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Discussion Starter #1
I have a 2007 TB with a 4.2L. I recently had the engine rebuilt over the summer due to the previous owner locked up the motor. The new rebuild was a totally different long block. Kept existing PCM.

The issue.....When the car has sat for numerous hours in cold weather below 40 degrees outside it will not start and idle. It turns over great, has ignition and will run for 2-3 seconds, stumble and dies. I have to try and start it 3-5 times until it will catch and idle without dying. It is totally outside temp related. Once the engine is warm regardless of outside temp it runs great.

When the outside temp is above about 40 degrees it runs and idles fine.

I have run Sea Foam through the tank, no change.
I have replaced plugs, no change.
I have no codes.
Today I let it sit cold, put on a fuel pressure gauge on and read 60 psi while starting and maintained 60 when dying.
I have good compression.
The emissions air pump seems to kick on at start. I can hear it. Maybe could check line?
I have read maybe need to have EMC data updated to new sensors? IDK
One fella mentioned soft code for Throttle body Ice?
Maybe mass air flow sensor? IDK

I am at a loss. Any ideas? Hard part tacking to a good tech is it only does it when cold outside and after sitting for hours.
 

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2004 chevy trailblazer_lt
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Have you connected a code reader/scanner to the OBDII port and checked for pending or historical codes?

Using a second person to sit in the drivers seat and start the TrailBlazer, remove the air cleaner assembly at the throttle body and spray starting fluid into the throttle body. Does the engine run as long as the starting fluid is being sprayed into the throttle body?

Please report back
 

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Discussion Starter #3
Have you connected a code reader/scanner to the OBDII port and checked for pending or historical codes?

Using a second person to sit in the drivers seat and start the TrailBlazer, remove the air cleaner assembly at the throttle body and spray starting fluid into the throttle body. Does the engine run as long as the starting fluid is being sprayed into the throttle body?

Please report back
Yes I’ve connected my scanner and no code. Frustrating. As far as starter fluid I have not.
 

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OK on there not being any codes. Try the starting fluid when it gets below 40 Deg F.
 

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Check the coolant sensor RANGE with a scan tool. It could have failed within the range that won't set a CEL. Make sure it reads cold temps, then heats up.
 

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I take it the theory behind the starter fluid is to see if it’s a fuel problem.
Yes.

Also, as NJTB04 suggested, be sure and check the engine coolant temperature sensor.
 

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Discussion Starter #9
Thanks. I’ll try both ways nice we get a freezing morning. I have a standard code reader and see minor live data. I’m guessing but before I start it the coolant temp should read temp outside or close to it and then up to running temp.
 

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Well, I don't know what the lowest temperature the ECT sensor will reliably show, but it should read at least 32 Deg F. You should be able to see the temperature going up fairly quickly once the engine starts.
 

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Discussion Starter #11
Well, I don't know what the lowest temperature the ECT sensor will reliably show, but it should read at least 32 Deg F. You should be able to see the temperature going up fairly quickly once the engine starts.
Update. It is 33 F out this morning. Car been sitting for 12 plus hours

ECT is showing 8 Celsius which equals 46F
IAT is showing 7 C which is 44.6 F

I suprised they both so close. Can’timagine after 12hours still holding that core temp. No way the inlet 10 off that’s just the plastic tube.
So is my ECM off or are the sensors?
 

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When you started it, did the temp rise and get to operating range (195-210)
 

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I/m glad to see your ECT and IAT sensors are as close as they are when the temperature is around 33 Deg F. The ECT sensor in my '99 Silverado was about 20 Deg F higher than the IAT sensor around 32 Deg F.

Not sure what temperature your thermostat is, but it should be a 195 Deg F one, and hence, your live data/code scanner should show at least 195 when you are driving around normally (these engines like to run in the 195 - 210 Deg F range as NJTB04 indicated). If the temp displayed on your code reader/scanner never goes above 190 Deg F, then I would be inclined to put in a new ECT sensor. Be sure and get one from ACDelco, Delphi or Standard Motor Products/BWD, and not an inexpensive, never heard of brand one.
 

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Discussion Starter #15
I/m glad to see your ECT and IAT sensors are as close as they are when the temperature is around 33 Deg F. The ECT sensor in my '99 Silverado was about 20 Deg F higher than the IAT sensor around 32 Deg F.

Not sure what temperature your thermostat is, but it should be a 195 Deg F one, and hence, your live data/code scanner should show at least 195 when you are driving around normally (these engines like to run in the 195 - 210 Deg F range as NJTB04 indicated). If the temp displayed on your code reader/scanner never goes above 190 Deg F, then I would be inclined to put in a new ECT sensor. Be sure and get one from ACDelco, Delphi or Standard Motor Products/BWD, and not an inexpensive, never heard of brand one.
So do you think my sensors are bad? Both of them? They are both reading 10-15 high when cold. I’d wish I had taken a block temp with a digital thermometer in the morning just due to them both reading high bothers me.
 

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I do not know what the lower temperature limit of the ECT sensor is, but I do know that the ambient temperature sensor on my 2004 TrailBlazer will send information to the outside temperature display on the HVAC control head such that below 0 Deg F temperatures are displayed. I am assuming that the ambient temp sensor also serves as the intake temperature sensor on my 2004 TrailBlazer because there is no separate IAT sensor.

Now, for your 2007 TrailBlazer, your engine has an MAF sensor, and mine does not. My 1999 Silverado's MAF sensor also has the IAT sensor built into it. I do not know if your 2007's PCM uses the ambient temperature sensor in place of an actual IAT sensor, or if your 2007 has an actual IAT sensor in addition to the ambient temperature sensor.

I would definitely replace the ECT sensor because they do go bad. If I were in your shoes, I would go ahead and replace the ambient temperature sensor as well especially considering that an ACDelco OEM replacement sensor sells for a whopping $3.25 on rockauto.com. I do know that they go bad because the ambient temperature sensor went bad on my 2004 TrailBlazer while it was under the factory warranty.

Since it looks like you will be replacing both the ECT and ambient air temperature sensors, be sure and purchase a good quality part and not some inexpensive no-name part off of ebay or Amazon.com. I would stick with sensors from one of the following manufacturers/parts brands: ACDelco, Delphi, or Standard Motor Products/BWD (non T series or P series parts).

Good Luck!
 

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Discussion Starter #17
I do not know what the lower temperature limit of the ECT sensor is, but I do know that the ambient temperature sensor on my 2004 TrailBlazer will send information to the outside temperature display on the HVAC control head such that below 0 Deg F temperatures are displayed. I am assuming that the ambient temp sensor also serves as the intake temperature sensor on my 2004 TrailBlazer because there is no separate IAT sensor.

Now, for your 2007 TrailBlazer, your engine has an MAF sensor, and mine does not. My 1999 Silverado's MAF sensor also has the IAT sensor built into it. I do not know if your 2007's PCM uses the ambient temperature sensor in place of an actual IAT sensor, or if your 2007 has an actual IAT sensor in addition to the ambient temperature sensor.

I would definitely replace the ECT sensor because they do go bad. If I were in your shoes, I would go ahead and replace the ambient temperature sensor as well especially considering that an ACDelco OEM replacement sensor sells for a whopping $3.25 on rockauto.com. I do know that they go bad because the ambient temperature sensor went bad on my 2004 TrailBlazer while it was under the factory warranty.

Since it looks like you will be replacing both the ECT and ambient air temperature sensors, be sure and purchase a good quality part and not some inexpensive no-name part off of ebay or Amazon.com. I would stick with sensors from one of the following manufacturers/parts brands: ACDelco, Delphi, or Standard Motor Products/BWD (non T series or P series parts).

Good Luck!
Thanks man. Been a lot of help and I’ll be sure to post follow ups if it helps and fixes issue. I worry here for Georgia it won’t be that cold soon enough and will have to wait till next winter to fix problems. I am meticulous when comes to my vehicles and like to have them running correctly.
 

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You are quite welcome. I know what you mean about it not being cold enough in Georgia - good thing that it does get hot enough though! :cool:

I too am meticulous about keeping our vehicles it top notch operating condition! I keep detailed repair notes which includes date something wasn't right, all symptoms, all DTCs, etc., plus corrective actions taken, part numbers & brands, costs, difficulties encountered during repairs, helpful hints, etc.

I have my fingers crossed for you!
 

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Default CTSs and IAC sensor value is approx. -45°F --- this assumes that the unit has gone completely OPEN or is disconnected.

I don't know what's TYPICAL on our TBs - but I have an air temp sensor in the intake runner to the throttle body and another air temp sensor up ahead of the radiator support, not mentioning the actual coolant temperature sensor.

Oh yeah - there's another couple of ambient air temp sensors inside the vehicle for the HVAC.

So - lessee ---> I have 5 temperature sensors on my '05 TB 4.2.

Wait - I messed up* --- there's another temp sensor inside the transmission to demand that the TCC locks up in every available forward gear but 1st if the unit gets too hot.

* this is a rare moment - mark it well!
 

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Thanks for chiming in Ravalli!
 
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