I have alternating idle RPM (Varies from 650  to 900). I have check, clean and replace
throttle body, spark plugs, ignition coils, o2 sensors (both), air and fuel filters, fuel pump
pressure, IAT and MAP sensors, and the truck idle RPM some days is fine some others is
not, I am getting crazy about it, please help (calling from South America).
It would help to know what year engine model vehicle you
have. Is it car or truck. If the idle seems to be surging
more when the engine is cold, you need to check for
vacuum leak.
I swapped out a 4.3 v6 for a 4.3 later model Vortec v6. The truck was a 93 GMC Sonoma. I
got the engine to run but the transmission won't shift. What makes the transmission shift
on a 4l60e.
If all you did was about the engine then that should not
affect the transmission in any way. The sure to check
your electrical connector and all fuses.
I'm looking for the mass air flow sensor on a 2003 GMC Envoy xl with 4.2 v6 I did a v8 but
this is different, is it called by a different name. Love your site.
The 4200 straight six cylinder engine does not have a
MAF sensor.
<<< Previous Page and Sensor Location Pictures
I have 2002 bravada, i also have rough idle,and its shaking bad,.i have this after cleaning
throttle body,changing
spark plugs with ac Delco. Then i realize my camshaft actuator
solenoid leaking,.At first i clean it and remove the oil from electrical connection, then it
runs like new. But after 80kms it goes back shaking bad. So i did clean it again because i
have to wait for my new parts,.So i put the new solenoid but after 70-80kms it happens
again,.What should i do? Oh and i forgot to tell that every time i have rough and shaking
idle i have blinking (CES) and then will stay.
A blinking engine light means the engine misfire is bad
enough to cause possible catalytic converter damage.
The solenoid would not be causing your misfire. If it is
only at a hit idle and goes away with a little throttle input,
you may have leaking valves in a cylinder. This is a
common problem on certain years.
Where is the schrader valve located on a 2004 GMC Envoy 4.2L to connect a fuel
pressure test gauge?
If it is not on the fuel line on the drivers side front of the
valve cover, then it is located of on the fuel filter under
the truck. It is a plastic valve tap.
I have a 2003 Trailblazer. It is showing a code for low coolant level even though the
coolant level is full. I bought a new level sensor and have no idea where the old one is to
replace it. Where is it? Please!
If it is not on the side of the radiator, then it does  not have one and you are reading the
code incorrectly. Please post the code number so we can check.
The pcv valve entry is incorrect.  The actual hose is in the middle of the intake manifold
down behind and below the computer.
This is a great website filled with lots of good info. Good job guys. I have a 02 TB just
got the a/c running again and it is working ok. The passenger side is cold. The driver
side is not as cold but not warm. The original problem ended up being the button on
control panel. I bypassed that with a toggle switch. Is there a reason the driver side is
warmer. Also the rear vent with the power button and control nob does not work I
don't think it ever has. Where do I start at to see whats going on with that?
Sounds like the drivers side temperature door actuator is
bad. It is located under the drivers side of the dash on
the side of the center HVAC case. There are a few there,
so look at the picture of the location when you are at the
dealer buying the part.
Where is the location of mass air flowsensor for a 2005 GMC Envoy?
On 2004 GMC High Sierra V6 1/2 ton PU, 4x4...where is the oil filter, I swear, I looked
all over for it!
I replaced a 4.2 in a 2004 trailblazer. This is one of the worst engines I've replaced. This is
a salvage yard motor (known good). I have everything hooked up except for adding
coolant (had to order an upper hose). I tried starting it and it won't start. I sprayed carb
cleaner in the intake and it ran on that and died. When I crank, I don't get any oil pressure
and the tach doesn't move. Not sure if I should get a tach reading without running or
not.Do I have two problems going on? Maybe an oil pressure switch and a cam sensor?
The came with the motor, could possibly been tipped over because I did have to replace
the upper coolant hose tube on engine. I have checked atleast 10 times to be sure
evrything is connected. Thanks for your time,I'm LOST!!!
There is no MAF on the 4200 engine. On the 5.3L v8 it is
on the intake air duct.
You probably wont see the tach or oil gauge move while
cranking. You need a scanner for that. You have spark
because it runs, to crank sensor and ignition or good.
Sounds like no fuel pressure or injector pulse. Is the theft
or security light on? Get a fuel pressure gauge on it. If
you have pressure, then you do not have injector pulse
signal.
I have a 2003 Chevy Trailblazer with the check engine light on. I had the codes ran at a
local shop, and was told that the crank shaft sensor needs to be replaced. Where is it
located????? I was also told there is a leak in the cooling system, but I dont know what
that means. Please help!!!
The crank position sensor on the 4.2L is located on the
drivers side of the engine block. Can get to it through the
wheel well or from under the truck. A leak in the cooling
system means you have a antifreeze leak.
02 Bravada 4.2 inline 6. Service Engine Soon (SES) and Reduced Engine Power (REP).
Restart clears REP. Multiple codes, but P1271 is always included. Dealer initially said they
found rodent chewed wires and charged $500 to splice. Problem returned. Dealer then
recommended replacement of the throttle body. After reading forums, I cleaned the
throttle body assy (TBA). Problem returned. I replaced the throttle body with new. Problem
returned. I replaced the Accelerator pedal assy (including the Accelerator Pedal Position
Sensor module) with new. Problem returned. I pulled a wire out of the connector attached
to the TBA. Replaced the 8 pin connector with new (with pigtail). This also replaced the
splices the dealer had done to repair reported rodent chewed wires. Problem still exists.
I'm looking for next steps. I strongly suspect a broken or shorted wire, but would like to
know if there are logical places this is known to occur.
If wires were chewed up and repaired, there may be
more in other places than were first found. You are going
to have to check all the harnesses. No common areas of
broken wires.
Thank you so much for the detailed picture of engine data sensor and control component
locations on the GMC Envoy
4.2 L engine. Already saved a lot of money just looking at
that picture. Good job.
The comment to add a PCV value is incorrect.  The correct hose to add a pcv value, is in
the middle of the intake manifold.  Because I did it that way!
2002 GMC Envoy 4.2 6cyl - I've removed the intake manifold (pain) to get to the injectors
and noticed a sensor on the engine block that's behind the alternator and under the
manifold on the driver's side. Thought maybe I'd replace it since it's stripped down this far,
not sure. Any idea what this 2-wire sensor is? Thanks.
A two wire sensor might be a coolant temperature sensor.
I have a 04 trail blazer why is it shaking nd it turned of i had the ac on an when i got off the
freeway nd stopped at a light thats when it starts shaking nd also turned off please help.
GMC Envoy 4.2 L 6cyl replace the lower thermostat but the lower hose is warm but no hot
hot the upper hose is hot what dose that mean.
Camshaft actuator & the camshaft position sensor was replaced and the oil pressure
gauge still didnt work and the computer throws the same codes still .... why??
OK, so what is the code? What makes you think that a
cam actuator solenoid was going to fix an oil pressure
problem on your truck?
if there is not a coolant sensor what did autozone just sell me?  and where does it go?  it
reads temperature sensor on the box part #  su1485
Who said there is no temperature sensor? if you are referring to the comment
from the last page about...
"There is no coolant below temperature sensor", then that is right.

There is no such thing as a
"COOLANT BELOW TEMPERATURE SENSOR" ! ! !

It is called a "Coolant temperature Sensor' just like you bought !

Why do you people not understand. The words...
"Coolant Below Temperature" is no such thing ! ! !

Now do you get is? The problem is in the words...
"COOLANT BELOW..."
there is no such thing as a  "COOLANT BELOW TEMPERATURE..."

It is called a "COOLANT TEMPERATURE SENSOR".
Note the word BELOW is not there ! !

Just because the free computer scan gave you a code P0128 with a description
of "Coolant Temperature Below Threshold" does not mean there is a sensor
called...
"COOLANT BELOW..."

And the "Coolant Temperature Sensor" is not your problem anyway !

You need a thermostat.

Do you see the pattern here !
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I have a 04 GMC envoy xl with a 4.2l v6 my service engine soon light is on I replaced the
map sensor and the light is still on i disconnected the battery for more than a half hour
then reconnected it started it up the light was off turned the truck off and back on the light
came on again its still reading the code for the map sensor need to get inspected but cant
because of this.
If replacing the sensor did not fix it, then you either have
a wiring problem at the connector or toward the PCM, or
something else causing that code. A vacuum leak or
carbon in the throttle can also cause this.

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4.2L Sensor Locations Comments Page 2