Loose flex plate bolts

Stopping a common Rattle

One of the common problems with Jeep Cherokees withe AW4 automatic transmission is that the flex plate bolts back out after a while.

The flex plate is bolted to the torque converter with four relatively small bolts.  With age and time they get loose.

The noise is often diagnosed as a rod knock or something more severe and the Jeep gets sold cheap or scrapped.  If all the bolts fall out the Jeep will have no drive in all gears and be misdiagnosed as a transmission failure.

Inspecting the bolts is a relatively easy task.  They are hidden behind a small metal plate at the bottom of the transmission bellhousing.

This little plate is very well secured to the transmission. It had two large bolts with 18mm heads and two smaller bolts with 13mm heads.

Flex plate inspection plate

If your Jeep is like most, this area will be covered in mud and oil from a leaking rear main seal.  So it may take some digging to find the two small bolts.

One big issue with this task is that the bolt on the left side of the transmission will not come out unless you also remove the exhaust pipe.  However for just an inspection and tightening, you can get by without totally removing this bolt.  Just loosen the nut so the bolt can be moved back against the pipe.

Flex plate inspection plate

With the other bolts out you can pull the plate back enough to see the flex plate bolts and get a 15mm box end wrench on them to snug them up as necessary.  If you want to work in a torque wrench or put on some locktight, you will have to remove the exhaust pipe.

Once the bolts are tight, you can turn the transmission with the wrench on the bolt. There is just enough room to bring one bolt to the bottom and be able to access the next one at the top of the opening.  There are four so keep count and you will know when they are all checked.

Inspect the flex plate for damage while you are there. If the bolts have been loose for a while the holse my be elongated or the plate cracked.  If this is the case, you will have to remove the transmission to replace the flex plate.

Grading the Driveway

Since I daily drive a Jeep Cherokee XJ, I often don’t notice the condition of the driveway. I live at the end of a dead end road and I have a long gravel driveway.   Instructions to my house include, “when you get to the end of the paved road – keep going”

When I drive one of my sports cars however,  the ruts and bumps in the droveway become very apparent.  The Porsche and the RX7 do a fairly good job at grading the center of the drive but it is hard on the air dams.

Grass in center of the driveway

So occasionally I have to get out my antique tractor and attach the grader blade.  Like today that usually involves working on the tractor first.  Today I had to remove and clean the carburettor before it would start.

I began by setting the blade at an angle and cutting the gravel that gets pushed to the sides of the road back to the middle. This creates a big hump in the middle of the road.  So I have to be prepared to finish once I get to this state.

I learned this method growing up on gravel roads in rural Mississippi.  I would watch as the county road graders came by once a month or so and smoothed the roads.

Back drag

After the gravel had been pulled back to the middle, I flipped the blade around backwards to do a back drag.  Allowing the curved part of the blade to ride on the pile of gravel smooths it out nicely.

Finished Drive

Now I am ready to take the Porsche for a test drive once I reinstall the brake cooling ducts.

XJ LED dash light upgrade

XJ cluster LED

Adding LED dash lights to the XJ

I recently swapped in a used cluster to replace mine where the odometer has=d stopped working. The bulbs in it were pretty dim. I decided to try using LED bulbs.

i bought these from Amazon:

The listing gave me a a warning that these would not fit my 1991 Cherokee. But since the measurements were correct I gave it a chance. They turned out to be the right bulbs.

XJ cluster LED

The trouble with the LED bulbs is that they are polarized while the originals don’t care how they are installed. Also, the LED bulbs were not marked for + and – that I saw. So I rigged up a test set up using my 12V jump box and some alligator clips.

XJ cluster LED

Now you can trace each of the copper traces on the board and see what is positive and negative, but I decided to just use trial and error. That technique got me through engineering school it can get me through five LED bulbs.
I hooked up a lead to the ground that is handily marked on the board. I touched the positive lead to the solder joint that powers the lights to test each one. See the photo:

XJ cluster LED

To make sure the bulb lit up, I removed the one next to it and peeked inside:

XJ cluster LED

If it did not light up, I just turned it around. It did not take long to get all five in the right way around.

Once the cluster was back in the Jeep I am happy with the way it looks. I also took some time to clean it all up while it was out.

XJ cluster LED
XJ cluster

Renix XJ injector upgrade

How to change injectors in a Renix XJ

4 hole injectors renix

My Dad’s 4.6 stroker is in a 1988 XJ Wagoneer. It has the Renix control system.

It has always run rich as we installed the recommended 24lb Mustang injectors with the build.

I recently upgraded the injectors in my 91 XJ so I decided to try my old injectors in his to see how it would run. The difference was immediate.

No more filling the shop with fumes and no more bog on initial throttle opening.

I decided to swap in a set of 4 hole injectors from K suspension. (By the way don’t buy them from any other Jeep injector site on the internet. Not unless you like filing PayPal claims to get your stuff. Just get them from KS.)

Make sure the engine is cool before you start as you will inevitably spill some fuel on the exhaust manifold. You can also disconnect he battery cable if that makes you feel safer.

Unbolt the bracket that holds the fuel return line in place. It is hidden under a bracket that holds some vacuum lines.

Injector install XJ renix

Unclip the fuel line from the regulator and move it out of the way. Remove the transmission cable from the throttle body if you have an Automatic. Then three torx screws that hold the bracket to the throttle body.

Trans cable mount

Use a pick to remove the spring clips and unplug the injector wires from each injector. Be sure to mark them somehow so they don’t get mixed up going back. Leave the clips that hold the injector to the rail for now.

Fuel injector electrical connection removal

Next, remove the four bolts that hold the fuel rail to the manifold. Now use both hands to pull the rail straight off the engine. It won’t have to move far. Make sure the O rings come out with eh injectors. If not, carefully use a pick to pull them out of the manifold. If one falls in; you are in for more work to retrieve it.

Now unclip the injectors from the rail and remove each one. A large screw driver can be used to pry on them carefully if they are really stuck. Gently twist the screwdriver between the flange of the rail and the electrical connector part of the injector.

Coat the new injector O rings with engine oil. I poured some in the bottle cap and dipped each end of each injector in. Be very careful when installing the injectors into the rail not to nick the O ring. Push in firmly and straight. If the o ring gets crooked, pull it out and start over. Some twisting may help.

Now install the electrical connectors. They are much easier to plug in than to remove. Now install the retainer clips to hold the injectors to the rail.

Now, carefully align all six injector with holes they need to go in. Use both hands to firmly press the whole rail in at once. Wiggle it around until all the injectors are seated in the manifold and the holes will line up to mount the rail back on the manifold.

Bolt the manifold back in place. Put the fuel return line back in. You may want to do a leak test before putting the transmission cable back on. To leak test, hook the battery back up and turn on the key. You should hear the fuel pump run. Cycle the key on and off to help pressurize the rail. Check for leaks. If none start up the Jeep.

It may take a moment to get all the air out for the Jeep to idle correctly. Inspect carefully for any leaks.

If none, shut the engine off and reconnect the transmission cable. If you have leaks, try twisting the injector. If it still leaks you have nicked an O ring and it will have to be replaced. You can swap the top and bottom O rings on the leaking injector to get you by if you don’t have spare O rings. If you are in a real bind, try using one from the old injectors.

The Renix computer adapts quickly to changes in the injectors. If it runs really rich after changing the injectors, check to see if the MAP sensor line was knocked loose while moving the fuel rail around. If there is a large vacuum leak check the crank case vent hose.

Enjoy your new better running engine.

Lexan Rear Hatch for Porsche 944

Lexan Rear Hatch for Porsche 944


In order to improve the aerodynamics of our Porsche 944 ChumpCar racer, we decided to add a Lexan hatch. The ChumpCar rules require all glass other than the windshield to be removed. For our first race, we removed the glass and ran just the hatch frame. After looking at the other 944s racing against us we decided to add a Lexan hatch like they had.

We ordered the material from Five Star Race Car bodies on the advice of one of the other teams. This is the same material sold by Porsche specialty shops for about $100 less. The material surprisingly comes rolled up in a small box so shipping costs were reasonable.

Since we already had the glass out of the hatch we were able to start right away. Removing the glass from the hatch frame is challenging and requires a lot of patience. I have seen youtube videos of people breaking theirs out but they still had to deal with all the little pieces in the channels. I used an oscillating tool to cut the bonding material and carefully removed the glass. I had a heat gun for some places but mostly where the bonding material was cut, the glass lifted out.

We began by laying out the screw holes making sure there was no more than ten inches between holes. We paid extra to have the material cut to the size of the original rear glass. We may have been better off buying the oversized version as ours was just a little smaller than we would have liked.

We marked and drilled all the holes in the perimeter of the frame. Then we set the Leaxan in the upper groove and pressed it into place. We then carefully drilled through each hole into the Lexan. I found that if the bit ran too fast, the material would melt rather than drill and would refill the holes when the drill bit was removed. After a few holes I had the technique down. The biggest trouble we had was finding the right place to drill the holes. The best spacing away fort eh edge of the window put us in a ridge on the inside of the frame. This caused some of the holes to be angled which gave us trouble later.

We used a hand brace and a large drill bit to cut the counter sinks. We used the screws provided in the mounting kit from Five Star. The kit seemed a good value as it came with the right screws, locking nuts and a drill bit.

Due to the way the nuts hit the back of the frame, the ridge caused the nuts to not seat right. We ended up using a cutting tool to notch the frame at each of the screw holes so the nuts could sit flat. This also allowed us to use the shorter screws in the kit allowing the hatch to fit better when back on the car. Notching the frame took away some strength but once careful handling allowed us to get the Lexan mounted without it bending. Once the Lexan was in place the rigidity returned.

We added the two required one inch wide aluminum strips over the hatch and bolted them top and bottom. We then put all the rubber trim pieces back on the hatch to cover the holes and retain the look and function of the original spoiler.

The new hatch is very light weight and looks nice. We hope the performance improvement will be worth the cost and two weekends of work required to make the swap.