After driving it around for a week or so, an exhaust leak became apparent on the R side. I quickly eliminated the Y-pipe, 2ndry air crossover pipe, & EGR tube as possible sources, leaving only the exhaust manifold. An inspection mirror & flashlight showed the telltale soot streaks behind the #3 exhaust port. Another way to find a leak is to stuff the tailpipe with rags and listen for hissing at idle, but only FORWARD of the muffler (which is designed with small leaks).

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To make access easier, I pulled the wheelwell. There are several 5.5mm (7/32") screws along the lip, an 8mm (5/16") bolt at the top going into the inner fender, four 11mm (7/16") nuts for the coffee can & 2ndry air filter, a 10mm inboard rear, two 8mms under the core support (fortunately not yet destroyed by battery acid), and a 10mm behind the charcoal canister, which itself is retained by an 8mm. 3 wiring harness retainers pop out, and the whole wheelwell comes out easily.

Before ripping out any emissions systems, read this article.

With the Right wheelwell gone, it's easy to inspect the frame ground, just inboard of the spring tower on top of the frame rail. The battery ground cable is stripped ~3/4" and a tab is soldered on so it can be bolted to the frame.



The thumbnail below is a 4.9L frame ground:



Ford doesn't specifically identify that ground point, so I call it G102:

Motorcraft F2TZ-14301-B Negative Battery Cable with body, frame, & block grounds
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"Grounding" is commonly misunderstood...

When electricity first became publicly available (when Edison & Tesla were fighting over DC vs. AC), Copper wire was very expensive. So rather than run 2 wires everywhere, Tesla realized he could run a "hot" wire, and then use the ground (the actual dirt of the Earth) as the return circuit path. (He also thought he could use the ionosphere as the hot side, but he never got that to work.) Inside a house, there still had to be 2 wires, but one of them went "to the ground" via a Copper rod driven into the dirt outside the house. That became known as "the ground wire". When vehicles acquired electric circuits (AFAIK, the first on any Ford was the electric horn, which Ford always numbers as circuit #1), it was equally-efficient to use the metal chassis of the vehicle as one the main electrical pathway, to reduce the amount of wire needed. And the term "ground" was carried over into that arena. Chassis grounding worked reasonably-well until alternators got up into the ~100A range (in the 80s) and vehicle wiring harnesses began to exceed the weight of the drivetrain (AFAIK, the first to cross that line was the '92 Lincoln Continental V6). Since then, more circuits are networked through high-speed data bus lines via communication modules so that you don't need a discrete wire running from one end of the vehicle to the other & another coming back to turn on a taillight, and confirm that the bulb isn't burnt out.

But as a result, the chassis/body ground is no longer sufficient to provide a reliable circuit path without introducing a lot of background noise (RFI) into those minuscule high-frequency data signals. So the trend for a couple of decades now has been to run actual Copper return wires so that far less current flows through the chassis steel. (House wiring standards added a return "neutral" wire decades before that.)

So by definition, if you're using a wire to return to the battery, you're not "grounding" that circuit - you're wiring it. And wiring it is a good idea when you're dealing with rusty 40- to 50-year-old body & frame steel. The catch is that the return wiring has to be AT LEAST as large as ALL the power wiring that it serves - IOW, very big like the alternator output wire, the starter wire, the winch wiring, and the ignition switch battery-supply wires. None of it needs to be bigger than the battery cables because you can't ever get more current flowing than the battery can put out (roughly whatever its CA rating is).

So if you want to be sure you have a good return path throughout any vehicle, just extend the battery (-) cable all the way to the trailer connector. Obviously, you can't run a cable that big into the trailer connector or anything else - you have to splice onto it to branch off with smaller black wire (or whatever color the particular circuit uses for "ground"). That's why I refer to that as a "trunk ground" system - the main return wire is like a big tree trunk, with the variously-sized smaller branches shooting out to hit each point on the vehicle that needs an exceptionally-reliable return (generally: the high-current devices; and those that require low RFI noise, like audio amplifiers).

Fortunately, those splices DON'T need to be insulated - they can be left showing bare metal. Copper & solder don't corrode very quickly in air, or even in common rainwater. Mainly just at the battery where acid leaks out. Road salt will eventually cause some corrosion, but probably not enough to matter within the remaining lifespan of even the best-maintained antiques.

And the body & frame should still be GROUNDED at a few points, just to reduce galvanic corrosion, and to serve the very-low-current chassis-grounded loads like taillights & fuel level senders.

Looking rearward, the cowl drain can be inspected. This & the one on the driver's side often hold rotting leaves which can rust the body & cause odors in the HVAC system. This one was fairly clean because a squirrel had used it to get inside the blower for the winter, and I already fixed that mess. I haven't checked the other side.



The silver insulation on the R side of the pic shields the evaporator box from the R exhaust manifold, and hides the heater core & condensate drain, which barely protrudes thru the firewall. The drain drips onto the frame below, which is why the frame is rusty there. The wetness on it right now is penetrating oil I sprayed on the exhaust flange. I didn't fix it on this truck, but the evaporator insulation can be replaced with a more-robust modern material, like this:



The yellow plate above the insulation is the blower resistor; notorious for setting leaves in the box on fire, and for defaulting to hi-speed only when its thermal fuse burns out. The leaf fire can be prevented by 1) cleaning the cowl & its drains regularly, &/or 2) adding screen inside the cowl to keep the leaves from entering the blower intake, &/or 3) adding foam to seal the wiper valance ('87-96 only) so leaves can't enter the cowl.

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The black bar above the cowl drain is the lug wrench. There should be a hard plastic (natural nylon) grommet in the mounting tab on the fender to prevent noise. It can be replaced by slitting a small rubber vacuum hose to cover the metal edge.

This is why I pulled the wheelwell; with it in-place, none of this is visible, and it's difficult to reach. The connector in the foreground is for the 4WABS sensor.

Before ripping out any emissions systems, read this article.

I didn't fix it on this truck, but the evaporator insulation near the top Left can be replaced with a more-robust modern material, like this:

I wasn't able to get any penetrating oil on the tops of the flange studs before removing the wheelwell, but it'll be easy now.

Surprisingly, the Jasper installers put the starter solenoid's white (yellow with age) plastic heat shield back into place. Obviously, they forgot the spark plug heat shields, and the wire ends are suffering.

The silver tube to the L is the 2ndry air downpipe to the catalytic converter. The black one is the trans dipstick/filler tube. The rusty fitting at the extreme L is a trans cooler line.

I didn't fix it on this truck, but the evaporator insulation hanging down in this pic can be replaced with a more-robust modern material, like this:

This is what I spotted with the mirror & flashlight. These black streaks are only formed by exhaust leaks. The reason it occurred is that Jasper put exhaust manifold gaskets on this engine when they installed it. If they had used grease like Ford does, and torqued all the bolts properly (the rearmost was loose), there wouldn't have been any leak.



In addition to venting toxic gases forward of the cabin where they might enter the ventilation system, exhaust leaks also affect the way the engine runs. The addition of unmetered air between the combustion chambers & the oxygen sensor(s) creates a false reading, indicating a LEAN condition. In response, the EEC will adjust the injector pulsewidth to add fuel and bring the mixture closer to ideal. But since the reading was false, the actual result will be a severely RICH condition, causing (among other things) low economy, black soot, elevated HC & CO emissions, increased blowby, diluted engine oil, and accelerated wear on all the bearings & rings.



Before ripping out any emissions systems, read this article.

Note that the crappy exhaust manifold gasket didn't even touch half the lip of the manifold, which is why it blew out here.



To check for flatness, I cleaned this face with a 12" double-cut file across 3 ports at a time. It was still true. If it had been warped, I'd have had it machined flat.

Left F4TZ9430E
Right F4TZ9431E

Most of the gasket material is gone, leaving only the rusty steel core. This is why gaskets should not be added - Ford designed the manifolds to seal with a layer of chassis grease that gets baked into varnish (like seasoned cast Iron cookware) the first time the engine heats up. Alternatively, high-temperature silicone may be used.

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The pointer in the background indicates the ONE bolt that sheared during removal. Fortunately, it broke just behind its head, leaving plenty exposed to make extraction easy.

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This shows the true extent of the problem caused by the gaskets. Notice the #4 port to the Left - it also has soot spots appearing on the head where the gasket material was breaking down.

The immediate effects of this leak were:
1) noise
2) risk of exhaust fumes (including Carbon monoxide) in the cabin
3) risk of heat damage to surrounding parts
4) excess air in the exhaust, causing the HEGO to report a false lean condition to the EEC, which compensated by running unnecessarily rich: lower economy, higher emissions, accelerated engine wear



If it had been allowed to continue, it could have burned the valve or washed out the rings, causing catastrophic engine failure. Those are probably among the reasons that Ford didn't put exhaust manifold gaskets on most of its engines.

Before ripping out any emissions systems, read this article.

I didn't fix it on this truck, but the evaporator insulation hanging down in this pic can be replaced with a more-robust modern material, like this:

To extract the broken bolt, I used a Snap-On A80A stud remover/installer. Afterward, I chased all the threads with a rethreading kit & thread files. Then all were rinsed with brake cleaner (including inside the heads & the EGR fittings) and coated with nickel anti-seize lube.

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I didn't fix it on this truck, but the evaporator insulation at the L edge of this pic can be replaced with a more-robust modern material, like this:

Because both the manifold & the head were still relatively true & UN-rusted, I used the same sealant as the factory - chassis grease in a thin film around each port. When the manifold gets hot, the grease will bake into a varnish, much like cast iron cookware. The varnish creates an effective seal. And like seasoned cast-iron cookware, it's also a non-stick coating, which allows the manifold to expand & contract without cracking. Gaskets can adhere and cause binding, which makes cracks more likely.

If the surface is too rough for grease to work, use high-temperature silicone.



Years later, I did this:

Because both the manifold & the head were still relatively true & UN-rusted, I used the same sealant as the factory - chassis grease in a thin film around each port. When the manifold gets hot, the grease will bake into a varnish, much like cast iron cookware. The varnish creates an effective seal. And like seasoned cast-iron cookware, it's also a non-stick coating, which allows the manifold to expand & contract without cracking. Gaskets can adhere and cause binding; or their steel laminations rust away because their paper or fiber layers trap water; all of which makes cracking, warping, & leaking more likely. The loss of material also loosens the bolts, which vibrate out.

If the surface is too rough for grease to work, use high-temperature silicone.



The white pointer indicates a thermal disk glued to the bore plug by Jasper. If the engine is overheated, the disk will show it, voiding any warranty. This one is out of warranty, but the disk can still perform its function.

After letting it warm up slowly at idle & most of the oil had burned off, I raised it to ~2KRPM for a few minutes, which got the manifolds glowing a dull red, baking the grease around the ports into varnish seals.

I did this before reinstalling the wheelwell so I could watch for fire or leaks. It's fixed, but too dark & cold to finish installing the wheelwell tonight. The spark plug wire heat shield (F2UZ12A406A/F4TZ12A406BA) is missing.

Before ripping out any emissions systems, read this article.

I didn't fix it on this truck, but the evaporator insulation hanging down in this pic can be replaced with a more-robust modern material, like this: