I recently took my truck/5th wheel on a trip to the U.P. of MI. On the first day out, a couple hrs into the drive, I glanced down at my gauges and noticed the voltmeter hanging low in the 12 volt area. At the time I was running with my headlights on which included all the running lights on the 5ver. First thing I did was turn off the lights - voltage came up slightly. About that time my better half informed me she was due for a pit stop so I pulled over on an exit ramp & let her into the trailer. While she was doing that I had a look under the hood. All looked fine but I detected a slight noise coming from the alternator that was unfamiliar; it did not seem to change pitch with rpm like a noisy bearing would do, not a belt slip - kinda hard to describe but like an electronic buzz. By this time she was ready to go so we got back underway. After a short while I noticed the voltmeter was looking normal again so I tried the lights to see if it would draw it down again - it didn't. At the next fuel stop about 2 hrs later I listened under the hood again for the noise but it had stopped. We finished our 2000 mile,13 day trip wiithout anoother incident, and I was watching the voltmeter like a hawk.

 

Since our trip (returned home 2 weeks ago today) I hadn't used the truck until yesterday to commute to work. It started right up & ran fine, voltmeter showing a normal indication. I have a Juice with Attitude unit installed on my truck and I changed the display to monitor ECM voltage. At idle with headlights and wipers it would read as low as 12.2, but would quickly increase to 13.9/14.2 volts while underway (1600 - 1800 rpm). After work the rain was gone so I started out without the headlights & wipers, and the voltage was 13.2 + at idle immediatly after start-up. I pulled out of the lot at work and drove the 1/2 mile to the interstate ramp, when I glanced at the ECM voltage which was now reading 12.2 volts. I closeely monitored the voltage during the 17 mile commute and saw it slowly going down to 11.7 at idle and a peak of 12.0 at speed. Once at home I parked the truck & shut it down, then i turned on the ignition (did not start) to see where battery voltage was - it showed12.2 volts. I then re-started the truck & the voltage read 11.8 volts.This morning I started the truck - voltage was down to 10.2 but I believe that was due to the grid heaters being activated. I didn't let it run long enough for the heaters to turn off before shutting it down.

 

Way I see it the problem could be one of three things - A bad alternator, a bad PCM (voltage regulator), or a bad connection at the alternator or PCM. Another contributing factor could be the batteries are getting a little weak - I think they are about 5 years old. I plan to pull the batteries & get them charged/tested first. In the mean time I plan to check connections at the field wire plug & BAT connection on the alternator, and check for a decent ground of the alt (they are case grounded aren't they?). I am suspicous of the alternator since it was making a wierd noise a few weeks ago, but would have expected it to stay bad & not miraculously fix itself for the duration of our vacation. Hopefully it is not a bad VR because I hate the thought of replacing a PCM.

 

Any testing and troubleshooting advice would be welcomed. Thanks for your time!

 

Joe in St Louis

 

 

You know when batteries are in parallel like they are on our trucks they typically last for a loner time than 5 years. However, mine are also around the 5 yr. mark and are showing signs of weakness. I think batteries are not made as good as before.

 

Then another time I had an alternator go out with my rv and 2 very low batteries. I think it overworked the alt. trying to keep up made it finally kick the bucket but had 240 k miles on it by then too.

 

Wish I could help better except try charging you batteries not hooked up to the truck. See if they stay at 12.5 or better after sitting for 24 hours after the full charge. If they take a very short time to fully charge up then they may be on their way out with little capacity.

Time to do some alternator bench testing. That would be my first thing. Second I would check the blue wire for matching positive voltage of the battery. The green wire is the variable ground from the the PCM controlling the field. Then I would do a voltage drop on the charge lead to verify the lead not damaged or weak. How about battery terminals and main cables? I've seen butt load of vehicles with absolutely mutilated terminals and wires corroded.

Thanks for the suggestions guys. I put a charger on the batteries overnight & they came up to 12.6. My charger is an automatic type that shuts off when the batteries reach "100%" then goes into a float mode; they hit the 100% mark sometime overnight. At this point I don't believe the problem is with the batteries - although they may not be like new it seems like they are still serviceable.

 

I pulled the alternator this morning and will get it bench tested at the local Auto zone. I'll report back later witth the results.

 

Mike, you mentioned checking the blue wire (field supply) for 12 volts. I quickly connected the L/H battery and did a quick check with the ignition switch on, but didn't register any voltage. Do you think the engine needs to be running before the power gets turned on to the blue wire, or perhaps the power is supplied by the R/H battery?

 

Thanks again for the help!

 

Joe in St Louis

You can check the quality of wires and connections using an Ohm meter.

 

0,00 Ohms means no resistance, a perfect connection and wire

 

Caution using an OHM meter to check for resistance must be done without the batteries hooked up as electricity running thru the Ohm meter will burn it up.

Well I had the alt checked at Autozone & it failed their test almost instantly. I decided to buy a replacement while I was there, a rebuilt-in-Mexico ND unit with a lifetime replacement warranty. Ran the replacement alt across their test bench and it passed - took about 3 times as long to do the test on the replacement than on my old unit. Brought it home, installed it, reconnected the batteries (cleaned terminals too), did the APPS reset, and started it up. After the grid heaters stopped cycling it holds a steady 14-0 - 14.2 volts, even at idle. So I guess I'm good to go!

 

Thanks for the help!

 

Joe in St Louis

Edited October 11, 201410 yr by jumpjg

Thanks for the suggestions guys. I put a charger on the batteries overnight & they came up to 12.6. My charger is an automatic type that shuts off when the batteries reach "100%" then goes into a float mode; they hit the 100% mark sometime overnight. At this point I don't believe the problem is with the batteries - although they may not be like new it seems like they are still serviceable.

 

I pulled the alternator this morning and will get it bench tested at the local Auto zone. I'll report back later witth the results.

 

Mike, you mentioned checking the blue wire (field supply) for 12 volts. I quickly connected the L/H battery and did a quick check with the ignition switch on, but didn't register any voltage. Do you think the engine needs to be running before the power gets turned on to the blue wire, or perhaps the power is supplied by the R/H battery?

 

Thanks again for the help!

 

Joe in St Louis

 

Possibly. But I doubt it though...

I realize this is off topic, but I tried to send a private message and it would not go through:

I  came across your post for "fix for leaky fuel filter".  I realize the post is quite old, but I'm wondering if you still have any of the spare o-rings you mentioned in the post, and if you are still willing to mail them if you do.  I look forward to hearing back from you.  Thank you.

M Sargent
Redding, CA