Engine 1999 Gt Issues, Need Advice

Discussion in 'SN95 4.6L Mustang Tech' started by schwoogies, May 7, 2013.

  1. I have a 99 GT 35th LE with 100K on it. Driving to work going about 60-70 mph if I step on the gas, to pass someone, it starts hesitating and stuttering. Sometimes it will recover, and this is the only time it happens. Last weekend I replaced all of the ignition coils and it did start to run better but still is experiencing the same issue. No check engine light comes on, so I can't pull the code.

    I can be at a dead stop and take off, nothing happens. Only happens when I am going at a steady speed and try to pass someone. This happened a few weeks ago and the car stalled and would not stay running.

    Please help, not sure what else to replace.
  2. Even if there is no CEL there still may be a code.

    Did this just start? It could be a bad tank of gas, a clogged up fuel filter, or several other things. I wouldn't go throwing all of these parts at it, although a fuel filter in a instance like this could be an inexpensive fix for these symptoms.
  4. It's been happening on and off for close to 6 months that's why I just replace all the ignition coils. Maybe I will try replacing the fuel filter and putting a gas additive in it. Thanks for the advice!
  5. Fuel filter would be the easiest step. Did you check the plugs? I'd have replaced those before the coils.
  6. Thanks Rick. The plugs were replaced like a year and a half ago. So I didn't think it would be them. The coils were still motorcraft so I knew they were original and thought that might me the problem. Going to try replacing the fuel filter, I hope that fixes it. If not I will be back for more advice :)

  7. +1 for fuel filter. I assume your air filter isn't clogged, etc.
  8. My '99 GT started dipping In the revs when stopped at a light going from 900 to 500. It was also running choppy. The car had started doing this on my trip down to Florida as soon as I left the gas station in Georgia. I thought it was bad gas at first but after putting Chevron techron in a bottle & then dry gas & 8 tankfuls of premium gas, I ruled out it being a gas issue. With 101,000 miles on the odometer, I was going to do a tuneup anyway, so I changed the original Motorcraft plugs with platinum Motorcraft spark plugs, fuel filter, IAC valve, & PCV valve. Did all that & the car was still idling crappy & had to almost floor it to get it moving fast. I then reached out to Scott Hoag, former Ford engineer & now President of MRT tuning, through the MCA/Mustang Club of America, & he said to check the MAF sensor & sure enough that was the problem & the car's running strong again after replacing the original MAF sensor.
    Let me know if this helps you out.
  9. I purchased my first Mustang dirt cheap. Granted it's a 3.8 V6;she's still fun to drive. This car had the same issue. I did a complete tune up, installed a CAI. The vehicle ran a lot better but still hesitated under a load. Seeing how I couldn't figure the problem out I went back to the basics. I started checking all my grounds and electrical connectors connected to the sensors. When I got to the crank shaft position sensor and pulled the wire/connector off the sensor I noticed that the insulation protecting the wires were melted/worn away exposing both wires. I've tried soldering a new wire with connector to replace the bad section with varying results. The first time the idle significantly improved and the bad hesitation under a load turned into micro burst hesitations/stumbles(barely noticeable). I redid the solder job and it's now hesitating bad under a load like it was when I first purchased. I performed a complete tune up- the works man. I believe this is my problem. Any ideas suggestions??? Would it be worth trying to replace the whole section of wire from the PCM to the Crankshaft position sensor?

    The only mods this Stang has is- X-pipe, Flowmaster mufflers, & a CAI which were all purchased by me.
  10. Something
    Something caused the melting of the sensor wire. Might be a bad CPS. Have that checked. Otherwise look to the MAF and make sure it is clean.
  11. Love it when OP's start a thread and dont give us an update on the issue...