Misfire and intermittent hard start

Tiny
LUIS MEDINA2
  • MEMBER
  • 2004 GMC YUKON
  • 4.8L
  • V8
  • 2WD
  • AUTOMATIC
  • 192,000 MILES
Hey, so at idle every once in a while the car stutters, RPMs will drop, ABS kick back up to regular idle. Car will shake quite a bit because of the idle drop. Then when I go to drive it if I press the gas a decent amount it’ll begin to feel a hesitation and somewhat of a small couple of backfires or pops. Kind of sounds like it coming from under the cab. There are no exhaust leaks. I used the thermo gun and checked catalytic converters and they’re fine. I checked all exhaust manifold ports and they’re all around 200-230. But I have cylinder 2 at 280-330. So I’m not too sure what that means. And I do have one that drops around 140ish. So maybe that’s why cylinder 2 is hotter because it’s trying to compensate for the other one? I’m not too sure just a thought. Also I have no check engine light on. And I replaced the crank position sensor and cam position sensor and re-learned them both and also nothing has changed. Also sometimes has trouble starting up. Then starts up and buy white cloud of smoke and then just goes away.
Do you
have the same problem?
Yes
No
Sunday, March 21st, 2021 AT 11:07 AM

1 Reply

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. We need to check two things. First is the fuel pressure when this is happening.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I would suggest taping the gauge to the windshield just so you can see it when it acts up.

Then we need to look into the compression and head gasket. The white smoke and elevated temp points to a misfire and it may be caused by coolant in the cylinder.

https://www.2carpros.com/articles/how-to-test-engine-compression

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know if you have questions and we can go from there. Thanks
Was this
answer
helpful?
Yes
No
Monday, March 22nd, 2021 AT 7:00 PM

Please login or register to post a reply.

Sponsored links