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Thoughts on 4.9L

Discussion in 'Ford Trucks' started by cuttinggreen, Dec 3, 2003.

  1. cuttinggreen

    cuttinggreen Junior Member
    Messages: 4

    First of all this is my first post so please forgive me if something is out of line.

    I have a 1985 F250 4X4 with the 4.9L Straight 6 with an automatic tranny. Runs very poorly at idle. Get into upper RPM's and runs fine. Also has serious exhaust leak from manifold as far as I can tell. Also has some vacuum issues....One of Ford's first attempts at Fuel Injection from what I have been told.

    Here is my question(sorry to rattle on)

    Do I take the time to work though the conglomeration of vacuum lines on this thing or do I install the carb intake (that I have) and get rid of 75% of the vacuum?

    What other issues could I run into if I do switch it over from FI to carb?

    Any thoughts or recommendations?????

    Thanks in advance for your help
     
  2. Plow Meister

    Plow Meister PlowSite.com Addict
    Messages: 1,174

    I wouldn't change to carb. The ignition, timing, and emissions are set to accept fuel injection. The vaccuum hoses aren't as bad as you may thing. There should be a diagram either on the valve cover or on the radiator support. Follow those diagrams and it will lead you to you problems.:D Have you exhausted all your other potential problems? Compression, valves, bearings, spark?
     
  3. ksland

    ksland Senior Member
    from ma
    Messages: 420

    You must have the year wrong, Ford didnt put fuel injection on the 4.9L's till 1987
     
  4. Ggg6

    Ggg6 Senior Member
    from IL
    Messages: 521

    EFI is the best thing that ever happened to this engine. The 1st year was 1987. Manifold leaks are not uncommon, and they can cause a vacuum leak due to common intake/exh. manifold bolts. If she starts fine, is good at high RPM, but will not idle. I would check out the MAP sensor, it can cause the same symptoms.
     
  5. 86burban

    86burban Senior Member
    from chicago
    Messages: 130

    I've had both. I lean towards the EFI. Its more reliable in the cold, Its easier on gas, and it has much more pep. My 80 F150 was always slow to start in any weather, and I went thru 2 fuel pumps in the year I owned it. My 90 F250 sits for weeks on end while I drive my 91 F250 with a 351, and every time I go to start it, It fires up with the first tap of the key. I am a die hard EFI fan.

    Tony
     
  6. 85F150

    85F150 Senior Member
    Messages: 340

    yea i have the 85 f150 with 4.9l, it is a carb in disguise...PITA to get right, but once set my runs awesome, better than my fuelie....it is a feedback carb, start by checking the TPS, IAC, oxygyn sensor, and ECT....most likely the IAC...but the idle and fast idle is also automatically controlled by a solenoid right by the throttle cable hookup...the sticker on the rad support says how to set the idle/fast idle....disonnect the ECT...tap throttle momentarily 3 times then plug int the ECT and adjust allen screw til 650 RPM....i usually drive around for the day with the ECT disconnected then reconnect and adjust the allen screw...
     
  7. CARDOCTOR

    CARDOCTOR PlowSite.com Addict
    Messages: 1,310

    fix the vac lines. should have vac diagram under the hood
    remove carb ,remove a/f mixture screw plug that way you can adjust the carb after reinstalling it

    the 4.9l is a bullet proof motor only 2 ci less than a 5.0l v8
    john
     
  8. 85F150

    85F150 Senior Member
    Messages: 340

    there is no plug on there it has a screw in it but last time i tried that on a computer controlled one it through the puter for a loop until i adjusted it back....
     
  9. PARTSMGR

    PARTSMGR Member
    Messages: 32

    4.9l

    The 4.9L is the best motor Ford had ever made. I have a 1979 F150 (HD) that has the 4.9L - carb with a 4 Speed (Creeper First Gear). This vehicle is bulletproof. Only problem with the 4.9L is it has a 1bbl carb and it sucks fuel. Since this has the intake and exhaust so close together, leaks are common. Make sure the manifolds are very flat and pay attention to the torque specs- use good gaskets and get a Ford vacuum diagram book if you can't find one on the vehicle. The only problem I have with this vehicle is the clutch is the old mechanical type and it takes a good left leg to clutch it. If this is a carb vehicle and you are going to keep it. spend a few $$$ and get a Clifford 4bbl intake manifold and a Holley 390 cfm carb. This is the great setup. I don't have one , but I know a few guys who spent the $$$ and it runs great. Fuel mileage is in the 12's around town and about 16 on highway. (As long as the 4bbl does not kick in).
     
  10. gt_racer50

    gt_racer50 Senior Member
    from Ohio
    Messages: 484

    I have a 4.9 in my 95. it's a great engine as long as your not in to speed. But for plowing and towing I don't think you can beat it.
     
  11. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Did you get it fixed? Or figured out? I been there did it with 86 EFI. seen me a PM if you need more help.
     
  12. Pickering snow removal

    Pickering snow removal Senior Member
    Messages: 151

    i would suspect a leaking intake manifold and poss cracked exhust check the intake bolts for tightness and stick with fi no carb
     
  13. juggernaut

    juggernaut Member
    Messages: 84

    I am having trouble with my 4.9 it seems to run better with little to no gas in the tanks full tank seems sluggish and runs slightly rougher. I am guessing fuel filter is there one main one or two one for each tank (dual tanks).
     
  14. Plow Meister

    Plow Meister PlowSite.com Addict
    Messages: 1,174

    You may have water in your fuel or possibly a clogged pickup tube screen. Kinda unusual for it to be running better with less fuel in it
     
  15. juggernaut

    juggernaut Member
    Messages: 84

    Yeah it is very unusual. Now that you mention it im guessing it is a clogged pickup because i normally run the tanks until it begins to sputter and then switch to the other (I know thats not good but I never really had a problem) Its not like it runs like crap it just runs a hair less smooth with full tanks and frustrates the hell out of me. I am going to take off the bed in the summer sandblast the frame and check out the tanks can they be cleaned (ie take out the pump and pickup) or do you just replace them? I have a feeling you cant do a darn thing since its fuel injection.
     
  16. Plow Meister

    Plow Meister PlowSite.com Addict
    Messages: 1,174

    You can replace the strainer I think. You may have to replace teh pickup tube. The strainer could be cleaned with clean fuel and a soft toothbrush. Just backflush the strainer with fuel and scrub. Shouldn't be too bad. Especially if you already have the bed off.
     
  17. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Your charcoal canister on the vapor system for the tanks could be gas logged. If the electric purge solenoid's not working it will fill the charcoal with gas after a while. Because it does open up and purge the gas it has collected. Or the lines pinched shut. This would cause you to get no air in to replace gas as it is burned, kinda a like vapor lock makes it harder for pump to draw gas out.