Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

21 - 33 of 33 Posts

·
Registered
Joined
·
1,105 Posts
Hmmmmm .... I'm not too sure, but I feel an engine with VVT is going to show low vacuum at idle.

You should get the engine to idle, up to somewhat normal temps and just spray a carb-cleaner into the suspect areas. This is an olde school style (can you say: "Boomer"?) carburetor test to find vacuum leaks or bad gaskets.

HTH ... jpv
 

·
Registered
2006 chevy trailblazer LT EXT
Joined
·
21 Posts
Discussion Starter #22
yes sir i did do the carb cleaner test . and only got it to rough idle a couple times and could not narrow down the area. so i thought i would just replace the gasket and inspect manifold when its removed . its starting to get a little warmer here so hopefully can replace the downstream o2 sensor. thanx for all the help
 

·
Registered
Joined
·
1,105 Posts
Me? I'd test a whole lot more before I would start tearing things apart.

Do you have a bi-directional scanner to check fuel trim?
Can you beg, borrow, rent or steal a smoke generator?
Do you have a set of electronic ears? (STEELMAN is a good set)
Do you have a propane enrichment set?
Teardown sux if you find you're actually chasing Zebras and you should be looking for horses instead.
 

·
Registered
2004 chevy trailblazer_lt
Joined
·
874 Posts
Rusty ground connections can cause all kinds of havoc! Can't say specifically if or how impactful they would be in your situation, but they certainly can be a factor.

FYI, I had a no crank condition on my riding lawnmower a couple of summers ago. Knew it was electrical. Checked every single electrical connection in the circuit between the ignition switch and the starter and they all appeared to be fine (or at least within a few tenths of an ohm from 0 ohms. However, when I looked at the resistance of the entire circuit, boy was I ever surprised and embarrassed with the total resistance of the circuit. I wound up replacing every switch and crimp connector in the circuit (about 8 if I recall correctly) and bingo, the mower lived once again.

I guess the moral here is every part in the circuit counts individually and collectively, so don't just look at them individually, look at them as a whole too. While a part might be weak or borderline, the electrical connection to it is just as important to the entire circuit if the circuit is to function properly.
 

·
Registered
2006 chevy trailblazer LT EXT
Joined
·
21 Posts
Discussion Starter #28
and yes sir i do have a good multi meter now so when the snow melts enough i will check the wiring for the ds o2 sensor thnx gents
 

·
Registered
2004 chevy trailblazer_lt
Joined
·
874 Posts
Sounds good!
 

·
Registered
2006 chevy trailblazer LT EXT
Joined
·
21 Posts
Discussion Starter #30
You k ow I thought that the map. Maf and o2 sensors put out a 5 volt signal plz tell me I'm wrong. And if icant get a resistance reading then what? Sorry off of the wiring harness plug ins . 1 sec going to computer
 

·
Registered
2006 chevy trailblazer LT EXT
Joined
·
21 Posts
Discussion Starter #31
also did check the intake manifold bolts and the last 5 from middle of engine to fire wall where all loose.
so i tightened them but of course frickin snow storm so yea couldnt check the vacuum again.
 

·
Registered
Joined
·
1,105 Posts
They don't "put out" a signal ... well .... not like you think.

I'm sure if I step on my tail here that I'll be corrected ... so here I go ......

Three wires typically .... and this is SOME sensors but not all ...... because some are 1-wire, 2-wire, 3-wire, 4-wire and even 5-wire .......... but you are interested in the 3-wire units ... I think........
1] A ground, ultimately back at the battery.​
2] 5.0V pure DC closely regulated voltage from the computer​
3] 0.0V to 5.0V as modified by sensor, returned to computer for interpretation.​

"Self Generating" sensors like the O2 units, create voltage according to free oxygen and it doesn't actually need a 5.0V reference signal. Modern O2 sensors will use 12VDC to help heat the sensor to get it on-line faster (quick start).

There are O2 units that generate 0.0 to 5.0 VDC, others that generate 0.0 to almost 12.0 VDC ... the latter not used much in modern vehicles AFAIK ... I might be wrong here.

  • Some piezoelectric sensors create voltage and some get "floored" by the 5.0V to raise it's operating at a voltage above 5.0 VDC where it can be more accurate over a larger swept voltage.
  • Some detect signals from Infrared or Hall Effect pulses, wherein the IR sensor needs the 5.0V to power up the IR diode AND send the counts to the ECM.
  • Some purely resistive sensors (ie: a radio volume knob) use the 5.0 VDC and present a swept resistance via a potienometer to indicate position or attitude.
  • There are also negative- (-) or positive- (+) biased thermistors that detect specialized conditions.
  • Another sensor that the cooling system uses is an ionic detection non-consummable anode to detect low coolant conditions in the radiator.
  • Some sensors create a pulsating digital voltage for computer analysis by gating the 5.0VDC from the ECM .and sendingit back to the ECM.
There're lots of variations.
 

·
Registered
Joined
·
1,105 Posts
PS .....

IIRC .... the MAP-IAT-MAF Combo sensor on my Isuzu has 7- or 8-wires.
This is exceptional and not an industry wide kinda typical.
Isuzu doesn't do ANYthing typically.

You ought to see where the fuses go in a circuit; I think they believe electricity is a wicked spirit and they try to confuse it as punishment.
 
21 - 33 of 33 Posts
Top