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Here's the Deal. 02 Focus, ZX3, 2.0 DOHC Zetec. Manual Trans. Powertrain Mods include::
Cold air intake
Exhaust resinator Delete, Cherry bomb in place of muffler.

Problem: Missfires at idle, Missfire on load (3rd gear, low rpms / up hills, at low R's). Plugs and Ignition cables good. NO MIL (check engine light).
I have a few ideas, but lookin for second oppinions.
Im thinking, Bad Injector pulse? Bad Injector? Burned valves due to low back pressure? Anyone have this prob?? Got any Ideas?? Last time i hooked a scanner up to it (generic obd), got no codes. Have had Problem with a Wire pulling Outta my Ignition Coil, But have repaired. Engine still puts out good power as well. HELP
 

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Had the same prob it ended up being a cracked plug, i didnt even notice it the first time i pulled them
 

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Check compression and do a cylinder leakage test to rule out mechanical. How do You know wires and plugs are good? Did You use a spark analyzer? Just because there is no MIL doesn't mean it's a spark issue.
 

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DPFE doesn't cause a misfire, more of a surging at low rpm/steady throttle condition. Sounds more like plugs, wires or mech.
 

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His description of a missfire may be diff than anyone elses.I tell you what I did when I first put my cold air on,I pinched my amp wire on the isolater bolt that goes by the coilpack.That will make a miss,eventually after 2 run cycles it will kick on a CEL light.Thats what it did to me.You may have possibly pinched a wire.There is a few bundles of wires that go that route,at least on the Zetec equipped.What he described is what my car did when my DPFE went out.If I hammered it it was fine,but on a load in a high gear it kinda lugged and chugged like a miss.
 
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