I just bought a 2002 trailblazer 4.2 l6 4x4, have had issues from day one. Most recently it refuses to start. Had a mechanic work on it, paid for fuel filter, fuel pump, fuel pressure regulator and fuel lines that he busted. All of which he said was my problem. But it still is not starting. It rolls over but no start. I have been trying to trouble shoot myself for 2 weeks now. Have checked every fuse, all are good. Do not have a fuel pressure tester, but seems to be good pressure at the filter, no clue how to test it at the rail. Or if it really is a fuel problem to begin with.
Need help, truck wont start
- Thread starter Newchevygirl
- Start date
After the vehicle has been sitting a while, you should be able to turn the key to on, but not start, and hear the fuel pump work and pump the fuel up to pressure. Can you smell gas?
Pump is kicking on. Got fuel to the rail and plugs. We are thinking it may be crank solinoid, it is full of oil and i was told thats bad.
Sorry cam solinoid
Sorry cam solinoid
Mooseman
Moderator
Cam solenoid (or CPAS) would not prevent it from starting. Might run rough or throw a code but will still run.
So it looks like you have fuel. Next would be to check for spark. Did you check all the fuses?
There is also a possibility it's the crank sensor. Read a couple of times that a bad crank sensor will not let the engine fire.
So it looks like you have fuel. Next would be to check for spark. Did you check all the fuses?
There is also a possibility it's the crank sensor. Read a couple of times that a bad crank sensor will not let the engine fire.
All the fuses are good. That was one of the first things i checked. I called the dealership near me and they said that it was most likely the pcm? Im not 100% sure if its getting spark, thats one thing ive never really messed with and my father has gone home for the night.
the quickest / cheapest way to find out if it will fire at all is to get a can of starting fluid and spray some in the intake while someone tries to start. IF the engine catches at all, then you likely have a fueling problem and the normal "fuel path" is not working. IF it does not even "burp / sputter" at all, then you have either electrical issues OR a major mechanical issue... mechanically, you need to do some form of compression test to see if things are happening at that level. Electrically, you need to check for voltages at key places... but first before you do much, when you turn your key to on (but don't start), the vehicle dash should do an "all light bulbs check / light" and go out and then the "check engine" light should stay lit "forever"... basically as long as you leave your key in ON... IF that state of the check engine light does NOT occur (stay lit), your vehicle will never start as the PCM is NOT happy about something which needs to be investigated.
Further, you have failed to mention whether you have scanned for any codes in the system.
Lastly, the last thing that I would do would be playing around with the pcm... they don't fail that often and the stealership is just after you for something "more" ... as is $$$$$$$
Further, you have failed to mention whether you have scanned for any codes in the system.
Lastly, the last thing that I would do would be playing around with the pcm... they don't fail that often and the stealership is just after you for something "more" ... as is $$$$$$$
Im not too worried about the money, i have multiple family members with used but good parts. Already have a pcm lined up for $40. I have run a scan, and the only thing that comes up is 2 cylinder misfires. Which didnt show up until after we started working on it and tried starting it a few times. We have tested the wiring for just about everything, all seems good there. I found a diagram online for that truck showing what voltage should be coming from what wires. When i turn the key on, after the lights all go out the check engine light goes out but then comes back on. The day the truck broke down, the check engine light started blinking on my way home. I parked it, then went out to move it to check it out and thats when it wouldnt start.
I_Shoot_Back
Member
Just to recap what has been looked at so far… as an Itemized List:
(1) Fuel Pump
(2) Fuel Pump Regulator
(3) Damaged Fuel Line
(4) Fuel Filter
(5) Fuses
(6) CPAS (Camshaft Position Actuator Solenoid ...Replaced with OEM New One?
The symptoms of the Misfires (which should code out as either P0300 for Random Misfires or P0301-0306 for each specific Cylinder Misfiring would make it a good idea to examine the Spark Plugs for them all looking Bone Dry...and a showing a nice, crispy “Fried Chicken Brown” color to prove that the Spark Plugs are igniting a nice Fuel-Air Mixture. If you decide to eventually replace them… Do not Gap them… they come from the factory pre-gapped so their Electrode ends ...coated with a thin layer of Rare Platinum ...will not get chipped or flake off.
Prior to removing the Spark Plugs… Remove each of the Six COP (Coil On Plugs) and use some “Canned Air” used for blowing out computer keyboards, etc… to blow out each Spark Plug Well of any Dirt, Debris or Motor Oil that may have leaked down around each Spark Plug. This will prevent any of that mess from dropping inside of the Cylinders as soon as the Plugs are removed.
Observe the ends of the Spark Plugs well… and look for a Black, Sooty appearance and whether or not they are still Wet with Gasoline. If it was not an Oversight in mentioning that the Plugs have already been changed… replace them with only the ones recommended for this odd engine: ACDelco ...and then swap around a few of the COP (Coil On Plugs) and check the Ignition Harness carefully for any damage where the Connectors plug into the Main Harness. Try and start the engine to see if any of these changes has had the right effect.
If those “Wet Cylinders” are present throughout each and every cylinder… Check that the PCM three Harness Connectors are properly attached to the PCM… and if not… remove all three and get some CRC Electrical Spray from Autozone (NOT WD-40 or Brake Cleaner)...and allow them to thoroughly dry prior to re-attaching the Three Harness Connectors. Another cause of “Wet Cylinders” happens under conditions of Very Low Compression… so low as to preclude complete combustion. Harbor Freight sells an inexpensive Compression Test kit that will do the trick in figuring this out...as both Wet and Dry Compression Tests.
Seek out the Youtube Channel of one of our respected Senior Members known as “MAY03LT” and search through all of his Trailblazer 4.2L Diagnostic and Repair Videos for "Cranks, No Start" Videos. I must warn you that he laces his dialogues with a great deal of Strong Profanity...so watch his videos when the Kids are not nearby. Nonetheless… his guidance and knowledge about solving the problems you are dealing with here are quite sterling and educational.
Use the Search Feature suggested by @Mooseman in the available FAQ here at GMT Nation and it will speed your access to these related topic links to a lot of other Threads that have a great deal more information as well.
(1) Fuel Pump
(2) Fuel Pump Regulator
(3) Damaged Fuel Line
(4) Fuel Filter
(5) Fuses
(6) CPAS (Camshaft Position Actuator Solenoid ...Replaced with OEM New One?
The symptoms of the Misfires (which should code out as either P0300 for Random Misfires or P0301-0306 for each specific Cylinder Misfiring would make it a good idea to examine the Spark Plugs for them all looking Bone Dry...and a showing a nice, crispy “Fried Chicken Brown” color to prove that the Spark Plugs are igniting a nice Fuel-Air Mixture. If you decide to eventually replace them… Do not Gap them… they come from the factory pre-gapped so their Electrode ends ...coated with a thin layer of Rare Platinum ...will not get chipped or flake off.
Prior to removing the Spark Plugs… Remove each of the Six COP (Coil On Plugs) and use some “Canned Air” used for blowing out computer keyboards, etc… to blow out each Spark Plug Well of any Dirt, Debris or Motor Oil that may have leaked down around each Spark Plug. This will prevent any of that mess from dropping inside of the Cylinders as soon as the Plugs are removed.
Observe the ends of the Spark Plugs well… and look for a Black, Sooty appearance and whether or not they are still Wet with Gasoline. If it was not an Oversight in mentioning that the Plugs have already been changed… replace them with only the ones recommended for this odd engine: ACDelco ...and then swap around a few of the COP (Coil On Plugs) and check the Ignition Harness carefully for any damage where the Connectors plug into the Main Harness. Try and start the engine to see if any of these changes has had the right effect.
If those “Wet Cylinders” are present throughout each and every cylinder… Check that the PCM three Harness Connectors are properly attached to the PCM… and if not… remove all three and get some CRC Electrical Spray from Autozone (NOT WD-40 or Brake Cleaner)...and allow them to thoroughly dry prior to re-attaching the Three Harness Connectors. Another cause of “Wet Cylinders” happens under conditions of Very Low Compression… so low as to preclude complete combustion. Harbor Freight sells an inexpensive Compression Test kit that will do the trick in figuring this out...as both Wet and Dry Compression Tests.
Seek out the Youtube Channel of one of our respected Senior Members known as “MAY03LT” and search through all of his Trailblazer 4.2L Diagnostic and Repair Videos for "Cranks, No Start" Videos. I must warn you that he laces his dialogues with a great deal of Strong Profanity...so watch his videos when the Kids are not nearby. Nonetheless… his guidance and knowledge about solving the problems you are dealing with here are quite sterling and educational.
Use the Search Feature suggested by @Mooseman in the available FAQ here at GMT Nation and it will speed your access to these related topic links to a lot of other Threads that have a great deal more information as well.
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The cpas and the spark plugs have all already been replaced with the specifics you stated. I do not remember the specific code it gave for the misfires. The spark plugs were wet when removed, but were not in a condition i felt ok to put back in so i bought new AC Delco plugs and installed them. I did blow out everything i removed, just because everything was full of sand and crud, which i am not sure why. My father is coming back in the morning to help, he knows more than I about these newer vehicles. I myself am used to older (94 and back) minivans and cars. So this is a huge learning situation for me.
I have watched numerous videos on youtube from the member you mentioned. And have tried everything he did. His videos is actually what led me to this site. I have also read through numerous threads here trying to find answers before posting to ask, which is how i knew to test other things i had not thought of before such as wiring and sensors.
I have watched numerous videos on youtube from the member you mentioned. And have tried everything he did. His videos is actually what led me to this site. I have also read through numerous threads here trying to find answers before posting to ask, which is how i knew to test other things i had not thought of before such as wiring and sensors.
Okay... in consideration of trying to describe the greater complexity of what is beyond the usual "Fuel, Air and Spark" Players... These are the Electronically Monitored and Controlled Sensors and the factors required in getting this GM Atlas LL8 4.2L Engine to start and run properly when all things are Nominal:
(1) PCM - Powertrain Control Module
As you well know... The Gray Box... The Ring Leader of PWM (Pulse Width Modulation) as to what follows. Among many other things... the PCM reads the signals from these following Sensors and tries to reconcile the ACTUAL positions of the Crankshaft and DOHC (Double Over Head Camshafts) in order to determine how much Fuel and the related Spark Timing to engage based upon PWM (Pulse Width Modulation).
(2) CKP - The Crankshaft Position Sensor.
Located in the Driver's Side of the Block... it picks up the gaps or notches in the Cast-In Reluctor Ring located on the Crankshaft between the 4-6 Cylinders and induces a Square Wave (Hall Effect) signal that the PCM picks up and determines WHEN to fire the Spark Plugs by using Pulse Width Modulation. Of all the Sensors in this array... if the CKP goes bad... The Engine will absolutely NOT Start. If replaced... a $100.00 Dealership CASE Re-Learn will be required to associate it properly again with what the PCM was used to reading ...just before it failed.
(3) CPAS - Camshaft Position Actuator Solenoid.
This sensor is probably the most unique of the lot in that it has the ability to employ infinite variability and allow an ever-changing amount of Oil to pass through and either advance or retard the Exhaust Camshaft's position and behave much like an EGR at idle as well. The GM Engineers design is for the Camshaft Phaser to receive this changing Oil Pressure and make micro-changes inside of the Helical internal gears of the Phaser...and make very responsive advances and retardation of the Exhaust profile for up to 25 Degrees of range. This Sensor is prone to malfunction if its internal Oil Filter Screens become clogged with Gummy Oil, Dirt and Deposits that get left behind due to Infrequent Oil Changes and low quality Motor Oil. If you can see Oil in the CPAS Connector... it will have to be replaced with an OEM quality component. When it works right... the CPAS allows for a very wide range of Torque and Power not achievable by other mechanical means to adjust the position of the Exhaust Camshaft Profile.
(4) CPS - Camshaft Position Sensor
This sensor located at the very front of the Engine close to the Passenger side... receives signals from a Reluctor Ring that is physically attached to the Camshaft via the TTY Through Bolt holding the Cam Phaser to the slotted nose of the Exhaust Camshaft.... so IT knows what the ACTUAL position of the Exhaust Camshaft is located in at any given moment, Thus, it informs the PCM so that a constant comparison between the readings of all three sensors: CPAS, CPS and the CKP can be made and reconciled in the PCM's "Brain" and determine the correct Fuel and Spark Delivery Timings.
(5) Camshaft Phaser
Your version of this device is somewhat different in its internal design and reliability than its later brethren... as it is quite complicated by having male to female Helical gears for adjusting its position over a range of 25 Degrees... and is also fitted with a Reluctor Ring to serve when signaling the CPS independently from the CPAS Sensor. Dirty Oil...and either Clogged, Lost or Ingested CPAS Screens can render it useless... as well as from having a Broken Internal Return Spring. The later model version is more robust and much less complicated than the one inside of your Engine. Choppy, Stumbling Idles and sketchy responses in the power band during acceleration are the clues to possible problems with a CPAS Sensor.
(1) PCM - Powertrain Control Module
As you well know... The Gray Box... The Ring Leader of PWM (Pulse Width Modulation) as to what follows. Among many other things... the PCM reads the signals from these following Sensors and tries to reconcile the ACTUAL positions of the Crankshaft and DOHC (Double Over Head Camshafts) in order to determine how much Fuel and the related Spark Timing to engage based upon PWM (Pulse Width Modulation).
(2) CKP - The Crankshaft Position Sensor.
Located in the Driver's Side of the Block... it picks up the gaps or notches in the Cast-In Reluctor Ring located on the Crankshaft between the 4-6 Cylinders and induces a Square Wave (Hall Effect) signal that the PCM picks up and determines WHEN to fire the Spark Plugs by using Pulse Width Modulation. Of all the Sensors in this array... if the CKP goes bad... The Engine will absolutely NOT Start. If replaced... a $100.00 Dealership CASE Re-Learn will be required to associate it properly again with what the PCM was used to reading ...just before it failed.
(3) CPAS - Camshaft Position Actuator Solenoid.
This sensor is probably the most unique of the lot in that it has the ability to employ infinite variability and allow an ever-changing amount of Oil to pass through and either advance or retard the Exhaust Camshaft's position and behave much like an EGR at idle as well. The GM Engineers design is for the Camshaft Phaser to receive this changing Oil Pressure and make micro-changes inside of the Helical internal gears of the Phaser...and make very responsive advances and retardation of the Exhaust profile for up to 25 Degrees of range. This Sensor is prone to malfunction if its internal Oil Filter Screens become clogged with Gummy Oil, Dirt and Deposits that get left behind due to Infrequent Oil Changes and low quality Motor Oil. If you can see Oil in the CPAS Connector... it will have to be replaced with an OEM quality component. When it works right... the CPAS allows for a very wide range of Torque and Power not achievable by other mechanical means to adjust the position of the Exhaust Camshaft Profile.
(4) CPS - Camshaft Position Sensor
This sensor located at the very front of the Engine close to the Passenger side... receives signals from a Reluctor Ring that is physically attached to the Camshaft via the TTY Through Bolt holding the Cam Phaser to the slotted nose of the Exhaust Camshaft.... so IT knows what the ACTUAL position of the Exhaust Camshaft is located in at any given moment, Thus, it informs the PCM so that a constant comparison between the readings of all three sensors: CPAS, CPS and the CKP can be made and reconciled in the PCM's "Brain" and determine the correct Fuel and Spark Delivery Timings.
(5) Camshaft Phaser
Your version of this device is somewhat different in its internal design and reliability than its later brethren... as it is quite complicated by having male to female Helical gears for adjusting its position over a range of 25 Degrees... and is also fitted with a Reluctor Ring to serve when signaling the CPS independently from the CPAS Sensor. Dirty Oil...and either Clogged, Lost or Ingested CPAS Screens can render it useless... as well as from having a Broken Internal Return Spring. The later model version is more robust and much less complicated than the one inside of your Engine. Choppy, Stumbling Idles and sketchy responses in the power band during acceleration are the clues to possible problems with a CPAS Sensor.
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so you are saying that you have tried starting fluid into the intake and you get nothing? and you checked the fuse that another poster suggested?
is it possible that your code reader is only reading a single code and not moving thru a list of possible "hidden" / previous codes. maybe a "reduced power" code which will cause a no start condition.
is it possible that your code reader is only reading a single code and not moving thru a list of possible "hidden" / previous codes. maybe a "reduced power" code which will cause a no start condition.