Symptoms.
This problem has been reported on 1998 and 1999 Dodge truck models.
Overdrive ON - The torque converter clutch cycles on and off at speeds between 40 to 50 miles per hour. The transmission feels like it is shifting, but it is not. The converter clutch is engaging and disengaging. This occurs in 4th gear. The problem typically disappears at speed above 50 mph. The clutch will disengage below 40 mph and stay disengaged.
Overdrive OFF - The torque converter clutch cycles on and off at speeds between 30 to 40 miles per hour. This occurs in 3rd gear. The problem typically disappears at speed above 40 mph.
The problem is actually related to the engine speed. In both cases the engine speed is between 1200 to 1500 rpm. See the problem theory below.
Dodge Dealer Solution.
The Dodge dealer is unlikely to make modification that are not sanctioned by the factory. Therefore, the only possible repair at the dealer level is to replace the alternator and accelerator pedal positions sensor (APPS). The APPS must be calibrated and the engine control module (ECM) and the powertrain control module (PCM) should be reprogrammed (flashed). The dealer fix is only temporary at best because the problem is caused by a faulty system design. A rebuilt alternator may not correct the problem. See the theory behind the problem as described below.
My Fix That Works.
This repair was the last of many attempts that failed. I have tested many other suggestion and all of them failed to provide a lasting fix. This procedure was successful in eliminating the converter clutch cycling. A toroidal inductance coil and capacitor circuit is installed on the wiring harness at the powertrain control module (PCM) on the accelerator pedal position sensor (APPS) signal circuit coming from the engine control module (ECM). The low frequency interference (LFI) noise that disrupts the PCM computer "learn" circuit is reduced.
This job is surprisingly easy to do.
Record the trip odometer reading because it will be reset to zero when the batteries are disconnected below.
Accelerator Pedal Position Sensor (APPS) Output Circuit
The signal wire from the APPS terminal number 3 is the problem circuit. This is wire number H102 that is light blue color with a black tracer. It runs to the ECM on the left side of the engine behind the fuel filter. The circuit is shown in the shop manual on page 8W-30-15.
The APPS signal circuit continues from the ECM to the PCM. This is wire number K22 that is orange color with a blue tracer. The circuit is shown in the shop manual on page 8W-30-7.
Powertrain Control Module (PCM)
The PCM is more than the name implies. It is the main computer for the entire truck. The location is on the right side firewall behind the air cleaner box. Access is easier than first thought. The air filter top does not need to be removed.
Noise Filter
The noise filter assembly is a model N-25 by Navone Engineering, 4119 Coronado Avenue, Suite 4, Stockton, CA 95204-2336. Telephone: 209-465-6139 or 1-800-669-6139, Fax: 209-465-2912. Do not buy model N-25T without the capacitor because it will not work. The noise filter consists of an inline ferrite core toroidal induction choke and a capacitor connected to ground.
Navone Engineering - Filters & Noise Suppressers.
http://www.davidnavone.com/cart.asp?24&cat=2Installation
Disconnect both batteries by disconnecting the negative terminal first.
Step No. 1 The wiring harness going to the PCM has three large connectors. Connector C1, manual page 8W-80-13 contains the wires for connecting the noise filter. This connector is on the side nearest the engine. It has a black plastic tip on the male connector. Squeeze the top and bottom release clips at the same time while working the connector up and down slightly and pulling straight out.
Step No. 2 The center connectors has a white plastic tip and the connector nearest the fender has a gray plastic tip. Remove both connectors as done in step 1 above.
Step No. 3 The entire wiring harness can now be gently lifted up to the top of the air cleaner housing. The air cleaner top does not need to be removed.
Step No. 4 Locate the orange wire with a dark blue tracer on connector C1 that has the black plastic tip. Cut the wire midway in the exposed section. Solder the RED filter wire to the cut wire on the connector side. Solder the GREEN filter wire to the cut wire on the harness side. Tape the wires. Do not use crimped connectors because they are not effective for suppressing noise.
Step No. 5 Locate any one of the three ground wires on C1. The ground wires are black with a tan tracer. Remove a small section of insulation. Solder the BLACK filter wire to the ground wire. Tape the wires.
Step No. 6 The noise filter unit is encased in a plastic tube but is probably not water tight. Place a heavy plastic bag over the filter assembly with the wire coming out of the open end of the bag. Wire tie the covered assembly to the harness with the open end toward the connector.
Step No. 7 Lower the harness assembly into position and plug in the three connectors. Both latches on each connector should click into place. Adjust the position of the filter assembly with the bag cover opening down.
Step No. 8 Connect the positive battery cables first. Then connect the negative battery cables. Reset the time on radio clock. Tell the truck owner what the trip odometer reading was before the batteries were disconnected.
Theory Behind the Problem.
The APPS signal goes from the APPS to the engine control module (ECM) and from the ECM to the powertrain control module (PCM). The PCM has a "learning" circuit in the computer that is disrupted by noise or low frequency interference (LFI) emanating from the APPS, alternator or both. The LFI noise appears to resonate with one of the circuits in the PCM causing incorrect changes in the learn circuit. The alternator can develop noise that is caused by "leaky" rectifiers. A rectifier passes current in one direction but blocks the current in the other direction. A leaky rectifier allows a small amount of current to flow in the blocked direction. Replacing the alternator repaired my Dodge for a period of more than one year. Beware of rebuilt alternators that could already have leaky rectifiers. Insist on a report that shows the leakage to be zero if you go this route. Replacing the APPS may fix the problem for a while also but this must be done by the Dodge dealer.
Disconnecting both batteries and reconnecting them fixes the converter clutch cycling for a few days. It is temporary fix because the "learn" memory in the computer is erases. The problem begins again as the computer begins to learn a new incorrect setting. The converter clutch cycling gets worse and worse as the learn setting is disrupted by the LFI noise.
Negative Downshift Side Effect Caused by the Noise Filter.
A new user discovered that the noise filter recommended here causes a negative downshift side effect. I have driven my Dodge for about 100,000 miles since installing the noise filter and didn't even notice the lagging in the downshift on full throttle. I now recall that the downshift on a few occasions in the past was sluggish.
I ran these tests:
1. At 30 mph the tranny would be in 3rd and no-lockup. At full throttle the tranny does not shift down to 2nd for about 4 seconds. This seems like a long time if you are trying to pass someone.
2. At 50 mph the tranny would be in 4th and lockup. At full throttle no downshift occurred.
Suggestions:
A. The noise filter is probably oversized which would delay voltage changes coming from the APPS. This design was not based on scientific research, so other sizes were not tested. You could try smaller sizes, but I don't have any other sources other than as listed on the web page.
B. You could try a noise filter on the alternation, since the alternator is the source of the problem. The present noise filter does not have enough amp capacity for mounting on the alternator output, so you would have to find a much larger unit to carry the high amps.
C. Other people have tried running the alternator output wire in a different manner, but I have no idea where or how to make wiring changes that will work. The Dodge factory solved this problem in newer models, but I have no idea what they did.
My conclusion:
I am not doing any further testing to find a better solution, since I didn't notice the downshift lag for 100,000 miles. It is not worth the effort for me.
I will manually shift from D to 2 when driving at a speed between 25 to 40 mph if a forced downshift us desired.
I will press the "O/D Off" button to force a downshift from 4th and lockup to 3rd and unlock at speeds between 45 and 60 when I want a forced downshift.
Please give feedback if you discover other methods of resolving the factory converter clutch cycling problem.
Good luck,
Kent R. Rieske, P.E.
Professional Mechanical Engineer
Automotive Specialist
