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Stall, throttle response loss mid operating temperature

Tiny
VOPRO
  • MEMBER
  • 2005 GMC YUKON
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 135,000 MILES
Never before/never after but intermittently right around mid-gauge on the temperature indicator when coasting/very light throttle or at idle the engine will not respond to throttle and will act as if leaning out to the point of stalling. No codes and no pending codes. Has happened a dozen times in past 3 months.

Already completed:

Replaced full throttle body assembly
Replaced all 4 o2 sensors
Replaced complete evap system
Cleaned mass airflow sensor
Checked torque on intake
Replaced gas cap

Oddly today “tighten fuel cap” came on. Will check for code when I get home.

Update: p0455 large leak is active now. The fuel pump assembly was replaced about 18 months ago so seems odd we would have an issue with a leak around there.


Really looking forward to pro thoughts. My efforts have come up pretty empty thus far and losing power is sketchy in traffic!
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Saturday, May 9th, 2020 AT 5:13 AM

24 Replies

Tiny
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  • MECHANIC
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Hi,

Since there are no codes, it makes it a bit difficult. If it was related to the throttle actuator control (TAC) module, it should have set a code. Do me a favor (and don't laugh), check the connector at the accelerator pedal position sensor to make sure it is not loose or the sensor isn't loose. Also, unplug it and check for corrosion or damage to the wires. I attached a pic of it to help you with location.

Let me know.
Joe
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Saturday, May 9th, 2020 AT 9:18 PM
Tiny
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Will do Joe thank you!

I updated an hour after it happened that P0455 set but this seems unrelated since we haven’t had that before. As soon as I check I will get back immediately!
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Sunday, May 10th, 2020 AT 4:22 AM
Tiny
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Okay Joe, just looked and all is secure. I pulled it and reseated. I find the fact that it only does it right around midway of the warm-up cycle interesting. And if it does stall you can start it back up immediately.
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Sunday, May 10th, 2020 AT 4:37 AM
Tiny
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Update: the P0455 was due to a charcoal pellet being lodged in the Purge Solenoid on the engine. I had a canister break about six months ago and I cleaned all the lines out as best I could and vacuumed them out, and then replaced the canister and the solenoid in the back of the vehicle as well as the purge solenoid up at the engine. I cleaned out the Pellets from the Purge and put it back on.
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Sunday, May 10th, 2020 AT 4:28 PM
Tiny
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  • MECHANIC
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I bet that took care of the idle issue, correct? Honestly, anything to make it more of a challenge. Is it running properly now?

By the way, great job finding that. Most people never would have.

Joe
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Sunday, May 10th, 2020 AT 9:01 PM
Tiny
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Hi Joe! Thanks for getting back. Would you happen to know if the purge valve opens or closes midway of the warm-up cycle?
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Monday, May 11th, 2020 AT 4:24 AM
Tiny
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Joe,

It almost did it again this morning exactly halfway on the temperature gauge in the warm-up cycle. The idle starts to go below 500 maybe 450 and it’s like the engine is leaning out. Once it gets past the midway cycle of the temperature gauge, it never does it again. So I’m wanting to know what sensor, for example, controls air fuel mixture midway in the cycle? Or does that purge valve open up at that time and then if so I would probably replace that again perhaps it’s damage?
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Monday, May 11th, 2020 AT 4:32 AM
Tiny
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The purge valve is normally closed. It opens when the PCM deems it necessary. There isn't a preset time that it does. It is all based on engine conditions, speed, engine load, RPM, and so on.

As far as air/fuel ratio, it is determined by the PCM as well based on input from the engine temperature sensor, O2 sensors, engine load and so on.

Did I already ask if you have a live data scanner? If I didn't and you do, check the short term fuel trims for me and let me know what you find. Also, check the O2 sensors for how they are reacting. In a perfect world, the fuel trims would be 0. The oxygen sensors should range back and forth between.1v and.9v.

Let me know.

Joe
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Monday, May 11th, 2020 AT 6:46 PM
Tiny
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Great info Joe. I do have a live data scanner and can get that information. Unless I hear back from you otherwise I will try to get that data around the same engine temperature where I experience the issues if that will help. But if you just need to see if your trims at idle in the O2 information I can do that unless I hear back from you otherwise I will try to get that data around the same engine temperature where I experience the issues if that will help. But if you just need to see if your trims at idle and the O2 information I can do that.
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Monday, May 11th, 2020 AT 7:04 PM
Tiny
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That will help. At least we can see what is happening when the problem occurs. Also, check the readings under both conditions. We can compare them. One last thing. Before you even start the vehicle, check what the engine coolant temperature is reading. It should be close to the outside ambient temperature.

I will watch for your reply.

Joe
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Monday, May 11th, 2020 AT 7:24 PM
Tiny
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Okay Joe, the engine temperature is at 73 before I started and the thermometer in the car says it’s 65. Attached is a picture of about the time that it would normally do it although it did not do it this time. I did run a three minute video from just after starting all the way until virtually near full warm-up so I can go back and review that if you need me to.
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Tuesday, May 12th, 2020 AT 3:55 AM
Tiny
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Did the ECT indicate the correct temps as the engine warmed up? Also, the fuel trims indicate the computer is trying to lean the mixture, but it's really not that far out of line.

Let me know about the temp readings. And I hate to say it, but it may not indicate a problem until the problem actually happens. You may need to do this again and hope the problem occurs.

Did you happen to get the O2 readings as well?

Joe
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Tuesday, May 12th, 2020 AT 8:49 PM
Tiny
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Thanks again for getting back. I think I mentioned that the ambient temperature yesterday morning was around 68° and before I even started the vehicle the temperature showed through the OBD 73° All four 02 sensors are brand new. This picture was taken around the time it would stall, but naturally for the past two days it has not reared its head.
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Wednesday, May 13th, 2020 AT 4:27 AM
Tiny
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I don’t think the picture attached so here it is again.
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Wednesday, May 13th, 2020 AT 4:42 AM
Tiny
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I will continue each morning until it happens and the. Report back - so I don’t bother you. But, can you tell me what you want the scanner looking at when it does occur? O2 or Fuel Trim or?
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Wednesday, May 13th, 2020 AT 5:26 AM
Tiny
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Hi,

You are in no way bothering me. Please feel free to come back as often as needed. As far as what is happening, check for both. If I had to choose, I would say fuel trim. If an o2 sensor is causing problems, I should be able to recognize it via that reading.

Take your time and let me know. And again, you are not bothering me. I'm glad to help.

Take care,
Joe
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Wednesday, May 13th, 2020 AT 7:35 PM
Tiny
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You are such a blessing. Okay, this morning the outside ambient temperature was around 68. I was recording for four minutes as the engine was warming up and I was driving. Right around the three minute mark of the video the temperature gauge was reaching around the point where I have issues. Although it did not stall this picture that I’m attaching shows that the RPM's were dropping to probably around 450 and normally it would idle at around 550. I could see the needle starting to fluctuate like it normally does. And this is as close to the condition as I can get without a stall. It showing all of the fuel trims leaning out pretty good. I have did the test previously were you spray carpet cleaner around the intake to see if there’s any vacuum leaks but didn’t have any detected. I also made sure all the intake bolts were torqued correctly. As I mentioned all the O2 sensors are brand new I just put them in a week ago.
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Thursday, May 14th, 2020 AT 4:02 AM
Tiny
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Did you send a video? Also, the trims indicate the computer is trying to reduce the fuel to the engine. It is getting more than is needed. But it isn't totally out of the norm. Was it fluctuating when this happened?

Also, I never heard of the carpet cleaner idea. LOL. Here is a link that explains how to check for leaks:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know if you have a video so I can see how the system was reacting.
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Thursday, May 14th, 2020 AT 8:17 AM
Tiny
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Hahaha. Siri kills me! Here is the video I took. I believe it was somewhat near the three minute mark was where I noticed the tachometer was indicating a drop from normal 550 idle to 450. If a stall happens it will start doing that and then of course the RPM's just continue to fluctuate a bit and drop all the way until the style takes place. Obviously it did not this time but here’s the full video from this morning:
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Thursday, May 14th, 2020 AT 8:48 AM
Tiny
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I watched the video, and everything was in spec, including the O2 sensor's reactions. There was nothing indicating a fuel pressure or vacuum leak related problem. That leaves the throttle control module. That is something that needs checked by a dealer or someone that has an upper level scan tool.

When you notice it dropping in RPM or stalling, does the timing correlate with the AC compressor or any added load being applied to the engine? And there are still no codes, correct? And, it is doing the same thing as it did prior to the new throttle body, correct?
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Thursday, May 14th, 2020 AT 6:44 PM

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