Irratic or no converter lock

[JMalik]

On erratic converter lockup (3/2/2010)

I have a 1996 2500 Dodge diesel with a 47RE automatic transmission equipped with an ATS Commander controller. I noticed on one of my trips out of the high desert here in California where I live that the converter would lock and unlock. Then after an extended period of sitting around in seasonal rain that the converter would no longer lock up at all.

Going onto the TDR site I researched the problems with converter lockup to find the following:

Alternator Noise was the primary source of the problem. So I put a scope onto the 12 VDC bus and found that when the manifold heaters would cycle that the noise would increase dramatically on the screen. Also that my instrument panel voltmeter would drop down to the next lower mark. I conclude any major load cycling including manifold heaters, fuel pump heater, electrically actuated exhaust brakes and the like would result in heavy loading of the alternator. If the batteries did not have enough reserve capacity to pick up the load or the battery or alternator circuit resistance was significant the resultant noise dropped across the 12 VDC internal source impedance would be enough to scramble the PCM converter lockup circuit.

My continuing research found an article on the Suncoast transmission site under their controller on dealing with the problem of irratic converter lockup. Their first order of action was to clean all ground and battery connections. If all else failed their fix was to re-route the ground and sink(connect) it to the instrument panel ground to provide a low noise reference point.

From an article by Kent R. Rieske comes a filter approach using the Navone Engineering N-25 noise filter. The filter is placed on the TPS (Throttle Position Sensor) signal line at the PCM.

People also broke the TPS lines out of the wiring harness and shielded them with foil.

The alternator rectifier can also be a problem if the rectifiers becomes leaky and allows a reverse current spike. I suspect that the alternator at 136 amp capacity is marginal for the loads dropped on the 12 volt bus and the reason for the 2 battery setup is more for stabilizing the 12 VDC power bus than for engine starting. Floating the batteries on the power bus provides for the peak current loads induced by the intake manifold heaters, fuel pump heaters, and any other added loads the customer installs.

Replacing the alternator was also suggested and is effective if the alternator has leaky rectifiers or worn brushes. The new 200 amp alternators are attractive and would provide much better load regulation for the 12 volt bus particularly under an engine idle condition. I found reports indicating that the instrument panel volt meter did not vary significantly with manifold heater cycling with a 200 amp alternator.

Allowing the engine heaters to complete their cold startup cycling is a way to minimize the application of noise on to the PCM TPS circuit during its active phase. At idle the TPS signal is basically grounded. Watch the instrument panel voltmeter. Initial cycling will be quite large and will reduce as the battery voltage increases to the alternator charge voltage and the intake manifold heater quit cycling. Once the alternator 12 volt bus is unloaded the circuit noise will be minimized.

With each disablement of the converter lockup circuit it is necessary to disconnect the batteries to initialize the PCM and allow the converter lockup circuit to restart its learn cycle.

I cleaned the battery terminals and associated connectors with contact cleaner and wire brushing after which converter lockup worked. I hope the above will result in a fast fix for some of you out there.
J. Malik