O2 Sensor Troubleshooting
Thread Starter
Staging Lane
Joined: Jul 2022
Posts: 70
Likes: 3
O2 Sensor Troubleshooting I have a new LM7 swap in my '66 Skylark. Using a new PSI standalone harness and a mail order tune to get me going.
The car is running and driving but smells very rich and the idle is rough. In looking at the data streaming the bank 2 O2 sensor reads a constant .440 or .445v.
The bank 1 sensor constantly changes after a minute or so of idling but the bank 2 sensor stays at .440 or .445. I tried some spirited driving to see if the bank 2 sensor would start working but no go.
I tested continuity for the ground and signal wires and they are good. The pink wire shows 12v with the key on. I put a new sensor in and nothing changed.
What should I be looking at next? Is it possible the tune has something to do with it?
The car is running and driving but smells very rich and the idle is rough. In looking at the data streaming the bank 2 O2 sensor reads a constant .440 or .445v.
The bank 1 sensor constantly changes after a minute or so of idling but the bank 2 sensor stays at .440 or .445. I tried some spirited driving to see if the bank 2 sensor would start working but no go.
I tested continuity for the ground and signal wires and they are good. The pink wire shows 12v with the key on. I put a new sensor in and nothing changed.
What should I be looking at next? Is it possible the tune has something to do with it?
Thread Starter
Staging Lane
Joined: Jul 2022
Posts: 70
Likes: 3
Thread Starter
Staging Lane
Joined: Jul 2022
Posts: 70
Likes: 3
I compared the wiring for bank 1 and bank 2 sensors and they are wired the same (same color wires in same spots).
Is there something else I should check? Appreciate the help.
TECH Fanatic
Joined: Dec 2017
Posts: 1,467
Likes: 265
From: Bossier City, Louisiana
It is a brand of oxygen sensor - sometimes slang for any O2 sensor. See below.
https://splitsec.com/product/ego1-un...xygen-sensor-2
Rick
https://splitsec.com/product/ego1-un...xygen-sensor-2
Rick
.44x volts is a default no signal to the computer. You likely have a bad connection at the pcm plug, or a break in the wire somewhere. You would show the same reading with the sensor unplugged.
edit-- With any aftermarket harness it is a good idea to make sure the pins are in the correct spots in the plug end at the computer.
edit-- With any aftermarket harness it is a good idea to make sure the pins are in the correct spots in the plug end at the computer.
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Staging Lane
Joined: Jul 2022
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Ok - here's an update:
I'm leaning towards a leaky injector in bank 2, but they are brand new injectors. Guess I need to start figuring out how to diagnose that easily (without disassembling the manifold).
- I've confirmed that I am using the correct O2 sensors for the PCM as described by PSI
- I've verified continuity with all of the O2 wires from the connector to the PCM
- I checked the pins on the connector against the LT1 diagrams and it looks to me like the connectors are pinned correctly for the PCM
- Spark plugs all look fine/dry
I'm leaning towards a leaky injector in bank 2, but they are brand new injectors. Guess I need to start figuring out how to diagnose that easily (without disassembling the manifold).
Thread Starter
Staging Lane
Joined: Jul 2022
Posts: 70
Likes: 3
In as interesting development, I picked up a smoke leak detector and found that smoke was coming out from under the intake manifold on the passenger side (bank 2).
I took it off and repositioned but the smoke still comes out. I'll take it off again tonight and take a straightedge to it to see if it's warped.
That has me a little confused though, because I thought that would create a lean condition, not a rich one? Why would the exhaust smell like fuel if it's running lean?
For reference, the bank 1 O2 sensor reads around .015 while bank 2 seems stuck on .445.
Is .015 lean?
Moderator
Joined: Aug 2010
Posts: 7,323
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From: Ann Arbor, MI
.015V is very lean.
Technically, O2 sensors don't send out a steady voltage, but a rapidly changing voltage where the average is what you read with a basic volt meter. A fancy scanner or an oscilloscope will show the rapidly changing O2 voltage when it is working. "Stuck on .445" tells us it is NOT working and/or effectively disconnected. @Full Power suggestion to swap the right and left O2 sensors is a good one.
This is looking like multiple problems; I think first step is to get both O2 sensors reading and they will tell you where to go next.
Also, when you say "brand new injectors" where did you get them? (Rare to find any reputable brand new injectors on ebay - they are either cheap replicas or rebuilt ones.)
Technically, O2 sensors don't send out a steady voltage, but a rapidly changing voltage where the average is what you read with a basic volt meter. A fancy scanner or an oscilloscope will show the rapidly changing O2 voltage when it is working. "Stuck on .445" tells us it is NOT working and/or effectively disconnected. @Full Power suggestion to swap the right and left O2 sensors is a good one.
This is looking like multiple problems; I think first step is to get both O2 sensors reading and they will tell you where to go next.
Also, when you say "brand new injectors" where did you get them? (Rare to find any reputable brand new injectors on ebay - they are either cheap replicas or rebuilt ones.)
Thread Starter
Staging Lane
Joined: Jul 2022
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Thanks for the reply. The O2 sensor would start at like .440 and then change to .445 and stay there. Not sure if that's a different scenario. I did swap the sides with no difference, meaning the known good sensor also did the same thing when installed in bank 2. Just really weird that it appears to be pinned out correctly and I have verified it gets power and the continuity checks out for the harness wires to the sensor.
The injectors are a new DW set I got from Summit - I was wary of the eBay stuff too.
I pulled the intake manifold and it was indeed warped out of spec on the the passenger side rear cylinders. Found another on eBay so hopefully that one isn't warped.
While I had the manifold off I hooked the fuel line back on and primed the system and there was no fuel coming from any of the injectors so that seems to rule out the leaking/stuck injector theory.
The injectors are a new DW set I got from Summit - I was wary of the eBay stuff too.
I pulled the intake manifold and it was indeed warped out of spec on the the passenger side rear cylinders. Found another on eBay so hopefully that one isn't warped.
While I had the manifold off I hooked the fuel line back on and primed the system and there was no fuel coming from any of the injectors so that seems to rule out the leaking/stuck injector theory.
Moderator
Joined: Aug 2010
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From: Ann Arbor, MI
Well, at least we know more now: Your O2 sensors are good as they work properly on one side; same side after a swap. And your injectors are good and not leaking.
Not sure if you checked the O2 sensor connectivity all the way to pins on the PCM. If yes, we might have to suspect the PCM itself.
The change from .440 to .445 is meaningless. As mentioned, it most likely will read that even with the O2 sensor disconnected.
I suspect you won't make more progress until you new intake manifold is installed?
Not sure if you checked the O2 sensor connectivity all the way to pins on the PCM. If yes, we might have to suspect the PCM itself.
The change from .440 to .445 is meaningless. As mentioned, it most likely will read that even with the O2 sensor disconnected.
I suspect you won't make more progress until you new intake manifold is installed?
Thread Starter
Staging Lane
Joined: Jul 2022
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Yeah, that's the plan now. Intake should get here in a couple of days and I'll see what happens once that's buttoned up. I do have a spare PCM (untuned) I can try to see if that fixes the O2 sensor problem. If I try a stock ytune PCM on my motor just to test the O2 will that hurt it at all? I have cam/headers/larger injectors.
Moderator
Joined: Aug 2010
Posts: 7,323
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From: Ann Arbor, MI
What size injectors were stock for that PCM? What size do you have now? With bigger injectors it will run very rich. If your fuel pressure is easily adjustable, you might be able to drop to e.g. 40 lbs to compensate for e.g. 25% larger injectors. Just for a O2 sensor test of course.
Thread Starter
Staging Lane
Joined: Jul 2022
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Update: I got the new(used) intake and it didn't measure out as warped so I installed it. Did the smoke test and it was good for a long while, but then started to leak some smoke around the base of the intake. Not as bad as it was before and it wasn't in the same spot (it actually looked a bit like it was more uniform on each side). That was pretty frustrating to see if I'm honest since I've battled that same issue previously and though I had fixed it.
I decided to start it up so I could see if it was running any differently and it's now in limp mode for the DBW pedal/throttle body voltage. In the couple of minutes I ran it bank 1 was even leaner than before on the O2 but I'm not sure if it really got warm enough to get a good reading.
I honestly had to start working on the rust repair so I didn't burn it down. Maybe I need to try new intake gaskets? This one is a new Felpro which I thought was supposed to be the best option. Not sure if something else could cause the smoke to come out? I followed the right sequence on the intake bolts and did a first pass torqued to 44 inch/lbs and then a second at 89 inch/lbs.
I decided to start it up so I could see if it was running any differently and it's now in limp mode for the DBW pedal/throttle body voltage. In the couple of minutes I ran it bank 1 was even leaner than before on the O2 but I'm not sure if it really got warm enough to get a good reading.
I honestly had to start working on the rust repair so I didn't burn it down. Maybe I need to try new intake gaskets? This one is a new Felpro which I thought was supposed to be the best option. Not sure if something else could cause the smoke to come out? I followed the right sequence on the intake bolts and did a first pass torqued to 44 inch/lbs and then a second at 89 inch/lbs.
Moderator
Joined: Aug 2010
Posts: 7,323
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From: Ann Arbor, MI
Is this a sheet-metal intake manifold? I read they are notorious for leaks, especially after a few heat cycles.
A leak is "unmetered" air. While a small leak contributes a noticeable percentage of unmetered air at idle, it becomes a negligible percentage at higher throttle positions.
So if the banks are even at cruising and high throttle, maybe you can just live with it.
A leak is "unmetered" air. While a small leak contributes a noticeable percentage of unmetered air at idle, it becomes a negligible percentage at higher throttle positions.
So if the banks are even at cruising and high throttle, maybe you can just live with it.
Thread Starter
Staging Lane
Joined: Jul 2022
Posts: 70
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It's a stock truck intake, which somehow makes it weirder in my mind.
I'll have to tackle this DBW issue and see what things look like when it's doing more than idling in limp mode.
Frustrating that I've been chasing random gremlins for 8 months now. I just want things to work!
I know it will be worth it in the end but holy cow.
I'll have to tackle this DBW issue and see what things look like when it's doing more than idling in limp mode.
Frustrating that I've been chasing random gremlins for 8 months now. I just want things to work!
I know it will be worth it in the end but holy cow.