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Discussion Starter · #1 ·
2003 GMC Envoy, 130k

First, I want to give a big thank you to all of you who replied to my thread on getting the alternator out in order to change the t-stat! I got that squared away (on the 2nd try - first try I crimped the o-ring!) and I thought everything was fine.

I took it out, dropped the hammer and really ran her hard, and the engine stayed right at 210 with no issues. This was after it previously was pegging after 2-3 miles of driving.

So, I thought everything was fixed. I was a very happy camper. This morning, I get in to drive to work and for about the first 20 miles, everything is fine...Then the temp slowly starts to creep back up, and before you know it it has settled at roughly the 3/4 mark of the gauge and is staying there.

On top of that, the car starts stalling out!!! When my speed gets down (when I'm coming to a stop or slowing) it just stalls out.

Any ideas on what could be causing either of these problems? If it is the water pump, is that easy to test? If it is the sensor, is that easy to test?

The stall issue - could I have bumped the fuel pump or something in my t-stat repair?

Your help is greatly appreciated!

Gary
 

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I sounds like you need to clean your throttle body. http://forums.trailvoy.com/articles.php?do=viewarticle&artid=91
Cleaning the throttle body will solve his overheating problem? It MIGHT help his stalling problem, but then again, might not! :undecided

2003 GMC Envoy, 130k

So, I thought everything was fixed. I was a very happy camper. This morning, I get in to drive to work and for about the first 20 miles, everything is fine...Then the temp slowly starts to creep back up, and before you know it it has settled at roughly the 3/4 mark of the gauge and is staying there.

On top of that, the car starts stalling out!!! When my speed gets down (when I'm coming to a stop or slowing) it just stalls out.

Any ideas on what could be causing either of these problems? If it is the water pump, is that easy to test? If it is the sensor, is that easy to test?

The stall issue - could I have bumped the fuel pump or something in my t-stat repair?

Your help is greatly appreciated!

Gary
When it started overheating, were you in stop and go traffic? I'm wondering if your fan clutch is bad.
 

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Cleaning the throttle body will solve his overheating problem? It MIGHT help his stalling problem, but then again, might not! :undecided



When it started overheating, were you in stop and go traffic? I'm wondering if your fan clutch is bad.
The stalling and the overheating might go hand in hand due to a slower idle speed not spinning the fan fast enough and the water pump not circulating the water. Did the PCM throw any codes?
 

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Discussion Starter · #5 ·
I haven't plugged up a PCM to check any codes - I don't have one and haven't had a chance to run to AutoZone and plug it up.

It is DEFINITELY idling low. But it wasn't doing that before the thermostat change out. Would it have anything to do with me unhooking the battery to remove the alternator?

I will try to get it to an AutoZone tomorrow and see what code(s) it throws.

Thanks again for all the help. For a total amatuer like myself, having a community like this is great!

Gary
 

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Discussion Starter · #6 ·
I almost forgot - the overheating issue. It isn't in stop and go traffic. After changing the t-stat, I can now drive it for 20 minutes solid at 70mph, and then it slowly starts to overheat, finally "landing" at around the 3/4th mark on the gauge and staying there.

Gary
 

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Have you checked the water level in the radiator and water reservoir, since the t-stat change? Do you still have the original hoses and radiator cap on the truck?
 

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Disconnecting the battery reset the PCM so it lost the adjustments for the throttle body's settings to compensate for build up of "dirt". Until the PCM readjusts the TB and relearns where to set the idle the idle won't be correct. Cleaning the TB or several restarts should get it back where it needs to be.
 

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The stalling and the overheating might go hand in hand due to a slower idle speed not spinning the fan fast enough and the water pump not circulating the water. Did the PCM throw any codes?
I was under the impression that the fan clutch speed is controlled by the PCM, not the engine RPMs.

http://forums.trailvoy.com/showthread.php?t=19604&highlight=fan+clutch+101

I would agree his low idle is most likely a dirty TB. But I've never heard of anyone complain about overheating due to low speed idle. Most I6's idle around 600 RPMs anyhow, if it gets too much lower than that and it will stall.

Not to mention:
I almost forgot - the overheating issue. It isn't in stop and go traffic. After changing the t-stat, I can now drive it for 20 minutes solid at 70mph, and then it slowly starts to overheat, finally "landing" at around the 3/4th mark on the gauge and staying there.

Gary
IDK. Could be a bad water pump, or a bad temp. sensor. BTW, have your hoses been replaced? Sometimes a hose can collapse and block the flow.

Also make sure the radiator isn't plugged up on the outside - with bugs, dirt etc. I like to clean mine about once a year.
 

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Disconnecting the battery reset the PCM so it lost the adjustments for the throttle body's settings to compensate for build up of "dirt". Until the PCM readjusts the TB and relearns where to set the idle the idle won't be correct. Cleaning the TB or several restarts should get it back where it needs to be.
:iagree: clean the tb for the rough idle/stalling issue.

as for the overheating problem..it could be anything from the wrong thermostat or even something being clogged in the radiator..
 

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2003 GMC Envoy, 130k

First, I want to give a big thank you to all of you who replied to my thread on getting the alternator out in order to change the t-stat! I got that squared away (on the 2nd try - first try I crimped the o-ring!) and I thought everything was fine.

I took it out, dropped the hammer and really ran her hard, and the engine stayed right at 210 with no issues. This was after it previously was pegging after 2-3 miles of driving.

So, I thought everything was fixed. I was a very happy camper. This morning, I get in to drive to work and for about the first 20 miles, everything is fine...Then the temp slowly starts to creep back up, and before you know it it has settled at roughly the 3/4 mark of the gauge and is staying there.

On top of that, the car starts stalling out!!! When my speed gets down (when I'm coming to a stop or slowing) it just stalls out.

Any ideas on what could be causing either of these problems? If it is the water pump, is that easy to test? If it is the sensor, is that easy to test?

Your help is greatly appreciated!

Gary
OK, the new thermostat worked, temperature came up to normal and stayed there. Gauges worked, sending unit must have been ok. Coolant level must have been OK and circulating so water pump good. This morning everything starts out looking good for 20 miles and then something goes sour. Has the new thermostat kicked the bucket?:weird: :(
 

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I guess I am either having a problem following your post, or not putting all the problems you are having together. Rough idle could be the TB. Low RPM's make me thing bad coil or spark plug replacement necessary. Are you still having a problem with the coolant temp? If so then I tend to agree it may be your fan clutch. Is the vehicle making any noises? Clicking noise or loud whine?
 

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The overheating at freeway speeds only/mostly points to a hose collapsing or air being blocked from the radiator. The fan clutch can fail and cause overheating without the roar. But, at smooth highway speeds, the air going through the radiator should be enough to keep the temps at a safe level.:undecided If the t-stat failed,it would either not reach operating temp. Or would overheat before 20 miles.
 

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The overheating at freeway speeds only/mostly points to a hose collapsing or air being blocked from the radiator. The fan clutch can fail and cause overheating without the roar. But, at smooth highway speeds, the air going through the radiator should be enough to keep the temps at a safe level.:undecided If the t-stat failed,it would either not reach operating temp. Or would overheat before 20 miles.
:iagree:

as I stated in post number 9.
 

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Lets go back to square one. Overheating: Have you taken the old thermostat and put it into a pot of 192 deg. water and did it open?

Most autoparts have a rad cap that has a temp gauge in it but I do not know if it will fit our rad. That would tell you the temp. (close) and if the sensor is giving a good number to the PCM.

Too many things going on at the same time. Clean the throttle body. That should get rid of one item, also take off the neg term of the battery for 1/2 hr or so while you clean the throttle body. It will run a little rough because the PCM will need to get new stats after the battery disconnect.
 

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The first thing that needs to be known is the engine actually overheating or is there a false instrument indication. The engine temperature needs to be tested.
As for the question about "bumping the fuel pump", gee, I hope not.:bonk:
 

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The first thing that needs to be known is the engine actually overheating or is there a false instrument indication. The engine temperature needs to be tested.
As for the question about "bumping the fuel pump", gee, I hope not.:bonk:
Trying to use a rectal thermometer will not work. Using a scanner to read what the PCM is saying only tells you what the sensor is telling the PCM, and that could be a bad number. I guess a digital infrared themometer pointed at the block in the same point on 2-3 tb's could tell if his block was much hotter than the other 2? A rad cap with a thermometer could work. Anybody know what the sensor costs? It still would be nice to know if the old thermostat opens in 195 deg water. Gives a good indication if the old thermostat was really bad.
 

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Discussion Starter · #18 ·
Hey all! Thanks once more for all the help.

I got the Envoy plugged up at Auto Zone on my lunch today and it came back P0303 which the tech told me means that Cylinder 3 is misfiring. Is there any chance that there could be coolant on the plug? I'm planning on pulling it tonight to find out if you guys think that could be it.

Otherwise, I'm leaning towards needing to change the plugs and wires (which it's about time for anyways).

On the issue of overheating - the old t-stat was definitely bad, as I tested it the way you guys have mentioned. It was stuck closed - which was what caused the original overheating. I have not been home today to be able to check on the hose collapsing - what is the best way to check that, as it only seems to happen when driving. If it is the bottom hose, I'll have to remove the alternator again to swap it out, correct?

Last question for now - how to do I test the temp sensor to see if it is throwing bad info to the PCM?

The roughness/dying problem, I think is being caused by whatever is causing cylinder 3 to misfire - as the engine is running ROUGH at low speeds, and then the idle is dropping under 500 at stop or slow down.

Thanks!
Gary
 

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My daughters Sunfire was doing the same misfire/ rough idle thing. One of her coil packs had a crack in it. Replaced it and the problem was gone.
 

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Hey all! Thanks once more for all the help.

I got the Envoy plugged up at Auto Zone on my lunch today and it came back P0303 which the tech told me means that Cylinder 3 is misfiring. Is there any chance that there could be coolant on the plug? I'm planning on pulling it tonight to find out if you guys think that could be it.

Otherwise, I'm leaning towards needing to change the plugs and wires (which it's about time for anyways).

On the issue of overheating - the old t-stat was definitely bad, as I tested it the way you guys have mentioned. It was stuck closed - which was what caused the original overheating. I have not been home today to be able to check on the hose collapsing - what is the best way to check that, as it only seems to happen when driving. If it is the bottom hose, I'll have to remove the alternator again to swap it out, correct?

Last question for now - how to do I test the temp sensor to see if it is throwing bad info to the PCM?

The roughness/dying problem, I think is being caused by whatever is causing cylinder 3 to misfire - as the engine is running ROUGH at low speeds, and then the idle is dropping under 500 at stop or slow down.

Thanks!
Gary
No wires, our coils packs are plugged directly on to the Plug
 
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