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2002 chevy trailblazer_lt
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Discussion Starter #1
Check engine light on and off. Did 2 Auto zone code reader checks. 1st read replace Camshaft Position sensor.
Replaced CPS. 2nd code reading said bad Ignition coil. Along the way the oil switch sender started going bad. Even though I replaced it about 1.5 years ago. Replaced the bad Oil Switch sender. Cleaned the Throttle. Results: Engine started to misfire. I tried doing an Idle relearn by disconnecting battery terminals and connecting a jumper wire to the negative bat terminal to the positive terminal. Waited 20 minutes. Turned ignition key not engine Acc twice. Started the engine bad news the engine started to misfire. Then tried resetting fuses from the front fuse box . Bad idle and misfire still going on.

Switched Ignition coil 6 with Ignition coil 3 in attempts to test for bad ignition coil. Still, engine rough idle and misfire?
Tried another code reading, This time reader showed bad spark plug in engine coil 3? I ran the car on expressway for about I mile. The engine continues to misfire and run rough.

Other than going to a mechanic is there another way to restore idle relearn codes?
 

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2004 chevy trailblazer_lt
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It sounds like you are being led astray by whomever is reading the OBDII codes for you. There is no specific code for an ignition coil nor is there one for a spark plug (to the best of my knowledge). What you should have been told is that there is either a nonspecific misfire (P0300) code or a cylinder specific (P030X where X is the cylinder number) code.

Exactly what codes did AutoZone tell you they retrieved from your TrailBlazer?

Did you replace the ignition coil that they told you was bad? If you did, which coil did you purchase (manufacturer)? Did you purchase the least expensive coil attempting to save a few dollars? For what it's worth, the only ignition coils for a TrailBlazer I would purchase from AutoZone are the ACDelco or Delphi. I personally would not purchase their Duralast ignition coils because I know who makes them, and they are not that company's premium line of ignition coils based upon the country of origin stamp I saw on them when I looked them over.

Did you replace any of the spark plugs? If you have not, you likely need too and please do not use anything except ACDelco 41-103 iridium spark plugs. These engines do not like any other spark plugs. If you are going to replace one spark plug, I would go ahead and replace all 6 of them.

Based on what you wrote, it sounds like you did not replace the "bad ignition coil" AutoZone said you had. It sounds like all you did was to swap coil #6 with coil #3, and if indeed you have a bad #3 ignition coil, your engine will still have a misfire.

You really need to have you own OBDII code reader/scanner if you plan on working on your own vehicle. If you have an android smartphone, you can get an OBDII Bluetooth dongle for under $25 on Amazon and get the Torque Pro app from the google play store for a one time fee of $5.00 (not one time use). Here is the link to the Bluetooth dongle I have:

Also, if you are going to do your own maintenance, purchase a Haynes Manual for your TrailBlazer. Those are filled with lots of helpful advice and details on how to troubleshoot various problems, along with step-by-step instructions on how to repair things.

You did the idle relearn procedure more or less correctly - disconnect the battery's negative cable for 20 minutes. I would have gone for 30 minutes, and I would have not shorted the battery leads together. I would have simply turned the headlights on to drain off any residual electricity in the various circuits. Shorting the battery terminals together could damage some of the sensitive electronics.

OK on replacing the camshaft position sensor, and regarding the leaking oil pressure sending unit, those can go bad at any time, especially some of the value priced brands. This is where purchasing a name brand like ACDelco, Delphi, Standard Motor Products, or BWD pays off. They are built to a higher standard and are less likely to develop leaks after only a couple of years.

Good Luck!
 

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I will second @plscolla post. Codes DO NOT identify a bad part. They only give a starting point for proper diagnostics.

For example, the code for a misfire in any given cyclinder,,, all that code really tells is that there is an engine vibration picked up by the knock sensors and it happens about the time when that cylinder is firing so the computer thinks that is what the cause is. Now what could be the cause of that misfire? Fouled sparkplug, bad wire connection at the coil, water in the sparkplug well, bad wire connection at the fuel injector, clogged fuel injector, poor compression in that cylinder, failing coil, and on, and on. But the code in no way can say it's a sparkplug or a coil or any one of the many possible causes.
 

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Discussion Starter #4
It sounds like you are being led astray by whomever is reading the OBDII codes for you. There is no specific code for an ignition coil nor is there one for a spark plug (to the best of my knowledge). What you should have been told is that there is either a nonspecific misfire (P0300) code or a cylinder specific (P030X where X is the cylinder number) code.

Exactly what codes did AutoZone tell you they retrieved from your TrailBlazer?

Did you replace the ignition coil that they told you was bad? If you did, which coil did you purchase (manufacturer)? Did you purchase the least expensive coil attempting to save a few dollars? For what it's worth, the only ignition coils for a TrailBlazer I would purchase from AutoZone are the ACDelco or Delphi. I personally would not purchase their Duralast ignition coils because I know who makes them, and they are not that company's premium line of ignition coils based upon the country of origin stamp I saw on them when I looked them over.

Did you replace any of the spark plugs? If you have not, you likely need too and please do not use anything except ACDelco 41-103 iridium spark plugs. These engines do not like any other spark plugs. If you are going to replace one spark plug, I would go ahead and replace all 6 of them.

Based on what you wrote, it sounds like you did not replace the "bad ignition coil" AutoZone said you had. It sounds like all you did was to swap coil #6 with coil #3, and if indeed you have a bad #3 ignition coil, your engine will still have a misfire.

You really need to have you own OBDII code reader/scanner if you plan on working on your own vehicle. If you have an android smartphone, you can get an OBDII Bluetooth dongle for under $25 on Amazon and get the Torque Pro app from the google play store for a one time fee of $5.00 (not one time use). Here is the link to the Bluetooth dongle I have:

Also, if you are going to do your own maintenance, purchase a Haynes Manual for your TrailBlazer. Those are filled with lots of helpful advice and details on how to troubleshoot various problems, along with step-by-step instructions on how to repair things.

You did the idle relearn procedure more or less correctly - disconnect the battery's negative cable for 20 minutes. I would have gone for 30 minutes, and I would have not shorted the battery leads together. I would have simply turned the headlights on to drain off any residual electricity in the various circuits. Shorting the battery terminals together could damage some of the sensitive electronics.

OK on replacing the camshaft position sensor, and regarding the leaking oil pressure sending unit, those can go bad at any time, especially some of the value priced brands. This is where purchasing a name brand like ACDelco, Delphi, Standard Motor Products, or BWD pays off. They are built to a higher standard and are less likely to develop leaks after only a couple of years.

Good Luck!

Thanks very much for responding!
For the moment the relearn "appears" to have fixed the idle.
Thanks to TJ Baker and Tigermike1.
As per the "oil pressure sender/switch. I installed a new oil pressure sender.
When I set the AC the OPSSwitch goes to Zero? Idle good with slight murmur if AC off.
Other than returning the oil pressure sender and reinstalling a new one;
what could be the problem?
I did replace spark and Ignition coil on #3.
Hopefully the idle problem won't return. Looks like disconnecting the negative on the battery prompted this? Would cleaning the Valve Actuator Timing Solenoid improve idle? For example, the subtle murmur?
Again thanks to you all. Sorry I did not get back to you all right away.
I had a password problem.
 

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Discussion Starter #5
It sounds like you are being led astray by whomever is reading the OBDII codes for you. There is no specific code for an ignition coil nor is there one for a spark plug (to the best of my knowledge). What you should have been told is that there is either a nonspecific misfire (P0300) code or a cylinder specific (P030X where X is the cylinder number) code.

Exactly what codes did AutoZone tell you they retrieved from your TrailBlazer?

Did you replace the ignition coil that they told you was bad? If you did, which coil did you purchase (manufacturer)? Did you purchase the least expensive coil attempting to save a few dollars? For what it's worth, the only ignition coils for a TrailBlazer I would purchase from AutoZone are the ACDelco or Delphi. I personally would not purchase their Duralast ignition coils because I know who makes them, and they are not that company's premium line of ignition coils based upon the country of origin stamp I saw on them when I looked them over.

Did you replace any of the spark plugs? If you have not, you likely need too and please do not use anything except ACDelco 41-103 iridium spark plugs. These engines do not like any other spark plugs. If you are going to replace one spark plug, I would go ahead and replace all 6 of them.

Based on what you wrote, it sounds like you did not replace the "bad ignition coil" AutoZone said you had. It sounds like all you did was to swap coil #6 with coil #3, and if indeed you have a bad #3 ignition coil, your engine will still have a misfire.

You really need to have you own OBDII code reader/scanner if you plan on working on your own vehicle. If you have an android smartphone, you can get an OBDII Bluetooth dongle for under $25 on Amazon and get the Torque Pro app from the google play store for a one time fee of $5.00 (not one time use). Here is the link to the Bluetooth dongle I have:

Also, if you are going to do your own maintenance, purchase a Haynes Manual for your TrailBlazer. Those are filled with lots of helpful advice and details on how to troubleshoot various problems, along with step-by-step instructions on how to repair things.

You did the idle relearn procedure more or less correctly - disconnect the battery's negative cable for 20 minutes. I would have gone for 30 minutes, and I would have not shorted the battery leads together. I would have simply turned the headlights on to drain off any residual electricity in the various circuits. Shorting the battery terminals together could damage some of the sensitive electronics.

OK on replacing the camshaft position sensor, and regarding the leaking oil pressure sending unit, those can go bad at any time, especially some of the value priced brands. This is where purchasing a name brand like ACDelco, Delphi, Standard Motor Products, or BWD pays off. They are built to a higher standard and are less likely to develop leaks after only a couple of years.

Good Luck!
Thank you bety much for your prompt reply! One more thing I did not replace the Oil pressure sender with an AC Delco product?
 

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2002 chevy trailblazer_lt
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Discussion Starter #6
It sounds like you are being led astray by whomever is reading the OBDII codes for you. There is no specific code for an ignition coil nor is there one for a spark plug (to the best of my knowledge). What you should have been told is that there is either a nonspecific misfire (P0300) code or a cylinder specific (P030X where X is the cylinder number) code.

Exactly what codes did AutoZone tell you they retrieved from your TrailBlazer?

Did you replace the ignition coil that they told you was bad? If you did, which coil did you purchase (manufacturer)? Did you purchase the least expensive coil attempting to save a few dollars? For what it's worth, the only ignition coils for a TrailBlazer I would purchase from AutoZone are the ACDelco or Delphi. I personally would not purchase their Duralast ignition coils because I know who makes them, and they are not that company's premium line of ignition coils based upon the country of origin stamp I saw on them when I looked them over.

Did you replace any of the spark plugs? If you have not, you likely need too and please do not use anything except ACDelco 41-103 iridium spark plugs. These engines do not like any other spark plugs. If you are going to replace one spark plug, I would go ahead and replace all 6 of them.

Based on what you wrote, it sounds like you did not replace the "bad ignition coil" AutoZone said you had. It sounds like all you did was to swap coil #6 with coil #3, and if indeed you have a bad #3 ignition coil, your engine will still have a misfire.

You really need to have you own OBDII code reader/scanner if you plan on working on your own vehicle. If you have an android smartphone, you can get an OBDII Bluetooth dongle for under $25 on Amazon and get the Torque Pro app from the google play store for a one time fee of $5.00 (not one time use). Here is the link to the Bluetooth dongle I have:

Also, if you are going to do your own maintenance, purchase a Haynes Manual for your TrailBlazer. Those are filled with lots of helpful advice and details on how to troubleshoot various problems, along with step-by-step instructions on how to repair things.

You did the idle relearn procedure more or less correctly - disconnect the battery's negative cable for 20 minutes. I would have gone for 30 minutes, and I would have not shorted the battery leads together. I would have simply turned the headlights on to drain off any residual electricity in the various circuits. Shorting the battery terminals together could damage some of the sensitive electronics.

OK on replacing the camshaft position sensor, and regarding the leaking oil pressure sending unit, those can go bad at any time, especially some of the value priced brands. This is where purchasing a name brand like ACDelco, Delphi, Standard Motor Products, or BWD pays off. They are built to a higher standard and are less likely to develop leaks after only a couple of years.

Good Luck!
Thanks very much for responding TigerMike-TJBaker-plscolla1
Check engine light is gone but the problem still persists with engine missing. Even though I replaced the "oil pressure sender/switch" pressure. I replaced the defective switch with the same "WVE" brand. Also, I replaced the coil and spark plug #3.
For example, the check gauge oil pressure lights up and thereafter the oil pressure needle goes to zero. I have to rev up the engine to its proper setting. Goes to zero especially when AC is set to 2? Oil gauge goes to zero less often with AC off? Moreso, an engine "knock" happens and is more pronounced with AC on or off?
Meaning when the engine is idling with AC on the engine knock is more frequent and louder about every 15/30 seconds. With AC off while the engine idles the engine knock still occurs less often and less loud?
Previously I cleaned the throttle. Also, would cleaning the Variable valve solenoid help solve the engine knocking?
 

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OK on replacing the oil pressure sending unit with a WVE branded one.

Regarding the knock, try this - remove serpentine belt and start the engine when cold and run it for no more than one or two minutes so you do not overheat it. Does the knock still occur? If no, then spin by hand the pulley on the alternator and see if it spins smoothly or feels gravelly. If it does not feel smooth, then you could have a bad bearing in it. Now repeat this with the power steering pump, and finally with the AC compressor. Also, don;t forget to check the belt tensioner and any other pulleys the serpentine belt goes around.

The AC compressor will likely take more work to spin the pulley, but if it spins, catches, feels rough, etc., you might have an AC compressor on it's last legs.

Trying to eliminate/isolate the cause of the "knock".

Regarding the camshaft variable valve solenoid, I would just change it out with a new one from either ACDelco, Delphi, or Standard Motor Products. Yes, some people have cleaned them successfully, but beings it is almost 20 years old, it could be fatigued as well and the seals might be wearing out.
 

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Discussion Starter #8
OK on replacing the oil pressure sending unit with a WVE branded one.

Regarding the knock, try this - remove serpentine belt and start the engine when cold and run it for no more than one or two minutes so you do not overheat it. Does the knock still occur? If no, then spin by hand the pulley on the alternator and see if it spins smoothly or feels gravelly. If it does not feel smooth, then you could have a bad bearing in it. Now repeat this with the power steering pump, and finally with the AC compressor. Also, don;t forget to check the belt tensioner and any other pulleys the serpentine belt goes around.

The AC compressor will likely take more work to spin the pulley, but if it spins, catches, feels rough, etc., you might have an AC compressor on it's last legs.

Trying to eliminate/isolate the cause of the "knock".

Regarding the camshaft variable valve solenoid, I would just change it out with a new one from either ACDelco, Delphi, or Standard Motor Products. Yes, some people have cleaned them successfully, but beings it is almost 20 years old, it could be fatigued as well and the seals might be wearing out.
Hey plscolla,
Once again thanks for getting back to me. I'll give the serpentine/pulley spin approach a good try. In the meantime, I did some digging on a worse case scenario causing the engine knock. As per a Trailvoy member, there may be a factory engine defect for certain 2002 and up TB's. A " cracking of an engine cylinder bore liner"? Sounds extreme but you never know? I hope not or it's "Salvation Army" donation time?
I'll dig a little more to see what can be done if, in fact, this could be the end of TB's happy trails.
 

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You are quite welcome, that is what we are here for - assisting others.

I'll keep my fingers crossed in hopes that you have a "clunky" AC compressor!

Good luck!
 
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