it briefly at one point lol.
Just wanted to share my 02 sensor experiences as I just revisited them for inspection purposes.
I've used emanage ultimate and ms3pro with good results on both is300s I've had.
When I ran the log manifold there was a primary sensor on bank 1 and bank 2 similar to stockish location so it worked well.
Currently been using the cx manifold and down pipe past 2ish years with one primary and one secondary spiced signals, b1s1 b1s2 plugged in under hood for all the heater signals to be present
 
#7 · (Edited)
any updates on this? did your p0032 code come back? so far that's the only code I'm now getting and I want it to go far away and never come back!


update. even with bank1 sensor1 unplugged I get the p0032 code. and even after swapping the EFI relay. so either wiring or ECU is messed up.
 
#8 ·
Yeah my P0032 came back twice.. Seems like a weekly occurance - despite my system monitors being "ready" most of the time. Really intermittant. My O2 opposite problem has come back too, although not nearly as bad as it once was. Idle it's pretty solid, but cruising under light throttle the banks start to seperate. I have no clue why -- my only guess is the stock ECU being a jerk.

Here are my fuel trims and maps. This is with 440 or 450cc injectors.










At Idle


At Cruise
 
#9 ·
Bro, how did you get that on your radio? That looks nice. I need that.
 
#10 ·
second that, my radio is pretty fancy but not THAT fancy!

ok I have been playing around with the fic settings, mainly O2 voltage maps/setting. have my high set to .999 low set to 0. on the map I put in .5 (sets to .401) and never get a slow response code only rich bank1/2 (dont have the skew set up) so the cars fuel trims are spotty for normal driving to full boost, again skew not set up. but thats the only codes I got were the rich bank1/2. oh and its set to OFFSET to fluctuate the voltage.

clear the O2 maps, set to 0 and run a fuel map I have it semi tuned for without any O2 voltage being sent to oem ecu from the fic. runs great once warmed up, codes for slow response bank1/2 pop up..........and my fuel trims become perfect..... ST fuel trim 1/2 at 0. LT fuel trim 1/2 at -5. this is with codes popping up, car fully warmed open loop-code caused with brand new denso O2 in bank1/1 in downpipe and ban2/1 plugged in but sitting out.

drove to work today like that and will check codes before I leave to see if heater code is back. but i think once I get the O2 skew down with the voltage set right it wont throw any rich/lean/slow response codes.

and why is you injector response time set to 688? what injectors are you using? I have wrx blue 440cc and set to 486. have you dynoed your car at all, thats my next step.

oh and I have checked the voltage at the ecm as per mitchell and the voltage is right. so Im really hoping the heater code isnt from a blown ecu
 
#11 ·
[IME] [/IME]
Is an Android based stereo - you can find them all over ebay and amazon. Pretty awesome little unit if you can get over the 30-40-second boot-up time each start.. and, like many custom-ROM androids, the occasional crashing and having to reflash the operating system. lol. I've heard the newer ones are much better though.


ok I have been playing around with the fic settings, mainly O2 voltage maps/setting. have my high set to .999 low set to 0. on the map I put in .5 (sets to .401) and never get a slow response code only rich bank1/2 (dont have the skew set up) so the cars fuel trims are spotty for normal driving to full boost, again skew not set up. but thats the only codes I got were the rich bank1/2. oh and its set to OFFSET to fluctuate the voltage.
I'll have to try offset versus percentage and see what it does. that's quite a decrease considering it's adding .5v to all O2 readings (on a scale of 0-1v with .5 being stoich). Wouldn't that mean you're forcing it lean, which causes the stock ECU to increase fuel-trim? Maybe I misunderstood that.

From my understanding, the O2 skew map was only supposed to be used for fine-tuning for closed-loop boost situations.. The fuel map should take care of closed-loop fuel trims in vacuum. Have you seen this?
Fried Rice BANZAI: Tuning: Closed Loop Tuning with O2 Maps

and why is you injector response time set to 688? what injectors are you using? I have wrx blue 440cc and set to 486.
OSIDETIGER 440cc. That's what was written on the testing doc that came w/t them. I've heard some horror stories about osidetiger... though when I finally resolved to buy a new set, tokensolutions closed down and I haven't really looked since. Did you have your injectors flow-rate tested or did you buy them new?

I haven't been on the dyno yet. Probably this summer.


so Im really hoping the heater code isnt from a blown ecu
ME TOO! Let me know how it goes.
 
#12 · (Edited)
I've been doing more and more reading on this subject over the weekend. I'm getting frustrated because I keep seeing my long-term Fuel-trims split (B1 going lean <0% and B2 going rich >0%) when they are sharing the same signal. Doesn't make sense. Unless the ECU is doing some tomfoolery.

So. I decided to go rogue, and run without any primary O2 sensors. Based on what I've read, I should expect the following:

1) A stable, open-loop fuel map that doesn't rely on input from the sensors
2) A constant check-engine light
3) Possibilty of two maps - a "cold" map and a "hot" map that apparently the stock ECU sets when the car is started (I've heard a temperature of 30C or 86F is the deviation point

I let the computer perform a deep reset overnight w/ no power. I started the car this morning and monitored some interesting results on my way to work. Along with accompanying thoughts...

1) Idle long-term fuel trims are still at -4.7% on B1 and B2 - despite the deep reset and no oxygen sensors. I'm wondering if my secondary O2 signal simulator is causing this. I think I heard rumors somewhere that the secondary O2's can have an influence in fuel trims as well.

2) Watching the ECU set the CEL for P0134 (B1S1 No activity) and P0154 (B2S1 No Activity) was fascinating. During a light cruise, the ECU progressively dumped up to 20% short-term fuel trim into B2 over the course of 5-10 seconds or so. It kept B1 at around -3%. As soon as it hit 20% fuel trim in B2 the CEL came on and it zero'd both short-term fuel trims.

3) Now w/ the CEL for Primary O2's, the long-term fuel trim is still off. During light cruise, tt's at -4.7% for B1 and +1.6% for B2. Short-term fuel trims are locked at 0.0%. During idle B1 and B2 Long-term fuel trims are -4.7%. I kinda expected to see 0's across the board.

I'm going to take two 45 minute drives today. I'll be interested to see how that goes.
 
#13 ·
OP with your FIC do you havea plug and play harness or wired into factory? I swapped things up on mine as well. took out b1s1, unplugged it, gone from car. plugged b2s1 into oem harness and installed it into downpipe. unplugged b1s2 from oem harness and removed from car. test drove and after a few miles CEL came on for b1s1/b1s2 heater codes. no codes for no sensor activity b1s1. took about 3 days for the ban1s2 heater code to come on, but no inactivity code. so plugged that back into harness and set aside out of exhaust stream to keep from getting code. fuel trims at idle ST 0, LT between -3/-5. LT goes up to -7 or so driving. so it seems only thing I have to defeat is the heater codes. my harness is a token solutions, I tried to contact him about it (I bought it used from here) to find out how he had it wired. if he already did the O2 mod to the plug and play harness with resistors etc. and if by me doing the O2 wire mod to the factory harness with his plug and play harness installed I may have inadvertently damaged my ecu wich is why I keep getting heater codes. I know hes busy and havnt heard back yet, but if anyone does know about his work please let me know.
 
#14 ·
Hi braintumor,

I have a DIY harness.. When I first did the FIC i cobbled it together from an ECU patch harness kit. I've since totally rewired it and checked it countless times. I've done the resistor adds for the O2 and cam/crank signals. In fact, I have a video on my youtube page showing an oscilliscope monitoring the cam/crank with various resistors so you can see the results they have on the signal.

There's tons of info on this site regarding these types of mods, it's just tough getting through all the threads and some misinformation (people usually posting when they aren't 100% familiar w/ stuff)...

Otherwise I don't have any information on what the TS plug 'n play harness consists of. Unfortunately.
 
#15 ·
Some more interesting data collected on my road trip.

First, it took about 2 trips before the ECU finally stabilized into it's open-loop. The short-term trims were the first to max-out... pegging at +19.5% on both banks and staying there. The long-term trims still acted like they were relying on some old learned map.



The bias between B1 and B2 in the long-term trims also became more divergent.. Here's a shot under light cruise (4th gear, 5-10% throttle on a flat road, just to maintain speed).



I parked the car, waited about 20 minutes, restarted and began my journey home.. Now the fuel trims are stable, pegged at +30.5% in B1/B2 long term and +19.5% in the short-term. No fluctuations



I retuned my fuel map (-51% across the board) and now my tune is stable. A solid 14.5 - 15.0 AFR during idle and cruise.

Other interesting notes,
1) by pulling this much out at the FIC, I notice a slight hestitation at tip-in from idle.. Aka.. pulling off the line.. just blipping the throttle a little causes a hiccup.. Going to try to work that out
2) I can't say for certain, but I think this open-loop mapping retards timing. The car felt kinda sluggish, I'll confirm though.
3) I can confirm the existance of a "cold" and "hot" open-loop map. When i started it this morning, it was running lean (15.5 - 16.0 at idle and cruise). I checked the fuel trims and the B1/B2 long-term trims were still at +30.5%, but the short term trims were at 0%. When I parked the car after warm-up and re-started, now the ECU puts the short-term trims back at +19.5%

I'm going to tweak the fuel maps and see what type of response I get. I'm also going to try messing w/ the MAF maps and see if that affects timing.

Stay tuned. (ha.. pun)
 
#18 · (Edited)
10-4 DIDN'T SEE THAT TORQUE APP, I am using stock ecu stage 2 bc cams,stock injectors, spliced b1s1 , sensor 2's in L defoulers . at first had multi misfires and code p0125. Did the b1s1 splice test drove was getting good afr's at idle and closed loop drove a couple miles good happy. next day p0172 and p0175 multi misfires mil on wtf cleared drove right back on. not sure why it worked that first day of splice but now running a little richer still has misfire at idle, off idle and part throttle afr's good and to full throttle afr's never go lean pulls good running on gate only with 8.7 spring. Idle sucks loads up rich if sitting a while going to try and splice sensor 2's. read some are drilling their throttle plate to lean out a little which i checked with a vacuum leak made. new o2 gone bad? or resistance needed I idle fuel pressure at 46-47 psi doesn't really change when lowered. anybody trick these codes on stock ecu? Answer = bad splice at ecu fixed codes now just get the ol random misfire codes running good closed loop so those codes listed related to s1 o2's if reader suffering same wtf issue.
 
#19 ·
An FYI on tricking the stock ECU.

I wired in an electrical shunt to the coolant temperature sensor circuit, controlled via pushbutton in the dash. I calculated the resistance needed to acheive 190 deg F and force the ECU into a hot map during a cold-start.

All in all, I wouldn't recommend this. It works -- the ECU consistently starts in the HOT map, although it does not like it, especially on cold-starts. It's also tricky to get the timing down.. you have to Key-On, push and hold the sensor shunt, wait for the temp gauge on the dash to get to operating temperature, crank engine, wait til turns-over, release pushbutton shunt, release key crank. lol. It's far easier to just program a hot and cold map in the FIC and flip a switch to accomodate whatever the stock ECU is doing.
 
#20 · (Edited)
my update on the O2 nonsense. so codes where b1s1 and b2s1 heater codes. ran a wire straight from my new O2 on b2s1 heater wire (pink) to the ecu........boom heater code gone for b2s1, my harness is screwed. still have b1s1, p0032 code. Im slowly tracking this down as Im lazy. currently running a wire straight from b1s1 heater wire (green) to ecu with and old O2 so we shall see how it goes.

edit/update. so still getting the p0032 code with heater wire running straight to ecu pinout for b1s1 heater. have voltage up to ecu pinout as well (PnP harness already had everything already converted for the O2 signal/heater wires to be run as 1 off of bank 2) so I may have fried it doing the wire splice again. ordered a new ecu and am going to see how it goes.
 
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