Changed Thermostat, Now its out of wack.

[03EnvoyV6]

Hi there, new to the forum. I am a mechanic by choice, so ill understand what people say here.

Ok my buddy has a 2003 GMC Envoy XL SEL 4x4 with the 4.2L....I attempted the thermostat yesterday. I was having a real hard time getting the alternator out due to the bottom bolt and the stupid a/c line thats in the way.

I had disconnected the battery first thing FYI

Well i disconnected the PCM and it made things much easier. Got the thermostat swapped out, and made sure it went in the same way as the old one. Put everything back together the EXACT way it was.....nothing was left unconnected or anything.

Well we hooked up the battery as the last thing, we filled it with coolant, had him turn the heat on full blast, and on defrost then we started it.

Truck was running fine for about two minutes, then the RPMS started stumbling. Bouncing between about 1100-400 rpms.....Then we got a CEL, and the REDUCED ENGINE POWER light came on.

We shut it down, and i thought the pcm just neded to be reset again. I disconected the battery for about 10 minutes, and we started it again, with the heat off. Truck started up and was running fine. As soon as we put the heat on, the RPMS started jumping again, and the REP light came on again.

Shut it down again, and i called my buddy who owns his own garage. So we started it with the heat off, and it would drive fine. Drove it all the way to his garage, about 10 minutes away, and there were no problems, didnt overheat or anything, but the CEL was on.

My buddy hooked his scanner up to it, and was doing a bunch of stuff to it. He said he reset the PCM. He had a 7000 dollor scanner, wasnt a cheap one like autozone.

Now i need to add all the extras the truck has. Has one of those touch screen headunits, hooked to a camera for the rear, and it is hooked to an alarm.

Aftermy buddy ot done with the scanning, he said there is something wrong with the radio. Because when you take the key out and open the door, the head unit stays on. You have to turn it off manually now.

Also there is no door chime when you open the door, and the auto lights dont turn on, and when you turn the fog lights on, all the lights come on...i mean thats not really a big deal. The headunit i thing needs to be reprogrammed, but we couldnt do it, because the settings are password protected, and we didnt have the password. (it was my buddies dad's truck and he wasnt with us)

Now the heat. It is still jumping when you turn it on, regardless of what setting it is on, if the heat is on, RPMS bounce. BUT theres no CEL or REP light anymore.

Could this just be an air pocket in the system? I know its not properly bled yet, but would an air pocket cause this issue?

Thanks for any help i recieve.

 

[siskokid]

It sounds as though you have an assortment of problems. I'm no mechanic,but I do my own repairs on my personal vehicles so here goes.
*On electrical problems check for a bad ground under the instrument panel. Just a simple loose wire can play havoc on your entire electrical system.
*On the thermostat, did you use the same temp range? The ECT sensor could be sending a signal to the ECM telling it to run lean or rich if it's other than factory temp range.
* Engine coolant can cause an o2 sensor to fail if you get any on one.(I did this by accident changing a heater hose).
* Sometimes the ECM must go through a learning process when it's reset and will require some drive time to adjust itself.
Like I said I'm no mechanic, but these are things I have run across in the past. Siskokid

 

[03EnvoyV6]

thank you for the reply.

What boggles my mind is that the truck runs perfectly fine when the heat isnt on. No bogging or anything.

And they "claimed" there was only one temp range for the thermostat, which i know can be false...my dodge ram has either a 195* or 180* stat, so i know there can be different temp stats.

Also, i forgot to mention this, and this could be critical to my problem....when we took off the thermostat some coolant poured over the alternator. Im thinking that when we turn the heat on, the extra amperage draw it requires is getting screwy since there was coolant on it. I havent talked to him today, but im going to ask how it is since it should be dry now.

Thanks again.

 

[happy 2011]

well i can tell you this. If the tk was fine before you replace the thermostat then it's some thing you did. (99 percent of the time) I am a 30 year tech and have seen alot of stuff. check every thing again. put up on a lift and look as well.

This is what i would do remove battery cable unplug and replug in pcm again. Check all work again with a fine tooth comb. If i rember right there is a sensor down near the lower hose where the thermostat is that some times can break or get cracked while doing the job.

Also make sure you did not leave any grounds off the motor or for testing add some with jumper wires.