SEFLS1

Hey everyone. I just joined this site today but I used ls1tech a few days ago for the first time. I just bought a 1998 Camaro Z28. Its a 5.7 v8 with the 6 speed t56. Its got 80k on it and after about a day of owning it, the engine light came on. I went and bought a scanner and ran the codes, and they were P0131 and P0151. I looked them up and it was apparently both front O2 sensors.....or so I thought. I googled the two codes together and it led me here where I noticed a lot of people were having the same issue, either having the same codes as I did, or those codes and more. I looked through pages and pages of forums to see if anyone had a solution but no one had a solid solution. Some people were saying it was the fuel pump, some said to swap o2 sensors, some said it was an ECU problem. But for those of you with this problem, I found the solution. I talked to my master tech friend Ive worked with for years since hes pretty smart, and asked him if hes ever seen both o2 sensors go out at the exact same time. I thought it was odd which is why I was led to believe it was not the o2 sensors like many people think. It turns out it was the MAF (mass air flow sensor). It was reading too low of a reading which made both o2 sensors read low air which then told the ecu to enrich the fuel to compensate. My symptoms before this MAF replacement were loss of power, felt like it had a misfire, ran rough, and if i'd reset the ecu the engine light wouldn't come on until I was at WOT (wide open throttle). So for those of you who either have, had or will have to struggle with these codes and issues, this is the solution. I installed a remanufactured MAF, reset the ecu, and it runs so smooth and fast now and no engine light.

Goobermix

Goobermix

Phoenix-Z28

I have a 98 z28 5.7 and I have been trying to figure this out for 2 years. My codes were all 4 o2 sensors. Car hesitates when trying to accelerate. Stalls in neutral while coming to a stop. I will try replacing maf. I started to think it was the cats. Especially after I sat down and learned how to use my stupid scanner. It said my cat efficiently failed test. Thanks for the advice. Hopefully now I can enjoy a nice ride again.

guy7bmwm83

iTrader: (5)

I also have been trying to track down this problem. My 2001 Trans AM WS6 has been triggering the P0131, P0151, and even the P0137, P0157 in the past, for many years. I have learned the scenario that causes these codes for me. I feel a slight hesitation at about 2500-2700 rpms during acceleration or passing a vehicle and acceleration doesn't feel 100%. The car drives and acts normally under moderate driving. The moment I accelerate hard there is a hesitation at 2500 rpms. After doing several acceleration runs, having fun, I get these codes in my AeroForce Interceptor gauge and I clear them before the car engine light is triggered. The car seems to go into a sort of limp mode if I drive the car with those codes.

I did discover that I am loosing fuel pressure above 2700 rpm. I have attached a fuel pressure gauge and at idle it reads 55lbs. The fuel pressure doesn't fluctuate much while driving normal. While idling, I rev the engine near redline and I watch my fuel pressure drop as the rpms climb. It used to drop about 25lbs, I have tried different things and the last time I checked the fuel pressure dropped less, but it shouldn't drop much or at all. I have tried torqueing down the intake manifold bolts, tried to seal the air lid where it attaches to the throttle body (the plastic lid and rubber connector don't appear to be attached tightly). I also just replaced both catalytic converters (CA) because the flange on the driver side was cracked about 75% around, and also the car has 239,000 miles so I replaced the pair of converters together. I also just installed the 4 O2 sensors while I was at it so that everything related to the exhaust emissions would be new.

I took the car for a test drive today and it ran better. I reset the computer before driving, but only have 30 miles so far. I need to drive the car more and normally until the ecu fully relearns the programming. The test drive revealed smoother acceleration around 2500-2700 rpms, but perhaps there is still a slight acceleration hesitation. I drove the car 30 miles on the highway, freeway, and city streets with moderate acceleration runs, and a few more spirited acceleration runs. There was only one 75% throttle run in a 2nd gear pull to about 4500 rpm. At first I thought, the car is fixed, but near the end of the drive I got P0131, P0151 again. The only other thing I can think of is if there is a vacuum leak at the intake manifold/gaskets, or if the exhaust manifold is leaking (did not try to remove the shield to inspect, but could not see cracks where I could inspect).

I did replace the intake manifold gaskets many years ago and noticed 1 bolt on the intake manifold seems to loosen. I have thought about redoing the intake manifold gaskets to try to repair on oil leak, possibly the valley cover. I am thinking about giving the MAF sensor a shot. It does have 239,000 miles and no part lasts forever. I am tired of this issue because it robs me of 100% performance and fun, so I drive moderately. I love my Trans Am, but I am holding back on using all the horsepower.

RPM WS6

iTrader: (3)

The part quoted in bold above, none of those things will correct poor fuel pressure. Sounds like you need a new pump and/or have a clogged filter. ~25psi is not remotely adequate at WOT, it should maintain 58-60psi regardless of load/no load and/or engine speed. Your power loss, and perhaps driviabilty issues, is likely related to this poor fuel pressure. Those other items might in fact have made it seem to run a bit better (after 240k miles I'm sure it didn't hurt to change any of those parts), but they are not the primary source of your power loss.

The mid-range rpm issue could very well be MAF related, (regardless of fuel pressure - though low pressure certainly isn't helping); I'd try cleaning the MAF first (prior to replacement), especially if the car has ever seen a K&N-style air filter.

New fuel pump & filter (or you could just try changing the filter first, then re-check pressure, but if the pump is original at 240k I'm sure it's not in the best of health), MAF cleaning, then re-evaluate performance. That would be my process, given what's known thus far.

guy7bmwm83

iTrader: (5)

I have tried cleaning the MAF in the past and the car ran about the same. I have changed the fuel filter several times and the car runs the same. As far as I know, the pump may be original and it's the same pump from when I bought the car at 118,000 miles. The last time I connected the fuel pressure gauge it was dipping to 35-40 psi. I did order the MAF to give that a try and will follow up. A new fuel pump may be next. I found this thread beneficial despite being from 2 years ago. Many threads end up being dead ends with no follow ups.

RPM WS6

iTrader: (3)

There is no question that you will need better fuel pressure to see full performance/potential from your setup (assuming that the FP gauge is reading accurately). If pressure is still 35-40psi after the filter change then the problem is likely with the pump itself. I would not spend one single dollar more doing anything else until the fuel pressure issue is corrected; a new MAF is not going to have any impact on fuel pressure, and any improvement that the MAF may or may not offer related to your other issues could be masked by overlapping issues related to the known poor fuel pressure/failing pump.

guy7bmwm83

iTrader: (5)

I did end up changing the mass airflow sensor with a remanufactured AcDelco version. I reset the computer, but want to put more miles on the vehicle. I have been driving the car normal for now. I did noticed that one of the bolts from the driver side exhaust manifold sheared off and I have a slight vibration while in gear waiting at a light. It is the second bolt starting from the front of the engine. That will need to be addressed. I do want to check the fuel pressure again.

RPM WS6

iTrader: (3)

An exhaust leak in front of (or very near) the forward O2 sensors could certainly cause some driveability issues, so if there is a leak at the manifold that should, in fact, be addressed for best results. But, none of this is going to fix low fuel pressure; MAF and exhaust leaks have no bearing on fuel pressure and you will be down on power until this is fixed.

guy7bmwm83

iTrader: (5)

Here is an update. My exhaust vibration went away after re-adjusting the catback exhaust. I have driven the car 430 miles with the remanufactured mass air flow sensor. The car accelerates smoother and more consistent. After driving the car a few weeks and doing acceleration runs I had promising results until today. Today I triggered the P0131 code on my aeroforce interceptor gauge while using the 0-60 feature after a few runs. I am still getting a whiff of an exhaust leak, which I am starting to suspect may be the drivers side exhaust manifold leaking or cracked.

I have not checked the fuel pressure yet, but have been meaning to do so. I am not much of an electronics or schematic guru. My question for the fuel pressure, can bad/cracked fuel injector o rings or o rings along the fuel lines be affecting the fuel pressure?