07 trailblazer 4.2L crank . no start

Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
My fuel gauge stopped working . and bit me in the butt . I told my ase certified mechanic friend about it and he said . that I should change the fuel pump at some point before the sending unit going completely out . so he comes over . we change The fuel pump . run it for 1t minutes . next day I drive it 9 miles to where I was,going . park it . let it idle while I was waiting . it died and would not start back up . in one of his code checks . there was a maf code . so I cleaned the maf a d throttle body .no dice . I am @ wits end 🤯
 

TollKeeper

Guru
Dec 3, 2011
6,886
Brighton, CO
Gotta start with the basics..
Is there fuel pressure at the fuel rail?
Is there spark at each cylinder?
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
Fuel pressure is the first thing I am going to check when I can get him back over here . as for spark . I do not see why not as it drove fine before . yet I have not checked it . I do not know how .
 

Ilikemy3s

Active Member
Dec 3, 2011
286
IF there is no crank or start .. did you try taking it out of park and putting it in Neutral and see if it works?
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
It did crank before . but didn't start . and now it will not crank anymore . I put my jump box on it . still nothing . I tried to start in neutral and still nothing
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
We have a thread in the FAQ on this subject.
 
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mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
Una Pregunta Mas... (One More Question...)

What was the Brand-Make & Model of the Replacement Fuel Pump?

If NOT a Bosch, ACDelco or Delphi... any other less expensive, After Market Off Brand Fuel Pump can be problematic ...Right out of The Box... especially where it might be a Re-Stock Item... Stuck back on the Shelf and later sold to an unsuspecting customer. :>(
 
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mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
Try pulling the Fuel Pump Relay AND the Fuel Pump Fuse and *feel* them as they come out of the slots. You are looking for any signs of Corrosion or Looseness when doing these actions. While you are at the Fuse Block...LIGHTLY Re-Tighten down the Galvanized Fasteners that hold the Under-Block Cables and snug them all up again.

I'm in Danger of being accused of *harping* on this subject a lot... But you are down in "The Deep South" ...So JIK... Use a Bright Flashlight while examining EVERYWHERE under the Hood and Engine Compartment looking for ANY signs of Rodent Infestation, Mouse Nesting and Droppings, Chewed Plastic Insulation, Connectors and Harnessing. Intermittent, inexplicable Engine Shut Downs can be caused by Shorted Wires and and Damaged Connections from these Critters' incessant "Need to Gnaw".
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
We have a thread in the FAQ on this subject.
I am going to try changing out the ignition switch tomorrow .
 
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Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
Maybe it actually is out of gas? It has happened. Do you hear the fuel pump run for a couple of seconds when you turn the key to run? Is there spark when you crank?
 
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mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
"I forgot that I disconnected something..."

What was the "Thing" that you re-connected... Precisely?

This Video concerns "Troubleshooting The Fuel Pump" and how this VOP (Video Original Poster) discovers a BASIC Electrical Problem that was first overlooked during this Fuel Pump R&R Repair.

In the end... it may come down to a "Powers & Grounds" Issue if you followed @Mooseman 's suggestion to listen for the "Fuel Pump Prime Humming" sounds that should occur for a just few seconds, right after turning the Ignition Key to the ON Position (...but NOT Start-Run) with the Driver's Door open ...and heard nothing:

 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
Its has gas . the pump came on and went back off. I disconnected one of the PCM connections because a video said it worked for them . I just forgot to reconnect it is all
 

mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
Double Check that the (CKP) Crank Sensor Connector is FIRMLY attached to the Sensor (Lower Rear Driver's Side of 4.2L Engine Block adjacent the 5th Crankshaft Journal position in the Block. The Engine will never start with its absence:

CKPSENSORLOCALE.jpg

Here are the Reasons WHY:

The (CPS) Camshaft Position Sensor AND the (CKP) Crankshaft Position Sensor MUST reconcile with each other in order for the PCM to instruct the EFIs to Spray Fuel ...and Time the Ignition Coils to Fire the COP (Coil On Plugs) at their precise positions BTDC (Before Top Dead Center) during Normal Engine Rotation.

High Mileage Engines with either damage to the #5 Crankshaft Thrust Bearing, a loosened Harmonic Balancer Bolt and HB ...or having a Severely Extended Timing Chain Tensioner along with Badly Grooved Timing Chain Guides and Worn Timing Chain can also contribute to having a No Start Condition.

If the "Falling Edge" of the Dark Blue A/C Sine Wave being picked by the (CKP) Crankshaft Position Sensor is even just a Few Degrees Off the "Rising Edge" of the Red (CPS) Camshaft Sensor Hall Effect Square Wave Signal... Then the GM 4.2L Engine Will NOT Start.

Note that the Light Blue Oval in this Image encompasses a PERFECT Meeting of the (CKP) Signal within the (CPS) Signal shown in this RARE attached PICO-Scope "Known Good Wave Form" for Automotive Oscilloscopes when used for comparison on all running GMT360 4.2L Engines during 720 Degrees of Engine Rotation:

BESTKNOWNGOODCKP2CPSWAVEFORM.jpeg

What is the present Mileage of your SUV?
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
About 125,000 miles . I replaced the crank sensor . I have not replaced the can sensor . how would I make,sure they are in sync with each other ?
 

mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
I edited my Last Post to show you what the "Known Good Wave Form" should look like when everything between the (CKP) and the (CPS) Sensors is correct.

Also, while the Engine should still be able to Start and Run after replacing a (CKP) Sensor ... it will become necessary to perform a CASE Re-Learn procedure to establish the correct Crankshaft Angle. This requires using a High End Scan Tool like a TECH 2 or some other similar, capable Auto Shop Quality Scanner.

Please visit THIS Link concerning "How To Use Inexpensive Oscilloscopes to Perform Engine Diagnostics":

 
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mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
One last suggestion...

@Mooseman has often recommended...

"Un-Plug the Connector to the Electro-Viscous Fan Clutch to see if the Engine Will Start..."

Here is The Reason WHY:

The A/C Signal being generated by a Failing EV Fan Clutch can cause an Interference Feedback Signal (...often referred to as 'HASH'...) that can interrupt the PCM's PWM (Pulse Width Modulation) Controls elsewhere on the Class 2 Network.

So Doing THIS... MIGHT be worth a TRY... :>)

If the Engine DOES Start... Keep an Eye on the Coolant Temperature Gauge and Don't Run The Motor for TOO Long before re-connecting the EV Fan Clutch.
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
We did have a cooling fan overspeed code . is that what that is .? ? ?
and could you tell me in simple terms how to disconnect it .I am not find much on it yet
 

TollKeeper

Guru
Dec 3, 2011
6,886
Brighton, CO
If you open your hood, and on your cooling fan shroud, on the right side you will see a plug. Thats the harness for the Viscous Coupler. Just unplug it.
 

mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
Sorry... I didn't get what you were writing...

Check that your Battery DC Voltage is at or above 12.5 Volts or so. This Engine (PCM) is very sensitive to having a Decent Battery Charge before it will Start.
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
I do not have,a multimeter . nor really know,how to use one anyway . I did put my jumper on it to make sure it had the juice it needed before . and same thing . the battery is duralast gold and its about 5 months old
 

mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
Also... if it were me... I'd re-install the Original (CKP) Sensor if you only changed it out just to have a "New One" installed. If the replacement (CKP) Sensor is NOT an OEM version... this may become a factor in failure.

The position of the Very Tip or End of the Micro-AC-Coil Pick-up of the (CKP) Sensor in relation to the position of the passing Reluctor Wheel Teeth nearby can become a factor if becomes either TOO Close or TOO Far Away from those passing "Sixty - Minus Two" Teeth of the 58 Tooth Reluctor Wheel.
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
I only changed that sensor since the code popped up . and the mechanic said to replace it . it has a lifetime warranty . wow thats complicated .I tapped it till it was flush. with a firm rubber mallet . will cranking it hurt it in any way ?
 

mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
Well... That depends upon whether it is either TOO Close...or TOO Far Away from those Reluctor Wheel Teeth. Forgive me for mentioning this while you are presently under all of this stress and pressure to get this repair done.

However, in addition to getting your hands on some Basic Diagnostic Tools, having a Decent Lighted "Scope On A Rope" Circuit Test Light-Probe and likewise, having a Decent DVOM (Digital Volt Ohm Meter) or DMM (Digital Muliti-Meter) it is axiomatic that "Best Automotive Diagnostic Practices" are to:

"Only Change One Variable (Think PARTS Here) At a Time".

NOTE:

I'm NOT Suggesting that what is mentioned below has occurred NOR suggesting that you must attempt to investigate this as a possibility:

Just know that in very rare cases... the Welds that are meant to hold a Multi-Tooth Reluctor Ring firmly in its proper place onto the Base Circle of the Crankshaft can break free.

Thus, this can allow the Reluctor Ring to Spin Loose and Free and not supply the PCM with any accurate reference points for TDC-BDC information afterwards.

This issue can be investigated using an inexpensive 7-9 MM Endo-Bore-Scope and view the Reluctor Ring through the Hole in the Driver's Side of the Engine Block after removing the (CKP) Sensor.

If it becomes easy to slide or nudge the Reluctor Wheel even slightly either up and down or from side to side with any effort at all, that would Tell the Tale and Instantly Condemn the Engine.
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
I do very much all your(s) efforts . but truth be told I am a layman . and much of what you are,saying and suggesting I do in going way over head . I and going to put it in a shop next tuesday . and my brain is turning into pudding in .racking my brain. my fuse is blown ( in my head ) and it seems I am in over my head I am pretty damn handy and have fixed a good deal of things to fix my trailblazer since I had it but this is beyond what I believe I can handle . I hope its a relatively simple fix that will not cost me to much . thank you very much you all for the help and suggestings and time all of you have given me to help me . wish me luck . cheers brother 🍺🍻🍺🍻🍺
 
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mrrsm

Lifetime VIP Donor
Oct 22, 2015
5,984
Tampa Bay Area
I forgot to mention that in the case of understanding how a Wheel Speed Sensor or in THIS case, How a (CKP) AC Sensor works to Create a Signal... You'll notice that the Wire Harness leading to the up to the (CKP) Connector is Twisted with a Certain Number of "Twists Per Inch".

This is the Reason WHY:

All Low AC Voltage Sensors rely upon Finely Wound Copper Wire Coils inside along with a Permanent Magnet to generate their OWN Alternating Current Field in order to Create an Alternating Electrical "Sine Wave" Signal.

Hence AC Sensors only have Two Harness Wires and Connector Pins versus the Three Harness Wires and Pins of all Hall Effect Sensors, such as with the (CPS) Sensor requiring a Signal Wire, an External DC Power Source and a Ground.

As such, an EXTREMELY Small Amount of AC Current gets generated by the passing of Each Steel Reluctor Wheel Tooth at the Rate of 6 Degrees out of a 360 Degree Circle ... Minus the 2 Teeth removed for creating a One Time Per Rotation TDC Demarcation Point as all of the Teeth move past the Tip of the (CKP) Sensor during Crankshaft Rotation.

Thus, Without having the Harness Wiring made with a certain number of Turns or Twists Per Inch, the (CKP) AC Sensor can suffer Failures Caused by ANY Slight Outside Electrical Interference.

So... If it "Turns" out that You (or anyone else) happened to "unwind" any length of that Twisted Harnessing, then go back under there and Re-Wind it back to its Original "Twists-Per-Inch"condition. :>)

*Whew*... I'm very sorry that So Much of THIS is So Damned Technical...!!!
 
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Yoda222

Registered Member
Original poster
Jun 14, 2022
22
New Orleans
I,got a fuel pressure test kit yesterday and I am trying to get the connector onto the Schrader valve on the fuel rail and its nearly impossible. no room to work . no way to get any torque or ass behind it . pardon my french .
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
And be careful with it. I cracked the rail at the valve on mine and had to replace the whole thing. Stupid way they put it in there.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,548
Ottawa, ON
This is le the third or fourth time we hear of bad Delphi pumps. I think we should drop them as a preferred brand. ACDelco and Bosch all the way.
 

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