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Discussion Starter · #1 ·
I purchased a GM certified 2005 GMC Envoy about a month and a half ago. I've recently noticed some things that are bothering me and I'm taking it in for service on Friday. I just wanted to describe the issues on here in the hopes of getting some help so I can at least know maybe what I'm talking about when I go. I don't enjoy working with dealer service and would like to at least have an idea of what it could be before I go and have them tell me something like I needed a $2 part just so I'll shut up and leave.

Here is my issue: It all started at a red light. I was sitting there idling when the light changed I pressed the gas and the engine bogged down and acted as if it was going to shut off. It did this for a split second and then took off like normal. I started to pay a little more attention and noticed when I was idling the oil pressure was around the 40 mark on the gauge. When I press the gas it goes up a couple of lines on the gauge. I decided to watch it for a couple of days. Well I was sitting in a parking lot waiting on my wife idling. She comes out and I put the vehicle in reverse and begin to press the gas. It bogs down again and dies. A error message appears where the odometer message is. It says "Low Oil Pressure". I start the vehicle and let it idle again for a minute and then back out with out another issue.
That brings us to today. I go to the gas station to fill up. I stop pumping when it clicks off and get in the vehicle. I didn't pay attention to where the gauge is. I drive about 7-8 miles and look and it says I have a little over 3/4ths of a tank. So of course I wonder what happened to all my gas...I just filled up. Maybe I didn't fill it up all the way and it stopped prematurely. So I begin to watch the gauge for the next two miles or so and I can actually see the guage slowly moving down. Now...of course the gauge moves down....I realize that, but should I be able to actually watch it decrease on a short 2 mile drive?

So....any help appreciated. Are they related? What do you think is the problem?

Thanks,
Joe
 

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Sorry I can't offer more help but to me I would look at the ECM, the brains of the computer. Or maybe the Throttle body and fuel sensor itself.

Good luck!!
:undecided
 

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Problem #1 is DEFINITELY a dirty throttle body. Fix it yourself for less than $5. You'll need to do this every 30-50K miles anyway.

http://forums.trailvoy.com/articles.php?do=viewarticle&artid=91

The oil pressure on the gauge is a fabrication of the engine computer. The sensor is only an on/off switch that clicks on about 18 PSI. So the PCM, which know what the RPM is, just fakes a message to the gauge to make you THINK it's a real analog sensor that rises a bit with RPM, which it isn't. This is a dirty little GM secret of the I6 engine. The V8 has a real sensor.

#2 is just worth watching for a while. Fuel senders have a reputation for early failure or bad readings, but you have to drop the gas tank to change it, so put it off if you can and just observe it for flakiness. The quick drop could just have easily been a quick rise in level, with no real change in the fuel's actual level.
 

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Problem #1 is DEFINITELY a dirty throttle body. Fix it yourself for less than $5. You'll need to do this every 30-50K miles anyway.

http://forums.trailvoy.com/articles.php?do=viewarticle&artid=91

The oil pressure on the gauge is a fabrication of the engine computer. The sensor is only an on/off switch that clicks on about 18 PSI. So the PCM, which know what the RPM is, just fakes a message to the gauge to make you THINK it's a real analog sensor that rises a bit with RPM, which it isn't. This is a dirty little GM secret of the I6 engine. The V8 has a real sensor.

#2 is just worth watching for a while. Fuel senders have a reputation for early failure or bad readings, but you have to drop the gas tank to change it, so put it off if you can and just observe it for flakiness. The quick drop could just have easily been a quick rise in level, with no real change in the fuel's actual level.
Kind of what I said, but better!! ha ha

:crackup:
 

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Discussion Starter · #9 ·
Just took it to the dealer and they said the fluctuation is normal and they can't recreate the failure due to oil pressure. They also said they ran a scan on the computer looking for a failure code and there was none present.

Majestic, I'm off of Tylersville.
 

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It's still a useful thing to clean the throttle body, since you'll be doing it every 30-50K while you own the vehicle.
 

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I recommend you go to wal mart or auto parts and buy a bottle of Techron Fuel System cleaner.

Though there is a large number of fuel level sender failures... theres also the possibility that the fuel level sender has buildup of sulfur... that is causing the beginnings of the erratic fuel gauge.

As a side effect... it will clean you fuel injectors too.
 

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Discussion Starter · #12 ·
Took it in again today. They are replacing the fuel level sensor. I filled my tank on Monday this week. After filling the fuel level dropped to empty and kept chiming saying that I was low on fuel. I took it immediately to the dealer and they "ran the codes" and figured out it was a bad sensor....Personally I didn't need any code to tell me it was a bad sensor, and if the codes are telling you today that it's bad why didn't it tell you that last week when I brought it in.....oh well at least they are fixing it.
 

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I have your answer

Hey not sure if you've got it figured out but I had the EXACT same problem with my 2003 Envoy SLT.

Took it to the mechanic and it turns out the THERMOSTAT and OIL PRESSURE SWITCH had to be replaced.

I was getting the same oil pressure message followed by the engine shutting down, the engine was being told it was running too cold and this also kept the check engine light on and caused the truck to guzzle gas.

Hope this helps.
 
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