Crown Victoria Project Update - Building a Panther, Part 2

The gravel pit under the floor mat was the easiest to fix, and I took care of it just after I finished painting the car. I took all the seats out and pulled up the mat. All kinds of interesting stuff had taken residence under there: sunflower seed shells, sheetmetal screws, electrical connectors, earplugs, loose change, broken glass, and one .40-cal round.

The wiring to the horn had been cut to splice into the siren control. When Santa Barbara County removed all the police equipment, they left the horn wires disconnected. That was also an easy fix with some solderless connectors. The driveline thunk took a little more work to fix. After the engine had warmed up, the car would leap forward from a stop, almost as if I had a transbrake installed. The sticky throttle only exacerbated the problem. Pulling off the intake ducting, I discovered a big ridge of carbon in the throttle-body on the backside of the throttle blade, which prevented the blade from opening smoothly when the engine was at operating temperature. That was easily cleaned up with a liberal dose of carb cleaner, but I ultimately replaced it and the intake duct with a Lincoln Aviator throttle-body (right) and elbow and a Mercury Marauder intake box I purchased from ADTR.net, a company that specializes in Performance Parts for Panther Platform cars. See our Mar. ’10 issue for the feature on Chris Adams

Through some clever cross-referencing, guys have figured out the Aviator/Marauder intake parts are all larger than the stock Crown Victoria stuff, yet all the connectors and mounting tabs are in the correct locations. Check out the bigger Marauder airbox opening on the right. The Marauder intake tube also comes with a larger mass airflow sensor, which requires the ECM to be re-calibrated. I bought an SCT X3 Powerflash programmer preloaded with the correct program from Blue Oval Chips. The combination is rumored to be good for about 15 hp, and though the engine felt more responsive, dragstrip times remained the same: 10-flat in the eighth-mile, roughly 15.6s in the quarter-mile.

The new, carbon-free throttle-body partially solved the neck-snapping launches, but the problem still remained, though to a lesser extent. In addition, the car would chug a little while backing up. This led me to suspect worn universal joints or a misalignment of driveline angles. With the car on our lift, I inspected the driveshaft and rear suspension. One of the lower trailing arms was caved in slightly, hopefully during some dramatic Code 3 car chase. I also measured the driveshaft runout, which was way out of spec at nearly 0.050 inch.

Our local Pick-Your-Part junkyards provided the easy fix. It is impossible to not find a retired Crown Vic taxi in any of the ones we visit. I paid less than 60 bucks for a used driveshaft and trailing arm, cleaned them up, and plopped them in, reusing the universal joints from the donor prop shaft. This didn’t fix my driveline problems, though. At least it didn’t cost much to find that out.

I also installed a shift kit because I hate lazy-shifting automatic transmissions. Known online as the J-Mod (named after Ford drivetrain engineer Jerry Wroblewski), it’s not a shift kit per se. Rather, it involves replacing the stock valvebody separator plate with one from a Mercury Marauder. You also replace a couple of the accumulator springs. This is a fairly simple job and works for all 4R70W transmissions. A thorough write-up is available on the Thunderbird and Cougar Club of America’s website: tccoa.com. Quicker shifts are the result because of bigger fluid passages and more line pressure. Rebuilding the transmission ultimately fixed my driveline problems. The clutch friction material was almost nonexistent, all the bearings were worn out, and there was a ton of endplay. Read about that in our Jan. ’10 issue.

With my tuned-up engine and fresh trans, I really began driving the car hard on the Malibu canyon roads. One Sunday morning in March 2009, I tossed a spark plug driving back from one of those outings. This picture shows some of the carnage. The spark plug had been backing out over time. Once it let go, the plug bounced like a pogo stick in its hole, destroying the boot and the threads in the cylinder head. I had to phone a friend for a ride home.

After some research, I discovered that this is a common problem for the modular engine family. Look closely at the threads in this picture. I brushed antiseize onto them prior to screwing the plug into the cylinder head. Notice how only the bottom five threads have been exposed? The rest of the threads are untouched. There are only five threads holding the spark plugs into the heads, and I’ve seen early, non-power-improved heads with only three spark plug threads. Supposedly, the 2004 and later versions of the 4.6 and 5.4 SOHC engines have seven threads. There is some debate online about whether you should use antiseize on new plugs when installing them. I do and will continue to do so because of modern spark plugs’ long change intervals. I’d rather have to retorque my spark plugs periodically than have them freeze up in the cylinder head. The spec in my factory service manual is 13 ft-lb.

Most shops will tell you to replace the cylinder head after a spark plug blowout, and you can imagine the outrageous price quotes I got from some of them. Ford has a service bulletin on this problem: the company’s recommended solution is the Lock-N-Stitch thread insert. Lock-N-Stitch loaned me the repair kit, which was very cool of them, because it is expensive to buy and way more than I could afford.

We won’t document the entire process in this article for a couple of reasons: Most of our readers may not care about 4.6 Ford spark plug blowouts (though there is good information here about thread repair in general) and the Lock-N-Stitch kit comes with very thorough and easy to follow directions. I doubt we could do a better job than they did.

For those who are interested, we’ll hit the high points of the repair. Basically, you drill out the damaged threads, tap new threads for the insert, and install the insert and roll pin that holds it in place. I was able to do the entire job with the engine still in the car over a couple of days. This tool cuts a seat for the thread insert to rest on. The red stuff is TransJel transmission assembly lube I spread on to catch some of the aluminum shavings.

The next tool drills out the stock spark plug threads. This kit is designed specifically for 4.6 and 5.4 SOHC engines—the dark collar around the cutter exactly fits the spark plug hole and prevents the cutter from wobbling or drilling off center.

Put more grease or assembly lube on this tool as well. There will be an alarming amount of metal shavings in this process. Stop often to clean the cutter and add fresh grease.

Next, I tapped the head to accept the thread insert. Again, I used TransJel to catch some of the aluminum chips.

It is impossible to keep all the aluminum shavings out of the engine, but I fished nearly all the debris by winding a pipe cleaner around a bent-up piece of welding rod. Adding some TransJel to the tip, I swabbed the top of the piston and was able to clean out the junk that fell into the cylinder.

The last few steps are to thread in the insert and drill one more hole for the roll pin that retains the insert in the head. The thread insert itself is hard-anodized aluminum rather than stainless steel. That’s why it’s the Ford-recommended repair. The aluminum insert has the same expansion and heat transfer properties as the cylinder head. The reasoning is that a stainless insert repair can cause overheating in that cylinder because it transfers less heat from the plug to the coolant than a repair with an aluminum insert does.

The repair was successful and here is that same cylinder two years and at least 10,000 miles later. The heads were off the engine recently for a performance upgrade (rather than a failure), and I was happy to see that there was no damage to the piston or cylinder walls either. You’ll read about the cylinder head swap in a later update.