Engine Shop Cant Find Misfire Problem

kevlar

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May 27, 2015
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I have a 2002 mustang gt has a slight misfire,an slightly smells rich.Ive taken it to two different shops one says possible computer problems one says something to do with cam timing bit they really don't have a clue.So far I've put new injectors in,new plugs,cleaned maff,new pcv valve,new o2 sensors on drivers side,fuel filter,fuel pump.Was throwing a p0413 code but has seemed to have cleared on its own shop says it's not there,but a couple lean codes have popped up,,I'm at my wits end an have no ideas left,,could use some help
 
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squeak93

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Jun 2, 2005
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Does the car have cats? Any mods done?

Also, replace both o2's at the same time. If one was bad odds are the other isn't far behind it.

Stop throwing money at it and check the small stuff. Vac leaks, loose coil packs (bad boots will cause issues) etc.
 

kevlar

New Member
May 27, 2015
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Thank s for the reply squeak,,I have a cold air intake,professional products plenum not sure what size,looks like the stock throttle body on it,bbk catted xpipe an slp cat back exhaust,I have checked boots a couple different times man,hooked up a noid light set on coil packs all looked good to me,has good acceleration an only seems to misfire at idle,I've looked for vac leaks an both shops have done a smoke test,,nothing,I've haven't checked the evap system but told the shop to check for leaks there ,,heard that could cause a problem with a misfire,Could bad alternator diodes cause misfire?
 

wmburns

SN Certified Technician
Aug 14, 2009
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Houston Texas
So far I've put new injectors in,new plugs,cleaned maff,new pcv valve,new o2 sensors on drivers side,fuel filter,fuel pump.Was throwing a p0413 code but has seemed to have cleared on its own shop says it's not there,but a couple lean codes have popped up,,I'm at my wits end an have no ideas left,,could use some help
If you paid a professional to replace all of those parts without a fix, then my best advice is to get a new mechanic.

T,heard that could cause a problem with a misfire,Could bad alternator diodes cause misfire?
Yes it's POSSIBLE for a bad alternator diode to cause a misfire. However it's usually associated with a cam related DTC as well. But given how easy it is to test an alternator there's no excuse to guess.

Does this car have cats?

Are there any exhaust leaks?

Does this car use oil or coolant?

Have you inspected the front crank damper for run out and dry rot of the the ring damper? A loose or incorrectly torqued crank damper bolt can cause unstable timing. As well as cheaply made under drive pulleys.

Has a compression test been done?
 
Last edited:

kevlar

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May 27, 2015
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Thanks burns for the reply.The car does have cats,an the shop it's at now did a compression test an all was good.I haven't seen any seepage out of the crank dampner,will take closer look when I get it back to be sure.Underside of the motor is oil free,I've looked for an exhaust leak a couple times haven't found anything yet . I also haven't noticed any loss of oil or coolant doesn't smoke at all,can only feel misfire under 1500 rpms an is intermediate,gonna check alternator and evap system when I get car back monday,will follow up with l results soon thanks
 

trombonedemon

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Jun 25, 2009
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U.S.A, U.S.A., U.S.A.!
In for result. I had a lean condition CEL, what it turned out to be was unmetered air through the cold air intake coupler. I had pushed the coupler to far in and it created some weird turbulence around the two couplers.

Sensitive little bugger, it was. Took me a while to figure such a silly mistake.
 
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