Archived 911...1995 Alternator Charging Trouble

[KOwens]

Hello TDR-911,



I'm in a pinch and could use your help!



My '95 has stopped charging... and tomorrow will be day two of driving to work and back without charging the batteries. I'm on thin ice, I know. The alternator field winding connector at the rear of the alternator is flat-line (zero volts DC) with the engine running... on either of the two field winding input screws to ground. I have checked the 30 amp fuse feeding the automatic shutdown relay... looks and tests fine. I pulled the automatic shutdown relay and have both circuit F18 winding side is hot and the 30 amp feed from the battery to the normally open contacts is hot. Seems the bird brain (PCM) will simply not fire this relay to begin sinking current through the field winding at the moment (no field current and no voltage regulation).



I have also lost the tach, speedo, odometer, A/C, TCC, overdrive, and cruise control. The PCM is extremely grumpy at the moment. I'm logging DTC's of 12, 33, 42, and 55, which decode to (I believe) "battery to bird brain disconnect during last 50 starts, A/C clutch relay circuit, automatic shutdown relay control (actually alt. field winding control, right), and of course, end of DTC codes, respectively. Surprisingly, I am not logging a DTC of 11 for loss of engine speed sensor output... since I have read so much about this notorious problem area concerning the charging circuit. At any rate, I have also checked and cleaned the engine speed senson connection at the front of the engine block (C178). Used 91% isopropyl and it looked very clean when I finished.



Just for grins, I removed the automatic shutdown relay and inserted a jumper wire between pins 30 and 87 to force feed the alternator field winding. Worked great in terms of providing 12 VDC to the field, but I didn't help in terms of getting the PCM to allow current to flow through the winding. I measured 12 VDC on both alternator field winding terminals at the back of the alternator to ground, but again, no charging and all other problems still exist. Since both terminals of the alternator field winding measure 12 VDC under these conditions, I can only assume the PCM is acting like an open circuit at the moment... otherwise I would expect at least most of the voltage drop to be across the field winding... and of course it would be charging then wouldn't it!



The bottom line is... I need some crucial spiritual advice on this one. So help me Obi-wan Kenobi !!! Any help you could provide would be greatly appreciated.



v/r Kevin

 

[bmoeller]

Since the PCM regulates the voltage, I wonder it took a dump.

 

[bodacious]

Alternator charging trouble

When I had same trouble you having on my 94, I replaced the speed sensor. That was 5 years ago,its been find since then.

 

[d906670]

Mine did this 2yrs ago replaced the alt. ,the pcm, still nothing turned out to be a bad wire under the fuse box next to the drivers side bat. had coraded and broke. This wie provided the read voltage to the pcm.

 

[bodacious]

When my was bad I read 94 manual. If I remember right it was either the pcm or engine speed sensor. Dodge wouldn't sell me the speed sensor and let me return it if that wasn't the problem, since I was in Az I let the dealer check it out they replaced the engine speed sensor.

 

[KOwens]

Thanks for the info.

Ok... thanks for the info. I've also got the manual for my '95... and I've been digging in. I'll look for the test procedure for the engine speed sensor this evening. PCM will be the last resort... but I will try to test the connections to the PCM with a test probe also (poke through the insulation and read the voltage). It seems the PCM is not getting something it wants... perhaps it is the engine speed sensor... but I wonder why I'm not getting the DTC-11 if it is really bad. Oh well, we will see! Thanks again.



Kevin

 

[K5IP]

It sounds like you are on the right track. If the PCM won't sink current from either the field winding or the ASD, the PCM is obviously not allowing the charging function. Since some of the PCM functions still work (code readouot), I would still be looking for a PCM input problelm.

I wonder if the speed sensor does not show an error report because only a continuity check is performed by the PCM. It is possible that the speed sensor (a hall effect device) still has continuity but is still inoperative. (It needs an 8VDC refrence from the PCM to operate). Also, the spacing between the sensor and damper is sometimes kinda fussy. It should be set to 1. 25 MM min to 1. 35 MM max using a non magnetic feeler gague.

Mine failed (also a 95) from these conditions and I remember it causing the tach and cruise to drop out but the failure was so intermittant I did not notice a charging problem.

Good luck

Rog

 

[KOwens]

Thanks K5IP,



I think you are right about the PCM needing an input. If I monitor the field winding with my voltmeter while I turn the key to "ON" the field lights up for a second (reads 12 VDC) then the automatic shutdown relay switches "OFF" and the field winding returns to ZERO VDC. If the PCM is looking for an input from the engine speed sensor... continuity or otherwise... perhaps that's what is missing. I just hate "shotgunning" problems (replacing parts I'm not completely sure are faulty)... and I really like to isolate the problem so I can understand how it really works. This helps me toubleshoot in the future.



For the record, I cleaned the connector for the engine speed sensor (up front below the valve cover for the #1 cylinder) the night before last... but I didn't look for the 8 VDC referrence at that time. Perhaps I should revisit this too. I'll bet the PCM is OK and the 8 volts is there, but it wouldn't hurt to eliminate this as a potential problem. I did check the "B+" input to the PCM and that looked fine (battery voltage present).



Getting back to the adjustment of the sensor, can you tell me where I can get a non-magnetic feeler gauge? Is this a common tool at auto parts stores? Mine is stainless steel, but I'm not sure it is completely non-magnetic. Sometimes magnets won't stick to stainless steel, but should I be looking for something that is copper based?



Lastly, can the engine speed sensor be bench tested? I'll have to look for a procedure in the manual... but I haven't seen that yet. Better get digging in the manual again this evening.



Anyway, thanks for the suggestion... I'm on it!



Kevin

 

[K5IP]

Keven,

My feeler gague was also steel but I was able to come up with some brass shim stock which measured about right. Jurry rig but it worked and fixed the problem. I was never sure it they were worried about schratching the sensor surface or if the magnet in the damper just makes adjustment difficult. I'll check my manual too but I don't recall a test procedure for the sensor. I expect i can see the signal with a scope so If you have a scope and need to know what the signal level is, I can check mine. It will only be a few millivolts.







let me know.

Rog

 

[JCrank]

Test & Fix Crank Position Sensor

I was having problems on my 93 with charging, but everything else was working fine. I finally installed a external voltage regulator last night, bypassing the PCM. This was a "quick" fix. I was wondering if my Crank Position Sensor was causing the problem, but since everything else was working, I didn't think it was the problem. I also utilized a Pathfinder II Diagnostic Tool, but it showed everything to be fine except charging and no tach signal. The Pathfinder II recommended the following test for the Crank Position Sensor : To quote Pathfinder II ;

The battery voltage for the field winding comes from the Auto Shutdown Relay. The ASD relay does not energize until the PCM receives an engine speed signal from the crank sensor. Test the sensor as follows :

Backprobe the sensor on the gray/black wire with a voltmeter. Bump the starter over & watch for output volts. They should fluctuate from 0. 0-5. 0 volts. This is the hall effect style sensor. Bump the engine over for one complete revolution. There are two notches cutout on the harmonic balancer. The voltage should fluctuate each time the notches pass the crank sensor. If using a labscope, it should show two 5. 0 volt sqaure waves per engine revolution. If not verify that the sensor is powered and grounded. The violet/white wire should be 5. 0 volts to power sensor. Black/Bluewire is to sensor ground circuit. Verify the ground by checking to see if there is less than 50mv on the sensor ground. IF powers & Ground are OK @ the snesor, replace the crank sensor. Hope this helps.

 

[KOwens]

Thanks Rog,



I can probably get a hold of a dual-trace oscilloscope at work, but it's been a while since I've seen one around. Seems we do more "off the shelf" implementation these days than circuit-level design. Ahhhh... the good old days! If you could pass the sensor signal level along anyway... just in case, I could be ready to make the measurement if it comes to that.



Concerning the sensor "continuity" test, can you tell me what the PCM is waiting for from the engine speed sensor at start up... especially before the engine is rotating? Since we don't have a test procedure, I'm not sure what to measure across the sensor. If it is a coil, I'm assuming a short circuit will be detected with an ohmmeter... and is this enough to satisfy the PCM? Like I said before, on my rig when the key is turned to "ON," the alternator field winding goes hot for about one second, then the automatic shutdown relay opens the circuit. If I can determine the sensor is an "open circuit" instead of a short (like a coil should be)... maybe that's all I need to do to prove it is bad.



Currently, I'm carpooling to work... and the truck is at home enjoying the rain here in San Diego. I don't think I've ever seen it this clean! But I'm off from work tomorrow... and have all day to mess with this problem if necessary.



By the way, one of my local dealers quoted $92 for the engine speed sensor. Is the dealer the place to buy this part? Are there any alternatives? Just wondering.



Thanks again for the help... hope to hear from you soon.



v/r Kevin

 

[KOwens]

Thanks JCrank,



Your post and my last reply to Rog must have showed up about the same time.



I appreciate the info on the "hall effect" sensor test procedure... that's something neither of us has a copy of. This should make it fairly easy to determine if the sensor if dead... or misadjusted (which would seem odd... since the damper hasn't gotten any smaller in diameter... and the sensor has been in place for 10 years! Ha !!!



Can you comment on the "cranking the motor" part of the show? Is the best practice to pull the connection to the fuel solenoid and crank the motor with the starter? Seems like you could watch for pulses fairly easy with the motor cranking at slow speed. Anyway, let me know what you think... and I'll get busy hunting down an oscilloscope to borrow for a day or two.



Thanks again for the input (everyone)... man-o-man what would I do without the TDR?



v/r Kevin

 

[K5IP]

Keven,

Here is some basic info in the hall effect switch. It takes only a few minutes to read and may help you trouble shoot the device. The info on testing doesn't mention typical resistance measurements to I suspect a previous post looking for output levels is the way to go.

In my case the probe probably deterioated and misadjustment (which had always been there) just became important.

Rog

http://sensors-transducers.globalsp...mfgcorp.com/counterpoints/Counterpoint3_1.pdf

 

[KOwens]

Thanks Rog,



I've got a scope to use... and have printed out the article. Thanks again for the help. I do appreciate it. I'll let you know what I find out... after the test.



v/r Kevin

 

[bodacious]

Alternator charging trouble

I got my brass feeler gauge from pep boys. Do you have anybody with a cummin that you could witch the engine speed sensor to rule that as the problem. If it is the problem then you could touble shooting as time permits.

 

[KOwens]

Oscilloscope testing results.

OK... if any of you are still interested, here is what I found after tonights series of tests.



First I pulled the engine speed sensor connector (just below #1 cylinder valve cover) and measured the 8. 0 VDC supply from the PCM with the ignition key in the "ON" position. Looks fine... approx. 8. 5 VDC.



I then measured the ground wire from the same connector to battery ground using an ohmmeter. Measures less than 0. 1 ohm... looks pretty good to me, and I didn't want to peel back the insulation on this wire unless things looked worse in terms of resistance to ground. So I haven't actually measured the voltage drop to ground with power applied.



Finally, I removed about an 1/8" section of insulation off the engine speed sensor output wire (Gray with a Black trace)... high enough on the harness above the connector to hook up my oscilloscope. I connected the ground lead of the scope to battery ground. I then started the motor and looked for the "Hall Effect" pulses I should see...



I set the scope's vertical to 1. 0 volt per-division... and the horizontal to 10. 0 millisecond per division (100. 0 milliseconds total horizontal sweep). Considering the engine idles at roughly 700 RPM (11. 7 revolutions per second)... and the damper has two notches 180 degrees apart, I figured I should see a pulse roughly every 1/(11. 7 RPS X 2 Notches) = 42. 86 milliseconds... not to put to fine a point on it. In other words, I should see roughly two full square-wave pulses with my scope settings. The actual pulse width I should see is unknown since there were no pulses present during this test.



What I saw on the scope's presentation was a constant 4. 65 VDC output... with some fine sawtooth noise on top if viewed on a very fast horizontal sweep (set less than 1. 0 milliseconds per division). The bottom line is... "No Joy" in terms of seeing any engine speed sensor pulses.



This sensor is not looking very healthy... based on my observations.



Just for the record, I couldn't resist checking the sensor to damper clearance... and again I only had a stainless steel feeler gauge... but I could slip my 0. 020" guage (the same one I use for my exhaust valve lash setting) and it slipped in with a tiny amount of resistance. In other words, the sensor is adjusted much closer to the damper than 1. 25 mm as is the suggested minimum clearance in the manual. On the other hand, it has never been adjusted and has been working in this position (at least in the past) for just shy of 10 years.



At any rate, that's where I am at... and I think I'm at a point where I can justify parting with the $92 to buy a new one at the dealer.



Any comments... concerns... questions? Please let me know.



Again, thanks for all the help.



v/r Kevin

 

[crabman]

Powertrain Diagnostic Procedures

Kevin,

I also had a charging problem in my 95. I posted about it in the "2nd Gen. 12V E. & T. " section, titled "Charging Gremlin".

I have a 94-95 Powertrain Diagnostic Procedures book by Chrysler. It has excellent flow charts with pictures. But, even with this book you really can not diagnose the problem(s) WITHOUT a DBR.

I have been looking for a DBR that is user friendly and could be used on my truck and newer imports.

My problem fixed itself(?) and I haven't had any charging problems for over 6K miles.

crabman

 

[K5IP]

Keven,

It sounds like you found it!

I have been buying parts from mopar4less (1-800-748-2139), ask for internet sales.

I am a long way from any local Dodge dealer, and these folks give you a break. Parts usually arrive in two days UPS if you can wait that long.



It looks like I was wrong about the signal level from that sensor. I was expecting a low level and it looks like they really get a high output from it. Perhaps some signal conditioning is included in the sensor package.



Rog

 

[KOwens]

Charging Problem Resolved

Hello again Rog,



Well the problem if fixed... finally !!! Oo.



I picked up a new engine speed sensor this morning at the Dodge Dealer... I couldn't wait to mail order it since my time to work on the old beast is limited, but I will keep the number you gave me for future reference.



I had trouble finding a "non-magnetic" feeler gauge in the large size needed to set up the sensor-to-damper spacing... so I made a trip over to the Metal Mart and found a small piece of 0. 050" copper sheet metal. I cut a small strip off with my Makita... filed and sanded the edges... and presto, I had the perfect feeler gauge. I followed the manuals instructions... pressed down on the sensor on top of the feeler gauge while tightening the nuts that hold it in place, then slipped the feeler gauge out from underneath when all was secure. Worked like a champ!



Once I got the harness re-routed and bolted in place, I hooked up the oscope one last time and fire that mother up. INSTANT PULSES !!! Oo.

As it turns out, at idle speed, the pulses are rising 5. 0 VDC square waves that are spaced approximately 32 milliseconds apart, and the individual pulse width is about 2 milliseconds. So you were right... the signal is at ground level most of the time, with just the short-duration pulses rising to the 5. 0 VDC level. The good news is it is all back... the alternator field, the tach, the speedo, the cruise control, the TCC lockup, overdrive, and A/C. Yeah baby !!!



I want to thank each of you that contributed to helping me isolating this problem... and limiting the cost of resolving it to an engine speed sensor. Special thanks to Bodacious for pointing right at the problem, Rog (K5IP) for the info on "Hall Effect" sensor technology, and finally JCrank for the exact test procedure for the engine speed sensor he got from his Pathfinder II Diagnostic Tool. You guys and the TDR are the greatest!!!



Thanks a million... Kevin (Charging up in San Diego)

 

[JCrank]

Yep, just bump the engine over without starting it. You could pull the wire on the fuel shutoff solenoid and the fuel will remain cutoff.