This car is slowly killing me with P0131 and P0171

[chadicenhour]

Alright guys, just a little background. Two days ago I replaced the cat because I noticed a lack in power when I drove the car longer. It restored alot of power after doing that, but today I was making a turn and the car suddenly shut off. It restarted, I got home and scanned the ecm and came up with a P0131 and a P0171. Also, the engine surges at idle like its hunting and ofcourse sometimes stalls when it surges. I checked for vac leaks and it came up clean, especially since its only got about 500 miles on new headgaskets and intake gaskets. I guess my question is will P0131 code cause a P0171? I looked at the wires on the upstream o2 sensor and noticed the wires looked a little mangled right on top of the sensor. I did notice this when doing the headgaskets, but didn't think it was a real issue. I'm assuming the o2 sensor is messed up giving the pcm the wrong signal and the pcm thinks that the engine is running lean throwing the P0171 code. Any suggestions? I just don't want to waste money. Oh, btw this is a 99 GAGT. Thanks, Chad

[3400-95-Modified]

Yes, a low voltage reading on the o2 sensor (P0131) will most likely cause a P0171, if not the other way around, the 171 is triggered prior and then the 131 gets triggered because the reading is dangerously low.

Change out that sensor if you do in fact see damage to the wires right near it.

[DefEddie]

You have either too much air or not enough fuel.
P0171 is lean condition,02 sensor showing extremely lean would be show low voltage at the pcm.
Looks like you have a lean condition unless the 02 sensor is damaged,i'm betting on the lean condition.
Watch the 02 sensor on a datalogger along with trims,also see what the freeze frame data shows.

Put your foot on the brake while in gear and load it up,if the pulsewidth's skyrocket you have a fuel volume issue such as restricted filter or pump going south usually.
Make sure you don't have an exhaust leak before the 02 sensor,that can cause lean codes also.

Depending on how "messed up" the 02 sensor is it could be ruined though.
It compares the air in the exhaust to the air outside (which it gather's from inside the metal housing). If the housing is damaged or the wires were pinched during the head gasket change that could screw up the 02 sensor reading.

[Joseph Upson]

This is a very interesting and probably confirming problem for me and my story may be of some help to you.

Currently I have a situation with a 98 V6 Accord that after driving usually about 15-20 minutes will intermittently gradually and quickly start to loose power without a skip or backfire as if you're turning a volume knob down. When the accelerator is pressed gradually to compensate the power loss intensifies until about 75% throttle is reached consistently where it suddenly picks up and takes off as if nothing is wrong. It has set no associated codes.

It will do this in cycles never stalling and idling fine when stopped. What's interesting about it is the first manifestation of the problem started with an uncharacteristically tight turn at speed recently nearly making the tires squeal. I thought it was bad gas bc I had filled the tank about 20 miles earlier but that wasn't it. I also had one episode of surging with off idle throttle (~2000 rpm) while parked once.

The problem is only predictable in that it may or may not occur after 20 minutes of driving and has gone as much as 50 miles without a symptom. It did show symptoms yesterday after a particularly tight turn (high Gs).

I broke down and bought a scanner earlier and recorded a string just as the problem started. What I found; bank 1 and 2 O2 sensors were reading very similar and opposite of eachother in their graphs for seconds straight without the characteristic swing. While idling in the driveway after the symptom display, O2 1 was barely moving above 0.00 volts while O2 2 was varying as high as .875 volts.

They are suppose to nearly mirror eachother the way they did today on a test drive recording with no problem. The graphs zig-zagged up and down for both.

Conclusion: I have a progressive oil leak that is hitting the exhaust, it has probably reached one of the sensors (#1 probably) and a sharp turn or appropriately placed tuft of rushing air is contaminating the external air sampling part of the sensor with oil and that results in the intermittent problem which apparently can be over ridden by ~75% throttle where the PCM probably stops reading the O2 sensor for WOT trim.

Your problem could be a brand new bad or contaminated sensor on install with incompatible gasket sealant or exposure to something else that could damage it.

I intend to do one more data record during the malfunction before replacing the sensor. Even at 11 years old sensors are expensive for this car with a distributor. ignition module $110, coil $90, MAP sensor $80, O2 sensor $70. That's a lot of cash for those parts relative to domestic so I need to be right about this.

[60dgrzbelow0]

These two threads may have relevance and provide additional insights...

http://60degreev6.com/forum/f98/stall-on-right-turns-t44965

http://60degreev6.com/forum/f100/aaaaaaah-phantom-stalling-again-t25818/page3

[chadicenhour]

I replaced the o2 sensor and it hasn't surged or stalled anymore, but I have another problem that was there before the o2 sensor problem. I was hoping the o2 would fix this problem as well. Anyway, the problem I have is that anything throttle below 1/2 feels really gutless. When I have to maintain speed to go up a hill I have to give it way too much throttle. If I accelerate normally, it just feels sluggish. If I gradually give the engine more throttle, as soon as it hits 1/2 throttle its like someone hit a swich for power. I don't get it. This car is killing me. My aunt has a Grand Am Gt and her car would run circles around mine just driving it normally. You can barely touch the throttle on her car and it wants to spin the tires. Any suggestions? Thanks!

[86FieroSEv6]

Unhook the EGR, this will eliminate it from the equation and force open loop as well. Then we will know which way to go.

[chadicenhour]

Unhook the EGR, this will eliminate it from the equation and force open loop as well. Then we will know which way to go.

I guess I'll give that a try in the morning after I replace the brakes. Any other suggestions?

[DefEddie]

Did you reset the computer and erase the code?

Reset the codes,complete the monitors and recheck.

[Joseph Upson]

I replaced the o2 sensor and it hasn't surged or stalled anymore, but I have another problem that was there before the o2 sensor problem. I was hoping the o2 would fix this problem as well. Anyway, the problem I have is that anything throttle below 1/2 feels really gutless. When I have to maintain speed to go up a hill I have to give it way too much throttle. If I accelerate normally, it just feels sluggish. If I gradually give the engine more throttle, as soon as it hits 1/2 throttle its like someone hit a swich for power. I don't get it. This car is killing me. My aunt has a Grand Am Gt and her car would run circles around mine just driving it normally. You can barely touch the throttle on her car and it wants to spin the tires. Any suggestions? Thanks!

That still sounds like the problem I have with the HONDA. You have two O2 sensors, replaced one and noted an improvement. The second one can be bad also. A recent data scan showed my upstream O2 sensor hanging around 0.00 volts especially when the car starts to loose power from cruise speed. It continues to loose power even when the accelerator is depressed further until about 75% where the car takes off. Not sure if OBD II follows the same protocol but that's about where the PCM stops reading the O2 sensor and switches to preset values. The EGR can cause a similar problem but my experience has been more of a surge with EGR malfunction.

I'd take it to Azone and have them do an O2 sensor read instead of just pulling the code if your unit can't do it. You need to see what the fuel related sensors are doing at this point.

[chadicenhour]

That still sounds like the problem I have with the HONDA. You have two O2 sensors, replaced one and noted an improvement. The second one can be bad also. A recent data scan showed my upstream O2 sensor hanging around 0.00 volts especially when the car starts to loose power from cruise speed. It continues to loose power even when the accelerator is depressed further until about 75% where the car takes off. Not sure if OBD II follows the same protocol but that's about where the PCM stops reading the O2 sensor and switches to preset values. The EGR can cause a similar problem but my experience has been more of a surge with EGR malfunction.

I'd take it to Azone and have them do an O2 sensor read instead of just pulling the code if your unit can't do it. You need to see what the fuel related sensors are doing at this point.

I have a Snapon Solus for diagnostics although I do admit I don't understand every bit of the data as far as the o2 sensors go. It seems to be measuring in milivolts I believe, I could be wrong. Anyway, I unplugged the EGR valve and it seemed to make some difference with making the power not kick in at half throttle, but it still seemed to be lacking. I was pondering the idea of the engine not getting enough fuel. I did a fuel pressure test and I don't remember the exact spec of it idling, but while driving it stayed around 40psi. I'm also pondering the idea of it having a bad MAF although it should throw a code. I dunno, I hate driving my car. I had a 97 GAGT before that had more power than this 99 GAGT.

[chadicenhour]

Did you reset the computer and erase the code?

Reset the codes,complete the monitors and recheck.

I did clear the codes. As far as the monitors go, I'm not sure if they are set yet. I'm gonna guess they probably aren't just because I haven't driven the car much because I hate how it runs. Everytime I have to accelerate in this car, it reminds me of how much I hate it.

[geldartb]

do you have another maf you could swap out or try some of the maf sensor cleaner.

[chadicenhour]

do you have another maf you could swap out or try some of the maf sensor cleaner.

Even though the MAF looked clean, I still cleaned it and got no change in performance. Unfortunately I don't have another MAF to swap out.

[Joseph Upson]

I have a Snapon Solus for diagnostics although I do admit I don't understand every bit of the data as far as the o2 sensors go. It seems to be measuring in milivolts I believe, I could be wrong. Anyway, I unplugged the EGR valve and it seemed to make some difference with making the power not kick in at half throttle, but it still seemed to be lacking. I was pondering the idea of the engine not getting enough fuel. I did a fuel pressure test and I don't remember the exact spec of it idling, but while driving it stayed around 40psi. I'm also pondering the idea of it having a bad MAF although it should throw a code. I dunno, I hate driving my car. I had a 97 GAGT before that had more power than this 99 GAGT.

Have someone drive it while you monitor the sensors on the scanner unless you have software that allows you to review recorded data in graph form, otherwise isolate your O2 sensors on the scanner and observe the voltage change while the car is being driven, low voltage is lean, high voltage is rich. The voltage should change constantly over the full range. Constant voltage or sluggish to small changes in voltage suggests there is a problem in that area. I believe your fuel pressure should be higher than 40 psi on a 99 car. A lean condition should show up in your O2 sensor voltage. Some of the GM cars have a dual speed pump control, not sure if that is part of the problem you're having.

Check your TPS voltage also for a linear change with accelerator position.