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Discussion Starter · #1 ·
Friend has a 2006 Trailblazer LS with the 4200 engine. Don't know the mileage.
It had been running good and then all at once it started shaking, won't idle and needs constant gas.
The owner's brother replaced one of the coils and found the spark plugs wet and black. He replaced them and they ended up the same way.
You can smell the gas and there is pressure in the fuel line.
Error Codes:
P0128 $10 Coolant thermostat coolant temperature below thermostat regulating temperature
P0135 $10 O2 sensor heater circuit bank1 sensor 1
P0300 $10 Random multiple cylinder misfire detected
P0449 $10 Evaporative emission system vent valve/Solenoid circuit
P0068 $10 MAP/MAF throttle position correction
P0030 $10 Ho2s heater control circuit bank1 sensor1

Where do we start this one one?
i do know that the gas cap is not factory.
The coil was replaced because there previously was an error on cylinder 4.
All of the spark plugs have been replaced.
All this started after she made the comment that it was running great.
 

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  1. Replace thermostat - it's helping to make it run very rich (read NOTE below) --THIS IS PRIMARY - DO IT!!!!!
  2. Isolate and fix the cylinder-by-cylinder misfires because they make it run rich. after #1 above is done because you'll just keep on fouling plugs until you do
  3. Replace B1-S1 Oxygen sensor AFTER you confirm battery voltage is going to the heater first --- if not, we've got more to talk about.
  4. TYPICALLTY the ECS solenoid goes bad all by itself and generally just needs to be replaced. BUT --- yours might be a power problem too - you've gotta diagnose this one carefully.

Don't spill water on any witches in the future.

NOTE ---> about #1 above ---- you've gotta make sure that the coolant really is cold FIRST --- or is it just the CTS?
If the CTS is reporting made-up numbers, then it can definitely screw up the fuel mixture.

It's a fair guess that your fuel pump is working pretty good though!
 

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Discussion Starter · #3 ·
  1. Replace thermostat - it's helping to make it run very rich (read NOTE below) --THIS IS PRIMARY - DO IT!!!!!
  2. Isolate and fix the cylinder-by-cylinder misfires because they make it run rich. after #1 above is done because you'll just keep on fouling plugs until you do
  3. Replace B1-S1 Oxygen sensor AFTER you confirm battery voltage is going to the heater first --- if not, we've got more to talk about.
  4. TYPICALLTY the ECS solenoid goes bad all by itself and generally just needs to be replaced. BUT --- yours might be a power problem too - you've gotta diagnose this one carefully.

Don't spill water on any witches in the future.

NOTE ---> about #1 above ---- you've gotta make sure that the coolant really is cold FIRST --- or is it just the CTS?
If the CTS is reporting made-up numbers, then it can definitely screw up the fuel mixture.

It's a fair guess that your fuel pump is working pretty good though!
Thanks for responding. Just so that there is no misunderstanding, this is with a COLD engine - just started it this morning in 45 - 50 degree weather. And this is the immediate reaction. Is the thermostat still your number one item? What is a CTS?

One additional piece of information that I left out - she had just purchased gasoline and filled the tank. They remarked that it isn't often to have a full tank of gasoline.
 

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Discussion Starter · #4 ·
Thanks for responding. Just so that there is no misunderstanding, this is with a COLD engine - just started it this morning in 45 - 50 degree weather. And this is the immediate reaction. Is the thermostat still your number one item? What is a CTS?

One additional piece of information that I left out - she had just purchased gasoline and filled the tank. They remarked that it isn't often to have a full tank of gasoline.
One more piece of information. The owner's brother is working on it and he is used to working on older cars - not the new electronic controlled vehicles. He did say that he checked the spark on each cylinder and the spark appeared to be weak all around. I didn't see it so I don't know what he saw.
 

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Friend has a 2006 Trailblazer LS with the 4200 engine. Don't know the mileage.
It had been running good and then all at once it started shaking, won't idle and needs constant gas.
The owner's brother replaced one of the coils and found the spark plugs wet and black. He replaced them and they ended up the same way.
You can smell the gas and there is pressure in the fuel line.
Error Codes:
P0128 $10 Coolant thermostat coolant temperature below thermostat regulating temperature
P0135 $10 O2 sensor heater circuit bank1 sensor 1
P0300 $10 Random multiple cylinder misfire detected
P0449 $10 Evaporative emission system vent valve/Solenoid circuit
P0068 $10 MAP/MAF throttle position correction
P0030 $10 Ho2s heater control circuit bank1 sensor1

Where do we start this one one?
i do know that the gas cap is not factory.
The coil was replaced because there previously was an error on cylinder 4.
All of the spark plugs have been replaced.
All this started after she made the comment that it was running great.
From the scanner, was there indications of the status of the listed codes? Current, pending, history, old, etc.?
 

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One more piece of information. The owner's brother is working on it and he is used to working on older cars - not the new electronic controlled vehicles. He did say that he checked the spark on each cylinder and the spark appeared to be weak all around. I didn't see it so I don't know what he saw.
Not too sure how the spark quality could be tested - it's not easy to take the individual coils out of the head and test them unless there's a bench test for them of which I am not privy.

Be sure to tell this older-car guy to keep any test lights out of the system!

Poking a 12V test light where it should not go can destroy too much to list here!

Cold starts require more fuel - like a choke on a carburetor - and the CTS (Coolant Temperature Sensor) detects the true coolant temperature and reports this to the computer.

If it's out of range, then it's telling the computer that the coolant temp can be as low as -45°F - as that's it's default value when it breaks into an open circuit.

The excessive fuel - black smoke and an oxygen sensor reporting bad things coming out of the combustion chambers and such, all have to be handled - in order!

FWIW --- fuel injected engines can start at amazingly low temperatures and just plain ol' run!

They really don't care and you shouldn't feel any running difference from ice cold to normal 215°F operating temperatures.

Just start it and let it do it's own thing for a few minutes if the temps are really low ---- below 20°F or so.

What you're waiting for is the oil in the engine to get to all the nooks and crannies before you ask it to work too hard - that's all.

Pay attention to chem_man and TJ since they have a lot more technical stuff to tell you..................
 

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Discussion Starter · #7 ·
In regards to the question "From the scanner, was there indications of the status of the listed codes? Current, pending, history, old, etc.? "
For my scanner - these were the codes that were "Stored". The only other option I have is Pending and I did not check them.
 

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It might be nice to tell the make and model of your scanner and that'll make it easier to understand if it is capable of doing whatever necessary things that will be needed. I have a small pocket-sized scanner in each of the vehicles I have that actually have an OBD-2 port - for "just in case" on the road.

But I leave the heavy lifting to much more expensive and capable gear at home.
 

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In regards to the question "From the scanner, was there indications of the status of the listed codes? Current, pending, history, old, etc.? "
For my scanner - these were the codes that were "Stored". The only other option I have is Pending and I did not check them.
For those who know how to read them, GM stores 8 levels of code status in these trucks. MIL requested, Pending, Old, History, Current, Immature, and two manufacturer defined levels one of which is "not ran since code cleared" and the final one I have not seen defined. All of these are "stored" in the status byte of the code.

I believe Pending codes are DTCs that require the fault to be seen at two consective ignition cycles before being set. They are "Pending" when they are present in the current ignition cycle. It is not uncommon for the same DTC code to have several status levels simultaneously.
 

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I wish I could just remove any hard-set codes and leave the "Pending" codes standing for future reference.

Can't say I've ever seen "Immature" codes --- but I DO definitely see the "Not ran since code(s) cleared" many times.

Aren't those usually OBD Drive Cycle codes though?
 

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Well this discussion caused me to go back and locate the specification where this stuff is detailed. After a few years of finding bits here and there it all becomes something of a jumble in the old grey matter.

So the definitions I posted I first saw posted at the following link. Scroll way down to the bottom.


Later I found a specification, SAE 2190 that set forth the specifics... Here is a screenshot of the table....

Font Rectangle Parallel Number Screenshot


So from this it appears that there is a status designation named "stored" and it is what the fastfieros document called "history with freeze frame". Seems the FastFieros document contained some guesswork at the time..


Here is an example: I have a 2006 PCM currently powered up in the kitchen here and when I request the status of code P0449 (circled in yellow below) the status byte (circled in red below) is 0x25. So that means bits 0, 2, and 5 are set. Refer to the SAE table for the corresponding status'.

Font Terrestrial plant Personal computer Laptop Darkness




So getting back to the subject thread here. That P0449 code is set when the PCM sees the control circuit for the EVAP vent solenoid is not what it is expected to be. Either it has a voltage on it when it should not or it has no voltage on it when it should. In that the reported troubles seemed to begin right after a fill-up and the EVAP system has the potential to pull in fuel vapors and even liquid if the tank is overfilled and the evap system is malfunctioning, I think I would try an experiment. I would disconnect the vacuum line from the throttle body to the EVAP system purge valve and cap it at the throttle body. Then start it up and see what happens. You might well set other codes for an evap system failure because of the disconnected line.
 

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@TJ:
Your -----> I have a 2006 PCM currently powered up in the kitchen here and when I request the status of code P0449 (circled in yellow below) the status byte (circled in red below) is 0x25. So that means bits 0, 2, and 5 are set.




I tend to do all my breadboarding in my bathroom in the area between my sink and the medicine cabinet.

The sink is within arm's reach for those small incendiary moments ....... and the medicine cabinet is on the other side for those "ouchie moments".

What're YOU gonna do? Slap some Mozzarella on it?
 

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I should have included a table there.


Bit 7 = 0x80
Bit 6 = 0x40
Bit 5 = 0x20
Bit 4 = 0x10
Bit 3 = 0x08
Bit 2 = 0x04
Bit 1 = 0x02
Bit 0 = 0x01
 

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Discussion Starter · #17 ·
Here's the response I received concerning disconnecting the vacuum hose from the throttle body:
It made a little difference in the idling but still idling rough.
I've asked but have not received a reply if it could have been driveable.
 

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Friend has a 2006 Trailblazer LS with the 4200 engine. Don't know the mileage.
It had been running good and then all at once it started shaking, won't idle and needs constant gas.
The owner's brother replaced one of the coils and found the spark plugs wet and black. He replaced them and they ended up the same way.
You can smell the gas and there is pressure in the fuel line.
Error Codes:
P0128 $10 Coolant thermostat coolant temperature below thermostat regulating temperature
P0135 $10 O2 sensor heater circuit bank1 sensor 1
P0300 $10 Random multiple cylinder misfire detected
P0449 $10 Evaporative emission system vent valve/Solenoid circuit
P0068 $10 MAP/MAF throttle position correction
P0030 $10 Ho2s heater control circuit bank1 sensor1

Where do we start this one one?
i do know that the gas cap is not factory.
The coil was replaced because there previously was an error on cylinder 4.
All of the spark plugs have been replaced.
All this started after she made the comment that it was running great.
I say plugged catalytic converter
 
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