1999 CHEVY BLAZER 1999 S10 BLAZE RANDOM MULTIPLE MISFIRE

  • Tiny
  • chandler39
  • 1999 Chevrolet Blazer

Engine Mechanical problem
1999 Chevy Blazer 6 cyl Two Wheel Drive Automatic 115000 miles

hi. I have a 1999 s10 blazer 4.3 vortec engine and it has a Random Multiple Misfire P0300.

I have changed the sparkplugs / plugwires / distributorcap / rotorcap /distributor gear / fuelinjectors/ fuelinjector cleaner / fuelfilter / throttle position sensor /fuel pressure gauge say's 55 to 60. I need help with this.

Friday, November 13th, 2009 AT 3:10 PM

7 Answers

  • Tiny
  • BMRFIXIT
  • Expert
  • 19,554 posts

Was the coil checked or replaced?

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Saturday, November 14th, 2009 AT 6:56 AM
  • Tiny
  • chandler39
  • Member

Yes the coil was ok. Tested out ok

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Saturday, November 14th, 2009 AT 8:01 AM
  • Tiny
  • chandler39
  • Member

When driving down the road at light throttle (cruise), the engine will misfire and shutter and backfire or it sound like it is backfireing 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 engine is getting horrible fuel economy.

When I changed Distributor Gear it run fine for a day or so.

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Saturday, November 14th, 2009 AT 8:25 AM
  • Tiny
  • BMRFIXIT
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  • 19,554 posts

I would've expect an EGR codes
I would still remove EGR and check and clean

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Saturday, November 14th, 2009 AT 1:30 PM
  • Tiny
  • chandler39
  • Member

=( 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.

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Saturday, November 14th, 2009 AT 9:04 PM
  • Tiny
  • chandler39
  • Member

Engine Mechanical problem
1999 4 Door Chevy Blazer 6 cyl Two Wheel Drive Automatic 115000 miles
Hi. I have a 1999 s10 blazer 4.3 vortec engine and it has a Random Multiple Misfire P0300.
I have changed the sparkplugs / plugwires / distributorcap / rotorcap /distributor gear / fuelinjectors/ fuelinjector cleaner / fuelfilter / throttle position sensor /new air filter/ coil checked out ok. EGR cleaned out and the mass air flow sensor was cleaned too. Throttle body was cleaned out too when I changed the Distributor Gear it run fine for a day or so
When driving down the road at light throttle (cruise), the engine will misfire and shutter and backfire or it sound like it is backfireing sometimes maybe just misfire. 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.
I did a Engine Compression Test all of the engine cylinder's were 150psi. And did a fuel Compression Test when the key was on 55-60psi and when the engine was on and running 50psi. Then push the gas down and it still say's 50psi and with it's off stay's at 50psi.
The engine is getting horrible fuel economy.

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Sunday, November 15th, 2009 AT 4:02 AM
  • Tiny
  • fredljordan
  • Member

Hi - looks like its been awhile. Have you figured it out yet? My 99 is doing the same thing. Looks like we tried all the same fixes as well. A p300 code on it's own isn't very definitive.
Thanks

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Tuesday, October 2nd, 2012 AT 9:28 PM

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