hello, newbie here.
i bought this cheap tahoe last may with 245000 miles on it.
very high miles but overall condition was pretty good for its age/price.
and it was my first chevy truck. and it has 4.8l engine.
had no problem at all and it always started right up and drove fine.
until last winter.
around around november, i bought qt of lucas fuel injector cleaner and added to fuel for about 5~6 tank fill. (just fyi. could be nothing to do with these issues.)
i'm in texas and winter temp is not that cold.
during winter, morning startup when engine is cold, idle felt little rough.
temp was around 40~50F
only morning start was affected. hot start or mid day start were fine or had very minimal roughness)
when temp dropped, the symptom got worse then eventually generated P0171/P0174 codes.
both banks were in lean condition.
and couple of times, temp was near or below subzero (32F), got P300, random misfiring.
now it is spring and temp is around 65F or higher.
and i still getting the codes.
1. last winter, when temp was around 40F, got 171/174 codes.
2. around 30F temp, got 300 code twice but it was resolved itself.
3. felt no noticeable changes in driveability, power, fuel economy.
4. fuel economy was constantly around 13~14 mpg at the pump (miles from trip meter / gallons went in) (about 70% city and 30% hwy)
5. time to time i can feel smell of gas around truck but can't pinpoint where.
6. found cracked vacuum line from passenger side of engine and used hose clamps.
i used water spray and brake cleaner spray but found no other vaccum leaks (yet)
7. replaced fuel filter from autozone. no change.
8. replaced MAF with cheap ebay knock offs. no change
9. replaced IAC (idle air control) with ebay one but no change
- after change, sometimes idle tends to go 2000 rpm and the truck tried to accelerate while crawling in parking lot without pressing gas pedal
10. noticed long term fuel trim was way too off. 25% constantly for both banks at idle.
- ltft went down to 7~8% when drive with wide throttle.
- during idle, stft for both banks are between positive 0~5 range.
11. ltft tends to drop with open throttle (aka WOT)
12. replaced fuel pressure regulator from autozone, but no change
13. tried autozone's fuel pressure guage but its o ring was messed up, so can't trust result. but it was around 50 psi while idle. in koeo(key on engine off) condition it was around 40 but again, can't trust that and had no problem to start it up.
14. still with codes, even with P300 code, truck starts up right away. (of course it will suffer few seconds later due to P300 code).(i can't fee any negative difference when 171/174 codes were on)
the codes cleared themselves after put gas to full tank like 3 times or so, but it could be coincident.
any thought on this???
i bought this cheap tahoe last may with 245000 miles on it.
very high miles but overall condition was pretty good for its age/price.
and it was my first chevy truck. and it has 4.8l engine.
had no problem at all and it always started right up and drove fine.
until last winter.
around around november, i bought qt of lucas fuel injector cleaner and added to fuel for about 5~6 tank fill. (just fyi. could be nothing to do with these issues.)
i'm in texas and winter temp is not that cold.
during winter, morning startup when engine is cold, idle felt little rough.
temp was around 40~50F
only morning start was affected. hot start or mid day start were fine or had very minimal roughness)
when temp dropped, the symptom got worse then eventually generated P0171/P0174 codes.
both banks were in lean condition.
and couple of times, temp was near or below subzero (32F), got P300, random misfiring.
now it is spring and temp is around 65F or higher.
and i still getting the codes.
1. last winter, when temp was around 40F, got 171/174 codes.
2. around 30F temp, got 300 code twice but it was resolved itself.
3. felt no noticeable changes in driveability, power, fuel economy.
4. fuel economy was constantly around 13~14 mpg at the pump (miles from trip meter / gallons went in) (about 70% city and 30% hwy)
5. time to time i can feel smell of gas around truck but can't pinpoint where.
6. found cracked vacuum line from passenger side of engine and used hose clamps.
i used water spray and brake cleaner spray but found no other vaccum leaks (yet)
7. replaced fuel filter from autozone. no change.
8. replaced MAF with cheap ebay knock offs. no change
9. replaced IAC (idle air control) with ebay one but no change
- after change, sometimes idle tends to go 2000 rpm and the truck tried to accelerate while crawling in parking lot without pressing gas pedal
10. noticed long term fuel trim was way too off. 25% constantly for both banks at idle.
- ltft went down to 7~8% when drive with wide throttle.
- during idle, stft for both banks are between positive 0~5 range.
11. ltft tends to drop with open throttle (aka WOT)
12. replaced fuel pressure regulator from autozone, but no change
13. tried autozone's fuel pressure guage but its o ring was messed up, so can't trust result. but it was around 50 psi while idle. in koeo(key on engine off) condition it was around 40 but again, can't trust that and had no problem to start it up.
14. still with codes, even with P300 code, truck starts up right away. (of course it will suffer few seconds later due to P300 code).(i can't fee any negative difference when 171/174 codes were on)
the codes cleared themselves after put gas to full tank like 3 times or so, but it could be coincident.
any thought on this???
