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Electrical 1st Gen Dodge Ram Electrical Problems and Questions.


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  #1  
Old 09-28-2012, 10:09 PM
cas390 cas390 is offline
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Default low voltage

ok, here is the problem. i got a 90 d150 318 auto 2wd ac
truck start fine, runs fine. alt meter shows about 13v when driving

When I come to a stop with engine still in drive and foot on brake the alt meter starts to drift back towards the low side if I have any accessory on. ie. blower motor, ac, headlights . will drift so low that the radio shuts off momentarily.usually comes right back on.
I can watch the alt needle drop and see lights dim if they're on.

if i put it in park, alt needle comes right back up to normal (take load off motor)
if I shut off the voltage using accessory off the needle comes back up.

if i hit the gas while still in drive and drive off , the needle comes back up.

I thought it might be the engine idle slowing down, and causing the alt to slow down, but I don't feel the motor run rough as if it's going to stall.

yes I had the alt checked at the local advance auto and it checked out.
guy mentioned the voltage reg. but it is incorporated int the CEM? computer module. not sure how to check it and don't want to change it if it's not bad.

no error codes except the "Maint required" which is for the 75,000 mile emission check. that light has been on for two years and this problem started about two months ago


any help would be great.....Chris
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  #2  
Old 09-30-2012, 02:29 PM
RedneckMechanic RedneckMechanic is offline
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Sounds to me like, even though the test showed normal, the alternator is going out. Not all testers at auto parts stores test the diode ripple. If the diode is bad, the power being put out by the alternator is allowed backwards through the system and is discharged. The only way it keeps putting out power is high idle with no load.

As for the regulator, I don't think it's built into the main computer for the truck. If it's not IN the alternator itself, it should be mounted externally on the firewall or inner fender. I believe it's in the alternator by then. I could be wrong.

Hope this helps a little.
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Old 09-30-2012, 02:50 PM
Gen1dak Gen1dak is offline
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Have the same problem with my '90 RC. I have a fresh hi-output alternator that puts out plenty juice. Lights stay bright, but volt meter still drops off. Those computer-controlled regulators (yes, it's built into the computer) don't last forever, and despite my PCM being 2 years old, I think it's fading. Have already ordered my bypass kit.
http://alternatorparts.com/external-...nator-kit.html
Do it and save yourself the cost of a new computer. Replacement regulators are only $20 bucks or so from then on, aaaaand you can then easily configure for higher-output alternators without PCM problems.

Last edited by Gen1dak; 10-01-2012 at 02:28 AM.
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Old 09-30-2012, 09:22 PM
cas390 cas390 is offline
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Gen1dak, sounds like you have the same problem. I have changed my alt. for years. it's not stock, but I got it when I was in bind out of town. I believe it is a 90 amp unit. has worked fine for years, never have a issue with dead battery.
this problem started two months ago. seems as though if I don't have any accessory on then the problem doesn't arise. if something is also on, ie. blower motor, ac, etc. it happens.

you think I should bite the bullet and get the kit????

thanks, Chris
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Old 10-01-2012, 02:23 AM
Gen1dak Gen1dak is offline
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Yep. If it isn't raining tomorrow, I'm doing mine. Naturally you want to rule out the other stuff, but this is my second dance with this issue. Volt meter starts acting as you described. Then it gradually fades. Before long it's under 12V even with everything off, but the truck still runs and the lights are bright. It'll start, then even run fine with the battery disconnected, but hook it up and the meter just dives. Eventually it's just pure discharge. Meanwhile multiple checks on the battery and altenator come up empty. New computer fixed it once and all has been good til now. These refurbs don't appear to hold up as well. First time around I wasn't sure what was wrong . It'd do okay in daylight, but I was actually unpugging one headlight at night to help things along. It's doing exactly the same thing now. I'd already planned on retrofitting with the kit and had already ordered it so here goes nuthin'. Good luck. Let ya know how it turns out.

Last edited by Gen1dak; 10-01-2012 at 02:26 AM.
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Old 10-01-2012, 04:00 AM
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GTyankee GTyankee is offline
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load test the battery
then check to see how many AMPS the 12VDC alternator puts out under load conditions
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Old 10-01-2012, 09:22 PM
cas390 cas390 is offline
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I'll have the bat load tested.

gtyankee,

If I put my amp meter in line with the alt it's only going to show what currnet is being used, not total amps available from the alt. (ie,90amp) Or am I understanding you wrong.

gen1dak, did you do the test on the retrofit site about testing voltage at two small post at idle and under accessory load?
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Old 10-04-2012, 08:19 PM
cas390 cas390 is offline
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Vehicle: 1990 D 150 2WD
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Color: Two tone blue
Engine: 1988-1991 318ci (5.2L) LA V8 140hp
Rep Power: 0
Rep:10
cas390 is on a distinguished road
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gen1dak, I tried to send you a pm but wasn't allowed. so here it is


hey, thought I'd send you an pm. If I get crazy and decide to change the ecm on my 1990 d150 is it a matter of unplug and put in a new one or is there some crazy electronic stuff I should follow.

thanks, Chris
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