colleen's silver bullet

I have a 2004 4.6 it is missing at idle only after putting a mac cat back H pipe with mil eliminator on it any idea.Checked out ok on ford's computer

teej281

Check the coil-on-plugs??? Mine did that on me too. But it always did that. So i dont know.

Hangwire

If you had ZERO problems before this install......Clearly there's a problem with either your pre-cat 02 sensors or the eliminator. Either your 02 sensors weren't re-installed correctly or for some reason your ECU isn't receiving the normal post-cat 300mV lean signal that its used to on stock exhaust. I know this is patronizing and insulting, but TRIPLE check your 02 and MIL eliminator installation to make sure its seated snug, wired right, and not cross-threaded. The engine doesn't seem to know the 02 levels in your exhaust it seems to me.

ridestang88

it might be an exhaust leak

98redstang

Check your plugs and wires. When i finished my build it was missing and it ended up being the wires. Does your volt meter jump when it misses? If it does that like a 99% chance its wires...

H0SS302

he doesnt have wires...

cliffyk

Is it throwing DTCs for the misfires, or just kind of "lumpy"?

My '03 has had a lumpy idle (no codes) since I got it at 30k miles (85k now). It had an o/r H-pipe and welded in Flowmaster 40s at that time, I replaced that with an UPR catted X-pipe and a Magnaflow catback--the slightly lumpy idle remained...

98redstang

oops sorry about that i forgot... I should read that it was an 04...

Brute03

is it a constant miss or are you hearing an intermittent pop thru the exhaust? it may be the typical "lumpy" idle that Cliff mentioned but now its more audible with the louder exhaust