Hate this misfire

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Tired guy

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I have a 96 suburban with a 7.4 vortec. I can not figure out this random misfire. I originally had an alternator issue (140 amp) replaced it with 2 remains and a brand new one (still an issue from time to time) but it started missing. I checked all grounds everything is tight. So far I have replaced plugs wires cap rotor cam sensor crank sensor fuel pump and filter ignition module and coil. Set my timing with a snap on scanner. At a loss at this point. Any help would be appreciated thank you
 

1997

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use a scanner that can isolate which cylinder(s) are miss firing.
i assume you're getting code P0300
 

Schurkey

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I have a 96 suburban with a 7.4 vortec. I can not figure out this random misfire.
As said--use a real scan tool to see the misfire counts for each cylinder. If the misfire is localized to one or two cylinders, you can check the things that affect only those cylinders. If the misfire is random, you'll have to check the things that affect more than one cylinder.


Set my timing with a snap on scanner.
Ignition "timing" is NOT ADJUSTABLE. However, the cam sensor-to-crank sensor synchronization is adjustable (Cam Offset, or similar terms.) Getting the Cam Offset within spec also gets the rotor-to-cap terminal alignment within spec, which can affect misfire.
 

Jeepwalker

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You say 'random' misfire. What are you seeing? When does the misfire occur? Does it idle perfect? Periodic stumbling (at idle)? Lack of acceleration? Sometimes going down the road? We kind of need to know what random means (a detailed description) in this case. So you have a snap on scanner, right? Ok, thats helpful.


Are there any specific mods, 'tunes' or 'chipping' which have been done in the past?
 
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