[Elkodelko]

Hello guys I’ve been having this ongoing issues for a while now, I have a 2004 TB LS 4.2 i6. 118k miles I bought it off an auction , since I have changed the fuel filter , spark plugs(good ones) and coil packs (cheap Amazon brand), oil filter , oil change, new alternator, new serpentine belt, etc. After changing the coils and spark plugs a while back it took off the check engine light and was running better but still a misfire on idle. I mainly feel the misfire in idle and very low rpm, but once I step on the gas I don’t feel a misfire. Any ideas to what my problem can be? I sprayed soapy water around the manifold and engine and could not find any leaks so to say. I feel a lot of shaking near the engine and under my feet as a driver .

 

[Ravalli Surfer]

Lots o' things
1. Chinesium coils
2. You missed the boot and spring when you replaced a coil - or two.
3. Bad-urinating injector
4. Low compression in #4 cylinder
5. Flat or going-flat cam lobe in #4 (each cylinder has 4 valves/4 lobes/4 followers/4 stems) --- get the pattern?
6. Say that you didn't check the sparkplug gap --- please --- say if you did!
7. Did you "read" each plug when you removed them?
8. Did you crack a plug?
9. Are the plugs Chinese counterfeit? Many are.

 

[Elkodelko]

Lots o' things
1. Chinesium coils
2. You missed the boot and spring when you replaced a coil - or two.
3. Bad-urinating injector
4. Low compression in #4 cylinder
5. Flat or going-flat cam lobe in #4 (each cylinder has 4 valves/4 lobes/4 followers/4 stems) --- get the pattern?
6. Say that you didn't check the sparkplug gap --- please --- say if you did!
7. Did you "read" each plug when you removed them?
8. Did you crack a plug?
9. Are the plugs Chinese counterfeit? Many are.

I got the coils on Amazon, again maybe not the best, I am considering going to the junkyard and yanking out some Delphi coils from a similar model. Will also open all the coils up and reboot them see if I might have missed a fitment, if it’s cylinder 4 does that mean just focus on that coil fitment or all coils could cause the misfire ? If still problem I will do compression test on cylinder 4. What should psi be? I did not check the spark plug gap, what should that be sir ?

 

[TJBaker]

did not check the spark plug gap, what should that be sir ?

Spark plug gap is NOT adjustable with these iridium plugs.

 

[Elkodelko]

What I’ve noticed lately is that my belt tensioner squeaks only on start up for a bit after I installed a new belt a while back. Some research shows that this could cause a shakiness and possibly the misfire ? I put some fuel injection booster as I filled up my tank for work and it took of the check engine light but still feeling a bit of a misfire.. the check engine light comes on and off every couple of weeks or so. Did order a new tensioner too, will let you guys know once I install it what’s going on

 

[chem_man]

Have you connected a decent code reader/live data scanner to the OBDII system to see what Diagnostic Trouble Codes are present? Please do not say that you had AutoZone/Advance/O'Reilly scan the system and gave you the codes.

Also, if you did not install ACDelco 41-103 spark plugs, then you can expect to see all kinds of driveability problems. Also any ACDelco spark plugs purchased from Amazon or ebay are more than likely counterfeit and not genuine ACDelco spark plugs.

 

[Ravalli Surfer]

WHAT HE (^) SAID.

DO NOT EVER CONSIDER TESTING THE PLUG GAP!!!!!! .... you'll ruin the plugs.

 

[Elkodelko]

I have just ran a simple ob2 scanner I have at home , it’s cheap it just told me p0304 , but I do see the tensioner rattling hopefully that will do.. they are the 141 all 6

 

[chem_man]

141 Spark plugs? Right off the bat I have to say those are not the correct spark plug for the 2001 4.2L inline 6 engine. That could be a major factor in the P0304 DTC.

What brand is the 141 plug anyway?

Regarding the OBDII code reader you have, if you intend on performing your own maintenance, you really need to look into getting a decent (not necessarily expensive) code reader/live data scanner. If you like we can recommend something.

 

[Elkodelko]

141 Spark plugs? Right off the bat I have to say those are not the correct spark plug for the 2001 4.2L inline 6 engine. That could be a major factor in the P0304 DTC.

What brand is the 141 plug anyway?

Regarding the OBDII code reader you have, if you intend on performing your own maintenance, you really need to look into getting a decent (not necessarily expensive) code reader/live data scanner. If you like we can recommend something.

I’m sorry man it was a mistype, they are the ones your are referring to. Yes please recommend some good OBD scanners. I got a read of my o2 sensors for a second , is this normal or too high?

 

[chem_man]

First the O2 Sensor voltages. The upstream O2 sensor produces a voltage that will bounce all over the place as the engine runs. It's normal to see voltages anywhere from around 0.1 to 0.9 Volts. Now the downstream O2 sensor will be more stable and while it might change a bit, it won't change like the upstream O2 sensor. Typical downstream O2 sensor voltages will be in the range of 0.5 to 0.9 volts.

What is more important than O2 Sensor voltages is the Short Term (STFT) and Long Term (LTFT) Fuel Trim values expressed as a %. Negative fuel trim values indicate that the engine is running rich and that fuel is being withheld (hence the negative value). Positive fuel trim values indicate that the engine is running lean and that fuel is being added (hence the positive value). Now comes the really "important" fuel trim value. This is the sum of the STFT and LTFT values.

What you want with the sum of the STFT and LTFT values is a number somewhere in the range of -10% to +10%. As long as the sum of the two fuel trim values is in the +/- 10% range, things with the fuel system are OK.

Now for the recommendation for a decent OBDII code reader/live data scanner. I use an Bluetooth OBDII dongle and the Torque Pro app for Android devices. The Bluetooth OBDII dongle for Android devices costs around $15 from Amazon (here is the link):

Veepeak Mini Bluetooth OBD II Scanner for Android Only, Auto Check Engine Light Code Reader Car Diagnostic Scan Tool

Buy Veepeak Mini Bluetooth OBD II Scanner for Android Only, Auto Check Engine Light Code Reader Car Diagnostic Scan Tool at Amazon. Customer reviews and photos may be available to help you make the right purchase decision!

www.amazon.com

And the Torque Pro app has a one time licensing fee of $5.00. So for under $20 bucks I can read and erase diagnostic codes, monitor various engine sensors, and I can also store the data in an Excel like file for later analysis on a PC. Note, this is all possible once the Torque Pro App has been set up. I can also have different vehicle profiles for different vehicles so that I do not have to add or remove things to be monitored when going from vehicle to vehicle.

If you have an iPhone, the Veepeak Bluetooth dongle for iPhones is a about 5 dollars more:

Amazon.com

Unfortunately, the Torque Pro app is only for Android devices so you'll need to look elsewhere for an equivalent iPhone app.

Good Luck!

 

[Brad_]

Unfortunately, the Torque Pro app is only for Android devices so you'll need to look elsewhere for an equivalent iPhone app.

The best app I've found for IOS so far is "Car Scanner ELM OBD2" by "Stanislav Svistunov".

It has the same basic functionality as torque pro, read/clear codes, view live data, raw sensor readings.

 

[Cmyer]

Hello guys I’ve been having this ongoing issues for a while now, I have a 2004 TB LS 4.2 i6. 118k miles I bought it off an auction , since I have changed the fuel filter , spark plugs(good ones) and coil packs (cheap Amazon brand), oil filter , oil change, new alternator, new serpentine belt, etc. After changing the coils and spark plugs a while back it took off the check engine light and was running better but still a misfire on idle. I mainly feel the misfire in idle and very low rpm, but once I step on the gas I don’t feel a misfire. Any ideas to what my problem can be? I sprayed soapy water around the manifold and engine and could not find any leaks so to say. I feel a lot of shaking near the engine and under my feet as a driver .

Hey so I have a 03 trailblazer and since I bought out two tests shop I’ve had the same issues I’ve dumped those of dollars into it trying to pinpoint what and where it was coming from did numerous things like a tinder on n my pcm and finally one day at work she was running rough I pulled the plug from the 4th cylinder and the top was completely burned off and the plug was purple all the way up the threads and I ended up just getting a new motor

 

[VoyBoy919]

I'm having a hard time wondering why these discussions get so complicated so fast. If it was me, I would keep it simple stupid..(not calling you stupid). I woukd start the vehicle, pull the injector wire off of cylinder 4...and see if it causes the vehicle to run worse or miss worse. If so..the injector is working, if not then it isnt. Next plug the injector wires back in, and unplug the wire harness going to #4 coil...while the engine is running.does it run worse after that or miss worse? If so the coil and plug are probably good..if it doesn't change anything with the wire unplugged than something is wrong with it. Why not try this first? I'm sure somebody will say it will blow out the computer or some kind of nonsense...I do this all the time, why not keep it simple before going onto other more complicated discussions?

 

[Ravalli Surfer]

Are we talking 4.2L engines here? They're a little hard to access the connex and have it together enough to run the engine too.

Perhaps - going to the appropriate computer and pulling individual pins out as you watch for RPM changes ---- but that's kinda hard and destructive too.

Other than that -- I like your idea.

 

[Elkodelko]

I changed the belt tensioner and idler pulley and I believe to have found my culprit. The shaky vibration is gone on idle and drive while I’m stopped. Seems to drive very smooth and sound great now! Probably the best I’ve had this car running yet, I’m excited! Hope this can help someone else out who is possibly troubleshooting

 

[Ravalli Surfer]

I changed the belt tensioner and idler pulley and I believe to have found my culprit. The shaky vibration is gone on idle and drive while I’m stopped. Seems to drive very smooth and sound great now! Probably the best I’ve had this car running yet, I’m excited! Hope this can help someone else out who is possibly troubleshooting

Which part made it go away?

That'd be the most help.

 

[Elkodelko]

Which part made it go away?

That'd be the most help.

Both, the idler puller was making a sound that I can’t describe, it made the gas pedal sound a little whiny when stepped on. And the tensioner fixed the shakiness , belt is more tight and sturdy

 

[Ravalli Surfer]

Hmmmmmmmm ....... ya got my attention here about the "shakiness" you reported .......

I'm a-thinkin' that there may be a motor mount job in your near future.

It marvels me to think you can detect a bad tensioner by saying there was a shake in the engine that fooled you into thinking it might be a miss.

Motor mounts - in good repair and in serviceable condition keep this engine from being felt any at all!

What I'm saying is that you may have bad or worn out motor mounts (think $$$$$$$ of 3^).


.

 

[chem_man]

And if you have to replace one or more motor mounts, be sure to only use GM Genuine motor mounts. Aftermarket motor mounts are junk compared to the OEM mounts.