1998 Camaro LS1 P1133 99% sure O2 sensor is good.

**tgonzalez** · 08-23-2020, 03:27 PM

Here is my history.
I am the original owner and only drive the car about 5 miles a day has about 80,000 miles on odometer.
Early spring check engine light came on and I parked car.
Car sat till I got me emissions notice last month and I decided it would be a fun project to try to fix it with my son.

Bought cheap scanner, found the only code is P1133 (upstream O2 sensor bank1)
Replaced O2 sensor same code came back.
Swapped bank1 & bank2 upstream O2 sensors, same code came back.
replaced spark plugs on bank1 side, same code. (I don't think I have misfires but not sure my cheap scanner would tell me)
I do not see any obvious exhaust or vacuum leaks.

At idle scanner shows good switching on both upstream O2 sensors.
As soon as RPMs go above 1200 bank1 flattens at full rich. (bank2 is good)

I'm on an extreme budget so if I can fix it for cheap good if not I'm going to trade it in.

***SMWS6TA*** · 08-24-2020, 07:23 AM

Swap the O2 sensors and see if it follows. If it does sensor is bad.

**tgonzalez** · 08-24-2020, 11:28 AM

I did swap the sensors and the same p1133 came back, Thanks.

***SMWS6TA*** · 08-24-2020, 11:59 AM

If you swapped sensor and it came back on the same bank then you need to look at the wire harness. Maybe a mouse etc got hungry or the wire got a little close to the exhaust.

Also the code can be popped by vacuum leaks and dirty MAF or exhaust leak.

Check around the egr tube that goes into the exhaust header is you're still running stock manifolds. They've been know to crack.

**tgonzalez** · 08-24-2020, 03:02 PM

I would think dirty MAF or vacuum leak would cause problems on both banks, I will get some MAF cleaner and test.
ERG looks like its fed from bank2 exhaust.
I'm assuming harness is good (O2 switching look fine below 1200 RPM).

Im going to look closer for exhaust leak on bank1 side.

Thanks for your help!!

**pajeff02** · 08-24-2020, 04:51 PM

I am with Scott on this one, sounds like a harness or connector issue since the problem stayed on Bank 1 even after swapping the sensors side-to-side. Misfires will definitely set a DTC and you will usually have a noticeable stumble in the rev range. Any work been done on the car lately? Just for giggles, take a look at your grounds under the hood -- radiator support and back of the driver side head are two to check. Make sure they are tight and corrosion free.

**tgonzalez** · 08-30-2020, 11:59 AM

Well this is interesting...
While looking for an exhaust leak I found a C-clamp looking thing on my manifold flange about 2 inches from the sensor.
I didn't notice it since it blended in with the rest of the rust

.
Im guessing it was put there by the dealer during a warranty repair many years ago.
It doesn't look like its leaking but I'm testing with a shop-vac and soapy water.
I'm guessing it might only leak when hot and under more pressure.
Clamp looks like this https://media.napaonline.com/is/image/GenuinePartsCompany/NWMDC?$Product=GenuinePartsCompany/1148713

**tgonzalez** · 08-31-2020, 02:50 PM

I had some time to look for an exhaust leak this weekend and found something odd.
On the manifold to cat flange there is a C-clamp thing I didn't notice since it blended in with the the rest of the rust

Im guessing it was added by the dealer during a warranty repair many years ago.
I did a leak test with a shop-vac and soapy water but did not find any leaks, but I'm guessing its leaking when hot and under more pressure.

Here is the c-clamp thing : https://www.amazon.com/Nickson-17350.../dp/B000COX90M

I'm going to try to pull the cat off and repair the flange the right way.

**pajeff02** · 09-01-2020, 02:41 AM

That's a possibility. Any air entering the exhaust system upstream of the 1st set of O2 sensors will skew fueling. You can look at your short and long term fuel trims on a scanner to see what the difference is between Bank 1 and Bank 2.

**tgonzalez** · 09-07-2020, 02:11 PM

I pulled the cat off the manifold and the gasket looked OK, (I give it a 25% chance it was leaking).
Since I broke the other 2 studs removing the cat I decided to pull the manifold to repair on the bench (and not laying on my back under the car

I think I found my leak, the last cylinder exhaust gasket did not look like it was sealing on the bottom (rusty and sooty).
I have a new gasket on order.
I will keep you updated, & thanks for your help.
By the way my fuel trims are the same on both sides LTFT +8 to +10.

**pajeff02** · 09-12-2020, 02:47 AM

Definitely acting like the computer thinks you are lean -- the trims should ideally be fairly close to zero, maybe in the 1 to 3 range.

**tgonzalez** · 09-12-2020, 09:20 AM

I'm still puzzled by that only bank 1 throwing a code.
Long term fuel trim is equal on both sides at all RPMs.
I will check for vacuum leaks after I get my exhaust back together.
Short terms stay low (- or + 4 )

**pajeff02** · 09-13-2020, 04:08 AM

Even though the PCM reads Bank 1 and Bank 2, it is not capable of adjusting fueling on only one bank. Not exactly sure what it does, maybe averages the readings from each bank and adjusts accordingly. I was doing a major on our car and crossed up the sensor harness one time (we have longtubes and aftermarket O2 senders). I fired the car up and after it went into closed loop fueling one bank went dead rich and the other dead lean. Took me a few minutes to figure that one out.

**tgonzalez** · 09-20-2020, 03:48 PM

I finally got the drives side exhaust back together and nothing changed.
Your post about bank 1 & bank 2 not being independent or each other makes sense (I will have to adjust my thinking and troubleshooting)
After driving for awhile today the LTFT sits about +8 at idle (600 RPM) and climbs to +13 above 1200 RPM (and that is when my bank 1 sensor stops switching and goes rich)
the second I lift of the gas it starts switching again (and bank 2 looks ok all the time)

**pajeff02** · 09-22-2020, 03:01 AM

Assuming that the O2's are functioning properly, there has to be outside air entering the exhaust stream. Is you secondary air system intact, or has it been removed?

**tgonzalez** · 09-26-2020, 03:57 PM

Secondary air is stock. I replaced the 1 way valves and small gaskets to the exhaust manifolds. I have plugged the hoses and still get high LTFT and rich bank 1 over 1500 RPM.
I tested fuel pressure today and its 58 at idle and all other RPMs. (and holds at 52 whit engine off)
Im going to remove / clean throttle body and IAC tomorrow.
I forgot to mention I did remove the MAF screen many years ago but had no problems till this year.
Thanks.

**pajeff02** · 09-27-2020, 01:25 AM

Ugh. The MAF is a metering device and any modifications will throw off its calibration. Best not to play with a MAF, however, I doubt that removing the screen would cause the issue you are experiencing. To be 100% certain though, it is very simple to test for a bad MAF -- simply unplug it and then run the engine. By unplugging it you force the PCM into speed density mode. Rather than measuring actual air flow it will estimate airflow utilizing other sensor readings, particularly the TPS and MAP. You will trip your SES light and then have to clear it later.

This one is a puzzle. Have you inspected your PCV hoses, particularly the portion that runs behind the passenger side head over to the driver side? An easy test would be to unplug the hose from the throttle body (or just behind it -- cannot recall exact location), cap the nipple, and then run the engine. Again, this may trip your SES but it would eliminate any outside air from entering the intake and messing with your fueling.

**tgonzalez** · 09-27-2020, 03:39 PM

Ok tested with the PVC hose port caped (and the hose that goes to the passenger valve cover) with no change.
I unplugged the MAF and got some strange results. LTFT when way high bank1 O2 sensor looked like it was trying to switch and bank2 looked flatter.
Im going to swap MAFs with a guy I know with a 98 trans am next week.
I was thinking I might take the intake off and inspect all the gaskets.
The other odd part is the engine runs great no stumbles idles smooth at 800.

**tgonzalez** · 10-04-2020, 01:04 PM

Good news, new MAF caused LTFT to drop to 0 at idle and 6 at 1500 RPMs.
Bad news P1133 returned.
My next step is to see if I have a blown head gasket, unless anyone has a better idea.
I did not think head gasket was a possibility till i noticed my coolant was low last week and again today

I will try to borrow some tools to do leak-down and combustion leak detection test.

**pajeff02** · 10-05-2020, 02:58 AM

In addition to the level dropping, here are your top three signs: 1) White exhaust smoke, 2) the exhaust will have a sweet, coolant like odor, and 3) the coolant will completely clean the carbon out of the combustion chamber, hence the spark plug in that cylinder will be almost spotless -- no carbon or other buildup. This being said, although anything is possible, our engines are not known for popping head gaskets. Pressure testing the cooling system will assist in the diagnosis, but I would be looking for an external leak first -- the plastic tanks on the ends of the radiator where they seal to the aluminum, the water pump and hose connections.