Hard starting


2007 trailblazer I use to just bumb the key to start it but last 2 days been cranking over a long time before it cranks anyone no what could be wrong it also stutter s sometime after it cranks


We need to know a little more information. What engine do you have? How many miles? What recent maintenance did you have to do? What troubleshooting have you already done?


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Welcome to GMT Nation...

When you changed the Throttle Body... did you remove the Negative Battery Cable for at least (30) Minutes and allow the PCM to Re-set itself afterwards? Try doing that next.

Also... Just to cover a few more required Basic Diagnostic Approaches that can help you to get Clear Answers from GMTN... Try following these suggestions:

(1) If you have No OBD2 Code Reader-Scan Tools... Consider looking over these Scan Tools gleaned from a quick search on Amazon and try getting your hands on the one that suits your Budget and Skill Set:

(2) Follow your New OBD2 Scanner Installation Tool Instructions and after plugging it into the Female OBD2 Port under the Driver's Side Dash Panel... Read the Engine Codes and then immediately Jot down any of those PXXX Codes that show up. Then you can post them right back here into your Follow Up Postings to Your Thread.

(3) Are you the Original Owner of this SUV? If not, please advise how long you've owned and driven the SUV and make mention of any other Outstanding Mechanical Issues you have encountered and repaired. Please include the information about any aftermarket Remote Starters, Radio Amplifiers or Add-In Alarm Systems you have already installed.

(4) Use Google with simple, direct expressions that Dial In on precisely what the names of the Topics are and many Well documented Threads with Answers to your Question can thus be found quickly here at GMTN, Here are some Basic Search Examples:

gmtnation PXXXX (Where 'X's are all four Numeric Trouble Code Indicators)
gmtnation Hard Start
gmtnation Throttle body
gmtnation Oil Pressure

...and so forth... and you might be surprised at just how Quickly you can Dial right in on Historic Threads with Solutions to those On-Topic Issues that concern you the most. Additional Help is always available from the Many Contributing GMTN Members. If you find the Solutions and Solve your Problems... Please Check Back in and advise any Moderator by mentioning:

"Thanks GMT Nation... My Problem is SOLVED.jpg..."
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That is fine... .now... Google THIS...

gmtnation cpas

...and after you Open the First Link you can see at the Top of that Page.

....look a little further down on that Google Search Page to find THIS Gem of a "How To Clean the CPAS...".. Thread for your BEST Answers:

After reading all of that Good Information... You can extend your knowledge of HOW To Do this CPAS R&R by the Following These Steps:

Google Youtube

Use the Youtube Search Line and Type In:

Trailblazer vvt cpas

...and pick THIS Third Video of MACT's Three Part Series on the CPAS Repair of problems involving both the CPAS and the CPS Solenoid-Sensor:

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When I install a new sensor do I have to relearn it I don't have a computer to do that with is there a work around


The CPAS is a solenoid, not a sensor so no relearn required. You can also try cleaning the cam sensor before replacing it. It doesn't need a relearn neither. It's the crank sensor that usually requires a CASE relearn so that one should be tried LAST because of that.


Lifetime VIP Supporter
If I'm interpreting your situation correctly... Your SUV WILL Start... However it STILL Cranks Over a Long Time before Starting? If so... indicate it in your next reply and consider these issues relating to "What Can Cause Hard Starts?" as Food for Thought:

Hard Starts can have MANY Causes and Origins... Here are The Most Likely:

In Order for any 4 Cycle Engine that follows the "Intake, Compression, Ignition (Power Stroke) Exhaust" Pattern, THESE Conditions MUST be Present:

(1) Air (In The Proper, Unobstructed Amount able to reach 14.7 Parts to 1 Part Fuel by Volume)
(2) Fuel (Clean, Proper Octane...and Neither Too MUCH Nor Too Little)
(3) Compression (In the GM Atlas LL8 Engine ...Approx. 10 to 1 Compression Ratio)
(4) Spark (Powerful enough to Ignite the Compressed Air/Fuel at 10 Xs Sea Level Atmospheres)

Because of the extreme variability of Engine Designs... the "Spark" as being most critical is not specified... but the TIMING of the SPARK is quite Critical.... If the Spark Ignites the Fuel too SOON as the Piston rises to compress the Fuel and AIR... the Power would not only be Weak... but happening Prematurely and actually prevent the Piston from rising to complete its Power Cycle.

The TIMING of the Spark Events must be varied by the PCM to know when to "Light The Fire" in each Cylinder just a little before each Piston rises to meet at Top Dead Center (TDC) in its Rotational Arc. By doing it this way, ALL of the Fuel and Air have enough time to COMPLETELY Burn... ,and extract every last ounce of Power available each and every time the Power Stroke pushes those Pistons back down and transferring the energy through the Connecting Rods and into the Journals on the Crankshaft to achieve Rotational Energy and Torque.

So... What Happens to Prevent these Events from working Normally? Here is a List of What can Go Sideways and Cause "Hard Cranking Starts" to Occur:

(1) A Weak or Dead Battery (The PCM Controlled Systems are VERY Touchy about Low VDC).
(2) Old, Incorrect Plug Designs (Too Hot or Too Cold) Damaged, or Poorly Gapped Spark Plugs.
(3) A Clogged Air Filter.
(4) Worn Pistons, Trapped or Worn Pistons Rings, Worn Out Cylinders (Low Compression).
(5) Weak or Inoperative Electric Fuel Pump, Clogged Fuel Filter (Low or "0" Fuel Pressure).
(6) Inoperative or Damaged Sensors: ACC, TPS, MAF, IAT, O2, MAP, CPAS, CPS, CKP.
(7) Shorts or Broken Harness Wires and Independent Wiring Connections, or Corroded PDC Fuse Block.
(8) Poor Electrical Ground Connections.
(9) Burned Fuses or Bad Relays
(10) Failed PCM-ECM... It is Rare ...But it Has Happened on Occasion.

These ...and perhaps a few other issues can work either singly... or in concert with each other in a bewildering variety of FUBARs to either Make it Hard to Start the Engine... or Prevent the Engine from Starting, Running and doing so with Nominal Performance
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Lifetime VIP Supporter
Ordinarily, your 'Marvelous Economy' with the English Language could be admired by most people, I suppose. However, as you seem to be a "Man of Few Words"... Providing Cryptic, One Word Replies will Not Help Us to Understand What you intend to do next to try and Solve Your Problem.

I've already 'Plowed the Field' for you with Plenty of Things to Consider. For Example... If it were me... my next step would be to Perform a Dry/Wet Compression Test and report back here with your unique findings for all (6) Cylinders.

These kinds of communications work best when all of the parties engaged Provide Plenty of Useful Information ...and with Equal Measure. It's like Having Any Conversation... It's a Participatory Sport...
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Well-Known Member
After your vehicle has sat for a while, say overnight or a few hours, turn all your blowers, radio off etc and then turn the key to run, but do not try and start it. Listen to hear if the fuel pump pressurizes for a few seconds then stops. Then try and start your vehicle, how does it do?


In that same train of thought, a fuel pressure check would help, and see if it holds that pressure after priming as described by @JerryIrons

CAUTION: when hooking up the pressure gauge to the port on the fuel rail, BE CAREFUL TO NOT PUT ANY SIDEWAYS PRESSURE ON THE PORT as I have caused a crack in mine, requiring the replacement of the whole fuel rail. The port is in an odd position which makes the hookup difficult and makes the gauge's attachment put pressure on the port sideways.

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