Engine/Transmission (1994 - 1998) 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

 

[JMalik]

March 3, 2010



Rough slip rings



With 190,000 plus on my Denso 20004150, 135 amp alternator I decided that it might need to be rebuilt. Geno's Garage offers a bearing and brush kit as a part of the rebuild so I decided to go for it. I also ordered a Transpo manufactured PN 318210 diode block from Quick Start. From comments by other TDR members it seemed an easy rebuild. It would have been except the front bearing seized on the rotor shaft and I spent hours fighting it. I finally took the whole thing to a local machine shop, which had a press, and it was out in seconds.



Frustrating. Then I was fighting time to clean well-worn slip rings and to get it back together. In retrospect I didn't do a very good job on the slip rings. Although they looked ok with the naked eye when I got the alternator back together and on the truck my problems with irregular converter lockup were back. As far as the electrical functionality of the generator it worked fine putting out plenty of power. The only problem was the alternator was noisy under load.



When I took the alternator apart one more time and inspected the slip rings with a 10x magnifying glass I found machine marks and surface irregularities. So I put it back on my lathe and sharpened my parting tool to a smooth keen edge and resurfaced the slip rings. I then got some fine polishing rouge and further finished the surface. My inspection with the 10x magnifier showed a smooth polished surface. I then buffed all the electrical contact surfaces on the new diode block and buffed the mating surfaces of the alternator then used contact cleaner to make sure there was no residue on the mating surfaces to effect electrical contacts. Once back on the truck the problem with disabling the PCM converter lockup learning circuit appeared to go away. The alternator rework improved its performance, resulting in much less drop in voltage when the manifold heaters cycled. After startup the instrument panel voltmeter would hold below the lower marking for at least 15 seconds and then pop up to just above the 14 volt mark. Then with the manifold heater cycle it would initially drop to the mid point below the 14 volt mark for the first cycle then about half that with each succeeding cycle. I recall that before the rework the first cycle would drop the voltage down to the mark below the 14 volt mark so the alternator rework was a good thing.



The Denso Alternator circuit had me confused because my Dodge manual indicated only 6 diodes and a capacitor. I located the alternator internal capacitor but counted 8 diode within the diode block. My research on alternator circuits revealed that Denso uses 2 snubbing diodes to suppress the 3-phase Diode Bridge induced switching transients. However, there is no noise suppression in the rotor excitation circuit controlled by the PCM. So rough slip rings will modulate the slip ring current to effect the 12 VDC. From the above this is another contributing factor in the irregular converter lockup saga.

JM

 

[JMalik]

March 13,2010



Lockup Logic



In the never-ending saga of irregular torque converter lockup I have moved on to the next problem. When the truck is cold soaked over night the torque converter will lock and unlock sort of randomly. Then after it warms up it seem to work normally.



It seems that there are two problems that I have encountered in dealing with my torque converter. One associated with 12 VDC alternator generated noise and the other with Power train Control Module (PCM) Torque Converter Control (TCC) enablement logic. 12 VDC noise will scramble the PCM learning circuit and cause it to just quit controlling torque converter lockup and go off line. Then the only way I know to bring the PCM back on line is to reset it by removing battery power and re-applying it. The Problem associated with TCC lockup enablement does not disable the PCM it just results in random lock and unlock. I can see this happen with my torque converter because I have an ATS Diesel Performance Commander transmission torque converter lockup controller which allows me to adjust and monitor torque converter lockup. It is very apparent when something is not right.



According to my 1996 shop manual the TCC lockup enablement is based on inputs from the following;



(1. ) Miles per hour from the Vehicle Speed Sensor, VSS (Left side rear transmission)

(2. ) The Module Timer (haven't located this one, likely in the PCM)

(2. ) Engine rpm from the Engine Speed Sensor, ESS (Front engine damper area)

(4. ) Throttle Position Sensor, TPS (Left side engine next to injection pump)



If any one of these inputs to the PCM is not within acceptable limits or is not readable by the PCM the torque converter lockup won't occur. As I checked each one of these I had two problem areas;



(1. ) The ESS was not adjusted to the specified . 050”. It was closer. I couldn't measure the distance since I don't have a non-magnetic feeler gage. I used some cardboard built up to . 050” to set the ESS gap between the sensor and the engine vibration damper.



(2. ) The engine idle was a bit high according to my instrument panel RPM gage. I set it to 1000 RPM with the transmission in drive and headlights on according to the manual. A bit high I know but without an RPM gage it's all guess work anyway.



I took the truck out for a test run and it seemed to work OK. But I will check it again after an overnight cold soak to make sure it is fixed.



March 14,2010



I did a short run this morning and converter lockup appears to be stable. Hope that did it

 

[JMalik]

I purchased a new 4alterstart.com 205 amp alternator to replace my 135 amp Denso alternator. Because I had so much trouble with the slip rings on my Denso Alternator I took the Alterstart alternator apart and did some inspection of the slip rings. This alternator is essentially a 135 amp Denso in configuration. The diode block may be higher current but all the Denso parts appear to be interchangeable. A visual of the slip rings showed grind marks and a visually rough surface. Regardless of my warrantee I felt the need to improve the finish. So I did a fine cut and polished the surface.

Although not a perfect mirror surface on the slip rings, the performance is essentially the same as my 135 amp Denso judging by it's response to the manifold heater load cycling when looking at the instrument panel voltmeter.



The reworked Alterstart alternator initial test runs show no instability in 47RE transmission operation. Before the transmission would go in and out of converter lockup under light throttle. With rough slip rings I would loose converter lock as engine rpm would increase. Now there is stable transition from no lock to lockup with light throttle and over engine rpm. Also the transition from lockup to unlock is very stable.



The lessons learned here are that an alternator will output great power with rough slip rings. The excitation current going through the slip rings is not all that high at under 4. 573 amps (from Alterstart test data). So it can be carried by rough slip rings with no problem. However, the noise induced in the current flowing through the slip rings will be sufficient to create problems for the PCM.



A synopsis of the changes made to fix my converter lockup problems are as follows.

First my battery terminals had corroded enough to increase the load current required by the alternator and from my scope measurements that created higher 12VDC noise.

Second my alternator slip rings were very worn after 190,000 miles and that compromised its load capacity. Slip ring rework showed that it is important to true and polish the slip rings to minimize brush contact irregularities for noise control.

Third my Engine Speed Sensor (ESS) being out of adjustment was definitely a problem as it resulted in lockup sensitivity to low temperatures (below 50 deg F. )

Finally, just to make sure I prevent problems in the future I added the Suncoast transmission fix with a little change. I used a T connector and some AWG12 stranded automotive wire between the TPS ground wire and an instrument panel ground. It was simple and required no wire cutting.

 

[JMalik]

I took my 5th wheel out this summer for an 8500 mile trip cross country from California/Minnesota/Washington State and back. At about the 7000mi point the converter lockup began to act up again. On coming home I pulled the 4alterstart 205a alternator and replaced it with my Denso alternator with the Genoes garage kit in it. The converter again locked up nicely. On pulling the brushes of the 4alterstart I found the the brushes had debris embedded in them and that the transfer of carbon from the brushes to the slip rings had made an irregular pattern on the slip rings. The deposits had built up enough to lift the brushes off the slip rings and they were only hitting the high spots on the deposits. My next move is to replace the slip ring brushes with some quality brushes. On further inspection the brushes also had cracks in the carbon along with the embedded particles. I think there is a subpar manufacturer of alternator brushes out there that is creating some serious problems with a too cheap part. A quality brush should lay down a smooth graphite track on the slip rings. The graphite track should both lubricate the slip surface and provide a low resistance electrical contact path between the brush and the slipring.



I sent an Email to 4alterstart to let them know they have a problem. I hope they take action on their supplier and get this problem fixed. Bad brushes will kill an expensive alternator by eating up the slip rings. Doesn't help the supplier's rep either. As a dissappointed customer I sure wouldn't recommend their product.

 

[JMalik]

Converter Lock/unlock instability and VSS sensor/Dana 70 differential oil level: Aug. 3,2011

The converter lockup saga continues. For those out there who are running with an ATS Commander Transmission Converter lockup controller the following will apply when using the controller. The ATS controller locks up the converter based on vehicle speed coming from the VSS sensor mounted in the differential housing. I was experiencing irregular converter lockup and drop outs after about 2,000 mountain miles. Removal of the VSS sensor showed a heavy coating of magnetic sludge oil all over the sensor. Installation of a new VSS sensor seemed to stabilize converter lockup, however at the turn on point I was still experiencing some switching instability. Then I again had problems during run with the converter lockup switching on and off with increasing engine power on hills. On checking my magnetic Mag-Hytec differential oil level dip sick for magnetic particles I saw very little accumulation of particles but noticed the oil was low. So I again installed my now magnetic sludge cleaned OEM VSS sensor. I checked the cleaned OEM VSS sensor on the way to buying more differential oil. Lockup worked better but still would drop out during run with lockup unstable under threshold conditions and on hills. After filling the differential to the top bar of the Mag-Hytec dip stick the converter lock up was stabile both at threshold, accelerating and run conditions. I am amazed that oil level would have that profound an effect on the VSS sensor operation. It appears that irregular oiling of the differential cogged ring which excites the VSS has an effect on the sensor signal. Then climbing hills caused the differential oil to move to the back of the differential case to change oiling of the cogged wheel still more. Regardless cleaning the VSS sensor and making sure the differential oil is up is a cheap fix if it works. I have the aluminum foil shielding I wrapped around the power feed going from the alternator to the battery. I will have to try removing the shielding to see if the improved VSS signal can over ride the system noise developed by the alternator.

My latest list of converter lockup instability contributors is:

1. Alternator Noise - verify slip ring finish and brush quality

2. Alternator feeder cable noise transmission - Shield to isolate noise

3. Battery terminal contact resistance - clean to keep power circuit resistance low

4. VSS differential sensor - clean magnetic sludge accumulation for max clean signal

5. Differential oil level - interacts with VSS sensor output signal, keep oil at specified level

6. TPS throttle sensor - set to specified voltage to satisfy computer mapping

7. PCM computer - low PCM TPS input circuit resistance defeats TPS voltage set point

8. TCC torque converter lock/unlock control loop - verify aux controllers and loop contacts

August 4, 2011: After 260miles of driving converter lockup and run remains solid. No drop outs on hills. No instability during lockup. It would appear for the VSS to provide a solid non ambiguous signal to the PCM and my ATS Commander Lockup controller that it needs to be clean and the differential needs to be sufficiently full to thoroughly wet the exciter wheel attached to the ring gear of the differential. Considering the converter drop outs on hills and operation during low lubricant then topped off lubricant, I have to conclude that the role of lubricant wetting the exciter wheel to be critical.

 

[JMalik]

August 8,2011: I have to apologize here for using the Vehicle Speed Sensor (VSS) interchangeably with the Differential Speed Sensor or Rear Wheel Speed Sensor(as part of the ABS there are also front Wheel Speed Sensors). Parts houses seem to use the term Differential Speed Sensor. Seems to be a common problem and I am sure that it creates some confusion. The VSS comes from the transmission. The speed sensor referred to in this discussion is the Differential Speed Sensor or Wheel Speed Sensor supposedly dedicated to the ABS braking system. However, it is a part of the converter lockup enablement input to the PCM for converter lockup. Therefore if it provides an erratic signal it will scramble the converter lockup input to the PCM and disable lockup. The Differential Speed Sensor is a part of the ABS system which my truck does not have. So I find it a bit confusing that I have ABS components scattered around my truck. The Differential Speed Sensor has a long wire run from the PCM to the DSS on top of the rear differential. This provides a long unshielded wire which can pick up noise which can become the dominant signal into PCM if the DSS signal is severely attenuated by magnetic sludge. The other problem with the DSS is with low lubricant resulting in an erratic signal which also disables converter lockup for my ATS Commander Converter Controller. Since my ATS Commander uses VSS and does not tap into the DSS signal the DSS effect on lockup has to come via the PCM.