Alright so just as a preface...this started yesterday. There are 320 miles on the new motor. The motor runs great and compression feels strong, and the cars run perfectly up untill now....

ok so the thing is, at completeley random times the car starts misfire horribly, belowing smoke...this lasts anywhere from 30 seconds to a couple minutes, then stops and goes back to running nice and strong. The weird thing is that its just so random, and it happens at any RPM. The car wont hold idle while its misfiring, and it sounds like a crazy chainsaw/ lawnmowor. in about 15 minutes of driving the car, it had this episode probobly 3 times. Weve checked the spark and its not being eratic or anything...what could the problem be...suggestions?

 

Does it begin when you first drive the car? or will it do it when you first start the car and leave it in idle?

 

fouled plugs/poor tune.

 

Yeah, remove and read the plugs. Your mechanic should be able to do that and at least get some ideas. If one or more plug is fouled, replace it/them and try again. If the plugs continue to foul, check all the wiring connections (since the engine was removed and reinstalled apparently), then check the ignitors/coils.

 

is your tach working correctly when it is backfiring?

 

wiring problem... short or exposed wire somewhere...

 

^ i figured it could be wiring since i just fixed a short a couple days ago. but when it comes to wiring, doesnt it just either just work or not work? why would it act like this at random?...the plugs are relativly new, and yes the tach works when misfiring. Another thing, it pretty much happens only when warm.

 

My Ar Did That When I Accidentaly Loosened The Wiring Harness Ground. Its Near The Transmision Bell Housing. Theres A Bolt That Holds It Into The Block. Its Located Kinda Near The Oil Filter. You Have A N/a Right?

 

add a couple grounds (the more the merrier), check your plugs, and also make sure your afm is in good shape and not bad (u can pull the black cover and make sure there is good tention on the spring)

 

its a turbo...thnx guys ima go check it out in the morning and see what we figure

 

check for vacuum leaks then I would get a bottle of water and dish soap and spray down all the couplers and see if u get any bubbles if u do tighten then up and wait till all the bubbles go away and check again..

boost leak will do this..

check all couplers even at IC and at TB spray intercooler etc.

 

If he has a little over 300 miles on this motor, i highly doubt he is getting into boost.

I'd get a wideband o2 system and moniter AFR's.

 

it dont matter if he is getting into boost he can still have leaks in the hoses or couples or around the couples which can and will cause problems trust me check it out its free to do and see if there are any leaks.

 

I'm guessing you have your leading and trailing wires mixed up...

 

its getting into boost already...the motors pretty strong...but i doubt the lead and trails are mixed caused the problem just started

 

hahah we figured it out....the in-wire ground coming from the ecu to the injectors was melted and broken...all 4 injectors would stick open at once and just dump raw gas into the motor...thnx yall

 

sound like a loose connecton/bad ground. If a ground bolt wasn't tightened enough it may have vibrated loose. check all your grounds and check for any exposed wires that may be shorting while driving. since it only does it warm pay close attention to sensors, since the computer "believes" sensors more when in closed loop.