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1998 GMC Sierra Misfire

Tiny
THEELDERS
  • MEMBER
  • 1998 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 140,000 MILES
My 98' Sierra has just started misfiring. The code I got siad it was misfiring on multiple cylinders and I got the code twice in one reading. I've already changed the fuel pump, fuel filter, pick-up coil, rotor button, plugs and wires, and cut both cats aloose. It seems to get worse when I put it under a load, it does not backfire. Do I need to replace the ignition control module? And where is it? Any advice would help cause im at a stand still now, don't know what else to do. Please Help!
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Sunday, March 1st, 2009 AT 7:03 PM

2 Replies

Tiny
OBXAUTOMEDIC
  • MECHANIC
  • 3,711 POSTS
Hello,

Check for bad vacuum lines, check compression, check IAC (Idle Air Control Valve), chek fuel pressure and pressure regulator. Check out link below for video on how to check fuel pressure and regulator....

https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm

.
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Sunday, March 1st, 2009 AT 7:23 PM
Tiny
JARED1794
  • MEMBER
  • 1 POST
98's have intake gasket leak issues and also distributor gear wer issues. You will need to pull the distributor. The wear is obvious by the very shiny wear points and some loss of ditributor gear thickness in most high milage vehicles.
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Tuesday, March 31st, 2009 AT 8:36 AM

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