86 Gt Acceleration Vibrations

Discussion in 'Fox 5.0 Mustang Tech' started by Young&Dum14, Jan 13, 2014.

  1. Hello Community,
    (Note: this is my first time posting on a forum.)
    I have an 86 Mustang 5.0 that has been running with out any notable vibrations. Over my holiday brake from school I did some engine work and never touched any aspect of my drive line. Now after the my work there is vibrations toward the top of each gear, mainly in 5th. The vibrations mainly occur when accelerating and completely stop as soon as I push in the clutch peddle. I removed my drive shaft and had a drive train shop check its u-joints and straightness. They say it is in good condition. My motor mounts and transmission mounts look to be fine and there is no slack in the transmission tail housing bushing where the drive shaft yoke inserts. I think the vibrations are from the engine because when I apply more throttle in 5th I can see my upper intake manifold violently begin to shake side to side (my car is currently hoodless).

    Here are the main modifications I made just before the vibrations started.
    -New SVE radiator and electric fans.
    -PVC to catch can / breather.
    -Upper/lower mountaineer intake manifold and throttle body swap.
    -Removal of all smog systems, and vacuum reservoir.
    -New spark plugs and distributor cap and rotor.

    The car sounds different from before the work. It now has a slight clunking sound. I appreciate the help!

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  2. i'd look at your harmonic balancer. is it a stock unit? They tend to seperate causing vibrations. You can usually spot it by watching it whle the engine idles.
  3. If you didn't touch the harmonic damper I'd suspect you have a high-RPM miss due to something in your ignition work.
  4. and, get that air filter out of the bay :)
    Bill Gordon likes this.
  5. Nice ride! Agreed, get rid of that hot air intake....
  6. sounds like u either put junk plugs in it or you didnt gap them right

    I hope u didnt put champions in it
  7. Inspect your harmonic balancer
  8. I have physically checked the harmonic balancer when the engine was off and have watched it idle. It runs smooth when it idles. I did not change the spark plugs till after it was out the shop with the vibration. I put Autoline platinum plugs in with a ~49 gap. I think I'm going to swap back to the stock cap and rotor (after school) and see if that is the problem. As for the air intake, I am thinking of sending it through the hole in the inner fender and mount the filter down behind the fog lamp hole, giving it a ram air effect. However I worry about water entering the system on rainy days. Do you think this would cause a problem?
  9. I had a very similar vibration issue several months back. I checked all the mentioned “usual” suspects. The harmonic balancer, drive shaft, u-joints, motor mounts, transmission mounts…etc. I even replaced several of them with no luck. I had pretty much given up on it and then one day my water pump went out. After installing a new one the vibration was gone. Might just have been a coincidence but who knows.
    Young&Dum14 likes this.
  10. I did remove my stock radiator fan. But I don't think a vibration this large would be caused by only that. Cdurbin, did the vibrations occur when you gave it more throttle at the bottom of the gears... when the engine sounds like it is under a lot of load? That is what my car is doing (not lagging the engine of course). I will defiantly consider the water pump as a cause.
  11. I noticed mine at around 2500 rpm under load regardless of what gear.
  12. Run the cylinder balance test of the EEC engine diagnostic routine. It's usually accessed by triggering the check engine codes with the engine running, and at the end of the codes, depressing the gas pedal 50% for a quick rev. The engine will then run through a test where it turns off the injector for each cylinder and monitors enginer performance to determine a weak cylinder.

    I used this test to discover a dead injector, when i had a slight engine vibration issue. Car ran perfectly fine, and had power, but had a vibration issue at low RPM. Come to find out, it was running on 7 cylinders.

    For spark plugs, 5.0's tend to not like platnium plugs. Not a critical thing here, but in the future, stick to a copper plug. The gap on the early 5.0's was smaller than the later models. Unsure if they opened the gap in 1986, or in 1987, but the later gap spec is 0.052" - 0.056"...most people run 0.054".
    Young&Dum14 likes this.
  13. In order to do the diagnostics I will have to go to a service shop and use one of their computer systems, right?
  14. No. You can do it with a paperclip, or a $25 tester


    Paperclip method is a bit of a PITA. I'd consider $25 plus shipping a good investment for any Fox Mustang owner. If you want to just get it done, read post #2


    1986 Mustangs do not have a check engine light, but they store codes like modern cars. Since you don't have a check engine light, you'll need a test light to blink the codes. So you can try this method with jumpers and a test light...or just buy a $25 reader. Might be cheaper if you shop around too
  15. i've had that code reader for 20+ years, well worth the $25!
  16. Old Head.... Someone had to say it ;)
  17. Makes a few of us!
  18. Thanks Mustang5L5, I have been wanting to check for error codes but have been avoiding paying $60 + to have a shop do it. I will defiantly look into getting the reader soon. I meant to test the car last night with the old cap and rotor but I spent my time finishing my cold air intake. (I will post a pic of it at my lunch break.) I am taking my car back to the shop where I did the work and will check the rear end. I am tempted to buy a new water pump after what Cdurbin said, and because my engine runs at the top of the 'NORMAL' scale on the stock coolant gauge. I was expecting this to change when I replaced my one inch thick single core radiator with the new two inch three core SVE radiator. I put a new 195 thermostat in... so I am left thinking maybe I was sold the wrong replacement temp sensor that runs to the gauge.
  19. Better?

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  20. Functionally better at least. o_O