Help- Running rough
Thread Starter
Racer
Joined: Apr 2011
Posts: 320
Likes: 2
From: Philadelphia PA
Help- Running rough
I have a 97 with just about every bolt on mod and a cam. The car seems to be running very rough lately and bucking/sputtering. The check engine light is on but it has been on for a while due to a failing O2 sensor but I was told it was tuned out. 'Ive had all my work done by Horsepower addicts which has been all great installations.
I was hoping for some pointers about what it could possibly be.
Also my dilemma is, I live 90+ minutes from HPA so I am trying to find a way to have this diagnosed locally at a speed shop instead of making the long trip both ways. HPA used HP Tuners to tune my car but this local shop uses Mustang...Is this an issue? What info would I need to bring to this local shop for them to help find the issue?
Im in the Bucks County section of PA so any advice or help is much appreciated.
I was hoping for some pointers about what it could possibly be.
Also my dilemma is, I live 90+ minutes from HPA so I am trying to find a way to have this diagnosed locally at a speed shop instead of making the long trip both ways. HPA used HP Tuners to tune my car but this local shop uses Mustang...Is this an issue? What info would I need to bring to this local shop for them to help find the issue?
Im in the Bucks County section of PA so any advice or help is much appreciated.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
WELL,,,, Reading and posting the DTCs would be a good start.Some things to check and do:
1. Clean the MAF and Throttle Body.
2. Check all hoses and PCV system for vacuum leaks.
3. Plugs and wires good? I would check the plugs and ohm out the wires.
4. Look for leaks between the MAF and Throttle Body allowing in UN-METERED AIR.
What kind of tune do you have? SD?? Are you using the O2 sensors readings in closed loop??
Bill
Acct Suspended APR 2026 by request
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2020 Corvette of the Year Finalist (performance mods)
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yeah you're gonna have to pull and post the codes in order for anyone to be able to help... if your rear o2's were tuned out and the cel is still on because of that then it wasn't done properly... and if the cel has been on the whole time and you assumed it was the rear o2 sensors and another issue pops up, well the cel is still going to be on regardless so without pulling the codes you are basically pissing in the wind
Last edited by StingrayRebel; Apr 5, 2016 at 01:54 PM.
Thread Starter
Racer
Joined: Apr 2011
Posts: 320
Likes: 2
From: Philadelphia PA
WELL,,,, Reading and posting the DTCs would be a good start.Some things to check and do:
1. Clean the MAF and Throttle Body.
2. Check all hoses and PCV system for vacuum leaks.
3. Plugs and wires good? I would check the plugs and ohm out the wires.
4. Look for leaks between the MAF and Throttle Body allowing in UN-METERED AIR.
What kind of tune do you have? SD?? Are you using the O2 sensors readings in closed loop??
Bill
P0135 Heated Oxygen Sensor (HO2S) Heater Circuit Bank 1 Sensor 1
P0155 Heated Oxygen Sensor (HO2S) Heater Circuit Bank 2 Sensor 1
I do find that the car runs very rough until warmed up but this isnt always the case.
Acct Suspended APR 2026 by request
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2020 Corvette of the Year Finalist (performance mods)
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those are codes for your front o2 sensors, not the rear... you can try clearing the codes and see what happens but they will probably come back... sounds like it's time to get under the car and start inspecting the o2 wiring, when headers are installed it's very easy to get the routing fudged up and end up melting the o2 wires on the headers
Thread Starter
Racer
Joined: Apr 2011
Posts: 320
Likes: 2
From: Philadelphia PA
those are codes for your front o2 sensors, not the rear... you can try clearing the codes and see what happens but they will probably come back... sounds like it's time to get under the car and start inspecting the o2 wiring, when headers are installed it's very easy to get the routing fudged up and end up melting the o2 wires on the headers
Yes- the LT get so damn hot. I had them melt on of my spark plug wires. from my symptoms does it sound like this could be the cause?
Are there any videos or anything on how to to replace the entire O2 wire piece? Ive swapped our the sensors but never traced it back to where the wires run to....
Apologize for the novice questions ahead of time
Tech Contributor
Joined: Dec 1999
Posts: 32,910
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
WELL,,,,,,,,,,,,,,,,,,,,, If your having heater circuit issues, you could have weak defective O2 sensors after you resolve the heater circuit issue. See how they cycle when the heaters are fixed..
Here is the schematic for your heater circuit. You need to ACTUALLY READ the 12 VDC voltage on top of the OXY SEN FUSE to make SURE that you have FULL BATTERY VOLTAGE available to that circuit.
THEN, you need to insure that you have 100% full continuity on the GROUND circuit to chassis ground. Go to the O2 sensor connector and disconnect it and take some readings. Make sure that the O2 sensor connector is not heat burnt/melted/damaged
IF, you turn the key on, after approx. 5 min, your O2 sensor/s body should be very HOT to the touch if the sensor heater circuit is working:
Splice Pack (SP-122) is taped to a wire harness behind the battery and has been known to get very corroded due to battery acid exposure:
BAD GROUND in that circuit can cause the heaters not to function just as much as no power!!
Here is the schematic for your heater circuit. You need to ACTUALLY READ the 12 VDC voltage on top of the OXY SEN FUSE to make SURE that you have FULL BATTERY VOLTAGE available to that circuit.
THEN, you need to insure that you have 100% full continuity on the GROUND circuit to chassis ground. Go to the O2 sensor connector and disconnect it and take some readings. Make sure that the O2 sensor connector is not heat burnt/melted/damaged
IF, you turn the key on, after approx. 5 min, your O2 sensor/s body should be very HOT to the touch if the sensor heater circuit is working:
Splice Pack (SP-122) is taped to a wire harness behind the battery and has been known to get very corroded due to battery acid exposure:
BAD GROUND in that circuit can cause the heaters not to function just as much as no power!!
Last edited by Bill Curlee; Apr 5, 2016 at 02:27 PM.
Thread Starter
Racer
Joined: Apr 2011
Posts: 320
Likes: 2
From: Philadelphia PA
Okay so I feel like an a$$. The MAF hose clamp was loose and not connnected . I took the whole CAI off and cleaned the MAf and TB with their appropriate cleaners. Its running really good now. I cleared all the codes and drove it around today and the check engine light popped back on but i am only getting one C code now.
So now I am getting this code only.
P0134 Heated Oxygen Sensor (HO2S) Circuit Insufficient Activity Bank 1 Sensor 1
Any thoughts?
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Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
YES
Your PCM supplies the O2 sensor with 450 millivolts on the signal line. As the fuel injectors provide fuel, the O2 sensor senses the rich AFR and the rich AFR causes the 02 sensor to increase voltage (900 mv) and shuts down the injector. As the signal get lean and swings to 100mv the injector fires again. Simplified but the O2 sensor output should constantly (at steady state throttle) swing form 100mv to 900mv and back. If its LAZY (defective) and hanging out at 450, you will see that DTC.
YOU really should check out that heater circuit before you stab in two new O2 sensors. YES, I would install TWO new ones!!!
Your PCM supplies the O2 sensor with 450 millivolts on the signal line. As the fuel injectors provide fuel, the O2 sensor senses the rich AFR and the rich AFR causes the 02 sensor to increase voltage (900 mv) and shuts down the injector. As the signal get lean and swings to 100mv the injector fires again. Simplified but the O2 sensor output should constantly (at steady state throttle) swing form 100mv to 900mv and back. If its LAZY (defective) and hanging out at 450, you will see that DTC.
YOU really should check out that heater circuit before you stab in two new O2 sensors. YES, I would install TWO new ones!!!
Thread Starter
Racer
Joined: Apr 2011
Posts: 320
Likes: 2
From: Philadelphia PA
So I am still having issues. I cleared the codes and P0135 and P0155came back on so I traced the O2 wires to see if anything is melted and there are no signs of any melting. I replaced the driver side sensor before the cat which was call for bank 1 sensor 1. I drove it for about 20 minutes then it began to run rough and the light cam back on. Now I am getting 2 current codes:
P0135 Heated Oxygen Sensor Heater circuit Bank 1 Sensor 1
P0155 Heated Oxygen Sensor (HO2S) Heater Circuit Bank 2 Sensor 1
Is there any explanation? Do I need to replaced both at the same time? Could this be an early C5 probes with ecm?? I sure hope not.
This car is 97 with H/C/I and tuned.
P0135 Heated Oxygen Sensor Heater circuit Bank 1 Sensor 1
P0155 Heated Oxygen Sensor (HO2S) Heater Circuit Bank 2 Sensor 1
Is there any explanation? Do I need to replaced both at the same time? Could this be an early C5 probes with ecm?? I sure hope not.
This car is 97 with H/C/I and tuned.
Thread Starter
Racer
Joined: Apr 2011
Posts: 320
Likes: 2
From: Philadelphia PA
Okay so I thought I found part of the problem. The fuse for the heater circuit under the hood was popped. I changed the fuse and drove for 25 minute and it seemed to be running strong but then the LIGHT came on again. I got home and checked, the fuse popped again. I ran for codes and it is not coming up with any current codes but the light is on.
Where do I go from here?
Where do I go from here?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Well,,,,,,,,,, If the FUSE blew, you have a short circuit or a BAD heater in one of the sensors. Your going to have to examine ALL the heater circuit wiring, connectors and sensors. Read the resistance of each sensor and see if one is very LOW.
Measure the heater wires to ground and see if you get any readings. Unplug the sensors and read between the two wires to each sensor. Should be OPEN.
Measure the heater wires to ground and see if you get any readings. Unplug the sensors and read between the two wires to each sensor. Should be OPEN.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Well,,, you have a SHORT in the system if the heater fuse blew and NONE of your heaters are working. Makes the sensor function poorly
Last edited by Bill Curlee; May 25, 2016 at 05:37 PM.
Thread Starter
Racer
Joined: Apr 2011
Posts: 320
Likes: 2
From: Philadelphia PA
Originally Posted by Bill Curlee;15922902x13
Well,,, you have a SHORT in the system if the heater fuse blew and NONE of your heaters are working. Makes the sensor function poorly
Thanks everyone for the help and bearing with me.