pop goes the weasel

[blktbon20s]

Well before i left on vacation driving home i heard a "pop" coming from the engine bay, my frist taught was that it was just a back fire or something. Now today i was waiting for my class in the truck and i heard the same pop. It was pretty loud, i mean not loud loud but very noticeable. I couldn't tell if the rpms droped b/c i was reading a book.

Also on that note, whats the the rpm suppose to be at while at idle?
I have i feeling mine is kinda high, i'm idling at about 1000-1200 RPMS. My other truck (Ford Explorer) Idles at 550-600 rpms

Thanks in advance

[ieatglue]

That's too high, it should idle at about 650rpm i think :undecided ry cleaning the throttle body, that should help some :undecided

[Jozuah]

i had idle issues, would idle at 1K - ~1200 and then drop down after awhile, i changed both upstream and downstream:hissy: o2 sensors and the problem went away. cleaning your TB would help also im sure.
Josh

[PROSPHOTO]

I'm guessing you don't have a check engine light on...start with the TB cleaning.

If the problem persists, you'll need to monitor the operating parameters ith a scan tool and look for anything out of range...let me know how you make out with the TB cleaning and we'll take it from there :yes:

[blktbon20s]

i cleaned tb not to long ago, probably like 800 miles ago( i do ~ 100 a week)
But my main concern is that pop that i heard twice, is it possible that it was just some unburned gas on the exhaust near the headers and it ignited?
Again, the higg rpms at idle does concern me but my biggest concern is that sound i heard.
Any help will be appreciated:yes:
Mike..no my check engine light is not on.
Jozuah..are the o2 sensor expensive? I might try replacing them. My rpms stay steady

[MisterP]

My suggestion - don't just go throwing parts at it in attempt to fix the problem. :nono: Idle settings on V8s is about 600-ish hot w/ A/C on, I don't know what the idle setting is on the I6 and it might be up to a hundred RPM higher but certainly not 1000-1200 RPM, there's something wrong with the basic air/fuel management.

One cheap/easy trick you can start with is verify there isn't a vacuum leak between the air cleaner and the intake, spray starting fluid where the intake tube meets both the MAF & throttle body & etc - if there is a leak the starting fluid will get sucked into the air stream and you will momentarily hear the engine idle change.

Mr. P.

[blktbon20s]

My suggestion - don't just go throwing parts at it in attempt to fix the problem. :nono: Idle settings on V8s is about 600-ish hot w/ A/C on, I don't know what the idle setting is on the I6 and it might be up to a hundred RPM higher but certainly not 1000-1200 RPM, there's something wrong with the basic air/fuel management.

One cheap/easy trick you can start with is verify there isn't a vacuum leak between the air cleaner and the intake, spray starting fluid where the intake tube meets both the MAF & throttle body & etc - if there is a leak the starting fluid will get sucked into the air stream and you will momentarily hear the engine idle change.

Mr. P.
Why do u say not to change parts that don't need to be changed?:confused:
:undecided vacuum leak huh
that is a big possiblity since i'm missing one vacuum line that goes from the engine to the intake. I stuck a regular piece of hose temp. until i get the right one, but i know its leaking.

[the roadie]

I6 idle is set at 620, when the coolant is up to temp. It's higher while it warms up. I could post the PCM control table if it's interesting to anybody. Could be the PCM isn't getting a proper reading of coolant temp? Definitely a job for somebody with EFILive and a laptop or a GM full Scan tool.

[blktbon20s]

I6 idle is set at 620, when the coolant is up to temp. It's higher while it warms up. I could post the PCM control table if it's interesting to anybody. Could be the PCM isn't getting a proper reading of coolant temp? Definitely a job for somebody with EFILive and a laptop or a GM full Scan tool.
If you can please post it.
I'm going to see if i can do the Case relearn for my PCM asap to see if thats it.
I really don't remember if it use to idle that high b4 the tune.:confused:

[PROSPHOTO]

Did you check all of your vacuum lines yet?

The symptoms that you are experiencing are not the result of not getting the crankshaft relearn yet :no:

You should not ever hear a backfire from these engines while you're idleing (or any time) :nono:

Unfortunately, there are a lot of variables that could cause your concerns; so this may take a while :worried:

[blktbon20s]

Did you check all of your vacuum lines yet?

The symptoms that you are experiencing are not the result of not getting the crankshaft relearn yet :no:

You should not ever hear a backfire from these engines while you're idleing (or any time) :nono:

Unfortunately, there are a lot of variables that could cause your concerns; so this may take a while :worried:
No i haven't check all of them. But to tell you the truth i don't know how to check them. Sorry to sound so neive but do i just make sure they are all connected? Or do i need to get a vacuum gauge and check it with that?

Also, remember i have a straight pipe (i do have a cat. now) and when driving if right before shifting into 2nd i let go of the gas it backfires pretty loud:D
I just hope this isn't a big issue. I have plans of selling it to get a newer one, but not now:no: :ugh:

[PROSPHOTO]

Follow MisterP's procedure, but I wouldn't use starter fluid...use intake/throttle body cleaner. Spray around the intake area with the vehicle running. When the spray gets sucked into the intake, you'll hear the idle change. If there is a vacuum leak, you're check engine light will come on in the future :yes: Visually inspect the engine compartment first for any hoses that aren't connected to anything

If you have a good cat in the vehicle, the exhaust shouldn't be an issue; you may hear the popping noise from the exhaust, but not from the intake.

[ylab]

Spray-Nine also works well in detecting leaks and will provide a static arc if you have a bad wire/coil that's shorting. (When they short/crack, the current still needs to go somewhere and will discharge into the air if you ionize it with the Spray-Nine). - My brother showed me one time on a friends car the light show due to a bad set of wires & coil.

[rbarrios]

were also assuming he has a working SES light.
Before you start the vehicle- put the key in and turn the key- look at all the dash lights that light up- make sure the SES light turns on momentarily and then goes off... at least well know if your bulb is ok...
throwing parts at is may get expensive...
I mean if you were to simply throw a set of O2 sensors to SEE if it fixes it... well I think each O2 sensor goes for what maybe $100 each?
theyre not cheap....

[blktbon20s]

were also assuming he has a working SES light.
Before you start the vehicle- put the key in and turn the key- look at all the dash lights that light up- make sure the SES light turns on momentarily and then goes off... at least well know if your bulb is ok...
throwing parts at is may get expensive...
I mean if you were to simply throw a set of O2 sensors to SEE if it fixes it... well I think each O2 sensor goes for what maybe $100 each?
theyre not cheap....
yes it is working(the SES light)

Oh wow, didn't know they were that expensive. I have never had to replace one so didn't know

[ScarabEpic22]

I6 idle is set at 620, when the coolant is up to temp. It's higher while it warms up. I could post the PCM control table if it's interesting to anybody. Could be the PCM isn't getting a proper reading of coolant temp? Definitely a job for somebody with EFILive and a laptop or a GM full Scan tool.

Interesting, my stock 02 and all the I6 tunes Ive looked at have the idle set at 612.5 RPM when warm...:rolleyes:

And my 02 idles right at that but I do notice a slight burp or pop right after I start up my TB, doesnt matter if its hot or cold.

[the roadie]

Interesting, my stock 02 and all the I6 tunes Ive looked at have the idle set at 612.5 RPM when warm...:rolleyes:The normal table says 612.5, yes. But my stock unmodified PCM and the PCM4Less Alvin tune table B0801 has an additional offset of 100 RPM that tapers off to 12.5 RPM after 16 seconds when warmed up, and I thought the two added together to give 625RPM as the desired steady state warmed-up idle. So I should have typed 625. Do you agree about B0801 offset?

Oh, I think I see what happened.

The stock 2003 Envoy tune included with EFIlive as a demo tapers off to 0 RPM offset, not 12.5, so I have no idea why GM changed in 2004. As a 2002, you have the zero offset when hot. Hmmmmmm.

PS: I like your "paint color". Get that idea from somebody?:D

[Str8blazin]

My car backfires or burps out the exhaust when it shifts from 1-2 when the engine is cold. Is that a bad thing? Does anyone else have the same noise? It almost sounds like it louds up when it shifts. By the way, someone earlier in this thread made the statement "if you have a good converter on there", is there a chance I could have bought a bad catalytic converter? I just had it replaced due to the original one being melted or stopped up. I bought it off ebay and the light went out for maybe a week and then came right back on with a code p420 catalytic not effecient or too low or something like that. Thanks for any help

[Blazernut]

My car backfires or burps out the exhaust when it shifts from 1-2 when the engine is cold. Is that a bad thing? Does anyone else have the same noise? It almost sounds like it louds up when it shifts. By the way, someone earlier in this thread made the statement "if you have a good converter on there", is there a chance I could have bought a bad catalytic converter? I just had it replaced due to the original one being melted or stopped up. I bought it off ebay and the light went out for maybe a week and then came right back on with a code p420 catalytic not effecient or too low or something like that. Thanks for any help

That makes a lot of sense if your post cat 02 sensor is picking up stuff. That cat may be really substandard as to GM spec.

[PROSPHOTO]

That makes a lot of sense if your post cat 02 sensor is picking up stuff. That cat may be really substandard as to GM spec.

:iagree: There are a lot of aftermarket cats out there that don't meet the criteria of the OEM 3-way catalyst :no:
You would need to watch the HO2S 1 & 2 signals on a scanner to determine if the HO2S 2 (post cat) is properly working. Also, visually inspect the post cat HO2S for physical damage or any of the wiring damaged/contacting the exhaust (short to ground)

Your original cat melting would have been due to a rich misfire condition some point in the past...Something you should check out.



...:hijacked

[Jozuah]

back to the POP....
could this be the AIR valve closing, mine goes TTTHHHUUMMPP after the AIR motor stops running, guess this "sounds" like a pop.
the idle is still too high. there is a picture of the vacuum hoses on your airbox that houses your air filter when stock. read that and follow it with all your vacuum lines to be sure you dont have a leak, even though the LL8 idle management should be able to compensate for a vacuum leak and if there were a vacuum leak a lean code would set IMO.

josh