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Thread: 93 F150 4.9 exhaust leak

  1. #1
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    93 F150 4.9 exhaust leak

    Fixing an exhaust leak in my truck. I was getting similar amounts of CO in the cab as Sammm was a while back and could hear a bit of a tick when it was running.

    Got it all apart, and found soot on the gasket adjacent to #4. The exhaust manifold has some corrosion, and needs to be resurfaced. I see mixed reviews on the replacements that are available.

    Looking at how this thing goes together, it shares fasteners with the intake manifold. I did some measuring and the mounting tabs on the exhaust manifolds are about 40 thousands thicker than on the intake. Exhaust is cast iron, intake is aluminum.

    Do I need to find a machine shop that can do all of them together, or am I ok to take 10 thousands or so off each manifold using a flat table belt sander?

    Anyone done this repair?

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    Re: 93 F150 4.9 exhaust leak

    i never had a ford truck, and dont know what ur describing looks like, but sounds similar to my situation about 25+ yrs ago, i did have an issue w/ a straight 6 ford 300 in my vermeer 1250 tree chipper. to best my memeory, i had a blacksmith shop resurface both the exhaust intake together on a long belt sander. i wouldnt try to surface each runners flange individually on belt , we did flanges to head at once. but that wasnt my problem, my problem was where carb mounts to intake, it bolted together w/perpendicular surfaces to the head surface as a carb/fuel preheat w/ tubes/cavities being shared, that had no adjustment. it was correded/blown out there, and i built it up there, and the guy resurfacing it screwed it up. thats why both needed to be bolted together there before surfacing flanges to head. i eneded up replacing the pair of mantifolds
    Last edited by 123weld; 04-23-2022 at 07:16 PM.

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    Re: 93 F150 4.9 exhaust leak

    The first two things Is duck tape and jb weld. Both will fail.

    First thing find the leak. Odds the exhaust piping will need replaced.

    Dave

    Quote Originally Posted by 123weld View Post
    i never had a ford truck, and dont know what ur describing looks like, but sounds similar to my situation about 25+ yrs ago, i did have an issue w/ a straight 6 ford 300 in my vermeer 1250 tree chipper. to best my memeory, i had a blacksmith shop resurface both the exhaust intake together on a long belt sander. i wouldnt try to surface each runners flange individually on belt , we did flanges to head at once. but that wasnt my problem, my problem was where carb mounts to intake, it bolted together w/perpendicular surfaces to the head surface as a carb/fuel preheat w/ tubes/cavities being shared, that had no adjustment. it was correded/blown out there, and i built it up there, and the guy resurfacing it screwed it up. thats why both needed to be bolted together there before surfacing flanges to head. i eneded up replacing the pair of mantifolds

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    Re: 93 F150 4.9 exhaust leak

    It's been a while and my memory is sketchy, but before you go trying to make those 2 manifolds the same height, check a new gasket set. It seems to me they are made that way because one gasket is thicker than the other.
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    Re: 93 F150 4.9 exhaust leak

    Hey............. Another thing to watch out for. The new style exhaust donuts suck on these trucks. That ball shaped stupidity. The old connections used a gasket, not the stupid metal on metal seal. Be real careful when you take it apart, and try to seat it the same as it was when you put it together.

  7. #6
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    Re: 93 F150 4.9 exhaust leak

    If you have to grind the exhaust manifold faces flat, I think that it would be less work to modify washers on the studs to compensate for any material that was removed, however I don't think that 0.010" is much to worry about. You should still get good pressure on the gaskets when everything is tightened down.

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    Re: 93 F150 4.9 exhaust leak

    You will need to resurface them as a unit. Do not separate them.
    Any good automotive machine shop should have the belt sander and experience to do it.
    When you reinstall them torque the fasteners in several steps in the proper sequence.
    If you just start hogging on it you will break at least one of the ears off!

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    Re: 93 F150 4.9 exhaust leak

    Quote Originally Posted by 123weld View Post
    i never had a ford truck, and dont know what ur describing looks like, but sounds similar to my situation about 25+ yrs ago, i did have an issue w/ a straight 6 ford 300 in my vermeer 1250 tree chipper. to best my memeory, i had a blacksmith shop resurface both the exhaust intake together on a long belt sander.
    I use to always buy 300 six ford with a 4 speed for snow plowing and towing. (they suck now though)

    I had one exhaust manifold where the back to openings were curled in. Nice big bow in the manifold.

    I flattened it by eye with a hand held crappy belt sander.

    Checked with straight edge until "right," elongated the holes - bolted right up - perfect
    Dave J.

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  11. #9
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    Re: 93 F150 4.9 exhaust leak

    i would be more inclined to check the gaskets thickness first. maybe different thickness because intake has to seal a lot better than exhaust.
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  13. #10
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    Re: 93 F150 4.9 exhaust leak

    Quote Originally Posted by farmersammm View Post
    Hey............. Another thing to watch out for. The new style exhaust donuts suck on these trucks. That ball shaped stupidity. The old connections used a gasket, not the stupid metal on metal seal. Be real careful when you take it apart, and try to seat it the same as it was when you put it together.
    Yes sir, I have a tick on the left side. I thought simple donut gasket replacement. Not a chance. I've gotten used to the tick

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    Re: 93 F150 4.9 exhaust leak

    Difference in thickness is due to some trucks having exhaust gaskets, and some not. I had everything surfaced and put it back together with an extra thick crushable gasket from Remflex that the ford truck guys pointed out to me. Seems to be running well, and the CO meter shows no increase in CO over background levels. I have only run it about 40 miles so far, but will be going about 150 today.

    We will see.

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    Re: 93 F150 4.9 exhaust leak

    Quote Originally Posted by Zimm View Post
    Difference in thickness is due to some trucks having exhaust gaskets, and some not. I had everything surfaced and put it back together with an extra thick crushable gasket from Remflex that the ford truck guys pointed out to me. Seems to be running well, and the CO meter shows no increase in CO over background levels. I have only run it about 40 miles so far, but will be going about 150 today.

    We will see.
    Intake and exhaust? How many studs did you have to replace?

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    Re: 93 F150 4.9 exhaust leak

    Quote Originally Posted by Denis G View Post
    Intake and exhaust? How many studs did you have to replace?
    Manifolds use bolts in 93, except for the one combination bolt/stud at the very front of the motor. That got replaced last time I was in there. The studs for mounting the exhaust pipes were replaced. Little heat (dull red) on the manifold and eased them out with an air impact. No biggie as the manifolds were out anyway.

    Did 150 miles and all seems well. Checked the CO a couple times along the way with negligible amounts detected.

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