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Crazy mis-fire under light/heavy load.

wrd1972

Full Member
Joined
Jul 19, 2013
Messages
94
Ive got a 07 Avalanche LTZ with a stock 5.3L Vortec.

The engine has an extremely noticeable mis-fire when under light/heavy load. If you just drive up a steep hill at low speed. The vehicle kicks enough that you can clearly feel it. The engine seems to idle smooth and there are no dash lights or codes being thrown.

Delco plugs were installed just under a year ago but they have not been removed for inspection. Wires were replaced, problem remains. Wires appear to be properly connected.

I just dont understand how a code can not be thrown for this. This is really making me nuts. All help appreciated.
Thanks
Bill
 
You should have the truck scanned for pending codes.

If I understand it correctly, a misfire code will be set once a misfire has occurred a certain number of times in a certain time frame.

If you are just under the threshold, you may possibly have a pending code for a misfire without actually seeing a check engine light.

I chased some pretty bad misfires in my wife's 2006 CTS for a while that never set a code and those ended up being several of the coils going bad.

The only time we got a solid CEL was when one of the intake valves developed a burned out hole in it and that cylinder completely stopped firing.

You may have something as easy as an oil-fouled spark plug, possibly in cylinder #7, which seems to be a common problem with the 2007 engines.

There are lots of discussions on this forum talking about engine problems with some of the 2007-2008 engines with the Active Fuel Management systems.

Most parts store should be able to read those codes for you for free.

I would start there.
 
You can get misfire codes without the SES light coming on.  It only comes on after it sees a set amount within a period of time.
 
Okay I took it to a shop and they scanned it and said it had codes...random misfires on all cylinders. They did not tell me the code number. They then stated it could maybe be an intake gasket leak or bad O2s. Is this plausible?
 
Certainly a possibility.

Demand the codes.

You own them.

Silly shop.

:beating:
 
I wouldn't expect an intake gasket but O2 sensors are a possibility, along with the MAF sensor.
 
IF there is a misfire then there is a CODE.
Maybe your OBD port is lacking power?..


Or maybe this is something MECHANICAL like tranny or rear end or very bad u-joint
 
Okay guys. I have the actual codes to help with the diagnosis.
BTW, none of these are throwing a SES light on the dashboard.
    P0113 IAT sensor circuit high input
    P0300 Random multiple misfire
    C0561 System disable information stored.
    U0073 Control module bus.

So if I understand correctly, the IAT is built into the MAF. I cleaned the MAF with spray a week or two ago and the misfire was very much reduced, if not gone. Then it returned a week later. So can a MAF with a fulty IAT but not faulty enogh to throw a SES light, be the real problem here?

Regarding C0561 and U0073. Could this be releated to using my ELM327 Bluetooth dongle to pull the OBD codes, using my cell phone? Irronically, the ELM 327 has not been able to pull the codes for some time. Plus on occasion if I leave it connected. The disabled traction control  and dinger will go crazy. But whey wont it pull the codes any longer?

Thanks for the assistance guys.
 
I can't help you with the C and U codes but it does sound like your misfire is related to the MAF/IAT sensor.

You may want to try driving it with the MAF unplugged.  This will force it into full-time speed density airflow calculations based upon intake vacuum and rpm.  Should run well, although obviously not as well as with a properly functioning MAF.  On the 2nd or 3rd, I forget which, engine start in which you have the MAF unplugged it should light the SES light and obviously you will be getting a MAF failure code as well.  But, if your misfire is gone, then I'd say try replacing the MAF, assuming the wiring and connector looks good.
 
C0561 = ABS system disabled
 
The first thing I would normally suggest is intake gasket leaking but I believe GM fixed that issue before 2007...

Check your main intake pipe. Make sure the connectors are solid and that you don't have any holes in any portions.

I assume you are not running a CAI? An improperly installed CAI or oil on your MAF sensor could cause issues leading to these codes.

Rodney
 
Update.
This crazy condition is definitely not a misfire or even engine releated.

This condition happens when the 4x4 knob is in auto only. When in auto, you will feel some tugs and jerks that feels like a sever misfire when lightly accelerating. But its not a misfire or even engine related. I have even noticed in some cases when in auto, that if you make a tight turn, you will feels some resistance and scuffing like one would normally feel in 4-low. Like something is engaging when it should not.

Switch the knob to 2WD, smooth as silk and the condition is completely gone. Everything works fine.

Any other ideas?
 
Check transfer case for loss of fluid... These cases are prone to wear through...

Also, how are your tires? If you have slightly different sized tires and you are in any sort of 4wd it can cause issues. Even if the tires are same brand/model but one or more tires are significantly more worn than others.

Also if you have an ELM dongle plugged in and it doesn't work right... Unplug it.. Can cause issues on databus.  Try running around without it too.

I have similar issue with an ELM bluetooth dongle I bought for like $20. Stopped working about a month later. Junk.

Can also check fuel pressure but the auto mode makes it sound like you have issues either in the TC or the front differential.

Rodney
 
redheadedrod said:
Check transfer case for loss of fluid... These cases are prone to wear through...

Also, how are your tires? If you have slightly different sized tires and you are in any sort of 4wd it can cause issues. Even if the tires are same brand/model but one or more tires are significantly more worn than others.

Also if you have an ELM dongle plugged in and it doesn't work right... Unplug it.. Can cause issues on databus.  Try running around without it too.

I have similar issue with an ELM bluetooth dongle I bought for like $20. Stopped working about a month later. Junk.

Can also check fuel pressure but the auto mode makes it sound like you have issues either in the TC or the front differential.

Rodney

On the transfer case wearing through.........

So far, I haven't come across complaints from NNBS (GMT-900) owners.  Maybe it's just a coincidence.
 
Thanks Rodney.

Tires are brand new Michelin and have been on for about t year. Pressures are the same so I don't think that is the case. Agree with you on the ELM327 dongle. I have seen it do some really crazy $hit but this particular issue appears to be unrelated. I now leave it unplugged like you do.

Will have to check TC fluid. Whatever it is, it feels like it is electronic related somehow. Could be wrong...like something is being tricked into engaging or disengaging the front wheel drive. Again I have noticed that with it in Auto, if I made a super tight turn, there was that typical 4X4 drivieline resistance which clearly it should not do unless in actual 4WD setting.
 
wrd1972 said:
Update.
This crazy condition is definitely not a misfire or even engine releated.

This condition happens when the 4x4 knob is in auto only. When in auto, you will feel some tugs and jerks that feels like a sever misfire when lightly accelerating. But its not a misfire or even engine related. I have even noticed in some cases when in auto, that if you make a tight turn, you will feels some resistance and scuffing like one would normally feel in 4-low. Like something is engaging when it should not.

Switch the knob to 2WD, smooth as silk and the condition is completely gone. Everything works fine.

Any other ideas?

Re-set your codes, then stay in 2-wheel drive for a couple of weeks.  If CEL light comes on, have codes read by a third party, such as an auto parts store.

This will take the 4-wheel drive & your personal code reader out of the equation.  Almost anything can cause a misfire.  Hard telling how long the code was there.

 
Anyone think the front axle disconnect could be causing this? This jerking in auto mode only does have a feel of connecting/disconnecting issue. And again, I sometime have big 4x4 drive train resistance when making very sharp slow turns with it in auto. I would expect that in 4WD.
 
wrd1972 said:
Anyone think the front axle disconnect could be causing this? This jerking in auto mode only does have a feel of connecting/disconnecting issue. And again, I sometime have big 4x4 drive train resistance when making very sharp slow turns with it in auto. I would expect that in 4WD.

4-wheel drive is partially engaged, when in "Auto 4-wheel."

The sensation of resistance when turning in this mode, is not your imagination.

Would like to say the front actuator is the source of your problems, but remaining in "Auto" 24/7 is hard on everything.

Not enough is known about the history of the vehicle.
 
wrd1972 said:
Ive got a 07 Avalanche LTZ with a stock 5.3L Vortec.

The engine has an extremely noticeable mis-fire when under light/heavy load. If you just drive up a steep hill at low speed. The vehicle kicks enough that you can clearly feel it. The engine seems to idle smooth and there are no dash lights or codes being thrown.

Delco plugs were installed just under a year ago but they have not been removed for inspection. Wires were replaced, problem remains. Wires appear to be properly connected.

I just dont understand how a code can not be thrown for this. This is really making me nuts. All help appreciated.
Thanks
Bill

I've had brand new wires arc right out of the box. I'm not even kidding....true story.
Also see if any of the plugs have carbon tracks on the insulators.

CarMech1969
 
Nick@Night said:
4-wheel drive is partially engaged, when in "Auto 4-wheel."

The sensation of resistance when turning in this mode, is not your imagination.

Would like to say the front actuator is the source of your problems, but remaining in "Auto" 24/7 is hard on everything.

Not enough is known about the history of the vehicle.

Thanks for the response.

So in short:
2WD = no jerking or bucking
Auto = Jerking and bucking all the time
4WD L/H = no jerking or bucking

So its pretty obvious it has something to do with engagement/disengagement of the front diff. Are there any other components such as sensors that are used to engage the front diff or determine when it should be engaged?? How is slippage detected...at the wheels? I definitely have my eye on that front diff actuator but wont have time to mess around with it likely for a few weeks.
 
wrd1972 said:
Thanks for the response.

So in short:
2WD = no jerking or bucking
Auto = Jerking and bucking all the time
4WD L/H = no jerking or bucking

So its pretty obvious it has something to do with engagement/disengagement of the front diff. Are there any other components such as sensors that are used to engage the front diff or determine when it should be engaged?? How is slippage detected...at the wheels? I definitely have my eye on that front diff actuator but wont have time to mess around with it likely for a few weeks.


On dry pavement, (while turning,) I would expect the traditional jerking & bucking in Low/Hi 4-wheel drive.  That's because the drive shafts are locked & spinning @ the same RPM, though the front & rear wheels require different rotational speeds.

On dry pavement, (while turning,) I would expect a small amount of jerking & bucking in Auto 4-wheel drive.  The front differential & CV's are fully locked, but limited to about 5% engagement in the transfer case until slippage is sensed.  The same axle bind (driveline windup) is present, but to a much smaller degree.

I would expect to sense zero axle binding in 2-wheel drive.

That's the limit of my knowledge.  Would have to drive vehicle to know or sense, more.

Also, if front differential is engaging 100%, probably wouldn't suspect the front actuator.    

Perhaps someone else can chime in.  Have been known to chase my tail, (be wrong,) from time to time.

 
Thanks Nick,
I am gonna take a look at the transfer case in the spring once it warms up. Might be as simply as a bad connection on a sensor or something minor. Iam totally convinced its not anything engine related and likely not the engagement servo on the front end.
 
I do not know the difference in 1st and 2nd gen 4x4 workings.
I travel with mine in auto whenever I want the extra insurance.
Yes I can tell when it is in auto, noise. But I have never felt the catching of the front tires like it is 4 wheel. When driving low speeds when the 4wheel is not needed. I can feel it kick in when the rear slips. Especially if I have a heavy foot on acceleration and corners. 
  How would you isolate between the axle actuator and the T-Case encoder.
So which controls the lock up when 4wheel is needed.
Just trying to think this through. In auto, t-case engaged, front drive shaft and front diff engaged, slippage message sent to axle actuator lock axles for 4wheel. So if the actuator is not releasing the front axle you?re in 4wheel high at all times. 



 
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