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S-10 Blazer Random Multiple Misfire

Tiny
CHANDLER39
  • MEMBER
  • 1999 CHEVROLET BLAZER
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 115,000 MILES
Hi. I have a 1999 s10 blazer 4.3 vortec engine and it has a Random Multiple Misfire P0300.

I have changed the spark plugs / plug wires / distributor cap / rotor cap /distributor gear / fuel injectors/ fuel injector cleaner / fuel filter / throttle position sensor /fuel pressure gauge say's 55 to 60. I need help with this.
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Friday, November 13th, 2009 AT 3:10 PM

6 Replies

Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
This can be either the MAF sensor or you have a vacuum leak. Here are two guide to help us run down the problem.

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

and

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let us know what happens and please upload pictures or videos of the problem.

Cheers
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Saturday, November 14th, 2009 AT 6:56 AM
Tiny
CHANDLER39
  • MEMBER
  • 3 POSTS
The coil is okay and I couldn't find a vacuum leak waiting to get paid to get the MAF sensor. When driving down the road at light throttle (cruise), the engine will misfire and shutter and backfire or it sound like it is backfiring sometimes. Under hard acceleration the engine smooths out and runs excellent with normal power. The shutter happens at light throttle either hot or cold and gets slightly better when it is warm. =( The EGR look's Clean. I did a Engine Compression Test all of the engine cylinder's and were 150psi. And did a fuel Compression Test when the key was on 55-60psi and when the engine was running 50psi.

The engine is getting horrible fuel economy?
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Saturday, November 14th, 2009 AT 8:01 AM
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
I am really leaning toward the MAF sensor being out. I wont leave a code when these sensors has problems FYI.
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Saturday, November 14th, 2009 AT 1:30 PM
Tiny
CHANDLER39
  • MEMBER
  • 3 POSTS
Great call on the MAF I finally got a new one and now the engine has never run better. Thanks for your help I love this site.
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Saturday, November 14th, 2009 AT 9:04 PM
Tiny
FREDLJORDAN
  • MEMBER
  • 1 POST
My 99 is did the same thing. A p0300 code on it's own isn't very definitive so I did the sensor and success over here as well.

Thanks
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Tuesday, October 2nd, 2012 AT 9:28 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,573 POSTS
Yep a P0300 can be caused by multiple items, 99% of the time it is from a lean mix though. So you check for vacuum leaks, low fuel pressure and see what the MAF or MAP is showing. Check the O2 sensors as well as they can cause it to run lean as well.

Now if you have a single cylinder misfire you look at different things.
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Tuesday, March 6th, 2018 AT 1:49 AM

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