1998 Chevy 1500 random misfire

chevyonly1963 · Sep 7, 2016

Its a 1998 1500 99,800 miles. I have replaced intake gaskets (upper and lower plenum) updated the injectors to mfi, replaced every thing I can replace on the intake. Coil, ign module, distributor/button/cap, map sensor, oil pressure switch (while it was easy to get to), plugs, has Napa belden wires that are 3 years old, Fuel filter has been replaced. All of this work has been done within two weeks. Fuel pressure is good. It feels like it's bogging a little bit and check engine light is always p0300 random misfire. Please help, I have replaced everything except the fuel pump, egr valve, and crank position sensor. I'm tired of throwing money at it. Thanks in advance!

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Jrgunn5150 · Sep 7, 2016

Try cleaning the EGR, rather than replacing, that doesn't cost anything.

People have found loose grounds, bad wires, etc etc. Have you at least looked at the crank sensor and checked the connection?

Do you have any type of scanning ability at all?

chevyonly1963 · Sep 7, 2016

I haven't thought of checking the crank sensor. And yes I do have access to a scan tool

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Jrgunn5150 · Sep 8, 2016

Sometimes it's as simple as unplugging it and plugging it back in. Probably not, but it's worth a shot lol.

If you can read live data, watch your CMP and see if it's staying consistent.

silverado98 · Oct 30, 2016

Change wires again same thing happen to me as well random misfire changed a year ago so didn't bother to check but after throwing a bunch of money at it I decided to change them and see what happens and then boom it when away my cylinder 5 wire was bent in side the wire so didnt see until I cut each one open just to see but solved my issue with p0300

1998OBS · Feb 7, 2022

silverado98 said:
Change wires again same thing happen to me as well random misfire changed a year ago so didn't bother to check but after throwing a bunch of money at it I decided to change them and see what happens and then boom it when away my cylinder 5 wire was bent in side the wire so didnt see until I cut each one open just to see but solved my issue with p0300

What was it? I’ve changed everything you can think of short of the entire engine… I can’t find my P0300… Check my post for readings. Anything helps *shakes plastic cup of knowledge coins

Teddygraham · Feb 7, 2022

Can you view live misfire data? Is it most constant on one cylinder? I would throw on new plug wires just to finish up the tuneup side of things.

SUBURBAN5 · Feb 7, 2022

If you dont want to throw more money hook up a good scan tool and watch live data like the others mentioned. You should be able to watch misfire data to see if it all pistons or just a few. Also how did you set the distributor??

Schurkey · Feb 8, 2022

Verify fuel pressure

Connect a proper scan tool that shows misfire counts cylinder-by-cylinder. Cheap scan tools LIE about P0300; the "real" code may be cylinder-specific (P0301--P0308).

1998OBS · Jan 29, 2024

1998OBS said:
What was it? I’ve changed everything you can think of short of the entire engine… I can’t find my P0300… Check my post for readings. Anything helps *shakes plastic cup of knowledge coins

I didn’t want to leave you guys hanging, although it might not be your case I found my P0300 solution, P0300 solved ended up being a performance chip someone added to the truck that was malfunctioning, took it off and it’s a brand new truck!

1998 Chevy 1500 random misfire

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