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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 05-10-2010, 10:57 PM
cody2979 cody2979 is offline
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2004 Chevy TrailBlazer LT
Summit White 4.2L I6 2WD
Join Date: Apr 2010
Location: Oklahoma
Posts: 32
Hard start after warm and sitting a while

I have an 04' TB with 132000 on the truck, but I just replaced the motor myself with one with only 800 miles on it. It runs and drives great with one small problem...it seems to really crank a while before starting when it is WARM or after it has been driven then sits for 1-2 hours. May crank 8-10 secs before starting and seems to start better when feathering the foot feed.

I haven't made complete sense of it yet, but it does have fuel pressure 50psi after the first cycle of the fuel pump before starting and 57-60 when running.

Not sure exactly what is causing this...
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  #2  
Old 05-10-2010, 10:59 PM
cody2979 cody2979 is offline
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Forgot to mention that it starts fine in the morning and if it has been sitting long enough...could be fuel pump I guess, but the pressure seems to be good when I check it. Need your help guys.
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  #3  
Old 05-12-2010, 04:51 PM
textallguy textallguy is offline
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2003 GMC Envoy SLE XL
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Same Problem

I've got the same thing on my 03 Envoy XL with all original equipment and only 89k miles on it. I happened to replace the battery a few months ago and the problem went away for a few weeks, then came back same as before. I wonder if it's a sensor problem...
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  #4  
Old 05-19-2010, 12:16 AM
cody2979 cody2979 is offline
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Quote:
Originally Posted by textallguy View Post
I've got the same thing on my 03 Envoy XL with all original equipment and only 89k miles on it. I happened to replace the battery a few months ago and the problem went away for a few weeks, then came back same as before. I wonder if it's a sensor problem...
I haven't tracked it down yet, but I think I've narrowed it to the idle air. It seems to start find when cold, but when warm I'm thinking it could be getting a false reading from a sensor as well...maybe the intake air temp sensor??? I don't have a shop manual yet, so I'm not entirely sure how it uses the reading from that sensor.

Something seems to basically flood the engine when it is warm. Once I hold the throttle body open just a little it starts up and after a short stumble it takes off and idles find.

Haven't had much time to trouble shoot just yet...but I will find it. Let me know if you guys have any ideas!

Come on moderators...where are you..lol. What is the test procedure for the intake air temperature sensor...what are the readings I should get across it with a meter?
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  #5  
Old 05-19-2010, 01:07 AM
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the roadie the roadie is offline
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2004 GMC Envoy SLT "Roadiemobile"
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Quote:
Originally Posted by cody2979 View Post
What is the test procedure for the intake air temperature sensor..
Get a scan tool and read the data stream. Checking resistance with a meter is a bit useful, but it doesn't check the integrity of the harness back to the PCM where the reading is made by an A-D converter. A medium or high end scan tool used by an experienced tech should be able to figure it out quickly - it might be a good investment to buy some diagnostic time.

How are the plugs in the new engine? Proper Delco 41-103?

I recommend never holding the throttle body open when the power's on. It can burn out the stepper motor.
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  #6  
Old 05-19-2010, 12:44 PM
cody2979 cody2979 is offline
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Quote:
Originally Posted by the roadie View Post
Get a scan tool and read the data stream. Checking resistance with a meter is a bit useful, but it doesn't check the integrity of the harness back to the PCM where the reading is made by an A-D converter. A medium or high end scan tool used by an experienced tech should be able to figure it out quickly - it might be a good investment to buy some diagnostic time.

How are the plugs in the new engine? Proper Delco 41-103?

I recommend never holding the throttle body open when the power's on. It can burn out the stepper motor.
Thanks Roadie. I checked the plugs and they look great. The only thing keeping me from getting a scan tool is the price. Your probably right it would be a good investment since I have a 4.2L in the TB and a 5.3L in a 63' chevy pickup. I could probably use the scan tool for both vehicles.

BTW what I meant by opening the throttle body was stepping on the accelerator pedal while starting. No harm in that and it is the only way to get it started without excessive cranking.
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  #7  
Old 05-19-2010, 12:45 PM
cody2979 cody2979 is offline
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2004 Chevy TrailBlazer LT
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Location: Oklahoma
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Quote:
Originally Posted by the roadie View Post
Get a scan tool and read the data stream. Checking resistance with a meter is a bit useful, but it doesn't check the integrity of the harness back to the PCM where the reading is made by an A-D converter. A medium or high end scan tool used by an experienced tech should be able to figure it out quickly - it might be a good investment to buy some diagnostic time.

How are the plugs in the new engine? Proper Delco 41-103?

I recommend never holding the throttle body open when the power's on. It can burn out the stepper motor.

Roadie...do you recommend a certain brand of scan tool?
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  #8  
Old 05-19-2010, 04:16 PM
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Chickenhawk Chickenhawk is offline
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What does your fuel pressure read after it sits for a while?

It sounds suspiciously like a dripping fuel injector or two.
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  #9  
Old 05-20-2010, 11:52 PM
cody2979 cody2979 is offline
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Fuel pressure maintains 50-55psi after sitting for over an hour...it's almost like it's fluided and not lacking fuel because it won't start until you step on the gas pedal and give it a little air.
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