1997 gmc sierra random misfire code
May 7th, 2016, 12:20 PM
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1997 gmc sierra random misfire code
was looking for some troubleshooting ideas for my 97 sierra misfiring. i took it into a local shop and they told me to change my dis cap. when i told them the cap, plugs and wires were changed last summer they said they needed to look deeper into it. the code is p0300 random misfire. On a longer trip I just took, I had cylinder 4 misfire code pop up but change back to random not soon after. need some insight to what else I could look into. Thanks!
May 24th, 2016, 5:40 AM
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It's usually clogged spider injectors with p0300 but let's hope not.
1. Definitely start with taking a look at the cap, rotor, plugs and wires because they CAN cause these symptoms. You should not see white green or black crust stuff anywhere, if you do, replace it and see how it runs. While you've got the plugs out do a compression test on each cylinder. If all that checks out, take your fuel filter off and see if you can blow through it, if you can't, replace it.
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Next would be test your fuel pressure should be between 50-60 psi, if not, you've got a problem. You can rent fuel pressure gauges from most auto parts stores for free just leave a deposit and you get all your money back when you return it or you could buy a set for around $50
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If fuel pressure is low the fuel pump is bad
If fuel pressure is good and DOESN'T bleed off quickly it's most likely clogged Injectors.
If fuel pressure is good but DOES bleed off quickly it's most likely your Fuel pressure regulator leaking which is mounted on the side of your spider injectors inside the intake.
If either the injectors are clogged OR the FPR is leaking, just replace the entire unit. Shell out the $300, upgrade from SCPI to MFI and save yourself some headaches.
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Now before you replace the injector assembly be sure to do a compression test on each cylinder. A dead cylinder (a cylinder with little to no compression) can cause p0300.
A compression tester can also be rented or bought from any auto parts store. Take your spark plug out screw in the compression tester nozzle, yank the coil wire so it doesn't start and crank it over. Do this with each cylinder. Should have 150 psi or more in each cylinder with no more than a 10 psi variance. If you don't have 150 psi in each cylinder, your piston rings are most likely gone.
Let us know what the results are and good luck.
1. Definitely start with taking a look at the cap, rotor, plugs and wires because they CAN cause these symptoms. You should not see white green or black crust stuff anywhere, if you do, replace it and see how it runs. While you've got the plugs out do a compression test on each cylinder. If all that checks out, take your fuel filter off and see if you can blow through it, if you can't, replace it.
-----------------------------
Next would be test your fuel pressure should be between 50-60 psi, if not, you've got a problem. You can rent fuel pressure gauges from most auto parts stores for free just leave a deposit and you get all your money back when you return it or you could buy a set for around $50
-----------------------
If fuel pressure is low the fuel pump is bad
If fuel pressure is good and DOESN'T bleed off quickly it's most likely clogged Injectors.
If fuel pressure is good but DOES bleed off quickly it's most likely your Fuel pressure regulator leaking which is mounted on the side of your spider injectors inside the intake.
If either the injectors are clogged OR the FPR is leaking, just replace the entire unit. Shell out the $300, upgrade from SCPI to MFI and save yourself some headaches.
-----------------------------
Now before you replace the injector assembly be sure to do a compression test on each cylinder. A dead cylinder (a cylinder with little to no compression) can cause p0300.
A compression tester can also be rented or bought from any auto parts store. Take your spark plug out screw in the compression tester nozzle, yank the coil wire so it doesn't start and crank it over. Do this with each cylinder. Should have 150 psi or more in each cylinder with no more than a 10 psi variance. If you don't have 150 psi in each cylinder, your piston rings are most likely gone.
Let us know what the results are and good luck.
Last edited by TBI_GUY; May 24th, 2016 at 5:49 AM.