1999 Toyota Tacoma, 3.4L, Automatic, 4X4, 321000 miles. Came in with check engine light on, P0171, bank 1 too lean. Failed Colorado emissions for High NOx. Found both oxygen sensors dead, replaced both sensors, reset check engine light after about 20 miles, had checked MAF and air intake temp sensor. Coolant temp sensor reading -40 degrees constant, accessed coolant temp sensor, found it broken, replaced it. Cleared check engine light, drove car 40+ miles, no codes. Went to emission testing, failed again due to excessive NOx, no check engine light. Live data shows short term fuel trim bank 1 readings between -1.469 and -5.468 % over the course of the test on the dyno, while long term fuel trim, bank 2 is between 2.341 and 5.409 during the test. Have checked for vacuum leaks, both visually and with brake cleaner. MAF and Cat replaced a little over 2 yrs ago. Only other thing I noticed was the timing belt is heavily cracked. The following readings are directly from the test. First readings are from the 1st e test, second are from the after repair test: 1: Check engine light, fail, diagnostic trouble code: P0171; 2: pass, no diagnostic trouble codes; NOx: 1: 3.3129; 2: 3.3024 (GPM); Hydro carbons: 1: .8328; 2: .6610 (GPM); CO: 1: 9.804; 2: 6.7861 (GPM); 1: CO2: 389.149; 2: 362.4064. If you have any ideas or further questions, I could use your help. Thanks in advance.
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EMISSION FAILURE, NO CHECK ENGINE LIGHT
- Thread starter david ott
- Start date
TacomaLoverExtroa9681
Well-Known Member
Hey David,
How are you? You certainly have done your homework as far as trying to get your old Tacoma to pass to its Colorado emission test, and you certainly know much more about the Toyota 3.4 Liter V6 than me, and I know a little bit about this engine since my family has one. We have the exact same 1999 rig as you except for our Tacoma is a stick shift with a lot less miles on it than yours. Our Tacoma only has 165,000 miles. You must be very frustrated with as much homework as you have done, and it is still failing its emission test.
Did you take the front side of the engine apart? Is that how you determined the timing belt was cracked? Not that the timing belt has anything to do with emissions, but did you replace it after determining it was cracked?
Okay, so you knocked out all of the possible emission culprits as far as I can tell with all of the work you have done. All of the emission sensors are now new and operational, and the catalytic converter and Mass Air Flow have been replaced. There are also no known vacuum leaks as far as can be determined. How about the muffler? Has the muffler been replaced, or is it the original muffler? Could that be the culprit?
Good Luck,
Paul
How are you? You certainly have done your homework as far as trying to get your old Tacoma to pass to its Colorado emission test, and you certainly know much more about the Toyota 3.4 Liter V6 than me, and I know a little bit about this engine since my family has one. We have the exact same 1999 rig as you except for our Tacoma is a stick shift with a lot less miles on it than yours. Our Tacoma only has 165,000 miles. You must be very frustrated with as much homework as you have done, and it is still failing its emission test.
Did you take the front side of the engine apart? Is that how you determined the timing belt was cracked? Not that the timing belt has anything to do with emissions, but did you replace it after determining it was cracked?
Okay, so you knocked out all of the possible emission culprits as far as I can tell with all of the work you have done. All of the emission sensors are now new and operational, and the catalytic converter and Mass Air Flow have been replaced. There are also no known vacuum leaks as far as can be determined. How about the muffler? Has the muffler been replaced, or is it the original muffler? Could that be the culprit?
Good Luck,
Paul
Took the front cover off, belt obviously heavily cracked. Also checked timing belt timing and it is spot on. Pulled plugs last night, all show lean burn. Next step this morning is to change the fuel filter and check fuel pressure pressure as low pressure could be the culprit. As there are no codes, I am fairly sure the air mass meter is good. May just replace the cat also, as it is one of those "cheapie" cats, and that is a small cat for the engine size.Hey David,
How are you? You certainly have done your homework as far as trying to get your old Tacoma to pass to its Colorado emission test, and you certainly know much more about the Toyota 3.4 Liter V6 than me, and I know a little bit about this engine since my family has one. We have the exact same 1999 rig as you except for our Tacoma is a stick shift with a lot less miles on it than yours. Our Tacoma only has 165,000 miles. You must be very frustrated with as much homework as you have done, and it is still failing its emission test.
Did you take the front side of the engine apart? Is that how you determined the timing belt was cracked? Not that the timing belt has anything to do with emissions, but did you replace it after determining it was cracked? Going to replace the timing belt/water pump after I get it to pass emissions.
Okay, so you knocked out all of the possible emission culprits as far as I can tell with all of the work you have done. All of the emission sensors are now new and operational, and the catalytic converter and Mass Air Flow have been replaced. There are also no known vacuum leaks as far as can be determined. How about the muffler? Has the muffler been replaced, or is it the original muffler? Could that be the culprit?
Good Luck,
Paul