Charging/Voltage Issues

[MAYoung]

First, my apologies for bringing up this matter once AGAIN within this forum. The questions that I raise have been discussed multiple times so I will gladly accept re-direction to appropriate threads or guidance from members.

I have owned my 1998.5, 24 valve 2500 since May 1998. I ordered it direct from the factory and have managed to put 262,000 miles on the odometer. I have had the usual problems with the VP44, accelerator pedal position sensor (APPS) and the like but I have never really solved the following issue with the charging system. I looked at the problem about 10-12 years ago but gave up since I do not have an automatic with torque converter lock-up problems and the truck pretty much started and ran.

Since the truck was close to brand new, I have experienced voltage drops when the fuel heater cycles on and off (or at least that has been the explanation given to me). The problem starts like this--if the truck has sat for maybe a week, when I get in and start the truck, I will get a "Check Gauges" light and a lower (but still above the lower tick mark) on the voltage gauge. The voltmeter will slowly rise after a short period of driving and the "Check Gauges" light will go out and the voltmeter approaches just under 14 volts. If I sit at idle, however, for any period of time, I hear what I assume to be the fuel heater cycling on and off. The volt meter will drop, the lights will dim momentarily until the fuelheater cycles off, or so I assume. It has done this for years and since it started and ran, I just lived with it.

I would like to know if there is a fix for this voltage "lag." In my mind, the alternator and electrical system should respond with the necessary voltage for truck operations. The truck is stock with few accessories except for a FASS DDRP and a fuel pressure gauge. The batteries are less than four months old and check good. The alternator is an Autolite brand from Autozone and has been in the truck probably 8-10 years (at least). I have no problems with the speedometer.

I have looked at Cummins Forum, Mopar1973Man and this forum for answers and have seen lots of information for alternator problems and torque converter issues. I will turn a wrench on this truck but I am not a mechanic and am ignorant of many electrical matters. Your guidance will be greatly appreciated.

Thanks in advance,

Mark Young
Fair Oaks, California

P.S. I do not live in an extremely cold environment but this truck spends lots of time in the snow in the Sierra Nevada mountains. You really notice the voltage drops in the colder weather.

 

[seafish]

FYI--That is NOT the "fuel Heater" cycling but rather the intake air "grid heater" which uses ALOT of amps, PARTICULARLY in cold weather. It is the Cummins equivalent of "glow plugs" on other Diesel engines, but is in fact a MUCH more robust and trouble-free design. The only drawback is the LARGE amp draw while they operating, but that is in fact perfectly normal and NOTHING to worry about as the size of the batteries and charging system take this draw into account.

If, for some reason, you wanted to, you COULD upgrade the battery sizes and alternator and wiring to produce even more amps under idle condition, but that is optional. And if in fact you are experiencing other electrical problems with your truck, then the first thing you should do is inspect the condition of your batteries, the battery wires, and EACH and EVERY of the battery connections and grounds.

 

[fest3er]

The voltage sag is the intake heaters turning on; they draw 200 amps. Your alternator only supplies 136A. 65A+ will draw the batteries down.

The PCM/ECM will cycle the heaters until (1) the vehicle reaches 18MPH or (2) 'some time' has passed (I don't remember how much).

One solution is to install a switch in the control side of the heater relays, on either the +V lead or the -V lead. This will let you easily flip the switch (if you install it in the cab) when you do or do not want the heaters to engage.

Another solution is to install a 300A alternator that can power the heaters and charge the batteries at the same time.

Yet another is to hack the intake manifold temp sensor so it always tells the PCM that the intake air temp is 100°F; that should be high enough to convince the PCM that it doesn't need to cycle the heaters. Come to think of it, you could switch a resistor (or something) in and out of that circuit to control the PCM's control of the heaters from the cab.

 

[MAYoung]

Thank you for educating me.

The truck experiences no other electrical problems that I am aware of.

This begs the question: Would it be worthwhile to install a larger alternator and upgrade critical wire paths with larger wires, as you suggest? Or would I just be creating problems for myself and the electronics of the truck in general? (All that I know of electronics is that no good intention goes unpunished.)

Other than the grid heater, I have no other large electrical demands such as a wench, snowplow, extra lights or RV needs. Thanks.

 

[Bill Lins]

I have no other large electrical demands such as a wench

The demands of wenches tend to be financial rather than electrical. Other than that, I have no advice for you.

 

[seafish]

If it ain't broke, DON;T fix it!!!

Without the need for more amperage for other uses, there is NO reason to upgrade the battery or charging system.

That being said, it IS important to properly inspect and maintain the ones that came on the truck from the factory.

just my .02

 

[MAYoung]

Wow. I just found the thread on this very issue from 2010. I see that it generated a lot of arguments concerning the increase to a larger alternator. All good points and food for thought.

The very first thing that I am going to do is go out and make sure that the grounds are clean, shiny and well connected. The next thing that I will do is get the volt meter and get the best voltage and resistance readings that I can on the system. The truck is, after all, 20 years old and corrosion is sneaky and insidious. As usual, back to basics.

 

[JR]

I seem to remember a TSB released years ago to lower the threshold for the low voltage light due to the high number of customer complaints. Didn't change the operation of the system one bit as it is indeed normal, it just prevented the light from coming on due to the grid heater operation.

 

[GAmes]

If I sit at idle, however, for any period of time, I hear what I assume to be the fuel heater cycling on and off. The volt meter will drop, the lights will dim momentarily until the fuelheater cycles off, or so I assume. It has done this for years and since it started and ran, I just lived with it.

If operating properly it isn't normal for the grid heaters to cycle after it has warmed up. You have an intake air temp (IAT) sensor on the top plate of the intake manifold. I suspect it is faulty. The procedure for testing and the resistance (ohms) chart by temperature when the engine is cold is in chapter 14 of your FSM. If the engine is at operating temp the ohms should be less than 1340. There is also a testing procedure for the intake air heaters.

On my '97 I have wired out the PCM controlling the heater operation and have a toggle to turn them on and off. Some people use a horn type push button. If the grid heaters come on and stay on they will draw enough amperage to cause the PCM to kick the alternator off line. Having a larger alternator won't change amperage draw, so the same would occur. When my truck was still in warranty the relays stuck closed and the result was two boiled, ruined batteries (that were not covered by warranty). The toggle was installed shortly after.

 

[Chief USA]

Plugging in the block heater about a half hour to an hour before starting will usually eliminate the grid heaters activating once the IAT is sensing I believe 60 degrees F. Preventing the HUGE surge of amperage from the batteries to run the grid heaters through a cycle will make your batteries last a lot longer. Keeping a Battery Tender on the batteries when the truck is not in use will also greatly lengthen the lives of the batteries and ensure they are at peak charge prior to start attempts.

 

[BigPapa]

As stated by several others, what you're experiencing is normal except for your statement "If I sit at idle, however, for any period of time, I hear what I assume to be the fuel heater cycling on and off." This should not happen. Once you exceed 15mph the PCM disables the grids until you shut the truck off and restart.