car started running rough... any ideas why?

Discussion in 'Fox 5.0 Mustang Tech' started by BelueLX, Dec 16, 2003.

  1. OK went to the gas station in my 91 lx (w/ sc-trim) was running fine. on the way back started running really rough. pulled all the plugs they looked fine. swapped the wires, cap and rotor from my 88 and made no difference. there is no vacuum leak (solid 19" at idle). pulled the FPR vacuum line it changed the idle. unplugged my MAF and it changed the idle by a very very small amount. no check engine light. can anyone tell me whats wrong with it?
  2. have another car to swap parts off with. So far its not the:
    distributor cap
    spark plugs
    vacuum is steady at 19" at idle
    plug wires
    throttle position sensor...
    timing is at 10* perfect
    fuel pressure regulator
    I unhooked the vac to the FMU to be sure nothing was coming out.

    Going to try another MAF tomorrow if I can get my hands on one. Its sort of sputtering and doesnt want to pull. I guess if the MAF was bad it wouldnt run right with the Vortech on there. What else is there ?
  3. What does your fuel pressure look like?
  4. i have to check that tomorrow also. im guessing computer, maf or possibly fuel pump.
  5. it looks like my problem is with cyl #4. i pulled plugs 1-3 and they look the same . i pulled 4 and it looks like it hasnt even fired since i bought it and installed it this morning.smells like i just soaked it in gasoline. i tried 3 diff. sets of plug wires and thats the 2nd plug. the first one was a little darker so i replaced it. is my injector stuck open (fouled, soaked in fuel) , stuck closed (not getting any fuel to burn) or is there a reason that the ignition isnt firing the #4 plug??? can i test the resistance or anything before i pull my upper to remove it? id like to go carbed but just put the charger on it :bang:
  6. pulled the valve cover and intake rocker arm #4 was broken in half laying in the bottom of the cylinder head. time to upgrade :nice: . is that a common problem with rocker arms breaking in half?
  7. Just checked your post again. Glad you found the problem. As a matter of fact, I had a rocker arm break on the 289 in my '65 four or five years ago. I had just bought the car and wanted to see what heads it had; pulled the valve cover on the driver side and was greeted by a broken rocker arm. From what I've heard it's not very common.
  8. Yeah i still have stock heads im just going to get a new one til I put the AFRs on. They use the 7/16" -vs- the stock bolts imho its not even worth pulling the intake to do the passenger side rockers. Another few months before I can do my h/c/i :nice: .