Offroad Trailblazers and Envoys

Intermittent Engine Power Loss and Stalling at Stops

Something not working right?

by Trail X » Mon Jun 12, 2017 8:05 pm

I finally got one of those bluetooth obd tools and the torque app, and decided to drive it around while watching the O2 sensor and the short term fuel trim.

Drove around the block a few times and all was well. No issues. No stumbling, nothing apparent. Decided to bring it out on a bigger road with a little higher speeds. As I was going up the first hill, the O2 readings flatlined. It hesitated for a minute, then the PCM switched into open loop mode.

So in my mind, I started thinking the O2 sensor could have a temperature dependant open or short circuit. Sure enough, a few minutes later, P0130.

I'll swap the O2 asap. I was also trying to listen for the squeaking noise that I heard the last time it stalled. I realized that as it was stalling I decided to roll down the window. I noticed today that the brakes have a slight squeak to them, which I probably heard only when I rolled down the window, and thought may have been associated with the stalling.

Anyways, well see what a new O2 does.
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by bartonmd » Mon Jun 12, 2017 10:09 pm

Hope that's all it is!
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by CHEVELLE598BB » Mon Jun 12, 2017 11:12 pm

Trail X wrote:I finally got one of those bluetooth obd tools and the torque app, and decided to drive it around while watching the O2 sensor and the short term fuel trim.

Drove around the block a few times and all was well. No issues. No stumbling, nothing apparent. Decided to bring it out on a bigger road with a little higher speeds. As I was going up the first hill, the O2 readings flatlined. It hesitated for a minute, then the PCM switched into open loop mode.

So in my mind, I started thinking the O2 sensor could have a temperature dependant open or short circuit. Sure enough, a few minutes later, P0130.

I'll swap the O2 asap. I was also trying to listen for the squeaking noise that I heard the last time it stalled. I realized that as it was stalling I decided to roll down the window. I noticed today that the brakes have a slight squeak to them, which I probably heard only when I rolled down the window, and thought may have been associated with the stalling.

Anyways, well see what a new O2 does.


At what voltage did the o2 sensor flatline at? Do you have access to the fuel trims short term being the more important one. What does the coolant temp read (the pid not the gauge), what reading is the maf when it is running bad and what is the map. Live data will be the only way to start solving this problem. A p0130 throws after it's running bad. The o2 could cause the p0130 but since it's intermittent I wouldn't swap it just yet. It sounds like the p0130 is being set by the condition the engine is running in ie overly rich or lean.

That being said a bad front o2 can cause horrible running conditions. I just like to diagnose a problem before swaping parts. If you need real data numbers from a good running 4.2 then let me know. I can post up some. Mine is an 2002 which would be the same for 02 to 05.

Seafoam could have definitely dislodged some carbon which could have logged in the o2 causing issues with weird readings and running problems.
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by Trail X » Tue Jun 13, 2017 8:27 am

Hey Jay. I can run it again later today to get some better data. I do have access to short term fuel trims, but not long term - at least not that I've found yet. Its a bit hard to keep an eye on the gauges 100% of the time and drive. I wonder if Torque can record data into a dump file. When driving lightly around the neighborhood, it was driving fine. O2 readings bounced around like I'd expect it to, a constant saw tooth up and down - small teeth when idling, larger when driving, reacting to the sawtooth STFT inputs (which may have been more agressive since I just cleaned the TB and reset the fuel trims via unplugging the battery). As I crested a hill on the secondary road, I felt it hesitate for a second. I looked down at the O2 gauge, and it had a sharp dropoff. At that point, both gauges flatlined further. I couldn't figure that out at first, and later realized that is how the PCM outputs those values when it goes into open loop mode. I may go drive it and try to recreate the problem and see if I can screengrab it for posterity.

I was trying to determine if the seafoam treatment could have anything to do with it, and concluded something similar, a higher evaporation rate from the crankcase may have elevated the exhaust temperature to damage the O2, or as you said, carbon buildup could have lodged in the O2 and damaged it. Or - there's a chance that it is a complete coincidence.
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by v7guy » Tue Jun 13, 2017 4:29 pm

The videos didn't sound particularly off to me, but like Mike, I'm not listening on anything with decent speakers I'm going more off the description you gave.

I'd definitely rule out other options first. Hopefully the 02 is just the issue
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by Trail X » Tue Jun 13, 2017 9:51 pm

Here's a quick screen shot of what would happen with the O2 feedback and STFT graphs in Torque when it would go flakey. When it did this, it would go into open loop. Unfortunately it doesn't display voltage, I didn't realize that was a separate display till just now. I drove it a bit more today and it acted fine other than popping between open and closed loop. Although, there was a tiny squeak once in 5 times I shut it off. But it may have been doing that for a while, I'm not entirely sure.

I'll try to drive it again in the morning to get some raw O2 voltage data, then swap the O2 tomorrow evening if I have time.
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by Trail X » Thu Jun 15, 2017 8:18 am

Well, I think the O2 has been confirmed. Drove it in today and it did great.

Here's a comparison between how it was acting with the bad O2, and how it acts with the good O2, including voltage displays. These screen shots aren't taken at the same point on the road, but it may give others an idea of what to look for in the future. It's a bit subjective.

I'm going to update the thread title with something a little more descriptive, and a little less dramatic.

Screenshot_2017-06-14-07-25-33[1].png
O2 sensor incorrectly reporting combustion and causing ECU to incorrectly rich the mixture. CAT had not completely warmed up, as this was a short drive, which I believe is why the O2 1x2 (post cat) sensor went low. It does that a bit before the cat warms up completely.


Screenshot_2017-06-14-19-53-40[1].png
Properly performing O2 sensors and fuel trims.
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by bartonmd » Sat Jun 17, 2017 12:28 am

Awesome!

Mike
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by CHEVELLE598BB » Mon Jun 19, 2017 1:36 pm

Looks like the scan with the new o2 sensor is still running rich. What was the engine temp when you did the scan?

At full temp the stft should be hovering around -5 to +5 in closed loop.

The new o2 is definelty working better.
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by Trail X » Fri Jun 23, 2017 9:03 am

Water temp was probably up to temperature, but I don't recall exactly. I had previously reset the fuel trims by unplugging the battery, then it had gotten used to a bad O2, and this was the first time it was ran with the new O2, so it may have learned some bad habits that it will need to average out. I'll keep an eye on it.
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by joemoto311 » Mon Jul 03, 2017 9:33 am

Before it got to this point, would your vehicle ever just randomly stall at idle? Like at a red light or if you are warming it up? I've never thrown a code but mine does this and has for about as long as I can remember but I've owned it for a long time. TB has been cleaned but could use another. I'm against seafoam unless the vehicle has always used it. Some have great success with it, others not so much. The noises you are hearing are normal IMO and probably been going on longer than you think. Just never noticed it until you started having problems. Every GM I have owned or friends/family have owned either always had a lifter or tick noise after 30-50k miles. I wouldn't call what you have to be a "knock" but others might I guess. No idea about your squeal you mention though. I would assume you would know the difference between a serpentine belt and something else. Like above, that all does point to a bearing but that doesn't mean its immediate failure. As long as you have good oil pressure which is seems you do, I would just keep an ear out for it.....I have also found in the past that a bearing in your alternator can sound like a knock when it is under load. It was wild when I finally tracked down the noise to be that. I was surprised but extremely relieved. Glad it seems you fixed your issue and turned out to be something simple! Wonder if my O2 or CPAS has just not decided to fail and make my troubleshooting difficult. Feel like I'm at work with these intermittent problems that aren't present when I'm troubleshooting
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by Trail X » Thu Jul 06, 2017 8:25 am

A few years ago I had some random stalls at idle. It was O2 related, but it wasn't a bad O2 sensor. It was a crack in my manifold, that was robbing the O2 of exhaust (especially at low flow - idle) and giving the PCM a bad feedback loop. Often it comes with a vibrating engine at idle or a misfire code. Something to check.

My truck is running great now, so I think you're right, some of those random sounds are somewhat normal. The squeal has gone away. I think its possible that I waited too long to change the oil. Since I don't drive it everyday, it had probably been a while - plus I had overheated it a bit this past year from time to time.
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