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  • 1 month later...
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What is bugging me to no end is the fact there is all these wild write up of people adjusting APPS sensors, wiring mods, extra grounds, filters, etc. I still say the truck ran fine without any of these mods for 10-12 years and now it needs it... I doubt highly. I say there is a part that is failed and needs to addressed not band-aided over. The more and more I kept studying this and the more I ran into people with this issue and what they done never resolves the issue. But now this is the second phone call where I helped a owner with this issue and found that just unhooking the alternator fuse and the problem goes away tests me instantly the alternator is at fault...Another way to verify...

http://www.youtube.com/watch?v=UveGtGuswBw

So I Check this at the battery or the Alt?

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(I have had my 2000 auto for two years now and am getting this same symptom more often now. I am usually able to get rid of it with an APPS RESET for 3000 km then it starts. I have a switch and relay to force an unlock of the torque converter without a limp mode or code that gets me by until I have time to reset the APPS.Here is my take on the problem:The alternator produces 3phase AC power and converts it to DC via 6 diode bridge. On an oscilloscope this "DC" signal would have extreme ripple that is smoothed to close to pure DC (neglligible ripple) via the huge storage effect of the two big batteries that act much like a capacitor. A bad diode will create a missing pulse at 0 volts and give a huge spike. The problem is that if the ripple gets to the APPS signal that feeds the PCM with "throttle position" as 0.5V= 0% throttle and 3.5 V = 100% throttle in that there is a problem that the sample can be taken on the ripple spike that indictes falsely that you have suddenly accelerated and want an unlock for power. The next sample sees no spike and locks up again and then it repeats at that critical cruise speed. As an example the computer probably samples about 5 times a second and the pulses are probably several kilohertz (depends on RPM and # stator poles). The threshold for unlock is especially sensitive at that 50 mph mark in my case. What I found is when I put in a Diablo Puck the problem is much worse. I rarely floor the truck with so much power and the "adaptive" software in the PCM adaptively reduces the 0.5 V = 0% to 2.75V = 100%,say, and the problem is bad again and the APPS reset is needed. The reduced dynamic range amplifies the noise effect. I do think that the noise is intoduced via poor ground connections that get worse with age. The PCM supplies a regulated 5Volts to the APPS potentiometer that should be clean (the 5V regulator chip "clips" any minor ripple off) so the alternator noise has to be from ground voltage drop from poor connections as age of truck and rust corrossion makes it worse. Some people get away with better battery connections, tightening/cleaning ground etc.. My next thing will be to check all grounds and put an electrolytic capacitor of about 10 uF 35V right at the PCM APPS input to ground to filter the ripple. The problem is so borderline that it should not take too much effort but I have to say the engineer that designed it did not do due diligence or his budget was way too low! I was in the business myself in my early career as an EE.I'll come back once I am able to get time on this thing.

So what grounds need to be cleaned do you think? I had mine cleaned on the batteries when I was using a Battery Tender over the Winter. Mine never left the Garage since November. Thanks, Dave!

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So I Check this at the battery or the Alt?

Dave, check at the alternator. Try that AFTER you try cleaning the battery terminals.

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Thanks Michael! Been locating & cleaning up my grounds & Alt conections. Not sure my tester is good enough, ACV has 200 & 750, not sure it will pick up a 0.1 or smaller. It's an Actron CP7672 model, bought it from Advance Auto, Dave

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All of these diode problems made me remember when Motarola made alternators in the 60s. Still have one on my jeep. It had what was called an isolation diode plate that was attached to the output post of the alternator. The plate acted as a protector. If the alternator was wired backwards, it would blow. We are talking 60s when retrofit alternators were replacing generators. Anyway as another quick fix, I was wondering if a external diode plate could clean up a marginal alternator output? The diodes in my alternator did not show as bad on a commercial alternator tester but it was putting out 3volts ac

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A couple of the manufacturers of construction equipment that I've worked for always installed an external diode in the wire between the alternator output and the battery.  I've heard several stories as to why it's needed (or was needed back when they started doing it, when they used Prestolite alternators).  One was that there was an path to ground somewhere in the alternator that would drain the battery.  This was purported to be only on an occasional alternator, but it was cheaper to put the diode in all the time than it was to sort out the bad alternators.

 

The other story was that if you didn't have it, you couldn't get the engine to shut off.  I can't make any sense out of that one anymore, but at the time it was explained to me, it made some sort of sense.  It's entirely possible that we were wiring things a little oddly--lots of confusion back at the point in history where solenoid shutoffs for diesels were new, and alternators were new, and everyone thought that a wiring harness with 10 wires was so unimaginably complex that we mortals would never be able to fully comprehend it.

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  • 2 weeks later...
  • 5 months later...

Just joined a few minutes ago.  1999 having the same issues again, have owned this truck since it was 2 years old, and have experienced this problem off and on for years.  Added the "noise filter" no go, getting frustrated.  We recently purchased a 27 ft travel trailer, drove from Washington to Oregon, 5 hours there and 5 hours back, no issues with the tranny, then on a trip to Puyallup Washington which is 3 and a half hours from our house the blasted hunt issue started.  Unlock, and lock.  At a couple of points in the trip I pulled over and shut the truck off for 30 seconds and then resumed and the problem was gone for about 30 minutes then it returned.  I have printed out all 10 pages of this thread and will start looking more aggressively into what is causing this issue.  We have a guy here that owns and operates an auto electrical shop, I bet money if I show him these pages, and have him do some testing he will know exactly what is going on.  I'm heading home for lunch and will do the fluke meter test to start things off.  I have to get it fixed, and I really need to get my transmission serviced, I've owned the truck for almost 15 years and have only put on 50,000 miles and have never had the tranny looked at.  Will post after lunch what I find.  Thanks guys, I am so excited to have found this site.  

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Ok update so as to add to the collective information here.  I went home and started up the truck and put my Fluke on the negative battery and the alternator.  Here is what I found. 

 

DC output to the batteries

 

20141118_112049_resized_zpsfc21fdfb.jpg

 

 

AC noise

 

20141118_112059_resized_zpse3d762df.jpg

 

Then I drove it to the Auto Electric shop that I mentioned, and he put it on a electrical analyzer and came up with 500mv AC which he said 60 or 70 is acceptable, so tomorrow he's rebuilding my alternator and I will report back.  This would be so cool if it fixes it finally!!!

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Ok just got a call, the alternator is all rebuilt with better than stock parts.  This guy always replaces with upgraded stuff.  Cost is $95.00 and that was him pulling and re-installing the unit.  Not bad compared to the cost of a new one.  Also with this rebuilt, I know its been tested ok.  It may be a few days before I can post the results, and on the 26th I'm pulling the trailer a little less than an hour away, so I'll report back as soon as I get it all tested.  Thanks guys!  :)

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