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2002 Oldsmobile Bravada Misfiring

Tiny
YLBILL
  • MEMBER
  • 2002 OLDSMOBILE BRAVADA
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 127,000 MILES
Truck was running fine. Got in it one day and it started misfiring and the SES light started flashing. Took it my mechanic and he scanned it. Said he was getting random cylinder P0300 code. Plugs were original, so he changed them, but still misfired. Took it to his GM mechanic friend to put on their scanner. Got the P0300 code. Shut it down to check some things, started it again and it ran fine, so I picked it up. Drove it about 20 miles and felt some skips. Got in it the next morning and it started misfiring and SES started flashing again. Took it back to GM dealer and he did a “leakdown" test. Said cylinder one was 20% and the other cylinders ran between 3% and 10%. His conclusion was it probably needs a valve job. He did something and it ran fine again for about 20 miles. Now when idling the RPM’s are bouncing from 500 to 8 or 900 about every 12 seconds. Took it up the road today and RPM's had random slight fluctuation a few times. Question: if it was the valves, would it run OK f or awhile then mess up again? How much is a valve job? Been reading all kinds of similar scenario’s and don’t know where to go from here? Any ideas? Thanks!
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Monday, February 16th, 2009 AT 5:56 AM

15 Replies

Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
That a 4.2L inline 6? I have seen the coils go bad on those and create misfires. It will come and go as well, drove a TrailBlazer 4 test drives, nothing. Customer got in it and it started misfiring within 50 feet of driving. When it is missing, have your friend put it on the scanner and watch the "misfire data" to see which cylinder it is. If you want to be sure it is the coil, take whichever one it says is missing (#3 ) and move that coil to the #2 cylinder and clear the codes. Drive it until it misfires again and see in the data if it is #2, if so you know the coil you moved there is bad
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Monday, February 16th, 2009 AT 7:56 AM
Tiny
YLBILL
  • MEMBER
  • 7 POSTS
Hi Jack,
Thanks for the reply. Its the Vortec motor. They did try swaping things around. Can't really remember all the details, so much has been discussed. If I remember, he didn't feel it was the coil, because when he took off one and put it on another the code would change to a different cylinder (does that make sense?). Last time I took it out, I didn't feel a misfire, but notice more the RPM's fluctuating from about 4 to 8 or 9. Not sure if the misfire's will come back.
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Tuesday, February 17th, 2009 AT 6:33 AM
Tiny
2CARPRO JACK
  • MECHANIC
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Misfires can make the rpms fluctuate like that. It will have to misfire again to be able to pinpoint the problem. If it didn give specific cylinder misfires (P0300 is a random misfire code), how does he know it isnt one of the coils. It would have to give a specific misfire so you could take that coil and move it to another cylinder
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Tuesday, February 17th, 2009 AT 7:27 AM
Tiny
YLBILL
  • MEMBER
  • 7 POSTS
Hi Jack,

If I can remeber correctly, the first code was a P0304 or cylinder 4. Then it moved to another cylinder and was jumping around like that? FYI, I did throw a take of 92 Octane gas in over the weekend. I took it to work this morning, about an 8 mile drive. Didn't notice any systems, not even an RPM fluctuation. Are you thinking its the coil and not the valves?
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Tuesday, February 17th, 2009 AT 10:34 AM
Tiny
2CARPRO JACK
  • MECHANIC
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I have experienced coil failures more than valve failures. See if the miss moves to the cylinder that has #4's coil in it now
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Tuesday, February 17th, 2009 AT 11:28 AM
Tiny
YLBILL
  • MEMBER
  • 7 POSTS
Hi Jack,
Okay, I haven't felt a misfire in awhile. Main thing now is the RPM's are fluctuating from about 600 to 900 rpm's about every 12 seconds while in park and I can see the needle jump accasionally jump while driving.
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Tuesday, February 17th, 2009 AT 11:52 AM
Tiny
2CARPRO JACK
  • MECHANIC
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Does the engine actually change rpm or is it the needle jumping? A slight miss can cause a rpm fluctuation like you describe
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Tuesday, February 17th, 2009 AT 4:05 PM
Tiny
YLBILL
  • MEMBER
  • 7 POSTS
Yeah, the speed of the engine does change. When sitting with your foot on the brake it will move forward slightly, so its definitly accelerating.
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Tuesday, February 17th, 2009 AT 6:38 PM
Tiny
YLBILL
  • MEMBER
  • 7 POSTS
Got in the truck today, it starting running real rough and the SES started flashing again, no power. Seems like I'm back to square one, any help would be appreciated.
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Wednesday, February 18th, 2009 AT 12:18 PM
Tiny
YLBILL
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  • 7 POSTS
Thought I would try starting again after about an hour, ran okay, just had the fluctuation in the RPM's. Anyone have an idea what's going on?
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Wednesday, February 18th, 2009 AT 1:15 PM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Need to have it scanned to see if it stored anything in the memory. If it was misfiring, now is when you see if it moved to the cylinder with the suspect coil on it
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Sunday, March 1st, 2009 AT 8:50 AM
Tiny
KYLEG001
  • MEMBER
  • 2 POSTS
I'm also having a similar issue, car started misfiring in cyl #3 p0303 then I switched the coil from 3 down one(cyl 5 I think) and am getting random/multi misfire p0300. I'm going to pull the coils and test the resistance. Not shure what they should read though?
I supose I'll have to go pick up a manual :-( I'll let you know. I also suspect the fuel injectors, 40K miles, and always used the cheap fuel. A new fuel filter wouldn't hurt either.
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Saturday, March 7th, 2009 AT 8:22 PM
Tiny
KYLEG001
  • MEMBER
  • 2 POSTS
Well, I didn't feel like getting a car manual, lol. I went ahead and tested the coil and found that the original coil for cyl #3 is defective. The other five coils read between 4M and 6M ohm on the Secondary(depending on temperature). The Primarys read between 11.98K and 12.01K ohm. I have attached a picture(really bad) that shows the pin-out for testing.
Notice N/A means no connection. The piece is angled , so it looks a little strang. Hope this helps.

By the way, my defective coil read 10K ohm on the Secondary :-( and 12K ohm on the primary, and was shorted to the N/A pins the the picture.


https://www.2carpros.com/forum/automotive_pictures/328442_IMG00017200903071858_1.jpg

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Saturday, March 7th, 2009 AT 9:34 PM
Tiny
HELPING YOU
  • MECHANIC
  • 100 POSTS
You mentioned ran well after refueling - when fault occurs try pumpin' a sample in a glass jar- just a thought.
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Saturday, March 7th, 2009 AT 9:54 PM
Tiny
ROBANDASH
  • MEMBER
  • 3 POSTS
Hey YLBILL I am wondering if you ever solved this issue, my 02 bravada is doing the same thing. I've changed all plugs and 2 coils plus a couple other parts and it didn't fix the problem. Please let me know before waste another $500 on parts and labor. Thank you
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Saturday, January 2nd, 2016 AT 5:43 AM

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