2004 GMC Envoy O2 sensor

[kickass audio]

Alright, So for the past 2 weeks my truck has been acting really weird.

First it would have issues with voltage when it was cold. If i started the truck up when it was sitting completely cold for about a length of one night, in the morning when i start it, the alternator would NOT turn on for 10-15 seconds. Then sometimes after it turns on it would start to fluctuate my voltage and you could see my lights flicker, almost as if someone was plugging and unplugging the connector in the back of the alternator itself. But that only happens for another 15-20 seconds and then its done. Sometimes on rare occasions that will happen when im driving.

Another problem i noticed with mine is that when im driving i would notice a very fast flash, and i mean fast, like for a millisecond you would see the area on my dash where the "service engine soon" lamp is would illuminate. Now it wouldnt stay light, just flash out of nowhere when im driving. I had it checked and no codes were being thrown when it happened. So i figured it was just a fluke thing that happened and wouldnt worry about it. But for the past week if i was just cruising at a steady speed such as a long road or on the thruway if i kept my foot on the gas at a constant pressure out of nowhere you would watch my RPM's go down and up and back down for 15 seconds. And after that happens i would have lost about 5 MPH of my speed i was traveling at. I also noticed that after it happens if i were to floor my gas pedal i would have little to none gain in speed. Like my trucks speed would go up but it was if i was towing a truck behind me for how slow it would increase and my rpm would not get above 4000. Like to better describe how it feels when im driving it would be to say that when the speed of my engine goes up and down a lot, its as if you are putting your foot on my gas pedal for a second and taking it completely off it the next second, and putting it back on and off over and over again.

Per Matt at MECHMAN i put a brand new belt on my engine and cleaned off ALL the pulley's just to make sure it was all clean because i had the OEM belt on the engine and had a glazed over belt and it was also sticky on some pulleys as well as the flat side of the belt. But even after i did that it is still malfunctioning. Havent seen the alternator problem as of yet though.

So my question (and i apoligize about the long post) is what would be wrong here?

I have a 2004 GMC Envoy with the L6 engine in it and it has 103,000 some odd miles on it. Since the belt was stock on it, im pretty sure my plugs and all that are stock as well and today when my check engine light came on while i was driving from work to my house i had it checked and it read that my O2 sensor in Bank 1, sensor 1 was malfunctioning. Now stupid me forgot to get the exact code to make sure my mechanic was meaning it was malfunctioning or just not reading the right condition.

Help me please!!

[JaM Customs aka mprete]

get that code. it will help with that problem. about the alt, its probably bad, take it off and bring it to autozone and they can test it for you... that would be your voltage problem also. and check your throttle positioning sensor for the bad gas pedal problem. let me know if any of this helps or not.

[kickass audio]

get that code. it will help with that problem. about the alt, its probably bad, take it off and bring it to autozone and they can test it for you... that would be your voltage problem also. and check your throttle positioning sensor for the bad gas pedal problem. let me know if any of this helps or not.

Ok if it comes back on ill get that code from him.

For the alt dont even joke with that, i swear if i have to get that swapped im gonna be done with mechman. As great as Matt has been for me this will be the second unit that has failed me from him. My first one we believe UPS manhandled it and caused it to break because Matt said he tried to swap out all the electronics on my old alt i had for my car and it didnt fix it.

One thing i did notice with this alt on my truck is that it has somewhat like ac voltage for a sine wave if i measure amperage on it. I have the tpi 440 with the clamp meter add on for it and when i measure its amp load that it is charging it goes from 25amps min to 30 max but the sine wave is like AC voltage, it has curves but it has quite a bit of ripple to them, it isnt smooth at all. IDK if that may be a bad alt but if it is im gonna be so pissed because it took me and my dad both an entire day to yank it out and replace it because how hard it is to get to the bolts on the side of my truck with the damn A/C line right next to it and you cannot move that line out of the way.

And just as an update, when i went to move my truck into the driveway the lights started to do that flickering affect again. Now i noticed that the speed these flicker at is the exact same speed that my RPM gauge will go up and down when it starts to screw up. So maybe the alt? i really hope its not.

[JaM Customs aka mprete]

probably the diode on the alt...

[kickass audio]

damn, i really hope it isnt that. it only does that on the occasion. sometimes i will not have the lights flicker at all so idk what my truck is doing.

[dereileak]

did you recently redo the big three or anything. I did mine and forgot to hook this tiny little ground that made it look like my o2 was failing and my cruise control went out and lots of other weird shit. Also on the battery side was a thin looking ground that if I took off it would cause my alternator to shoot to 16 volts, this is a stock dodge grand caravan, but still, make sure you didnt remove any of the factory wiring, causes lots of issues

[kickass audio]

well i redid the big 3 since i had a little bit of rust under the connectors and i checked resistance on all my wires and only one wire, that goes from my battery's negative terminal to the engine has .1 ohms of resistance but everything else is perfectly 0 ohms resistance. i still have the damn problem with my truck though. Today it did the same affect where i was driving and my truck would hesitate to accelerate for a few moments and then would act like there was no problem until a block later i was at a red light and the damn thing stalled out. I was just sitting there and as soon as the light turned green i went to get off my brake and hit the gas and it wouldn't go anywhere. So i looked at my gauges and the rpm instantly dropped to 0 and my oil pressure did as well and my voltage dropped to the usual 12.89v when the engine is off (don't ask me how i have such a high voltage when the engine sits, even after a few days of not using it the voltage is still very high but im not complaining, XS FTW!!) and so i put it in park and re-started the truck and it started just like normal and i was able to get home.

Since it stalled out i decided to bite the bullet and take it to a shop to see wtf is up with the damn thing and hopefully my warranty covers a majority of it. I am going to have the shop do a complete tune up on it after they find the problem with my truck.

And just a FYI, the lights did the usual flickering affect on me when i first started it up at work so idk what it is. The only thing i didn't do was swap out alts but i really don't see how its broken. I haven't had any problems with it charging and even under a load (nothing intense though) i had all my lights on, vents on full blast, rear window and mirror defrosters turned on, a/c turned on, and was putting the windows up and down and it would only get a fraction of a second where the voltage would drop 1 volt but it would pick right up after that brief delay. The alternator doesn't make any weird noises or get warm one bit. If it wasn't such a bastard to get out of my engine i would have swapped it out but its such a pain i left it in there.

Hopefully the truck acts up on the mechanic and he can see what it does because i tried to take my dad for a drive with it and of course my truck would make me a liar and wouldn't do anything bad.

[kickass audio]

oh and forgot to mention, i also kept the stock wiring in place, all the ground points throughout the truck and the charge wire for the alt was used after the big-3 so its still there. The only thing i had to do was the charge wire from my alt to batt had a very small hole in it and it wouldnt fit over the large bolt that mechman uses so i had to ream the hole out on it just a little bit to make it fit but everything else was pretty straight forward.