O2 sensor readings
Thread Starter
Drifting
Joined: Oct 2002
Posts: 1,774
Likes: 66
From: SoCal
O2 sensor readings
I just had a supercharger installed and I am having surging issues. Car is a 99 coupe.
I am trying to figure out a issue i am having with the surging. My O2 sensors when hot and in closed loop will stay high (850-900) at idle. When driving steady throttle they will stay high but the front ones will fluctuate a bit but mostly read high. Although today on steady throttle they dropped to 35-45 and stayed there until I got on the throttle then they went high again and stayed there.
They do not fluctuate from low to high much at all. Its either low or high for the most part. Pretty much flat lining. The car drives fine as long as i am either on the gas or off. If I am keeping a steady throttle it misses/surges. Idles fine too. No CODES thrown at all. That is the puzzling part. Since the O2s read strange you would think there would be codes. Any ideas what to look for.
Thanks.
Greg
I am trying to figure out a issue i am having with the surging. My O2 sensors when hot and in closed loop will stay high (850-900) at idle. When driving steady throttle they will stay high but the front ones will fluctuate a bit but mostly read high. Although today on steady throttle they dropped to 35-45 and stayed there until I got on the throttle then they went high again and stayed there.
They do not fluctuate from low to high much at all. Its either low or high for the most part. Pretty much flat lining. The car drives fine as long as i am either on the gas or off. If I am keeping a steady throttle it misses/surges. Idles fine too. No CODES thrown at all. That is the puzzling part. Since the O2s read strange you would think there would be codes. Any ideas what to look for.
Thanks.
Greg
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
The 02 sensors when in closed loop should oscilate very quickly from
.150 to .950 (apprx) If they are flatlining anywhere they are not working---could be several things causing this----Did you buy the SC as a kit ? If so they should have sent you a handheld programmer to load a viable tune---If not you need to get it tuned---most likely if both 02's aren't working it is something that affects both sides--It may be stuck in "open loop" where the 02's are not functioning yet--You could have blown 02 heater fuses--You may have a bad ground--make sure you didn't accidently plug the rear 02 pigtails to the front 02's ( this happen quite often)--check the closed loop temp enable --should be around 130-140*
The surging is most likely caused by it staying in open loop where the fuels trims are NOT being applied to correct the fuel mixture--and its running in the "start-up or cold" engine mode all the time
It would run fine at PE or WOT beacuse there it would trump the 02 issues---At idle there is no load so it could idle fine too---but at part throttle acceleration where it is under a load it could cause surgingif the trims are not being adjusted by the 02 readings--
.150 to .950 (apprx) If they are flatlining anywhere they are not working---could be several things causing this----Did you buy the SC as a kit ? If so they should have sent you a handheld programmer to load a viable tune---If not you need to get it tuned---most likely if both 02's aren't working it is something that affects both sides--It may be stuck in "open loop" where the 02's are not functioning yet--You could have blown 02 heater fuses--You may have a bad ground--make sure you didn't accidently plug the rear 02 pigtails to the front 02's ( this happen quite often)--check the closed loop temp enable --should be around 130-140*
The surging is most likely caused by it staying in open loop where the fuels trims are NOT being applied to correct the fuel mixture--and its running in the "start-up or cold" engine mode all the time
It would run fine at PE or WOT beacuse there it would trump the 02 issues---At idle there is no load so it could idle fine too---but at part throttle acceleration where it is under a load it could cause surgingif the trims are not being adjusted by the 02 readings--
Thread Starter
Drifting
Joined: Oct 2002
Posts: 1,774
Likes: 66
From: SoCal
Thanks for the info. Something else I forgot to mention. the LTFT is at 0.00 and the STFT is at -2.15. It stays like that all teh time. does not fluctuate. Idle on the gas or cruising it keeps those readings. Bought the SC as a kit. No programmer. it was tuned. trying to figure out what is going on here. I cant believe 4 O2s would go out at the same time. Probably not a bad idea to change out the O2s as they are probably old and it wouldn't be a bad idea, just not sure if that is going to help. Then with the static LTFT and STFT readings as well, something else must be going on.
Thanks.
Greg
Thanks.
Greg
Racer
Joined: Mar 2006
Posts: 277
Likes: 1
From: Springfield Missouri
Stop were you are. If I read your profile right we have the same s/c kit. I was told by the owner of the shop that the tune is for you to drive from your home to a tuner. I know my tune on my 02 Z06 was rich and safe. Your stock 02’s can neither read nor handle what you need them to do. You need a tuner with a wide band 02 sensor and to stick that thing on a dyno or take it down the road. IMHO you should switch to an SD mode for permanent operation. To be honest with you, you are barking up the wrong tree looking at fuel trims. FYI narrow 02’s read 14.5-15.2 give or take and my wide band 02 read 20’s and 19’s and on the other side 12 and 13 A/F ratio’s while I was tuning. You just spent 5k on the s/c kit now go get a tune and you will be able to give it hell.
Thread Starter
Drifting
Joined: Oct 2002
Posts: 1,774
Likes: 66
From: SoCal
This is after it having a tune and being on the rollers. Apparently it was fine and tuned. Something happened afterwards i guess because it has surged since picking it up. But I am lost as to what it is. I have been told to look at the injector pulse width. Like I said, I have a hard time believing 4 o2 sensors going bad all at once. Just called GM to find out what they charge for o2 sensors ~600 bucks for all 4. 115 a piece for the front two that really matter for tuning i guess. Fun stuff.
Greg
Greg
Stop were you are. If I read your profile right we have the same s/c kit. I was told by the owner of the shop that the tune is for you to drive from your home to a tuner. I know my tune on my 02 Z06 was rich and safe. Your stock 02’s can neither read nor handle what you need them to do. You need a tuner with a wide band 02 sensor and to stick that thing on a dyno or take it down the road. IMHO you should switch to an SD mode for permanent operation. To be honest with you, you are barking up the wrong tree looking at fuel trims. FYI narrow 02’s read 14.5-15.2 give or take and my wide band 02 read 20’s and 19’s and on the other side 12 and 13 A/F ratio’s while I was tuning. You just spent 5k on the s/c kit now go get a tune and you will be able to give it hell.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Depends on how much boost you are making---Most typical street S/C 's only make about 4-5 lbs boost--well within the operation of the MAF and the fuel trim system--If your trims aren't changing, more than likely it is stuck in open loop as i mentined-While in open loop the trims will lock on the last recorded trims in closed loop-Ask your tuner if he did a Speed density tune--he may have --then you wouldn't have any fuel trims
The front 02's are the only ones that operate in conjuction with the MAF and the fuel trims---the rear 02's are there only to report on the cat converter performance and cooling them down if they overheat--I doubt that you would have ruined both the fronts at one time--again check the 02 heater fuse and check the pigtails--check with your scanner to see if it is in closed loop after it warms up--As a test you can install the rear 02 sensors onto the front and see if anything changes--many people make that swap regardless as the rear 02's are much more sensitive and some people believe they work better that way
The front 02's are the only ones that operate in conjuction with the MAF and the fuel trims---the rear 02's are there only to report on the cat converter performance and cooling them down if they overheat--I doubt that you would have ruined both the fronts at one time--again check the 02 heater fuse and check the pigtails--check with your scanner to see if it is in closed loop after it warms up--As a test you can install the rear 02 sensors onto the front and see if anything changes--many people make that swap regardless as the rear 02's are much more sensitive and some people believe they work better that way
Racer
Joined: Mar 2006
Posts: 277
Likes: 1
From: Springfield Missouri
If you had a tuner do the work and he did so on a dyno you should bring this issue up to him or her. There are a lot of things that could be wrong but we have a hard time knowing what they are. I would not mess with the injector pulse width. I think you are like me and love getting knowledge of what is going on with your car, while I love my brethren here on the corvette forum the availability of good reliable tuning information is sparse. You should look at some of the sticky treads on hp tuners and ls1 tech forums. It will help clear up some of the issue. You need to find out if you are running in SD all the time or if you still operate in open loop. Also the surging could be from a spike in your ve table we just don’t know, did you replace your map sensor to one that can read boost and did your tuner give you the correlating ve table to read the map sensor, if not your cpu is guessing when you are in boost. There is a lot of info that we do not have and your might not know about so before you spend more money read up on the fundamentals of tuning and talk to your tuner.
Racer
Joined: Nov 2007
Posts: 441
Likes: 3
From: Huntsville Alabama
What was the fix? I am having the same problem, 1 month after upgrades and a dyno tune, the car started missing and serging,,,,,,,,,,,NO CODES
After pluging a laptop up to it, the 02 sensors show little activity.
After pluging a laptop up to it, the 02 sensors show little activity.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
