04 Bravada random misfire keeps coming back

gladesteen

Original poster
Member
Aug 19, 2014
83
Hi all,


For the past 2 years, I've been chasing an issue that I cant figure out.
I am getting a misfire after the engine is fully hot. Usually after driving for 30 mins or more.
This causes fuel to get dumped into the Cat, and I've had two Cat's replaced in 3 years.
It misfires the worst with cruise control on and going up a slight uphill. REALLY bad stumbles there. Most of the time it does not throw a code, but when it does it rarely identifies which cylinder misfired. Usually its the "random" misfire code.


I have done all the regular stuff. Cleaned the throttle body numerous times.
Changed the plugs (iridiums) at least 3x, changed the ignition coils 3x. Changed the VVT.
One thing I have noticed is the plug tips are burnt almost completely off on some cylinders.
I dont know if this happens because of the misfire or if something is causing them to burn up quickly.


After I change the plugs and coils, the misfire will go away for a few months and even longer. Then it comes back.
Any ideas ?? Its a 2004 Bravada with 200k miles
Mark
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Have an OBD2 adapter or a scanner that will read live data? Monitor/record each cylinder misfire count to see if it is always the same cylinders affected?

Screenshot_20190314-170316.png
 

gladesteen

Original poster
Member
Aug 19, 2014
83
I do have that. And have done the live monitoring via the Torque app and OBDlink. The issue is that it jumps from cylinder to cylinder when it starts stumbling. That's usually why it ends up throwing that "random" misfire code.

I cant figure it out. New plugs and Ignition Coils always solves the issue, but then it eventually comes back again several months down the road. Like i've mentioned the only thing I noticed is the plug tip is nearly burnt off on a few of them.

In the past 3 years or so, i've changed plugs and coils every year. And what really sucks, the Cat twice. Thats expensive. I've got to figure this crap out or just sell it.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
One thing I have noticed is the plug tips are burnt almost completely off on some cylinders.
Which plugs are you using and where are you getting them? These engines like only ACDelco 41-103 iridium plugs. Even if they say ACDelco, they could be fakes, which would explain why it would initially fix the issue and eventually comes back as the fake plugs wear quickly.

Counterfeit ACDelco Plugs
 
  • Like
Reactions: gladesteen

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
Some other things to consider...

(1) Obtain a Can of Spray Starting Fluid and with an ABC Fire Extinguisher close at hand, while the Motor is Idling ...lightly... Spray around the Driver's Side Intake Manifold Flange and observe whether or not the Engine RPM rises. If it happens to do so, check each of the (10) Staggered, Trapped IM Flange Fasteners for being snugged back down to NO MORE THAN (89) Inch Pounds of Force. If you freelance with over-tightening these small bolts, they WILL Snap Off.

If the Random Misfires subside... Well Okay. If NOT ...the jobs gets much more complicated for performing an R&R of the IM and also the Valve Cover and replacing all of the Old, Flattened "O" Ring Style Gaskets including the Plastic one in between the IM and the Throttle Body. Don't try to do this work if you are inexperienced with Mechanical Repairs... THIS Link will show what is involved:


(2) In this Video, Paul "Scanner" Danner shows how to perform Engine Misfire Diagnostics while examining the EFI Fuel Pressure Performance on a 2005 Trailblazer with a 4.2L Engine. He also checks into issues with the MAP Sensor secondary to a Persistent P0306 Misfire Code on Cylinder #6. Paul discovers that someone had previously worked on the EFI Harness prior to his inspection and eventually, he locates a Short in the EFI #6 Harness Wire. Such Electrical Shorts can also be caused by Rodents (Deer Mice) Chewing on the Engine Wiring. If necessary, You can also do this level of examination for Powers & Grounds using a DMM (Digital Multi Meter).


(3) Please note that since you've had to replace the expensive Catalytic Converter more than once... getting a decent Scan Tool capable of Bi-Directional Control and GM Component Testing ("GYMKO" Tech 2) or using a similar, High End Scanner could help in pin-pointing these issues before they create even more expensive problems. Money Well Spent.
 
Last edited:
  • Like
Reactions: gladesteen

gladesteen

Original poster
Member
Aug 19, 2014
83
Holy CRAP Moose ! I ordered the exact iridiums from Amazon !!!

I wonder if these damn things have been what's causing me fits this whole time !?!?

Going to Autozone or similar and getting 6 new ones.

T H A N K Y O U !!
 
  • Like
Reactions: Mooseman

gladesteen

Original poster
Member
Aug 19, 2014
83
Some other things to consider...

(1) Obtain a Can of Spray Starting Fluid and with an ABC Fire Extinguisher close at hand, while the Motor is Idling ...lightly... Spray around the Driver's Side Intake Manifold Flange and observe whether or not the Engine RPM rises. If it happens to do so, check each of the (10) Staggered, Trapped IM Flange Fasteners for being snugged back down to NO MORE THAN (89) Inch Pounds of Force. If you freelance with over-tightening these small bolts, they WILL Snap Off.

If the Random Misfires subside... Well Okay. If NOT ...the jobs gets much more complicated for performing an R&R of the IM and also the Valve Cover and replacing all of the Old, Flattened "O" Ring Style Gaskets including the Plastic one in between the IM and the Throttle Body. Don't try to do this work if you are inexperienced with Mechanical Repairs... THIS Link will show what is involved:


(2) In this Video, Paul "Scanner" Danner shows how to perform Engine Misfire Diagnostics while examining the Fuel Pressure Performance of the EFIs on a 2005 Trailblazer with a 4.2L Engine. He also checks into issues with the MAF) (a Mass Air Flow Sensor may NOT be involved with your engine) and for Shorts in the Engine Harness while looking for other possible culprits that can cause Random Misfires:


(3) Please note that since you've had to replace the expensive Catalytic Converter more than once... getting a decent Scan Tool capable of Bi-Directional Control and GM Component Testing ("GYMKO" Tech 2) or using a similar, High End Scanner could help in pin-pointing these issues before they create even more expensive problems. Money Well Spent.
Thank you MRRSM, I will try the starter fluid trick, but Moose just sent me the "fake" Iridium from Amazon link. And indeed those are the exact ones ive been using 3x over the past 3 yrs. I wonder, and hope, this is the issue. It seems logical as the tips were frying within 1 year.
 
  • Like
Reactions: mrrsm

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Like the old saying goes, if the price is too good to be true....
 
  • Like
Reactions: gladesteen

gladesteen

Original poster
Member
Aug 19, 2014
83
Like the old saying goes, if the price is too good to be true....
Owe you a beer Moose if this solves this (sounds legit).

THANK YOU !!! And Merry Christmas to you and yours. I will post results. Picking up 'legit' $8.99 41-103 "REAL" iridiums either tomorrow or Wed.....i get 10% off for Military, so that will help !
 
  • Like
Reactions: Mooseman

Reprise

Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
One more thing...
When the plugs fry... is it always in the same cylinders?

If not (it's random locations, instead), that gives even more credence to the 'counterfeit plug' theory.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
One more thing...
When the plugs fry... is it always in the same cylinders?

If not (it's random locations, instead), that gives even more credence to the 'counterfeit plug' theory.

That is the direction I was going with the misfire monitoring. Truly random or some pattern to it.
 
  • Like
Reactions: Reprise

gladesteen

Original poster
Member
Aug 19, 2014
83
One more thing...
When the plugs fry... is it always in the same cylinders?

If not (it's random locations, instead), that gives even more credence to the 'counterfeit plug' theory.
It was random. I am picking up the new plugs this afternoon and will tackle this either tomorrow or thursday. Will take a few pics to show the new/old plugs differences.
 

gladesteen

Original poster
Member
Aug 19, 2014
83
Picked up the new plugs and installed today. Also cleaned the TB. It was not even that dirty. The old plugs had no tip damage this time. She idles better and smoother throttle (probably the TB), but the cruise control stumble is still there. I also tried the starter fluid trick. Nothing happened.
Before it stumbles it feels and sounds like the engine is starving of air.....almost groaning. Its weird because I can almost sense when its going to start. It always does it on Cruise Control about 40 to 50 mph slight uphill. I hope im not in for another Cat replacement. That would suck. At this point I'm going to run without cat or some hi flow system.

So i'm back to chasing Coils again I guess.

I dont really like the Torque app for monitoring. Is there another real time cylinder APP anyone can recommend?
 
  • Like
Reactions: mrrsm

budwich

Member
Jun 16, 2013
2,027
kanata
have you checked your fuel trims just to get an idea of what the PCM thinks it wants to "prime" your cylinders with? I would suspect that they are probably running rich.
 
  • Like
Reactions: Mooseman

gladesteen

Original poster
Member
Aug 19, 2014
83
have you checked your fuel trims just to get an idea of what the PCM thinks it wants to "prime" your cylinders with? I would suspect that they are probably running rich.
Is that through OBD2 port monitoring via an App ?

I have the OBDlink App and a special OBD2 port connector for my 2020 M550. It allows me to code different things into the car. Pretty neat. I will try it on the Bravada and see what options are available.
 
Last edited:

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
I dont really like the Torque app for monitoring. Is there another real time cylinder APP anyone can recommend?


Car Scanner has a nice facility for recording and graphing data. Saves everything you monitor so you can review it later. Just like Torque Pro you need to load PIDs for your vehicle. I have a file around for that somewhere.
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
When you are using Cruise Control and approaching that 45-50 MPH "Shudder Speed" on a slight Highway Incline... Does it feel like the Transmission is trying to shift into-out of Gear; perhaps involving the 3-4 Shift Solenoid? How is the Xnsm Fluid Color and Fluid Level on the Dipstick when the SUV is Idling in Park?
 

gladesteen

Original poster
Member
Aug 19, 2014
83
When you are using Cruise Control and approaching that 45-50 MPH "Shudder Speed" on a slight Highway Incline... Does it feel like the Transmission is trying to shift into-out of Gear; perhaps involving the 3-4 Shift Solenoid? How is the Xnsm Fluid Color and Fluid Level on the Dipstick when the SUV is Idling in Park?
MRRSM, it does Exactly feel like that, but i ruled out transmission issues because there were times where I swapped out the plugs/coils and the shudder/stumble went away. Also, and maybe im not right here, but would the trans not shifting from 3-4 cause massive fuel dumps into the Cat where it gets clogged up ? The fall of 2020 I had the Cat replaced and it was so badly clogged that it blew 1/3 of the donut seal to the manifold. I had the flashing SES light / limp mode.

I did a full trans fluid and filter in Feb 2020.
 
  • Like
Reactions: mrrsm

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
How complicated is it to add the "PID" for this ? From your screenshot Cyl #5 was having some issues. This would help me a LOT to trace this down i think.

So that screenshot was taken at the point where one is going to add a gauge to a dashboard. You hold down a blank spot on a dashboard and select "add display" . Then select the type of display. At that point Torque provides a listing of the available parameters with the ones currently reading appearing green. It was at that point I took the screenshot. You need to be already connected to the vehicle for the readings to show up.

The downside is that none of this is recorded or saved and truthfully itnis a pain to record stuff in Torque Pro.
 

gladesteen

Original poster
Member
Aug 19, 2014
83
So that screenshot was taken at the point where one is going to add a gauge to a dashboard. You hold down a blank spot on a dashboard and select "add display" . Then select the type of display. At that point Torque provides a listing of the available parameters with the ones currently reading appearing green. It was at that point I took the screenshot. You need to be already connected to the vehicle for the readings to show up.

The downside is that none of this is recorded or saved and truthfully itnis a pain to record stuff in Torque Pro.
Ok, and that is why I did not like the Torque Pro. It was hard to nail down REAL TIME stuff. Maybe I can just see it happen when the stumble occurs to pinpoint the issue down to the cylinder, but who knows. I'm going to see what the OBDlink adapter and APP shows me. It's crazy what you can do to BMW's with it.

I just ordered 6 new OEM Delphi coils. Cost me $180, but thats still cheaper than a car payment.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
I cannot recommend strongly enough that the Car Scanner app is far superior for logging data and catching intermittent issues. All you need do after setup is remember to start the recording. You don't need to, and shouldn't be watching an app while driving. The data is recorded right in the app and can be reviewed later in the built in graphing facility. Any misfires will be indicated in the recorded data.
 
  • Like
Reactions: gladesteen

gladesteen

Original poster
Member
Aug 19, 2014
83
I cannot recommend strongly enough that the Car Scanner app is far superior for logging data and catching intermittent issues. All you need do after setup is remember to start the recording. You don't need to, and shouldn't be watching an app while driving. The data is recorded right in the app and can be reviewed later in the built in graphing facility. Any misfires will be indicated in the recorded data.
Thanks TJBaker57, just to be sure you're talking about the Car Scanner ELM OBD2 app.
Is that correct ?
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Thanks TJBaker57, just to be sure you're talking about the Car Scanner ELM OBD2 app.
Is that correct ?
Yes. That's the one. I have a file of PIDs for import to that app as well. It does not come with a set like the Torque program does but it can do most all of the PIDs in that set
 

gladesteen

Original poster
Member
Aug 19, 2014
83
Yes. That's the one. I have a file of PIDs for import to that app as well. It does not come with a set like the Torque program does but it can do most all of the PIDs in that set
Thank you ! They have much better ratings vs Torque. I'm going to install it and play around tomorrow. Might not be driving. Its supposed to be Ice/Sleet/Snow here in NH tomorrow.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Thank you ! They have much better ratings vs Torque. I'm going to install it and play around tomorrow. Might not be driving. Its supposed to be Ice/Sleet/Snow here in NH tomorrow.

Grab this file and import in "Settings/Sensors".

This will give you the set that Torque has for GM.

I have more PIDs as well but this will at least get you the basics.


 
  • Like
Reactions: gladesteen

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
I still use Torque Pro for some things as it can do a few things other apps can not.

But the right tool for the job is key.
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
With such a High Mileage Number now in your Rear View Mirror, if you have any Multec II EFIs getting "Stuck OPEN" ...then instead of rapidly pulsed spray of fuel misting into the cylinders... a straight stream of liquid could be pouring in and invite the Clogged CAT problem in very short order. The Key feature of this happening is the presence of a *Blinking* CEL which more or less demands an immediate response.

As mentioned in Post #5, Paul "Scanner" Danner's use of either his Autel and Snap-On High End Scanners (along with a decent Fuel Pressure Tester KIT) can discover if this is problem during a Fuel Injector Balance Test.

The "GYMKO" Tech 2 also provides for this Diagnostic Test as well... but is unlikely to be done with the average Blue Tooth OBD2 Scan Tool. Without observing your Prior Code History and perhaps watching and listening to a Video of you actually driving and filming the Instrument Panel Cluster readouts and catching these events "Inflagrante Dilecto"... what we know right now is too vague to say for certain what is actually going on.

You are not at this point yet... But for the sake of argument, this Owner of a 2002 Trailblazer shows How to R&R the Full Set of the Multec II EFIs (not an easy task and a Real Shame that he only replaced ONE) and he describes the Engine Performance differences he experiences after doing so while mentioning prior similar symptoms to those you've had as well:

 
Last edited:

gladesteen

Original poster
Member
Aug 19, 2014
83
I still use Torque Pro for some things as it can do a few things other apps can not.

But the right tool for the job is key.
Just checked and the Torque app had a nice big update to it. Honestly I havent used it in years, but I will check both out. As far as my troubleshooting, its not the spark its the fuel either by the Coil or Injector. IMO
 

gladesteen

Original poster
Member
Aug 19, 2014
83
With such a High Mileage now in your Rear View Mirror , if you have any Multec II EFIs getting "Stuck OPEN" ...then instead of rapidly pulsed spray of fuel misting into the cylinders... a straight stream of liquid could be pouring in and invite the Clogged CAT in very short order. The Key feature of this happening is the presence of a *Blinking* CEL which more or less demands an immediate response.

As mentioned in Post #5, Paul "Scanner" Danner's use of either his Autel and Snap-On High End Scanners (along with a decent Fuel Pressure Tester KIT) can discover if this is problem during a Fuel Injector Balance Test.

The "GYMKO" Tech 2 also provides for this Diagnostic Test as well... but is unlikely to be done with the average Blue Tooth OBD2 Scan Tool. Without observing your Prior Code History and perhaps watching and listening to a Video of you actually driving and filming the Instrument Panel Cluster readouts and catching these events "Inflagrante Dilecto"... what we know right now is too vague to say for certain what is actually going on.

You are not at this point yet... But for the sake of argument, this Owner of a 2002 Trailblazer shows How to R&R the Full Set of the Multec II EFIs (not an easy task) and he describes the Engine Performance differences he experiences after doing so while mentioning prior similar symptoms to those you've had as well:

MRRSM, the recent instance where i had the flashing SES light was after several Months of stuttering / stumbling issues. I think it finally got to the point where the Cat was completely clogged up. It actually sounded like I was driving with half a muffler. Was so loud and ridiculous. When I had the downpipe/Cat replaced the "donut" flange seal where it mounts to the manifold was completely blown out all over the place. The cat was what they called "plugged"
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Just checked and the Torque app had a nice big update to it. Honestly I havent used it in years, but I will check both out. As far as my troubleshooting, its not the spark its the fuel either by the Coil or Injector. IMO

Most if not all updates to Torque Pro now seem to be the minimum required to keep it operating on new versions of Android.
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
Yeah... it would have been much better if GM would have disabled the Motor until the CAT issue could be cured or by Sounding an Alarm about just how really FAST things can go sideways when Pure Gas starts getting Burned Up inside the CAT Canister. :>(
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
To check the cat, you could do an exhaust backpressure test either using an actual backpressure tester like this or making something up with a vacuum/fuel pump gauge. As a functional test, you could remove the O2 sensor and see if it improves while driving.
 

gladesteen

Original poster
Member
Aug 19, 2014
83
You are not at this point yet... But for the sake of argument, this Owner of a 2002 Trailblazer shows How to R&R the Full Set of the Multec II EFIs (not an easy task and a Real Shame that he only replaced ONE) and he describes the Engine Performance differences he experiences after doing so while mentioning prior similar symptoms to those you've had as well:

WOW, not an easy task is right ! I also dont understand why he did not replace all the injectors ??? You have to tear half the engine apart. That's a whole lot of labor.
 

Forum Statistics

Threads
23,271
Posts
637,476
Members
18,472
Latest member
MissCrutcher

Members Online