2002 Pontiac Aztek Random Chugging/ Misfiring

Tiny
SCOTT49601
  • MEMBER
  • 2002 PONTIAC AZTEK
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 116,000 MILES
The problem seems to come and go. The vehicle will run great for a day or two, then it'll start acting up again. I put on a new fuel filter and had about the same pressure readings. I then had new plugs and wires installed. That seemed to help for about a day. The "Service Engine Soon" light always comes on when it's running rough. And it flashes often too, indicating a misfire. Two different mechanics confirmed it was misfiring on cylinder 1. I then had my fuel system and injectors cleaned. It ran great after that. For a few days. Last night, I sprayed down the MAF with some special MAF cleaner. That didn't help either. I also misted the engine with water to check for arcing, but didn't see any. Could it be the coil pack? Help please!
Saturday, August 21st, 2010 AT 12:02 PM

6 Replies

Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Hi
Was code P0300? Fuel pressure 52-59 psi? Histry code of missfires always cyl #1?
Let me know
Thanks for donate
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Saturday, August 21st, 2010 AT 12:26 PM
Tiny
SCOTT49601
  • MEMBER
  • 4 POSTS
The code was P0301- Cylinder 1 misfire

Probable causes listed were:
Ignition system fault- spark plug, ignition wires, coil
Vacuum leak
Injector fault
High or low fuel pressure

As for fuel pressure: (Last checked on 7-9-10)
Ign. On- 57lbs.
Crank- 62lbs.
Start- Steady at 57lbs.

And yes, the misfire is always at cylinder 1.

Thanks for the quick response.
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Saturday, August 21st, 2010 AT 2:43 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Possible vacuum leak at intake runner or injector itself is faulty. There is a TSB on a new intake gasket to solve cylinder miss due to vacuum leaks.
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Saturday, August 21st, 2010 AT 3:00 PM
Tiny
SCOTT49601
  • MEMBER
  • 4 POSTS
If the injector was bad, wouldn't it run bad all the time? I also had them all cleaned just a few weeks ago. Is there some way I can check for a vacuum leak?
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Saturday, August 21st, 2010 AT 4:37 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Intermittent injector failure common can OHM check 11-14 ohms. Vacuum leak spray around intake runners when missing if idle stablizes then that spot is where leak is. Has a crank/cam sensor relearn been performed?
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Monday, August 23rd, 2010 AT 11:43 AM
Tiny
SCOTT49601
  • MEMBER
  • 4 POSTS
I had a mechanic check more into it. Cylinder 1 measured 30psi on a compression test. He figured possible burnt valve. A few days ago, he tore into it. The head gasket had an air leak and both were very close to blowing. So, new gaskets all around. Once all was put back together, the pressure was back up to 120 but there is still a miss on cylinder 1. I'm still thinking the injector. Because it ran great after the initial injector cleaning. Could it be a wiring/computer problem or more likely the injector?
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Sunday, October 31st, 2010 AT 5:29 PM

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