o2 sensors and fuel trims

[3000gttom]

hi, i was wandering which of the 4 o2 sensors have what tasks

i have an n/a dohc and i put headers in and i have a fuel trim code for bank 2, or does any one have the evoscan ID locations for all 4 sensors?

i have the front o2's with their respective banks but the bank 2 rear o2 is not with its bank because there just wasnt the room on the headers for it

[mb3000]

IIRC Bank 1 is the front, bank 2 is the rear. Sensor "1" is the primary, closest to the engine.

I.E. "Bank 2 Sensor 1" would be the rear primary sensor.

[3000gttom]

do the primaries have full control over the trims or do the secondaries also play a part in that?

[Hans@GZP]

secondary O2's are just there to make sure your precats are working. They do no effect fuel trims. You may have to space out your downstream O2's so you don't throw a CEL.

[3000gttom]

ok good thats what i thought, i just did some logging and my o2's are working just fine, my low trims are around +5 for the front and +11 for the back and mids are +11 front and +12 back

i reset the trims and immediately they started adding lots of fuel...

right now i dont think there are any problems with my car other than the headers give more than 12.5% VE more than the stock DP and the ECU is throwing a CEL because of that...i guess i need to learn how to tune the ecu to expect more VE now

[99 vr4]

Just a quick note, using Mitsubishi notation, Bank 1 is actually the LEFT side of the engine, other wise referred to as the "rear" or the side closest to the firewall. It is commonly though that Bank 1 is the front or right side of the engine, but that is a common mistake. The stock EVOScan locations that EVOScan provides are incorrect.

[3000gttom]

got my fuel trims to +/- 5% but i still threw a CEL, i guess i'll read it later and see if its the same one or something new

[3000gttom]

fuel trim is no longer a problem, the codes now are from not having precats... guess i need to find a fix for this now...

[NOMIEZVR4]

Kinda on topic, but how much a variance in fuel trims is allowable between the 2 banks of cylinders? I'm talking about the lo and mid trims...

[3000gttom]

i dont think the difference between the banks matters... my bank 1 trims are about 5-8% less than my bank 2 trims... i would believe this is due to the rear manifold definitely being more restrictive than the front

i just tuned it so they split across 0 and the bank 1 are -2.4 to -4 and bank 2 are 2.5 to 4... they can go either direction to +/- 12.5 i believe before it throws a CEL

[Greg E]

Kinda on topic, but how much a variance in fuel trims is allowable between the 2 banks of cylinders? I'm talking about the lo and mid trims...

I'd see wonky trims on my stock 98. +6% front low, +2% Front Mid then turn around and see -7% Rear Low and +5% Rear Mid.

Got me why this is... Car runs butter smooth so it doesn't bother me.

[iceorphen]

finally getting around to tinkering with trims.. is it normal for the trims to remain a steady number..with 0 change? I have been driving for a few weeks and they are set at 12.5%. (both o2s cycle fine) front+rear mid+low are at 12.5% with the rear low at 12.3xxx. Just wondering before I go and mess with the VE if this is normal to have such "steady" numbers?

Thanks :)

[Greg E]

Your trims are max rich that's why they are steady. Better track down your vac leaks. ;)

What injectors are you running?

[iceorphen]

Rc 660s

[DG]

I'd see wonky trims on my stock 98. +6% front low, +2% Front Mid then turn around and see -7% Rear Low and +5% Rear Mid.

Got me why this is

Small exhaust leak letting fresh air in at idle.

DG

[Greg E]

Small exhaust leak letting fresh air in at idle.

DG

I thought that at first too. But normally you can hear those little leaks. Even after removing the heat shields and inspecting them closely, I found no evidence of a leak.

Always figured it was a dirty injector or something trivial like that.

[DG]

Put a little Seafoam in and watch the fun.

I'm going through this right now trying to get my car to pass emissions. New injectors, fuel pump, and plugs but rear bank is reading way lean at idle and the O2 correction on that bank is huge. Back three cylinders full of carbon so poured a little Seafoam directly into those holes while I had the plugs out to help clean it a little. Fired car up and a steady column of smoke pours out from underneath the back turbo.

No audio indication of leak, but oh yes it is there - and the light goes on as to why the O2 correction at idle is so friggin' wonky.

DG

[iceorphen]

Upped my entire VE table +5 clicks (]x5) went for a longggggggggggggggg drive, and let it idle a ton. The rear mid began at ~10% and eventually settled on 12.5 again :|

Im going to reflash with +15 clicks and see where it gets me. Anyone care to share their injectors/pump and how much of an adjustment was needed? Curious to compare my results.

rc660s
hw wally400

[Greg E]

Hmm... Where did you get your injector from?

Can you post your injector scaling and latency values?

[iceorphen]

Injectors from maximal, scaling is @661
V mS
4.69 3.315
7.03 2.100
9.38 1.065
11.72 .630
14.06 .360
16.41 .180
18.68 .045

[iceorphen]

Didnt get to flash the +15click but with +10 the mids are settled at around +6% so im almost there. My lows however are still maxed at +12.5.

When looking at the stock ve table the 100hz and below values are lower than the 125hz and up values. Looking at my situation now my numbers will flip, by the time my lows are within +-5% leaving the 100hz and under higher than the 125hz+.

It probably isnt an issue at all, but I wanted to bring this to the attention of other chrome users

[niterydr]

Didnt get to flash the +15click but with +10 the mids are settled at around +6% so im almost there. My lows however are still maxed at +12.5.

When looking at the stock ve table the 100hz and below values are lower than the 125hz and up values. Looking at my situation now my numbers will flip, by the time my lows are within +-5% leaving the 100hz and under higher than the 125hz+.

It probably isnt an issue at all, but I wanted to bring this to the attention of other chrome users

Did you ever flash the +15? I ask as I've got a similar car here I am tuning, one injector is 18% off the others pre cleaning (11% off post cleaning still) and that was causing a huge issue with fuel trims bouncing around/drifting.