Bad O2 sensor?

The car hesitates and bucks between 2-3k. I searched and it sounds like it may be the O2 sensor. I have an accessport and if i resent the ecu the problem seems to go away but it comes back pretty quickly. I just got the car 3 months ago and to my knowledge it's stock besides the cobb with 81k miles. I logged my drive home from work and will upload that. Thanks for the help.

datalog17.csv

looked at the log . the o2 sensor appear to be working , however there appears to be quite a bit of knock.

 

in the knock sum it counted up to 34 3 times so about a 100 hits of knock .

 

can you data log the iam ( ignition advance multiplyier) this typically starts off at about .7 .. when the ecm sees knock the value will decrease and remove timming. when it gets below a certain point (.5) it will start taking away boost.

 

you may have a bad batch of gas , knock problem or even false knock problem

looked at the log . the o2 sensor appear to be working , however there appears to be quite a bit of knock.

 

in the knock sum it counted up to 34 3 times so about a 100 hits of knock .

 

can you data log the iam ( ignition advance multiplyier) this typically starts off at about .7 .. when the ecm sees knock the value will decrease and remove timming. when it gets below a certain point (.5) it will start taking away boost.

 

you may have a bad batch of gas , knock problem or even false knock problem

 

Is ignition advance multiplyier the same as dynamic advance multiplyier? I don't see iam on the Cobb.

 

The car did have some bad gas put in it by the dealer before I bought it. They only put about a quarter of a tank in it and once we realized what happened the tank was drained and they replaced the fuel pump. The car also had the headgasket, wastegate, clutch, and flywheel replaced before I bought it. I will run another log and upload it later after work.

Yes, Cobb and OS use different terms for the same thing.

 

OS IAM = Cobb DAM

OS A/F Correction = Cobb STFT

OS A/F Learning = Cobb LTFT

 

just for starters. With rough stumbling between 2 and 3k, those are going to be 3 important things to log when it comes to diagnosing the problem.

Hi, friend Welcome to the club (the low load knock, crazy IAM/DAM FUN).

 

First order of business: Check for leaks and loose components that can rattle

- inspect intercooler for burst tabs at the endtank

- check intake for tears

- listen for audible noises (could be endlinks, heatshields or other pieces rattling near the knock sensor)

- listen for a misfire while parked in garage or against a wall (I can hear one in closed loop - I finally got a CEL for misfire in cylinder 1 and I will be checking spark/ignition coil/injector)

 

 

 

Second order of business:

- since you are stock, uninstall the AP and see if it continues to act up. The Cobb OTS tune has been known to have some issues like this.

 

 

I will link my thread, and search the site using google "[your knock question here]" site:legacygt.com for best results.

 

 

I have replaced my O2 sensor thinking it was the culprit as well, $85 spent unwise. You should get new plugs if you have not already.

 

Worst case scenarios: burnt exhaust valve(s) or cracked piston ringland (typically #4)

I checked the dam on the way to work this morning and it was at 0. I've checked the blue t connector and clamped all the connections so no leak there. I will check the intercooler and intake too.

 

The car got a cel for misfire in cylinder 4 about 2 months ago and that is when the headgasket was replaced. They also sent the head to a machine shop to inspect the valves because they originally thought it had a bad valve. I would hope that if there was an internal problem the dealer would have noticed it when they had it apart.

you might wanna check this T fitting under ur intercooler that slip out from time to time. I got a new front a rear o2 sensor before i realize that it was the T fitting for some kind of vacuum line. Think i also got a code for misfire one 2 & 4 (p0702) i think....

-11* of knock is far more serious than a vac leak. get a compression test ASAP

-11* of knock is far more serious than a vac leak. get a compression test ASAP

 

The car had a compression test done before the head was pulled to replace the headgasket which was around 6 weeks ago. It was doing the same exact thing it's doing now before I took it to them. It sounds like they just tried to tell me they fixed it without really figuring out what the problem was.

Other possibilities are: Dual mass flywheel, noisy engine, rod bearings. Mine was occasionally pulling 11 degrees of timing. it's still a mystery. I am going to do a leakdown test this weekend, but I had a compression test done in January and it was 140psi on all cylinders.

 

I have a misfire right now that is pointing towards a bad injector (will know once I get the injector swapped). I put some seafoam in on a 1/4 tank and it seemed to run a lot smoother, filled it up a few mins ago and it's misfiring again. Have misfire at WOT ~4500-5500 rpm.

 

My working theory is bad injector: causing a slight misfire that is interpreted as knock by the ecu. I'll keep you posted.

 

Also, FWIW, Infamous1 has stated that some engines just seem to be "noisier than others". However, a few of us have had this happen for a while then suddenly have the #4 cylinder ringland crack. My misfire is on cylinder #1.

 

Upload more logs: one cruising around, one 3rd gear pull 2k rpm-redline

 

Also, try doing a seafoam treatment using hte bpv vacuum line and some in the fuel tank (do it on a low tank for better results)

Other possibilities are: Dual mass flywheel, noisy engine, rod bearings. Mine was occasionally pulling 11 degrees of timing. it's still a mystery. I am going to do a leakdown test this weekend, but I had a compression test done in January and it was 140psi on all cylinders.

 

I have a misfire right now that is pointing towards a bad injector (will know once I get the injector swapped).

 

My working theory is bad injector: causing a slight misfire that is interpreted as knock by the ecu. I'll keep you posted.

 

When this happened the first time the dealer thought it was a bad injector but when they replaced it the problem didn't go away. I'll probably take it back to the dealer since this is exactly what it was doing before.

 

I'm kinda pissed that I had to spend the money to replace the headgasket and it didn't change a thing. I was just hoping someone be able to give me an idea what's wrong that way they can't screw me again.

 

I haven't been able to read your thread yet but I will when I get home from work. Thanks for all the help.

 

Edit: The car came with a limited warranty that expires on the 23 of this month. I was hoping someone would tell me this was a simple issue I could fix myself but it's sounding like I should just let them handle it and hope that the warranty covers whatever is wrong.

 

I will log my drive home from work and also do a 3rd gear log and upload those in about 2 hours.

Another possibility is the knock sensor. They rarely ever go bad, but it might have cracked and can cause crazy readings like this. I am also going to swap mine with a known working one.

Ok here are two more logs. The first one is 3rd gear 2k to redline and second one is just cruising around. I also noticed a few drops of oil on the up pipe down toward the bottom where it connects to the exhaust manifold. Any ideas where this could be coming from?

datalog20.csv

datalog21.csv

You should reset your ECU and get some logs driving around immediately after. Everything is at -11 FLKC so it's hard to tell what's going on.

the oil leak in that area could be a leaky valve cover gasket....they may have reused the original one when doing your gasket.

oil could be from the head or turbo. Is your oil level ok?

Oil is defiantly lower than when I checked it a few days ago. Gonna add some and watch that.

 

Just reset the ecu and changed to the 91 octane stage 1 map. I was on the 93. Went for a drive around the block and logged it. Car feels much smoother but it usually does right after I reset the ecu. Looked at the log and it is still detecting knock.

 

About to go for a longer drive and log that.

datalog23.csv

More logs!

 

Got some gas and reset the ecu. Did a 3rd gear pull right after that and that is the first log. Second log is my drive home.

 

The car feels normal right after i reset the ecu but within a few minutes it's back to sputtering between 2-3k. Could this be caused by the tune? I've read about people getting knock on the cobb maps.

 

Pretty sure the oil is coming from the valve cover. Gonna watch it over the next few days to make sure. I don't see any oil spots in my driveway but it was low. I could see where some had dripped on the up pipe and it was wet underneath the pipe.

datalog26.csv

datalog27.csv

humm .. do you cylinder roughness detection ? ie one parameter for each cylinder..

should be able to tell you witch cylinder or all the problem is with.

 

if all cylinders rough its a general fueling or roughness problem..

if one cylinder is rough there is some thing wrong there..

 

but just try going back to stock settings.. see how it goes.

Well after looking at some pictures on here I figured out that I have an aftermarket catless uppipe. My downpipe is defiantly still the stock catted downpipe though. Could running a stage 1 tune with a catless uppipe be causing this? Thinking about ordering a downpipe and seeing if the problem goes away.

not sure why you keep saying defiantly as the definition of the word has no meaning to this subject. A catless uppipe shouldn't cause any problems, unless you get a cel for EGT sensor, in which you can do the resistor trick, which can be found by searching.

Your problems have nothing to do with downpipe.

 

You have a warranty on the car, I suggest you take it to them and have them do a leakdown and compression test, test injectors, inspect coil packs, verify correct plugs, replace the leaking valve cover gasket. Check for loose heat shields, suspension components (endlinks, swaybars, strut towers).

 

If it fails compression or leakdown, you will have a better idea as to what your issues are.

not sure why you keep saying defiantly as the definition of the word has no meaning to this subject. A catless uppipe shouldn't cause any problems, unless you get a cel for EGT sensor, in which you can do the resistor trick, which can be found by searching.

 

Autocorrect on my phone. I meant definitely. I did get a cel for the EGT sensor already and I did the risistor mod.

 

Your problems have nothing to do with downpipe.

 

You have a warranty on the car, I suggest you take it to them and have them do a leakdown and compression test, test injectors, inspect coil packs, verify correct plugs, replace the leaking valve cover gasket. Check for loose heat shields, suspension components (endlinks, swaybars, strut towers).

 

If it fails compression or leakdown, you will have a better idea as to what your issues are.

 

I'm gonna run some more logs with the cylinder roughness included and see if I can figure out which cylinder the problem is in. After that it will probably go back to the dealer.

Might as well check plug gap as well. Mine came gapped at 0.040" and I installed them as such. They have since been regapped as they should be 0.029-0.031" IIRC.

 

Hope for something simple, plan for something big.

Here is the latest log with roughness in each cylinder added. Something happened in cylinder #4 toward the end of the log but other than that it's 0s all the way through.

 

Might as well check plug gap as well. Mine came gapped at 0.040" and I installed them as such. They have since been regapped as they should be 0.029-0.031" IIRC.

 

Hope for something simple, plan for something big.

 

I believe the plugs were changed by the dealer right before I got the car but I will check them anyway.

datalog30.csv