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Intake Manifold Gasket Replacement

1993 Ford Explorer - earlier pushod based engine

Before we dive too far into this article, I want to emphasise that this is a "not for beginners" type task. To be honest, I hate having to repair daily driver type cars. The reason for this is that you have a limit to the time you can spend on the car and you have to have it fixed by the end of the day. This combined with the nature of engine work, and how easy it can be to do it wrong, makes for a stressful day. And, if I ever meet the engineer(s) who designed this particular motor I will beat them with a stick! This repair job, with my father-in-law's assistance took us about 8 hours to do. Now, I'd never worked on this type of car before. With a little experience I think it could be shortened to 5 hours, but it's still not a small job!

Here's the engine at the point where we started the work. My father-in-law had already pulled the air tube that connects the air box to the plenum. As with most modern cars you can see that everything is crammed in there as tightly as possible. While this saves space, and isn't a huge deal when the car is assembled, it sure makes it hard to do maintenance. Our first major target is the plenum on the top middle of the block. This will expose the intake manifold. Of course, though, there's going to be a fair bit more removed before even the plenum may be taken out.

First order of business is to mark the plug wires to help us remember how they go on the ignition box. I prefer to make a diagram in my notebook of the connections, number them, and then use tape to make matching numbers on the plug wires. Once marked, disconnect the wires and pull them away from the top of the engine. You don't need to remove them at the spark plug, just get them out of the way.

To remove the coil unit undo the three bolts (one of them is hidden down low) and the two electrical connections. You can then set this part aside to get it completely out of the way. While we're working across the top of the plenum we need to unbolt the accelerator cable by removing the bolts that attach it's retaining plate. Replace the bolts into their installation points on the plenum once the bracket has been removed and the cable assembly pulled over to the driver's side out of the way.

Here you'll see the vacuum tube connections at the back of the plenum. There's a fair number of vacuum tubes and they all look very similar. This is another bit that I like to diagram and mark. It saves a lot of head-scratching time later on when you're trying to reassemble everything. Finally, there are a number of electrical connectors on the plenum, so go ahead and carefully remove them. Please note that this plastic is beginning to age. Take your time and carefully remove them otherwise they'll get broken.

Remove the nuts that hold down the intake plenum. There are eight of them. Put them in a coffee can (or other appropriate storage device). Once you've got them off you'll need to release the plenum from the intake manifold. Give it a whack or two with a rubber mallet to loosen it. Never use a screwdriver or prybar at the mating surface to loosen items like this.

With the intake plenum removed you've taken the first big step. The next major target is the valve covers (talk about a deign flaw.. geez.. who thought that having valve covers overlap the intake manifold was a good idea?!?!). It's helpful to get the wiring harness as far out of the way as possible (which is easier said than done.) Diconnect the harness at the fuel injectors. While you're at it, disconect the fuel lines as well. Put the ends of the fuel lines into plastic bags and tae them shut. Don't want to leak fuel all over the motor. The driver's side valve cover is much easier to remove. Start there. Note that the rear inner bolt is different from all the other bolts. The extended part on it is used as a hold-down connector for the wiring harness.

Here you can see the first valve cover removed. Remember that this is the easy one. Repeat the steps for the other side. This area is much tighter and you'll likely bust a knuckle here. Start by making sure the wiring harness is out of the way. Remove the bolts that hold down the valve cover. You'll need to whack it with a rubber mallet a few times to knock it loose. The trick to getting the valve cover out of the area is to lift the unit and then rotate the back end of the cover across the top of the block to get it out from under the wiring harness and other bits.

Believe it or not, we have both of the valve covers off in this photo. There's just that much junk in the engine bay to obfuscate the fact that the valve covers have been removed. At this point we can finally remove the intake manifold.

Here you can see the intake manifold and gasket finally removed. Once you remove the bolts, again you'll have to wonk it a few times with the rubber mallet to loosen it. Now, here we see what I can only deem to be a ridiculous engineering flaw in this engine. The engine itself is totally exposed and the only item protecting it is the intake manifold and it's gasket. Considering that coolant flows through this mating point (which is where the gasket failure occurred) there is little to no protection outside of the gasket to keep coolant from flooding into the motor.

Before we go ahead with reassembly of the unit we need to prepare the mating surfaces. The first step is to clean them with a razor blade and use carburetor cleaner (or it's ilk) to ensure that there is no oil on the mating surfaces. Then you need to use gasket sealant around the water passages on the block (both at the front and the back of the block). Then it's time to add the new gasket, and the rest is the reverse of the disassembly process. Please note you'll also need to replace the gasket between the intake manifold and the plenum as well as the valve cover gaskets.

My final warning, this sounds a lot easier than it was!

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Contents copyright 2008, 2009 - Jody F. Kerr

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