my_99Z

iTrader: (4)

Hey guys, I just bought a 99 z28 about 3 weeks ago. I'm not new to getting dirty, after buying the car I replaced the water pump and power steering pump because both were leaking. I noticed the car hesitates around 2300-2500 rpms, not a wild amount just enough to push you into your seatbelt and then the car picks back up once it's outside of this rpm range. I checked my MAF sensor and the screen was full of junk so I cleaned that and my throttle body, I also made sure the intake elbows were sealed correctly after that. I'm getting an SES light when I bring the rpms above 3500 rpms they are p0137 and p0157. Bank 1 sensor 2 and bank 2 sensor 2 low voltage. So I realize my 02 sensors need to be replaced but my question is this my cause for hesitation? Anything above or below the specified rpm range of 2300-2500 rpms and the car runs like a champ.

Wondering if anybody can give me some insight on my problem. Could this all be my MAF?

It's a 99 z28 with an m6 tranny. Only mods that I know of is a magnaflow cat back and it's lowered.

TankTheTurtle

probably your o2s, change them out for some decent ones (i'm running NTKs) and then go from there.

Onyx_Black_Z28

iTrader: (2)

It definitely sounds like your O2 sensors. Obviously if the front two are not working properly then your fuel trims are going to be affected which could cause some hesitation. If you want to check if your MAF is the culprit, just unplug it. You will get an SES the second or third time you start it afterwards and the car will default to Speed Density. If the problem is fixed, you know it was the MAF. If not, you know to look elsewhere.

Honestly, the O2 sensors are cheap enough that I would swap them out regardless. They were part of the tune-up I performed on mine when I bought it.

my_99Z

iTrader: (4)

Would the front sensors be bank 1 sensor 1 and bank 2 sensor 1? Sensor 2 would be the rear o2's wouldn't it? And I would think those wouldn't affect the performance of the car with how it's running now would it? I know the sensors arent expensive. I unplugged the MAF earlier in the day and drove around with it like that, car did seem to run better but after plugging the MAF back in it doesn't seem to be doing it anymore so now I'm kinda stumped.

Onyx_Black_Z28

iTrader: (2)

I'm actually not sure of the order - if they are the rears then you are correct that they wouldn't affect the fuel trim. However, if it's the rears throwing the codes, you could always have a partially clogged cat or cats? That's of course if the sensors themselves aren't the problem. I'm just speculating here. Glad to hear the problem has gone away for now - hopefully it stays that way!

my_99Z

iTrader: (4)

That is true, I'll probably replace the o2 sensors first since that's the least expensive compared to a cat lol. Hopefully it's either those or the MAF. Then again, since I just had the car smogged, if it is the cats I could always gut them and just replace them in two years. Stupid smog regulations for CA

TankTheTurtle

the banks are the left and right sides, sensor 1 is the front, sensor 2 is rear.
Sounds like both front o2s are throwing codes, and that will definitely be affecting your performance.

my_99Z

iTrader: (4)

I'm having sensor 2 codes thrown. My front o2's arent throwing any codes. That's why I find it hard to think it would be my o2's causing this problem, and if my cats were plugged then I would think I would have hesitation on all aspects of the rpm band not from 2300-2500 rpms. I think my only other option is my MAF? Unless someone else has seen something else cause this problem?

my_99Z

iTrader: (4)

My rear o2's only throw codes when I'm above 3500 rpms. So would they be malfunctioning at 2300-2500 rpm's?

GMtechmatt

best thing to do would be get a tech 2scanner on it an what the voltage of the o2's and then check back pressure i have the same problem on my 2002 z28 throughing cat codes. fuel trims were in spec and so were O2's come to find out cat is semi clogged

TankTheTurtle

oh, my bad. misread the first post.
In that case I understand the confusion. good luck, hopefully something cheap and easy.

99ws6ls1

Everyone on this entire tread is giving miss imformation. o2 sensors cannot give a hesitiation problem or any drivablitily problem for that matter. rear o2 sensor are onlyy there to make sure that the cats are working properly. the front o2 sensors are the ones that the amount of oxygen in the exhaust stream and adjust fuel as needed. even if a front o2 sensor is stuck lean or rich it still will not cause a drivabilty concern. the reason for your rear o2 sensor codes is the result of another problem, as is your hesitiation. I cannot give any more advice because i do not have all the information and the pids in front of me.

omarrakeen

iTrader: (2)

WRONG. low switching O2s wont cause driveablity issues that is true. but busted O2s can give you all types of crap! my car was literally undriveable. black smoke, hesitations hell i couldnt get it to idle while in gear! and it happened while installing my LS6 intake so i totally ignored them at first till i re did the whole swap 3 times and then realized it was them and car is perfect now! OP if they are front sensors then that is your problem. if its the rears then it could be the cats. rear O2s should not impact driveablity but it is a sign of bad cats. you could disconnect all the O2 sensors and go for a ride and see if it runs better in open loop if not then i would say cats.

my_99Z

iTrader: (4)

I think I might have found the root of all problems. I drove to school with my MAF sensor plugged in, the car continued to hesitate. Once I got to school I unplugged it and drove around with it unplugged and then I drove home with it unplugged. It was a completely different car, my check engine light came on so I have to read the codes and see if my o2's are throwing codes or if it's just because my MAF is unplugged. Kind of hoping it's just the MAF and I don't have to get under the car. Im going to go down to the auto parts store today and buy a new MAF and see if that makes a difference. I'll keep you posted.

99ws6ls1

wrong...stop giving false info on something you cleary do not know the entire story to.

omarrakeen

iTrader: (2)

this is NOT a false info. O2 sensors WILL effect driveability as well as fuel trims. just because your car hasnt done it, doesnt mean it wont mess someone else's car.

OP by disconnecting your maf this means running in an open loop. try to borrow someone's maf and plug it in your car and see if it helps before wasting money on a new maf. good luck with the fix!

my_99Z

iTrader: (4)

Hey guys. I appreciate all the help and advice, I don't know anybody with a MAF that I could have used, so I just went and bought me. I figured if it didn't fix the problem I could just take it back. However, it did. My car runs great, and it actually stopped throwing the o2 sensor codes as well. Don't really know why but that seemed to fix the hesitation problems and the o2 sensor codes too.

99ws6ls1

gee what do you know the o2 sensors werent causing the hesitation. O2 SENSORS WILL NOT CAUSE A DRIVABILTY PROBLEM... not on my car not on your car or anybody elses for that matter. his rear o2 sensors were throwing codes because the cats were not working properly as a result of the maf air sensor being deffective. the ecm not knowing the correct amount of air coming into the engine throws stft's off and not giving a rich lean rich lean affect that the cats need to do there job correctly. if he had listened to all the people that posted here he would of ended up wasting money on 2 o2 sensors and still not fixing the problem, but instead he ffixed the real root problem and what do you know everything else falls back into place and works as it should

omarrakeen

iTrader: (2)

glad you solved it OP. ^ i never said "rear" O2 will cause problems. i clearly said "fronts" and mine did. am ready to ship you my defective O2 sensors from middle east to your door step at my expenses just to show what they can do.