redline8300 Report post Posted February 25, 2018 I have a 1996 Beaver Marquis with a 3126E and an Allison 6 speed and I have an electrical problem that has me stumped. Going down the road for about an hour I noticed the voltage gauge at slightly above 12.5. Checking the electronic readout, it was bouncing from 11.8 to 13.0. After another 30 minutes the hp from the engine dropped off, wouldn't build boost. I pulled into a parking lot and tried to rev the engine still no boost. It did the same thing when I lost the HEUI. After 30 minutes of idling, the voltage was bouncing from 12.3 to 13.6 and building boost again. I turned around and headed home. The voltage stayed above 12.3. I got home and checking the voltage at the chassis battery, with the engine off it is 12.89, per my manual it says 12.3-12.6 is the correct range. I tried doing the Field Test on the alternator and I'm not getting anywhere. After an hour off at the house I started the RV and the voltage gauge is around 13 an the readout bounces from 12.6 to 14.2. The chassis battery is less than a year old and starts the engine without an issue so I don't think this is the problem. The coach batteries are old, could they be causing this issue? I think the inverter is on it's way out, could this be causing the problem. I'm going to continue to dig into wiring diagrams and see if I can find anything. Share this post Link to post Share on other sites
kaypsmith Report post Posted February 25, 2018 1 hour ago, redline8300 said: The coach batteries are old, could they be causing this issue? I think the inverter is on it's way out, could this be causing the problem. I'm going to continue to dig into wiring diagrams and see if I can find anything. Yes and yes, I would try to desulfate the batteries, then have them load tested. Of course an alternator test is in order as well. Share this post Link to post Share on other sites
redline8300 Report post Posted February 25, 2018 I pulled out one of the old ones and they weigh slightly more than half of one of the new ones. Hopefully this is the problem and I can hit the road for New Orleans tomorrow. Or else the universe is telling me to not head down there for work. Share this post Link to post Share on other sites
richard5933 Report post Posted February 25, 2018 Have you tested it with the chassis battery only? Disconnect/shut off the coach battery and turn off the inverter. See if you can duplicate the problem while only running the chassis battery. If it's still there, then the problem is most likely with the electrical system in the chassis. I'd check the alternator and regulator (if you have one.) If you shut down the house systems and batteries and the problem goes away, then you know where the problem is. If your chassis battery is being over-charged it will do damage. Sure sign that either your alternator or regulator is not doing its job, or whatever the equivalent system is in your rig (computer control, regulator, etc.) Any truck shop should be able to diagnose a charging problem. Share this post Link to post Share on other sites
redline8300 Report post Posted February 25, 2018 I tried, but when I shut down the coach batteries I loose the ability to get the digital readout. After changing out the batteries in the morning I was going to get a cat tech computer to read it from the data port and see what he comes up with on the chassis side. Share this post Link to post Share on other sites
richard5933 Report post Posted February 25, 2018 You can always just try a simple multi-meter to check the voltage at the battery in real time. Old school, but it would work. Do you have a start button in the engine bay? (It would sure make things more simple) Share this post Link to post Share on other sites
manholt Report post Posted February 25, 2018 When you say, Voltage bounces from 14.2 to 12.6, is that fast back and forth? Or does it go to 14.2, then drops to 13.7+/-, then 12.6 and stays there. That's normal. Share this post Link to post Share on other sites
redline8300 Report post Posted February 25, 2018 Inside of 20 seconds, back and forth, the electronic readout bounces between the numbers. Share this post Link to post Share on other sites
manholt Report post Posted February 25, 2018 Acid batteries or AGM. if acid have you looked at level of water and added as needed? Checked the ground wires for corrosion or bad, loss connection? any of them swollen and how old are they? Have you turned on the generator and gotten the same result? What line of work are you in? Reason I ask, if your a consultant or contractor and making more than $70 an hour...take the car and rent a hotel room. Then take care of coach, when you have time! Share this post Link to post Share on other sites
redline8300 Report post Posted February 25, 2018 Acid batteries and they are all bad. In the process of changing them out. With the generator running the gauge is bouncing. If this doesn't work I'm flying out tonight. I'm going to be down there for over a year so $500/month lot rent is cheaper than a hotel or apartment. Share this post Link to post Share on other sites
kaypsmith Report post Posted February 25, 2018 Most likely that is all that is wrong with the inverter also. Share this post Link to post Share on other sites
wolfe10 Report post Posted February 25, 2018 A quick major change in voltage often indicates a loose or corroded connection. Second would be to fully charge and load test the batteries. Also, for fluctuations in voltage from the alternator, check carefully if you have a SENSE terminal/wire from chassis battery side of the battery isolator to the alternator. They are small gauge wires and are easily damaged. Also, the Beaver Marquis will NOT have a Caterpillar 3126. It will have a larger Caterpillar engine-- one over 10 liters, not 7.2 liters. Share this post Link to post Share on other sites
hermanmullins Report post Posted February 25, 2018 To really load test your batteries, it would be best to fully charge each one separately. Then load test it. This way if you do have one bad battery it will not give you a good charge. If you find one bad battery change both or all four depending on which bank you are testing. IMHO if one battery is bad the rest are soon to follow. Herman Share this post Link to post Share on other sites
manholt Report post Posted February 25, 2018 Ditto x2! Share this post Link to post Share on other sites
redline8300 Report post Posted February 25, 2018 2 hours ago, wolfe10 said: A quick major change in voltage often indicates a loose or corroded connection. Second would be to fully charge and load test the batteries. Also, for fluctuations in voltage from the alternator, check carefully if you have a SENSE terminal/wire from chassis battery side of the battery isolator to the alternator. They are small gauge wires and are easily damaged. Also, the Beaver Marquis will NOT have a Caterpillar 3126. It will have a larger Caterpillar engine-- one over 10 liters, not 7.2 liters. Per the 1WM in the serial number on the engine, it should be a 3126 and per the Gillig Chassis Manual, the pre-96 models were a 3116. I'll double check the connections, but they all looked clean and tight. I'll check the sense wire as well. Share this post Link to post Share on other sites
wolfe10 Report post Posted February 25, 2018 Sorry for my mis-information. Yes, the 1WM is a 3126. But the Marquis was a high-end offering, which generally meant heavier chassis and larger engine. Perhaps that description (larger engine) only applied to slightly newer model year Marquis. Gillig made an excellent chassis-- have worked on a friend's CC on that chassis. Share this post Link to post Share on other sites
manholt Report post Posted February 25, 2018 Brett. 1996 came in 300hp and 380hp, 36, 38 and 40 foot, no slides! Carl Share this post Link to post Share on other sites
wolfe10 Report post Posted February 25, 2018 19 minutes ago, manholt said: Brett. 1996 came in 300hp and 380hp. Carl Thanks, Carl. Two very different engines. Suspect the the 380 HP is a 3176. the 300 HP being the 3126. Share this post Link to post Share on other sites
bm02tj Report post Posted February 25, 2018 I have a 99 Freightliner and the voltage was fluctuating I pulled alternator as I had bad diodes problem fixed Share this post Link to post Share on other sites
jleamont Report post Posted February 26, 2018 redline, to answer your question "can low voltage cause low power" YES. Low voltage will drop the injector input voltage resulting in stress to the coils on them and will result in low boost, over time it will damage those injectors. Bad batteries are the first place to start, clean up all of those connections while replacing them, take it for another driver afterwards. I have a feeling you have a broken plate in one or more batteries causing the voltage fluctuation. Don't forget to check the other battery bank as well. Share this post Link to post Share on other sites
