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1997 GMC C1500 Misfire

Tiny
BRYCEKEATS
  • MEMBER
  • 1997 GMC C1500
  • V8
  • 4WD
  • AUTOMATIC
  • 208,000 MILES
My 97 GMC pickup has a cylinder 4 misfire code. I have changed the spark plugs and wires, and EGR valve. I have cleaned up the distributor cap and it looks in good shape (no cracks, etc). I did a compression test and had 150 to 180 range over all cylinders. I have checked the #4 spark plug for a spark and it fires every time. I have ohmed out the injectors and they are ok. I inspected the #4 injector tip and it is shiney and gold colored. I have ran 1 liter of Lucus injector cleaner through it over 2 1/2 tanks. The truck also has trouble starting. I can hear the starter engage but won't turn the engine hardly at all. It's like it's compression locked and sometimes when I realise the key it stumbels 1 rotation like a back fire. The exhaust has a rich smell fuel in it and the fuel milage has droped from 12-14 MPG to 8-9 MPG. HELP? I'm out of possabilities that I can think of.
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Saturday, October 18th, 2008 AT 4:34 PM

2 Replies

Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
Sounds like the starter is on the way out, and I would change the cap and rotor to eliminte the guessing over them. Then check your fuel pressure and fuel pressure regulator, the regulator, or injectors might be leaking down while the engine is off. Heres how, check this video out.

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

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Sunday, October 19th, 2008 AT 8:03 AM
Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Don't forget that the fuel pressure on a vortec engine that the fuel pressure must be 65 psi at initial start up otherwise they do not like to start. They run on around 55 psi. Just thought that this might help if this is low it will most likely be a fuel pump.
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Saturday, November 1st, 2008 AT 12:40 AM

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