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random cylinder missfire when idling

random cylinder missfire when idling

Postby buttersstoch [OP] » Jun 16 2016, 12:01am

after putting new heads, lifters and pushrods on my truck it ran fine for an hour then started idle very rough and it threw up random cylinder missfire. it seems to run fine when driving but when at a stop light it will get really rough. what do you guys think it could be? thanks
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buttersstoch
Firing on 1 cylinder [L1]
Firing on 1 cylinder [L1]
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Re: random cylinder missfire when idling

Postby 72chevy » Jun 16 2016, 1:41am

hello buttersstoch! Are the replacement parts all stock? Why did you replace them? What was the original problem? (this may be a clue to what is occurring now) start simple, check all connectors including plug wires, and a quick vacuum leak check..(use carb cleaner for this NOT brake cleaner!!) Might be a good idea to try cleaning the MAF sensor too..Use qd electronic cleaner, or MAF cleaner for that.
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72chevy
Firing on 7 cylinders [L1]
Firing on 7 cylinders [L1]
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Re: random cylinder missfire when idling

Postby 72chevy » Jun 16 2016, 2:42am

A P0300 can be a lot of things, If these checks do not find a problem, It might be a good idea to go for a few short drives(a few blocks) to see if another codes sets. Can you view freeze frame and live data?
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72chevy
Firing on 7 cylinders [L1]
Firing on 7 cylinders [L1]
Posts: 78
Topics: 1
Images: 12
Joined: Jun 05 2016, 10:49pm
Years of membership: 4 years of membership4 years of membership4 years of membership4 years of membership
Location: ks
Year: 2001
Make/Model: Chevrolet Silverado
Extra Info: 2001 Z71 5.3l
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Re: random cylinder missfire when idling

Postby buttersstoch [OP] » Jun 17 2016, 12:25am

yes i used stock replacement parts. cant view live data unfortunately. how do you do a vacuum leak test using carb cleaner??
Original Poster
buttersstoch
Firing on 1 cylinder [L1]
Firing on 1 cylinder [L1]
Posts: 10
Topics: 5
Joined: Apr 06 2016, 10:50pm
Years of membership: 4 years of membership4 years of membership4 years of membership4 years of membership
Year: 2003
Make/Model: Chevrolet Silverado
Group Membership:
Registered users

Re: random cylinder missfire when idling

Postby 72chevy » Jun 17 2016, 2:13am

Engine running, spray all around the base of the intake, and any vacuum lines..if you have a leak the rpms will change. Be sure your plug wires are all in good shape, any ignition arcing while doing this can create a fire real quick! Vacuum is higher at idle...so your condition could POSSIBLY be a vacuum leak.
User avatar
72chevy
Firing on 7 cylinders [L1]
Firing on 7 cylinders [L1]
Posts: 78
Topics: 1
Images: 12
Joined: Jun 05 2016, 10:49pm
Years of membership: 4 years of membership4 years of membership4 years of membership4 years of membership
Location: ks
Year: 2001
Make/Model: Chevrolet Silverado
Extra Info: 2001 Z71 5.3l
Group Membership:
Registered users

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