8.3L Cummins, Surge/Dip every 15 Sec. 2000 Windsor 32PB - Solution

[Bjohnsonmn]

Hello all,

I have a 2000 Windsor 32PB with 124,000 miles. The coach has been well maintained with all relevant filters, hoses, etc in good, fresh working order.

The situation: It is cold here in Minnesota. We needed to move the coach out of the shop to complete our overhead electrical so it was sitting outside for two days. We plugged in the coach and ran the engine block heater for 2 hours prior to starting the coach.

After starting the coach and setting it to the recommended higher idle speed using the cruise control, it produces a strange behavior. This has happened other times, including when it wasn't too cold.

1. The engine will momentarily increase in rpm (approximately 10-20 rpm, just enough to hear it) which also causes the lights to brighten for the same one or two seconds. Then return to normal.

2. Approximately 10-15 seconds later, the rpm dips the same amount and the lights dim for approximately the same 1-2 seconds.

Repeat.

Based on the instructions in the manuals, I do not let the coach idle for more than the time it takes to fill the air tanks and then to secure the coach after I move it in or out of the shop.

Any ideas on where to start? Has anyone else seen this? The chassis battery seems like it is in good condition and the engine starts easily.

Edited March 4, 2022 by Bjohnsonmn
Update to reflect a solution.

[DavidL]

10-20 rpm variation is normal.  Not sure what motor your RV has (gas vs. diesel and then which one) but rpm is regulated by the engine controller by moving the AIS motor in and out to vary how much air goes into the engine.  The engine controller then tells the fuel injectors to open a tad longer for more fuel.  The engine then goes a little faster.  The engine controller then does the opposite.  Hence a 10rpm swing.

The lights going brighter might be from the alternator spinning a tad faster which then puts out more output and then more voltage and then brighter lights.  But I can't imagine 10-20 rpm making much difference.  You should put a tachometer / scan tool on the engine CAN bus to see how it's doing.  But if no check engine light on, then it's probably doing just fine.

Put a voltmeter on the 12 volt circuits to see what voltages the system is producing.

Are your lights on the coach or engine (starting) batteries?  Check both 12 volt circuits just to know how both are doing.

Not seeing anything worth consideration based on the description.

Edited March 4, 2022 by DavidL

[Bjohnsonmn]

9 minutes ago, DavidL said:

10-20 rpm variation is normal.  Not sure what motor your RV has (gas vs. diesel and then which one) but rpm is regulated by the engine controller by moving the AIS motor in and out to vary how much air goes into the engine.  The engine controller then tells the fuel injectors to open a tad longer for more fuel.  The engine then goes a little faster.  The engine controller then does the opposite.  Hence a 10rpm swing.

The lights going brighter might be from the alternator spinning a tad faster which then puts out more output and then more voltage and then brighter lights.  But I can't imagine 10-20 rpm making much difference.  You should put a tachometer / scan tool on the engine CAN bus to see how it's doing.  But if no check engine light on, then it's probably doing just fine.

Put a voltmeter on the 12 volt circuits to see what voltages the system is producing.

Are your lights on the coach or engine (starting) batteries?  Check both 12 volt circuits just to know how both are doing.

Not seeing anything worth consideration based on the description.

I have a BlueFire that I can put on the unit and turn logging on. I'll do that the next time I need to move it. What is strange about it is that it is very "regular". The time between alternating dips and surges are like a metronome. It makes me wonder if it is related to an electrical component demanding power, etc. I will be taking a look to see if I have the DUVAC or regular alternator as well.

Thanks!

[Rocketman3]

That sounds like what happened to me in Alaska as it got cold. (And we were going south).
 

I also noticed the voltage drop a lot when the lights got dimmer. What I finally figured out (I believe) what the diesel grid heaters we coming on and cycling because it was so cold. (Trying to warm the cold air intake).
 

Those draw a LOT of power. So the alternator cycles up to max and the engine slows down. When the engine got up to working temperature- that behavior stopped. 

Maybe next time you need to move it - take it for a 20 min drive - so it can get fully warm and see if it stops. 

Edited March 4, 2022 by Rocketman3
Added more info

[Jim Byrd]

The intake heater will continue cycling until the engine temperature reaches a pre determined temperature. The RPM' will vary as the load on the alternator changes.

What you are seeing is normal.

Jim