Engine Power Loss, Not Sure Of The Problem.

Discussion in 'Fox 5.0 Mustang Tech' started by James.Little, Apr 26, 2013.

  1. I am unsure of what my problem is but here are the symptoms:
    • Fails to start, unless I play with the gas pedal. Sometimes it starts, but you can hear it lag for a second before it takes. (if that makes sense)
    • Sluggish when speeding up and seems to struggle on the higher RPMs. (Like it doesn't have enough energy)
    • some backfire when down shifting. (this doesn't occur all the time)
    • TFI module is not hot after driving (does this matter?)
    • Car does not shut off by itself or acts like it is out of gas when it is running (not fuel pump, is it the TFI module?).
    I am unsure what the problem is, I originally thought it was the TFI module, but the TFI module is not hot after driving around all day and it does not turn off by itself. Any thought on what the problem is or how I canfind it?
    Thanks a bunch!
  2. Sounds like it could be a fuel delivery issue. I'd get a fuel pressure gauge on the rail and make sure everything is on rhe up and up. You should be seeing about 40psi with the vacuum line off. If it has trouble reaching, or sustaining that pressure, it could be a fuel pump issue. When was the last time the fuel filter was changed?
  3. I have never touched my fuel filter, I have only had the car for about a year.

    Secondly, how do I check the fuel pressure? You said I need to get a fuel pressure gauge, then what?
  4. Screw it onto the schrader valve on the fuel rail.
  5. 40 with the vacuum off.... About 34 with vacuum. If it has fuel pressure check the tps voltage... We will get to that if your pressure is fine. If you have never touched the fuel filter replace it anyway. It's an easy job.
  6. I am not sure on what you mean. How do I turn the vacuum on and off? Sorry I am pretty new at all of this, but I am learning!
  7. lol....maybe this isn't something you should be tackling. Your automotive knowledge seems pretty basic. The vacuum line is either plugged in, or it isn't. It's just a small vacuum hose that attaches to the top of the fuel pressure regulator. Plug the hose onto the regulator and it should read about 34psi on the fuel pressure gauge. Unplug it and it should read about 40psi.

    Give it a couple of whacks of the throttle while the gauge is on there to see if the pressure drops significantly when the engine revs. If it does, there's a good chance you've got fuel delivery issues.

    My recommendation....before you go changing any major parts, do a full tune up on the car. Fuel filter, plugs, wires, cap and rotor, PCV valve. You said it seems like it's running rough....might as well take the basics out of the equation before you go spending any real time or money on the car.
    88LX5.Oh likes this.
  8. Thanks for the detail information. There is two reasons why I bought this car. 1. I have always wanted a Mustang. 2. I wanted something I could work on and learn from. I have learned so much these last couple of months. I am a quick learner and I love to do it. Lol, so it is all good!

    I will need to go and grab a fuel pressure test kit and I will report back. Tomorrow I plan on changing the plugs and fuel filter. I have the plug wires on the way and I will change the cap and rotor next week.
  9. A Haynes manual will be a wealth of knowledge for you then when I first started out I practically rebuilt my whole car with one. Advanced auto parts usually has them for about 25 bucks. Well worth the money.
  10. Yeah I have been meaning to buy one.

    So, I changed the fuel filter and now it will crank, but it won't start. I made sure I put the filter on the right direct. I primed it the system for a bit, it still wont start. What the heck?
  11. haynes manuals have nothing in them that you cannot find online for free. i too bought one and it is brand new still sitting on the shelf. in fact they lack more than they provide. don't waste your time on code readers either, a paperclip is all you will ever need.
  12. I disagree. However it does lack some info. But for torque specs it has all I need.... A fuel filter will not cause it to not crank...... You have other issues. Do a tune up first. Check fuel pressure. Charge your battery. Not necessarily in that order...
  13. sure, it has useful info. but it will not help here. the trouble shooting sections are a joke and the diagrams are usually not correct either for the year you need. when they make the haynes books and say good for 79-93 they really mean they tore apart a 1989 and this is what they came up with. to each his own i guess
  14. Yeah, I kinda need this thing to work, seeing as its my daily driver. I changed the plugs since I already had those available. I killed the battery trying to get it to fire, but it is charging now, so we shall see.
  15. Find the jrichker checklist for cranks but does not start. Do it NOW. It may get you to work on time.
  16. Yeah I got it to fire, woot! The idle seems smoother. It still struggles to start, but it fires up easier. I have noticed when I slam on the throttle it drops in the RPMs for a slight second then revs up. It also seems to struggle in the higher RPMs. I noticed when I took off my CAI to change the plugs, the throttle body plate was pretty dirty, could that mean something? I also gaped the plugs at .54, that is what it said at fordparts.com. I put in autolite double platinum plugs, since I got them for the same price of copper plugs. Also the old plugs looked pretty good. They where gaped at .44 and had a touch of gas on them, does that mean anything?
  17. Have you checked the fuel pressure yet like I mentioned above?
  18. No I am broke college student, that will have to wait till next week, when I get paid again.
  19. Fuel on the plugs means they are fouled out. I gap my plugs at .4 but I run higher compression. What you are describing sounds to me to be a fuel delivery issue... Pull the cai again and use an old toothbrush and some carb cleaner clean the tb. Hold the butterfly open and clean as much of it as you can. A dirty tb can cause some strange issues.
    Look up the crank but no start checklist mentioned above. Jrichker has a wealth of knowledge that is very reliable.and it all works. Just follow the steps in order.