Maintenance Tips for the 1993 Corvette

I am not a mechanic by profession and have learned most of the following from the Internet or the factory shop manual. When at all possible I prefer to repair and/or modify my own car as I know that no one will be more careful when working on the car then I will be.

Replacing the Power Window Motor

Repairing the Lumbar Seat Air Pumps

Cutting Open the Air Cleaner Lid

Making a Tool to Open the Hood

Installing a Custom EPROM in Your Vette

Mod to Radiator shroud to prevent cracking of the hood

Changing the Fuel Filter on a Late Model C4

Replacing the Power Window Motor

Tools and materials required:
Socket wrenches, ¼ drive, SAE and metric sockets, Phillips and straight bladed screwdrivers, flashlight, needle-nose pliers, torx screwdrivers, electric drill and bits, 3/8 X 1 inch rivets or ¼-20 X 1 inch stainless steel nuts and bolts, grease, Loctite, RTV silicone, replacement motor from Ecklers ($90 with S & H), 12 volt test light, electrical jumper leads, battery charger capable of 6 amps output, duct tape, and of course the shop manual. Total time to actually replace the motor is approximately 5 hours the first time it is done.

Testing for a defective motor:
There is a detailed troubleshooting procedure in the service manual and I will not cover it in this procedure, but will add a few tips. Since it is a time consuming process to disassemble the door to get at the motor, it is best to eliminate all other possibilities before replacing the motor. Remember that when the manual refers to right hand or left hand side of the car it is as you are sitting in the car. In other words, an inoperative right hand window would be the passenger window. This is especially important when ordering a motor as the right and left motors carry a different part number.

Using the shop manual and a 12 volt test light determine if 12 volt power is at least getting to the window switch and the wires going to the window motor. The switch can be pried out of the door using a large flat-bladed screwdriver. It is important to use a light rather then a voltmeter. The voltmeter can show a voltage, but due to a poor connection it will not pass current and therefore operate the motor. If the light operates you have power up to that point. I wasn’t sure where to get a good ground connection for one side of the test light so I ran a lead out to the engine compartment and connected it to some metal on the engine.

I determined from the wiring diagram in the manual which two wires went directly to the motor. I disconnected the two connectors going to the window switch so I would not blow any circuits in the car. I momentarily connected the battery charger directly across the wires going to the motor. When the window still didn’t move I proceeded to take the door apart. As a note, I found a mistake in the color code of the wires in my shop manual compared to the actual color of the wires going to the motor. I didn’t determine this until I had the door apart.

Disassembling the door:
Taking the door apart and removing the window regulator took me about one hour. Start by disconnecting the negative terminal from the battery to protect the wiring. Remove the door trim panel as described in the manual. There are sheet metal screws located along the bottom edge of the door carpeting, in the door recess where you put your fingers to close the door, and several hidden screws. The hidden screws are located in the following places: One is behind the slide that locks the door. The door slide I’m referring to is under the inside door handle. One screw is located inside the door and access is gained by removing the window switch. Disconnect the two wiring connectors from the switch and lay it aside. Using a flashlight locate the screw now visible through the hole where the switch was removed. If memory serves me correctly, the screw is about 1.5 inches long and is the only one this size in the door. I used a small plastic bucket to place all the small parts I removed in the process. There is also one or two screws behind the courtesy lamp bezel. The bezel is pried out from the top. Carefully remove the bezel so as to not break it or the two lamps mounted inside it.

The manual says to lower the window to remove the trim panel. I suppose this is okay, but cannot be accomplished when the window doesn’t work! Carefully remove the trim panel from the door. If it does not remove easily , check to see if you have overlooked a mounting screw.

Behind the trim panel is a water deflector. This is really nothing more then a sheet of dense foam rubber. Use care when removing it as it could be easily torn. It will be necessary to remove 4-6 plastic clips that hold the wiring harness in place that run along the door. I used needle-nose pliers to pry the plastic clips out of the door. The water deflector is held onto the door with double-sided tape. Lay the water deflector aside.

You can now see inside the door and see the window motor and regulator mechanism. It was at this point that I discovered the wiring color coding error. I again tested the motor using the battery charger, as I could see the color of the wires going to the motor. Since the window still didn’t move, I next removed the metal accessory mounting plate. This is a large piece of sheet metal almost the size of the door that various items are mounted onto. You have to reach behind the accessory mounting plate and disconnect the rods that connect the inside locking mechanism and also the inside door handle. These rods are held in place by either a plastic or metal clip. Use care that you don’t break the mounting clips or the rods can fall off of their respective place after you re-assemble the door. It was only necessary to disconnect one end of each rod tin order to remove the accessory mounting plate. Remove all the screws or bolts that hold the accessory mounting plate to the door. You have to twist the mounting plate inside the door to remove it. Once the mounting plate is out of the door you have access to the window and window regulator.

Removing the window regulator:
The manual recommends to mark the location of everything you remove from this point on to aid in aligning the window when putting everything back together. Remove the window stabilizer pads. Remove the 3 nuts that hold the window to the regulator. Again this is best done with the window in the down position. At this point I removed the 4 torx screws from the cover of the motor. I now turned the motor armature with my fingers and lowered the window. It takes a lot of turning to lower the window even a couple of inches. When the last nut is removed that holds the window to the regulator, carefully lower the glass into the door. Remove the mounting bolts that hold the window regulator in the door. I had to play with the window regulator, turning the motor armature, so that the window regulator mechanism would be as small as possible to remove it from the door. I still had to twist the regulator assembly to remove it from the door.

Removing the old motor from the regulator:
The window regulator contains a large flat coil spring to aid the motor in lowering and raising the glass. Use care when removing the motor from the regulator. I did not allow for the tension on the spring and found parts flying across the garage. The motor is fastened to the regulator with three 3/8 inch by 1 inch long rivets. Rivets are used so that there is clearance for the window regulator gear to move. I used a drill press to drill out all three rivets. Two rivets were drilled out from the regulator gear side of the motor and the remaining one from the motor side. I could not figure out a way to remove the third rivet without more disassembly of the window regulator. (Replacement regulators cost $200 from Ecklers). I left the rivet that was directly behind the window gear in place and attached to the regulator. According to Ecklers new rivets could be obtained for any Ace Hardware store. Yeah, right! They only carried small aluminum pop-rivets. The rivets in the regulator assembly appear to be made to steel and would have had to be peaned over after installation. Since one rivet was still in the regulator assembly, I used two ¼-20 X 1 inch stainless steel nuts and bolts to mount the re-built motor. I had to grind the head of one bolt so that it was very thin and would clear the operation of the regulator gear. I used Loctite on the threads of these bolts. Removing the old motor and mounting the new one took me 1 hour. My motor failure was due to moisture getting into the motor. My car had sat outside for 6 weeks for some body repair, plus I drove it several days in the rain going to the NCM. One motor brush was rusted in place and not making contact with the armature. There is a rubber gasket between the motor halves. I coated the outside of the new motor at this joint with RTV silicone. I wanted some extra insurance against water entering the new motor because of the amount of labor involved with this repair, besides I wasn’t able to drive my vette for 10 days from the time I took it apart till it was back together. After the regulator is installed lubricate the window motor gear with grease. Check to see if any other moving part of the regulator assembly requires additional grease. I greased it after it was mounted to prevent the grease from getting on my hands and then on my car’s interior.

Aligning the window:
Aligning the window was not as difficult as I thought it would be. I installed the regulator and fastened the window to it. I then used the battery charger to raise and lower the window as I made adjustments. The adjustment procedure is in the shop manual. I compared the contact of this window with the rubber molding of the door frame and targa top with the window on the other door. When I re-installed the water deflector I used some duct tape to hold it in place. Installing the regulator, window, accessory panel, and door trim panel took me 3 hours. Total time for the entire job was approximately 5 hours.

I figured I saved approximately $150 in labor charges and about $100 on the part. I also made sure all the screws and bolts were put back into the door, something that does not always happen when a someone else works on your car.

I didn't include any pictures as I did not own a digital camera when I did this repair.

Repairing the Lumbar Pump in the seats

I have been told that this repair was covered in the May 1995 issue of Corvette Fever Magazine, although I do not have a copy of this article.

Tools and material required:
5/16 wrenches, one unlined latex rubber glove, #1 Phillips screwdriver, and a flashlight.

Diagnostic procedure:
When my car was approximately 7 years old both lumbar pumps in the seats stopped working. This is not something that I adjust every time I use the car so I had a difficult time believing both pumps would stop working at the same time. I first suspected a wiring problem. From the shop manual I learned that the power to the pumps comes from the same buss as the power for the motors that move the seat in all other directions. I also learned that power is available to the seat motors and pumps at all times, you don’t have to have the key turned on to make the lumbar pumps operate. When the car was running I could not hear the faint clicking sound the pumps made when I pressed the pump switch. It was only with the engine off that I could hear the pump click, as if trying to start when the switch was pressed. This told me that the problem was in the pump.

There are two procedures here for replacing the diaphragms. The first one is my first attempt at repairing the pump and is the long version. The second procedure is the short version and also the easy way to do it.

Access to the pump motors is gained by raising the seat cushion in the front of the seat. In the bottom front of the seat is a metal wire about 3-4 inches long that when pressed down and towards the back of the seat, releases the seat cushion. Lifting the seat cushion 5-6 inches exposes the pump motor and motor wiring. The pump is held to the seat frame with three 8x32 by ½ long bolts. The bolts can only be removed from the underside of the seat. I did this by using a flashlight to see the bolts, placed my head on the floor mat, and loosened the bolts from below the seat. The pump motor feet have recesses for the nuts so it is not possible to loosen the nuts from the pump side of the seat until the bolts are loose. Disconnect the wiring for the motor at the two connectors located under the seat cushion. The three tygon tubes that connect the pump to the lumbar switch can be disconnected at the pump. Carefully pry each tube off the pump. It appeared to me that there was very little slack in the tubing and therefore the tubing could not be cut off of the pump.

The end plate on the pump is removed by removing the two Phillips head screws. Once I had the end plate removed the pump could be separated from the motor. The diaphragm in my pump was completely ruptured. The plunger that connected the diaphragm to the motor shaft was jammed and this is why I could not hear the pump run even though power was getting to the motor. This is what caused the clicking sound when the pump switch was pressed.

Replacing the ruptured diaphragm:
I used part of the pump to trace a circle on the rubber glove approximately 1.25 inches in diameter. Use only the smooth part of the glove. Carefully punch or cut a hole for the screw that holds the pump cam to the diaphragm. Note that the hole in the pump cam must line up with the offset rod on the end of the motor shaft. I lubricated this rod with a drop of silicone lubricant before putting the pump back together. I tested the operation of the pump by connecting it to a 12 volt battery charger, with the white wire being positive. From the picture on the right you can see that the diaphragm has a large hole in the center where the pump cam attaches.

Diaphragms can also be purchased from the pump manufacturer, Jasco Products. They are located in Sun Valley, CA, and their phone number is 818-504-2516.

Place the pump back into the seat and redo all the mechanical and electrical connections. This job took me about 1 hour.

The short procedure:
This procedure removes the pump assembly from the motor and while the pump motor remains bolted to the seat. Remove the wire rod holding the seat cushion to expose the pump. Remove the two Philips screws in the end of the pump without removing the pump motor from the seat. Slide the pump assembly off of the motor. Replace the diaphragm as noted above. I had to use a mirror to align the pump cam to the motor shaft. Using this procedure, the repair took me about 45 minutes. I didn't save as much time as I had expected to, as I found it difficult to align the motor shaft and pump cam, and also to put the bottom screw back into the end plate of the pump.

In a new after-market parts catalog that I just received (Sept 2000), the pump goes for $85 and the repair kit for a the pump is $40. I paid less the $2 for the rubber latex gloves to fix mine.

Opening up the air lid on a 93 LT1

In order to restore my car’s originality, if I desired to, I decided to purchase a spare air cleaner lid to modify. I found a used one at Carlisle for $25, and it looked brand new.

I found that this air lid was made of aluminum. The picture on the left shows the lid I purchased and what it looked like before I started cutting. I removed the shroud by drilling out the five aluminum rivets with a 1/8 inch drill bit. The shroud was stuck to the lid because of the paint, and had to be gently pried off with a large flat bladed screwdriver. I cut the lid along the lines of the louvers in the top. I used a metal blade in my saber saw. This took about 3 minutes. I did find I had to stop and insert ear plugs because of the level of noise when cutting the metal. I dressed all the edges with a file. I painted the lid using gloss black enamel. The picture at the right shows the completed air lid.

When I removed my old stock lid I was surprised, as it had an air opening of 24.37 square inches. The modified lid had an opening of 84.5 square inches. Now I can't feel any SOTP difference, maybe I can after I get my butt cheeks calibrated and certified. It just makes sense that by providing 3.5 times more air intake that the engine will breathe better.

How to Make a Hood Release Tool

I have heard the horror stories about the hood release cables breaking or stretching and then not being able to open the hood. I had been meaning to buy a hood release tool, but got in a creative mood and made my own. I had a 5/16" steel rod and used this. I welded the tab and the handle to the rod. The overall length of the rod is 19",and the handle, B, is 3 ½" high. The tab, A, that drops into the slot in the hood latch, is 1 1/8" long and is 5/16" wide. I filed a notch in the rod and marked it with black permanent marker, C, at the point it lines up with the black metal molding at the lower corner of my windshield. This point is approximately 13 ¼" from the metal tab end of the rod. It is important to practice using this tool and get use to the feel of opening the latch before the need actually arises.

Installing a Custom EPROM in Your Vette.

The engine in my 93 is basically stock, and I do not foresee my going into the motor in the near future. The main reason I wanted to change the Eprom was to lower the temperature at which the cooling fans turned on, I did not like the factory setting of 226°, and to raise the MPH at which the transmission shifted into overdrive. I did not like the extra wear on the transmission as it shifted into and out of OD when driving around town.

I met Shalin on the corvetteforum about a year ago. He drives a 93 that is blown with a 14 PSI Vortec and dynos at 555 RWHP. Shalin told me he has probably burned over 100 EPROM’s as of this writing. Since he has done most of the work on his car, including the custom EPROM, I decided to get a chip from him. I had spoke to him about 8 months before, but at that time hadn’t convinced my wife that a new chip was a necessity, not a luxury. Shalin lives about 90 miles from me. I contacted him and set up an appointment for a Friday afternoon.

My engine only has the following minor modifications: Open air lid, K & N air filter, 160° thermostat, and Borla performance mufflers. The first order of business was to connect the notebook computer to the diagnostic plug under the dash on the driver's side and get a baseline reading of how my engine was running. I drove the car under WOT while Shalin watched the Diacom software record the data. The initial run showed that the engine was running slightly rich at WOT, the automatic transmission was shifting at approximately 5200 RPM's and there was some spark knock and the knock sensors were telling the computer to retard the ignition.

Back at Shalin’s he removed the three bolts that held the computer in place. Shalin disconnected the power to the computer by pulling the fuse located behind the battery. On another notebook CPU, he first loaded the information from my stock Eprom into the software. He then made the following changes: The rev limiter was raised from 5,600 RPMs to 6,200 RPMs. The timing was retarded 2° at WOT. The fuel was leaned out at WOT. The cooling fans were set to turn on at 85° and 86°C respectively (185°F and 187°F with a 2° differential). The torque converter lock up was raised to 48 MPH in third gear and the transmission is now set not to shift into overdrive until 48 MPH instead of the factory setting of 42 MPH. The piggy back circuit board with the new custom Eprom was attached to my stock Eprom and the EPROM assembly was reinstalled in the computer. We then took the car for another test run at WOT while Shalin monitored the engine with the Diacom software. Since Shalin has a fair amount of experience at the drag strip, I appreciated him saying I would get better performance if I manually held the transmission in each gear, and shifted it at 5,600-5,800 RPMs. Doing this, and taking into account the slight lag in the transmission shifting, the actual shift would occur at approximately 6,000-6,100 . The Diacom software showed that actually to be the case.

IMHO this is the only way to install a custom Eprom. Without a baseline run to analyze exactly what your engine is doing, you are just adding a generic chip that will do an average job for most engines. I feel it is even more important to have a chip custom programmed for your engine if you have more extensive modifications.

Modifying the radiator shroud to prevent cracking of the hood

This modification came from a tech secession that I attended with Gordon Killebrew at the NCM in April 2000. Since that time a member of our club who owns a body shop and three C4 corvettes, has also confirmed that this is a problem with C4 corvettes. Another club member ask him to repair a small crack in the hood paint. Upon closer inspection he found the fiberglass was cracked at the point where the hood was resting on the corner of the radiator shroud.

The problem is that the corner of the radiator shroud makes contact with the hood when the hood is closed. This puts an upward pressure on the hood and will eventually lead to a crack developing in the hood directly over the corner of the radiator shroud. In the picture I have placed an orange sticker on the shroud where the hood was making contact with the shroud. I used a file to remove about 1/8 of an inch of the height at the corner of the shroud. To check that enough material was removed, I put some white silicone pipe dope on the corner of the shroud and then closed the hood. When I opened the hood I checked to see if any of the white pipe dope had been transferred to the underside of the hood. This mod is easy to do and will prevent a costly repair due to a crack forming in your hood.

Changing the fuel filter on a 1993 C4

Tools required: 16 mm and 13/16 inch open/box end wrenches, 13/16" socket, 10 mm open end wrench, 10 mm socket, safety goggles, latex gloves to keep the gas off your hands in case you get to hold your lady that night, small to medium size hands, a fire extinguisher close at hand, and finally, two buckets of patience. If you tend to have a lot of table muscle (from eating too much) you will never fit under the car with it on jack stands.

The fuel filter is located along the frame rail on the right side of the car. This job could best be accomplished with the car on a lift, but can be done with the car on jack stands. I used the jack stands. The car should have less than ¼ tank of gas.

Procedure: Loosen the fuel filler cap to relieve the pressure from the tank. From this point on I wore safety goggles, not safety glasses. Remove the right fuel rail cover. Place a rag under the shrader valve where you would normally attach a fuel pressure gauge. Remove the shrader valve dust cover and press the valve stem to relieve the pressure on the fuel system. My car had not been started for two weeks and the gas cap was left loose for several hours before I started. About 4 tablespoons of gas came out of the shrader valve. Replace the dust cap on the valve and the fuel rail cover. Tighten the fuel filler cap.

I used a quartz work light under the car to see, but made sure to keep it a distance from any gas or gas vapors. I opened the garage door and turned on the ceiling fan. Remove the two screws that hold the two fuel lines to the under side of the car using a 10 mm socket. These are located along the right rocker panel and are the two screws located closest to the fuel filter. This is necessary so that you can remove the stainless steel tubing on the input side of the filter.

Remove the strap that holds the fuel filter to the car frame using the 10 mm open-end wrench. This screw was behind the return fuel line. I had to wedge a ½ socket extension between the frame and the return line in order to have enough room (enough room is a relative term when working on a Corvette) to remove the screw. Even then it was very tight quarters. Remove the input fuel line from the filter by holding the filter with the 13/16-inch wrench and turning the nut on the fuel line with the 16 mm wrench. On my car about 1 cup of gas ran out when I loosened this connection. I caught it in a coffee can and a rag. Once it stopped draining, I dumped the gas out of the can and placed the gas soaked rag outside of the garage.

The top fuel line on the filter is another story. I have heard that some remove the fuel line where it connects to the fuel rail and pull the filter up and out of the engine compartment to change the filter. I couldn't figure out how to break the connection at the fuel rail so I removed the line from the top of the filter. The catalytic converter is in the way of the upper fuel filter connection. I had to place the 16 mm open-end around one side of the cat closest to the fuel filter, and then use my index finger of my right hand and hold the wrench this way. My right hand was around the other side of the cat. Since I was replacing the filter I didn't care if I ruined the old filter. I used a 13/16 socket on the bottom of the filter to loosen the filter while holding the top fuel line with the 16 mm wrench. I ended up bending the bottom fitting on the filter, but got the filter off of the top fuel line.

Inspect the o-rings on the two gas lines before installing the new filter. New O-rings are not included with the new filter. Place the filter on the top fuel line and reverse the procedure to tighten the fuel lines to the new filter. Use care when turning the new filter with the socket wrench so that you don't bend the filter. One of the hardest jobs was replacing the retaining strap around the new filter. I had to wedge the return line out of the way and it still took me 15 minutes to get the holding screw started into the frame of the car.

When everything has been re-assembled tightened, start the car and let it run for 1-2 minutes. Shut off the engine and check for any fuel leaks. This is very important as a leak could drop or spray fuel on the catalytic converter and you would have a really hot set of wheels, no pun intended. I repeated this staring procedure several times over the next several hours to insure I had no leaks.

Not counting the time it took me to get the car on jack stands, this job took me about 90 minutes. I'm not sure I could do it again in less then 60 minutes.

Now if I could only find a good price on some new muffler bearings I replace them while the car was still on the jack stands.

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