00 Mustang Gt - Misfiring & Harder To Start Lately.

Discussion in 'SN95 4.6L Mustang Tech' started by jayrw, Feb 5, 2014.

  1. Lately when I start my car it has to turn over longer than usual (usually a few seconds, normally it would fire almost immediately).

    I'm also experiencing a loss of power or misfire, it feels like the car isnt running on all 8 cylinders but its random, when the car is idling you can tell it's dropping a cylinder every once in awhile (At least I think it is, can feel a random rough spike)

    If I try to run it WOT it just falls on its face and sounds terrible, but this is also random, sometimes it will run strong at WOT and sound fine (Not very often tho, getting worse I think)

    The spark plugs were changed a little over 2 years ago and havent had many miles put on them, car is at 93K miles and all Stock.

    I had a JLT CAI but it failed smog inspection (Not legal in CA, Oops!) I put my stock air intake back on and it started acting up about a week later.

    I'm guessing it could be a spark plug or coil pack but would either of those be associated with the car taking longer to start too?

  2. No CEL or codes I scanned it earlier today. It seems like taking it on the freeway helped, the car is running a lot better than yesterday but I still feel a slight sputter or loss of power as I'm taking off from a stop but not always, also when the car is idling the rpms sometimes fluctuate between 500 - 800 (No heater or AC running).

    I've read testing the coils with a multimeter isn't a guaranteed way to check for a bad coil but I decided to try it anyhow, the Haynes manual says to check resistance and replace if they don't match the specifications listed but it doesn't give you any range to work with, how far off spec can they be?

    |I ask because my results were a bit off from Haynes specs.

    The primary resistance ranged from 01.10 ohm to 02.2 ohms (multimeter set @ 200 ohm, its lowest setting) Haynes lists the spec @ 0.55 ohms (?)

    Secondary reading ranged from 5.18k ohm to 5.59k ohm, Haynes lists the spec @ 5.5k

    #3 jayrw, Feb 5, 2014
    Last edited: Feb 5, 2014
  3. Sounds mechanical to me, most of the time I had bad Coil on Plug there was a check engine light. Gets some stats like emmissions and get a tune up, compression ratings at your local tech shop; your symptoms can be a result of any amount auto parts gone bad. Wish you had a check engine light, though.
  4. I don't know if this helps with diagnoses but I notice when the car is cold (sitting overnight) it runs great for the first 5 minutes and then starts to randomly miss or sputter, to me it sounds like one of the spark plugs is partially fouled but not 100% sure, I dread having to remove those plugs lol (ive only done it once).

    Also the problem is more likely to occur accelerating from a lower rpm, so if I were to hold it at 3,000 rpm on the freeway it stays running fine without sputtering, but if I'm in 3rd gear at a lower rpm and then accelerate it's a lot more likely to sputter / lose power.

    Today I chanced it and attempted to get it Smogged, It passed without any issues the technician even mentioned it running clean in the results, I'm no mechanic so not sure how to really process all of this, when you say it sounds mechanical are you talking internal engine problems (more serious?) or something else, The whole time it was in the shop running through the tests It sounded fine except for a random but quiet "pup" sound coming from the exhaust when it was idling, Thanks again.

  5. Looks like I got a break in the case finally.. I was driving home last night and the check engine light came on for the first time, P0302 cylinder 2 misfire, hopefully its just a bad COP or fouled plug. Ill post an update after I get it resolved.
  6. New coil solved the issue! No more problems since replacing coil #2 yesterday :nice: