Anyone good at interpiting OBD II datastream?
Thread Starter
Race Director
Joined: Sep 2002
Posts: 14,552
Likes: 24
From: Washington County, South UTAH
Anyone good at interpiting OBD II datastream?
Hi! RE My 1996 Impala SS stock, LT1.
I am getting DTC P0171 & P0174. (lean) LT FTRM1 & LT FTRM2 are both 25.
O2S11, O2S21 sensors go to .830 volt while I spray carb cleaner into the intake. (and respond normally w/o carb spray)
Fuel PSI running 38PSI 40 w/ Fuel PSI regulator vac hose disconnected. (I installed a new Delphi fuel pump and in-tank wiring harness 20,000 miles ago).
Todays SMOG test results
25MPH %CO 14.6 HC 3 ppm co% .08 NOX 163 ppm
I cleared the codes B4 the test, it passed. (Smog tech claims the "%CO 14.6" reading is the air/fuel ratio)
This problem began right after I installed an ATK reman long block, 8 new Delphi fuel injectors, all new vacuum/PCV hoses, Ac plugs, Delphi ign wires ***EDIT*** AND 4 NEW DELPHI O2 SENSORS. Opti-spark, has 20,000 miles.
I conducted a "smoke test" for vacuum leaks, but did not locate any.
HELP!
I am getting DTC P0171 & P0174. (lean) LT FTRM1 & LT FTRM2 are both 25.
O2S11, O2S21 sensors go to .830 volt while I spray carb cleaner into the intake. (and respond normally w/o carb spray)
Fuel PSI running 38PSI 40 w/ Fuel PSI regulator vac hose disconnected. (I installed a new Delphi fuel pump and in-tank wiring harness 20,000 miles ago).
Todays SMOG test results
25MPH %CO 14.6 HC 3 ppm co% .08 NOX 163 ppm
I cleared the codes B4 the test, it passed. (Smog tech claims the "%CO 14.6" reading is the air/fuel ratio)
This problem began right after I installed an ATK reman long block, 8 new Delphi fuel injectors, all new vacuum/PCV hoses, Ac plugs, Delphi ign wires ***EDIT*** AND 4 NEW DELPHI O2 SENSORS. Opti-spark, has 20,000 miles.
I conducted a "smoke test" for vacuum leaks, but did not locate any.
HELP!
Last edited by Mikeceli; Dec 8, 2013 at 12:46 PM. Reason: I forgot to list new O2 sensors.
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I agree with the other guy, oxygen sensor replacements fix these problems usually most of the time. But also post those readings at idle and note your idle rpm.
Oxygen sensors are bad if they are black or rusted. Or if they have a bad connection.
Oxygen sensors are bad if they are black or rusted. Or if they have a bad connection.
Thread Starter
Race Director
Joined: Sep 2002
Posts: 14,552
Likes: 24
From: Washington County, South UTAH
The O2 sensors responded to my richening the mixture (w/ carb spray) by staying @ .830 volts, during my spraying. Does this not confirm there good? I visually inspected the 2 left side O2 sensors for carbon/soot with negative results.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Is fuel trim the same at idle and 2500 rpm? Do both pre cat O2s vary the same amount? Was any milling done when engine was done? Possible intake leak at runners internal to engine. MAF what does it read at idle, if unplugged what does fuel trim do? AIR system another possible cause.
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
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Pro
Joined: Aug 2012
Posts: 663
Likes: 1
From: Nashville TN
No that doesn't mean they are good. What if they are feeding faulty data into the computer to begin with?
Mine were reporting lean while the sparkplugs were black so the computer would add even more fuel and the 02 sensors were still not happy. I failed the emissions test horribly.
My readings before 2 new sensors
HC 719 max allowed 220
CO 8.27 max allowed 1.2
After 2 new sensors, nothing else of significance
HC 105 max allowed 220
CO .67 max allowed 1.2
I dropped nearly 684% on HC and 1234% on CO.
Mine were reporting lean while the sparkplugs were black so the computer would add even more fuel and the 02 sensors were still not happy. I failed the emissions test horribly.
My readings before 2 new sensors
HC 719 max allowed 220
CO 8.27 max allowed 1.2
After 2 new sensors, nothing else of significance
HC 105 max allowed 220
CO .67 max allowed 1.2
I dropped nearly 684% on HC and 1234% on CO.
Thread Starter
Race Director
Joined: Sep 2002
Posts: 14,552
Likes: 24
From: Washington County, South UTAH
Corrected on edit.....I forgot to mention that I installed 4 new Delphi O2 sensors, with the reman engine. (Of course NO guarantee there OK)
Yesterday I found that when I disconnect the air inlet hose, at the AIR check Valves (engine running) the LEFT AIR Check valve, is allowing some exhaust to blow back. I ordered 2 new valves and will take a FTRM reading, with the valves temporally corked. I will post back my results.
YIKES! I did not inspect the intake manifold to head match, except noting that the bolts lined up fine. I did not see a leak, on the smoke test, but I did NOT remove the oil filler plug, during the test.
FWIW My smog reading were good.
KENOVA, I will run your tests and advise.
It might be 5 days before I post back. Daughter has the car and I am beginning my 4/12 hour work week. PLEASE DON'T FORGET ME!
Thanks!
Yesterday I found that when I disconnect the air inlet hose, at the AIR check Valves (engine running) the LEFT AIR Check valve, is allowing some exhaust to blow back. I ordered 2 new valves and will take a FTRM reading, with the valves temporally corked. I will post back my results.
YIKES! I did not inspect the intake manifold to head match, except noting that the bolts lined up fine. I did not see a leak, on the smoke test, but I did NOT remove the oil filler plug, during the test.
FWIW My smog reading were good.
KENOVA, I will run your tests and advise.
It might be 5 days before I post back. Daughter has the car and I am beginning my 4/12 hour work week. PLEASE DON'T FORGET ME!
Thanks!
Thread Starter
Race Director
Joined: Sep 2002
Posts: 14,552
Likes: 24
From: Washington County, South UTAH
Thread Starter
Race Director
Joined: Sep 2002
Posts: 14,552
Likes: 24
From: Washington County, South UTAH
4/12 HOUR NIGHT shifts DONE! I am back.
Today I installed the 2 NEW AIR Check Valves. After about 4 minutes running, the LT FTRM1 & LT FTRM2 are both STILL 25. So if the leaking check valve was the cause of the problem, perhaps it takes more time for the readings to respond?
I did NOT have time to do anything else. I will post back, tomorrow or Sat.
THANKS!
Today I installed the 2 NEW AIR Check Valves. After about 4 minutes running, the LT FTRM1 & LT FTRM2 are both STILL 25. So if the leaking check valve was the cause of the problem, perhaps it takes more time for the readings to respond?
I did NOT have time to do anything else. I will post back, tomorrow or Sat.
THANKS!
Last edited by Mikeceli; Dec 13, 2013 at 07:16 AM.
Thread Starter
Race Director
Joined: Sep 2002
Posts: 14,552
Likes: 24
From: Washington County, South UTAH
***UPDATE *** INTERPET MY OBD II datastream?
1 LT FTRM1 & 2 Is the same at IDLE and 2500 RPM: 25
2 Do both pre-cat O2's vari the same (SEE BELOW READINGS)
O2S11 IDLE .08-.685 2500RPM .06-.670
O2S12 IDLE .08-.11 2500RPM .08-.71
3 MAF AT IDLE .97
4 UNPLUGGING THE MAF MAKES NO CHANGE IN LT FTRM 1 & 2 DOES THIS MEAN THE MAF IS BAD? I have another 1996 Impala SS from which I can "test swap" parts.
5 MAP IDLE 10.9 2500RPM 9.2
6 MAF IDLE .89 2500RPM 3.04
THANK YOU!!
__________________
2 Do both pre-cat O2's vari the same (SEE BELOW READINGS)
O2S11 IDLE .08-.685 2500RPM .06-.670
O2S12 IDLE .08-.11 2500RPM .08-.71
3 MAF AT IDLE .97
4 UNPLUGGING THE MAF MAKES NO CHANGE IN LT FTRM 1 & 2 DOES THIS MEAN THE MAF IS BAD? I have another 1996 Impala SS from which I can "test swap" parts.
5 MAP IDLE 10.9 2500RPM 9.2
6 MAF IDLE .89 2500RPM 3.04
THANK YOU!!
__________________
Thread Starter
Race Director
Joined: Sep 2002
Posts: 14,552
Likes: 24
From: Washington County, South UTAH
Thread Starter
Race Director
Joined: Sep 2002
Posts: 14,552
Likes: 24
From: Washington County, South UTAH
I still have the 4 old O2's, that were in place before the reman engine install.
First chance i get to put the car on a lift, i will substitute 2 old , pre-cat O2's.
Thanks.