Really bad misfire

Tiny
DAVIDO1001
  • MEMBER
  • 2005 PONTIAC GRAND AM
  • 3.4L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 201,000 MILES
Got the car from a buddy blown head gasket, I fixed it, threw in new coil packs, plug wires and spark plugs, when doing the job. It’s been a few months since I fixed it and I put 2,000 miles on it without any problem until it started to misfire on a ride home after the engine is warm, every time it got warm it misfired, I had 3 new coil packs sitting at home and knew those are an issue sometimes so I changed those first and it fixed it for maybe 20 miles after it got warm but then started to misfire again, I then OBD II tested it and got a cylinder 4 misfire, so I replaced the plug wire on cylinder 4 and it didn’t work so I changed the spark plug on cylinder 4 and it’s still not working. Please help, the car is almost undrivable.
Thursday, March 17th, 2022 AT 4:56 AM

8 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

If it is only happening when hot, it sounds like it could be a faulty crankshaft position sensor (CKP). Do me a favor. Take a look through this link and let me know if you feel it mirrors what you experience:

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

Also, let me know if there were any other codes.

Take care,

Joe

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Thursday, March 17th, 2022 AT 3:30 PM
Tiny
DAVIDO1001
  • MEMBER
  • 6 POSTS
There was a high idle code as well, that article seems pretty much like what’s going on. I bought a new sensor, the CKP sensor that goes into the block under the power steering pump. There was confusion at the auto part store when he told me there were 2 different sensors, but I got the block one. I will install it tomorrow and let you know what happens. Thank you!
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Thursday, March 17th, 2022 AT 11:11 PM
Tiny
DAVIDO1001
  • MEMBER
  • 6 POSTS
So, I replaced the crank and camshaft position sensors, the misfire initially seemed gone but after a while I decided to give the engine a little stress test and sure enough in high idle it misfired again really bad, when the RPMs are steady and low it runs beautifully, but any aggressive acceleration gives the bad misfire again. Please help, thank you.
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Friday, March 18th, 2022 AT 3:39 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

What codes did you find? Also, can you record what it's doing and upload it for me to hear? It may be helpful. Also, when at idle with the hood open, see if you hear any hissing or whistling sounds.

Let me know.

Joe
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Friday, March 18th, 2022 AT 6:33 PM
Tiny
DAVIDO1001
  • MEMBER
  • 6 POSTS
First video is cold start idle.
Second video is a quick acceleration while cold still.
Third is a quick acceleration while warm.
Fourth is normal driving.
It seems like the engine has the same problem when it’s cold now it happens when RPMs are high cold or warm, there it is though.
Videos (Click to make bigger)
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Saturday, March 19th, 2022 AT 3:35 PM
Tiny
DAVIDO1001
  • MEMBER
  • 6 POSTS
Forgot to mention the cats got stolen a long time ago and never fixed it. So, it’s basically strait piped and really loud which kind of helps when trying to hear engine noise! I know part of the engine code is cats and I’m fixing it this summer, but it’s ran fine for a long time without cats.
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Saturday, March 19th, 2022 AT 3:37 PM
Tiny
DAVIDO1001
  • MEMBER
  • 6 POSTS
I put wrong video for cold hard acceleration so here’s the right video.
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Saturday, March 19th, 2022 AT 3:42 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi,

I watched each of the videos. I noticed that the check engine light wouldn't flash until it was under a heavy load. When it flashes, that indicates the misfire is occurring. When it stays solid, there shouldn't be a misfire occurring.

Okay, the idea that the converters were stolen led me to ask what was done with the oxygen sensors. Also, when the light isn't flashing, do you still feel a misfire? Is the only code stored a P0304?

Let me know. Also, let me know if you feel the misfire when the check engine light is not flashing. One last question. If your scan tool has live data settings, check to see what the short-term fuel trims are and check the engine coolant temperature sensor signal as well. With the engine cold, the ECT signal should be very close to ambient temperature.

Take care,

Joe
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Saturday, March 19th, 2022 AT 7:35 PM

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