What follows is a procedure for removing the passenger's side exhaust manifold from a 1991 Ford Explorer with 4.0L engine. This may prove useful if you are replacing a head gasket, or installing aftermarket headers.
I recently had an engine rebuilt for my 1991 Ford Explorer. I installed the engine myself. When it came time to put the plugs in, I found that the aftermarket exhaust manifold gasket webbing covered the plug holes. I grabbed a pair of diagonal cutters and cut and tugged at the gasket to gain access. Later, when I started the engine, I was disappointed to hear that I had torn the manifold gasket back under the manifold and it was leaking. And of course, it was the passenger's side. I've seen aftermarket dealers of headers print that the passenger's side gasket will "try your patience." After checking the Haynes manual, I found no procedure for removing the manifold with the engine in place. In the end I bought a new gasket set (Felpro, $5 at Pep Boys) and just had at it. Here's how I did it, with relatively no pain. Keep in mind, I did just have the entire engine out, so none of the bolts were frozen.
I had just had this motor out. The first time I took out the exhaust bolts, I had to apply my torch and a lot of WD-40 to the exhaust flange bolts to get them out. Likewise, the engine builder applied heat to the manifold bolts to avoid breaking them. If you don't have access to this type of equipment, you may want to START the procedure with the exhaust flange bolts to see what you're up against. Don't just crank on the bolts. Apply short impacts to them. If you feel the tell-tale easy turning without any "erking noise", stop before you break the bolts. Apply plenty of heat and penetrating oil and avoid the headache of extracting a broken bolt.
I will often give dimensions of a fastener. This is usually the size of the tool used to remove them, not the thread size. I may have replaced some of these fasteners in the past and your sizes may be different. In all cases, the dimensions are from memory and may be totally wrong. All fasteners are metric. If you don't have a 11 mm socket (many sets don't), 7/16-in is pretty close. Don't get me started on Ford's choice of fasteners.
1. Place front passenger side on jack stand and remove the wheel.
2. Remove plastic snow shield from intake plenum. [2@ 8mm bolt] Remove the intake hose connecting the throttle body to the airbox. [2@ 8mm clamp screws and slip fit hose to oil filler neck]
3. Partially drain radiator at petcock. Remove upper radiator hose from radiator. [8mm clamp screw] (I replaced the thermostat at this time too, so I removed the upper hose to get it out of my way. You may find you don't have to.)
4. Remove plastic airbox cover: Label and disconnect two vacuum hoses [A][B] from cover and electrical connector [C] from mass airflow sensor. Two hold down screws from above and top pivots up. [2@ 8mm]
5. Remove plastic airbox base. One hold down screw [8mm] and pull box out of two rubber grommets. Pinch the intake hose to remove.
6. Remove plastic airbox platform. It's screwed from inside the fender well. Be careful, as the captive screws are only held by the weak plastic casting. [3@ 11mm]
7. Label and remove wiring harness connector hold downs from plastic fender liner [D][E][F]. Remove four bolts securing fender liner to body. [4@ 8mm] Remove four Philips headed trim screws securing fender liner to fender [4@ #2 Phillips-- drill out with 3/16-in bit if stuck]. Remove plastic inner fender liner.
8. Remove air duct leading to exhaust manifold heat shield [2@ 8mm clamps]
9. Remove manifold heat shield. [4@ 10mm nut and lockwashers]
10. Remove two exhaust manifold-to-collector pipe flange bolts from under car [2@ 18/19mm]
11. Remove six stainless exhaust manifold-to-head bolts through wheel well. [2@ 10mm] Two short [60mm?] and four long [80mm?] bolts.
1. File manifold mating surfaces clean and flat. The engine was originally assembled without manifold gaskets. Its up to you whether you reinstall them with gaskets, but I would invest the $5 in a set of Felpro gaskets, especially if the mating surfaces show any signs of corrosion. One little misalignment of a rust particle when you assemble without gaskets and it won't seal.
2. Chase manifold bolt holes with a M8/1.25 tap, flange holes with M12/1.50 tap. Replace damaged hardware and coat new bolts with anti-seize.
3. Remove #1 and #2 sparkplug wires. Start two lower end bolts. Drop gasket in place. Start the rest of the bolts. (short bolts go through shorter manifold bosses). Carefully line up gasket and tighten. Loosen a bit, then torque to 15 ft-lbs.
4. Carefully cut the gasket webbing out of the #1 and #2 spark plug areas. Use aviator snips or something sharp. Cut, don't tug.
5. Reverse the REMOVAL steps above. You can replace the Phillips head fender screws with hex-head trim screws (the HELP! parts brand has a kit of four screws for about $2). Don't forget to replace any rubber screw covers that were on the ends of the bolts. Remember to refill radiator and replace any spark plug wires you removed.
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