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2004 chevy trailblazer_lt
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221 Posts
Regarding your upstream O2 sensor reading zero, I think you have a bad O2 sensor, and if I were in your shoes, I would go ahead and replace it with a Denso oxygen sensor. Just as an FYI, I have used Denso O2 in all 4 of my vehicles with zero problems.

Regarding your attachment, leave the Engine variable timing sprocket alone for now - that is a major job requiring special tools. As far as the variable valve timing (VVT) solenoid goes, if you have been changing your oil regularly and using a decent 5w30 oil, it should not be a problem. However, if you don't know the maintenance history or oil is leaking out of the electrical connector, then I would replace it - it is not too difficult. By the way, the prices shown in the attachment are extremely high in my opinion. I would order either an ACDelco, A Delphi, or a Standar Motor Products (SMP) VVT solenoid for about half of what is shown in the attachment if ordered at rockauto.com. If in the very end you need to order the sprocket, then those are also available for about half of what is shown.

Again, Good Luck!
 

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471 Posts
Here I am! I was in surgery --- so there's that....

The two black wires, like I said are really SUPPOSED TO BE the same ground VALUE in that they will not have any difference in ground value. They will not be grounded at the same place however.

How's that?

The ECM provides one of the grounds and the frame of the vehicle provides the other.

Now ---> remember that many if not most electrical problems are ground related.

And NO - you cannot just willy-nilly tie them together even though they are the same - philosophically. Everything goes back to the negative post of the battery - but they take separate routes to get there. I have never been able to answer the next question - and I'll tell you where I don't understand this dual-ground thingy.

How can TWO BLACK WIRES be separate yet the same? And No - it's not a theological question.

You (I think) have the upstream and downstream O2 sensors confused if I read your statement correctly.

The front (upstream) O2 sensor will be very active - seeing that it 'sees' raw exhaust that hasn't been run through the cat yet. It's important to know (as a sidebar here) that this upstream O2 sensor can differentiate from the individual exhaust signals from each and every single cylinder - yup! It's somehow psychic! (not really - but a genius GM engineer dood it)

This way - if one cylinder isn't providing power like the others, the ECM can modify the injection fuel volume or ON-DWELL time or the spark timing for that one cylinder! Kewl - huh? I thought you'd like that....

So - if the upstream is active - conversely, the downstream should be very quiet! It should gently move on-off center in very limited voltage differences - not TOO much mind you --- or it'll pop a code saying that the cat is not function or is dying and you get a blinking CEL/SEL - when instead there should be a small hammer that comes outta the driver's headrest to get his attention!

The center-voltage position is called : "NULL POINT" and is the 'home' plate for any O2 sensor. They have to (sweep) cross that center threshold a certain number of times per engine count-cycles. If they don't cross it as prescribed by their functional coded-in percentage - then the CEL/SEL just lights up... not necessarily blinking this time --- again.

ECMs are kewl!
 

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471 Posts
Regarding your upstream O2 sensor reading zero, I think you have a bad O2 sensor, and if I were in your shoes, I would go ahead and replace it with a Denso oxygen sensor. Just as an FYI, I have used Denso O2 in all 4 of my vehicles with zero problems.

Regarding your attachment, leave the Engine variable timing sprocket alone for now - that is a major job requiring special tools. As far as the variable valve timing (VVT) solenoid goes, if you have been changing your oil regularly and using a decent 5w30 oil, it should not be a problem. However, if you don't know the maintenance history or oil is leaking out of the electrical connector, then I would replace it - it is not too difficult. By the way, the prices shown in the attachment are extremely high in my opinion. I would order either an ACDelco, A Delphi, or a Standar Motor Products (SMP) VVT solenoid for about half of what is shown in the attachment if ordered at rockauto.com. If in the very end you need to order the sprocket, then those are also available for about half of what is shown.

Again, Good Luck!
PLUS a BIG +1 on NIPPON-DENSO!

Never NEVER NEVER use a Bosch sensor! Champions suck too.
 

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2003 gmc envoy_slt
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3 Posts
03 envoy problem so when I go wide open (stomp on the gas pedal) seems to go to 3000rpms and doesn't really go any faster kinda seems to go slower but if I barely push the gas down I can actually get up too 60+mph but seems to take a bit it almost seems like if you were to max the weight on a car and then pull whatever it is that maxed it out , up a hill just seems to rev if you do find out what this is would u plz let me know I have spent atleast 300+ just in parts in this thing , and that's just for only this week not Including what I've spent in the past weeks , I've bee.trying 2 figure out what is going on 4 months now , so far I have replaced the variable valve timing solenoid twice , crankshaft position sensor 2 , pulled the throttle body and cleaned it , still hasn't resolved this issue I have replaced the spark plugs with the iridium plugs , it has 260k+ miles on it plz any help would be greatly appreciated I've been trying to figure this out so my wife and kids bought me a code reader that allows you to read codes and also does everything in real time plz let me know what 2 look for on or to check in real time on my code reader , thank you for everyone that responds or any help
One of the biggest things that this points to is a plugged Catalytic converter.. at about 180000 miles on my 03 envoy I was noticing those same symptoms as well as reving with no acceleration on the up hills. It all comes down to air flow...at low pedal you don't have the pressure built up on the cat and it is able to move but as soon as you stomp on it, it creates back pressure and bogs down the motor....think of it like breathing through a coffee straw
 

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2005 buick rainier
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17 Posts
This is what the diag would look like entering our shop. Record codes and freeze frame data. Clear codes and test drive. Check for active & pending codes. P1345 & P0340 present - going to look @ crank & cam PID data on the scan tool. Most shop scanners will have functional tests to control the VVT and monitor cam & crank data (current & desired).

Your approach current approach is what as referred to as a parts shower. You may get lucky or you may just keep wasting time & money. You really need to know how modern electronic control systems interact w/ mechanical engine controls to properly diagnose problems.
 

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2004 chevy trailblazer_ls
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15 Posts
This is what the diag would look like entering our shop. Record codes and freeze frame data. Clear codes and test drive. Check for active & pending codes. P1345 & P0340 present - going to look @ crank & cam PID data on the scan tool. Most shop scanners will have functional tests to control the VVT and monitor cam & crank data (current & desired).

Your approach current approach is what as referred to as a parts shower. You may get lucky or you may just keep wasting time & money. You really need to know how modern electronic control systems interact w/ mechanical engine controls to properly diagnose problems.
 

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2004 chevy trailblazer_ls
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15 Posts
Did you have to replace the thermostat or is your engine heating normally? My Cat was clogged after failing to replace the thermostat. Wouldn't go up a hill hardly.
Gutted the Cat(emergency fix), and runs like a new one.
 

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2003 chevy trailblazer_lt
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3 Posts
I just got done with replacing my transmission because of a CLOGGED CAT! that stupid thing, basically choked my 03 Trailblazer at 4500rpms. Had NO power, struggled on the highway, and wouldn't pass anybody. When I could get it to rev higher than 4500rpms with the new transmission (which was a struggle) I heard a bit of rattling metal. I cut the catalytic converter off and the TB was alive!! I was so happy - this was just a few days ago. The cat melted inside, destroyed at 179k. I replaced my fuel filter as well, that is always a good/cheap thing to do while you are under there.

Good luck!
 

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2004 chevy trailblazer_lt
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221 Posts
Sorry to hear about the clogged cat, but thank you for letting us know what the problem was and that your TrailBlazer is now running properly.
 
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