ok here is what i got. when motor is started about 20 seconds later my dome light and headlights pulse or flicker like there is a amp draw on charging system. they dont go clear dark but just enough that it is noticeable. now when this is happening if i rev the motor it doesnt get any faster but it is a rythemic pulse. at first i thought it was the altenator or batteries but both checked out good. last night when it was doing this it seemed that the HCFM was making a slight noise that matched the flicker in the lights but was hard to tell with engine running. the fuel pump or heating element was what i was thinking that might be cycling at a constant rate. I also wondered about glow plugs or a intake heater. I have a edge insight installed and it doesnt show any codes. any thoughts on this?

 

My 04 does the same thing and always has, even with a higher amp alternator. It's worse when I turn on a turn signal and I can hear my fuel pump pulse also, so I know it's some kind of current draw. I've done everything to it that I can think of with the exception of changing the dash panel and battery cables. I'd be willing to bet it's alternator related because it doesn't do it until the alternator energizes, which is "about" 20 seconds after cold start.

 

My first reaction would be a weirded out voltage regulator, that is not maintaining a steady voltage. But that'd just be a guess.

If you could find one, I'd put an old fashioned needle volt meter on it and see if the needle is jumping.

 

i also thought it was altenator related but had it checked at oreillys and auto zone both said it was good. also when i have had alt problems before on gas engines that caused this type of pulsing , the pulses sped up with the rpms increased this doesn't i am wondering if it might be the fuel heater energizing. can i just pull the fuel heater fuse without hurting anything else? also after driving three hours home to night when i pulled into the driveway and stopped it wasn't doing it. my trucks coolant temp was about 187 on the insight. i was wondering if it only did it when it is cooler.

 

I don't think disconnecting the fuel heater will cause a problem, unless something else runs off of that fuse. Later models don't even have a fuel heater.

 

start by removing the drive belt and start the truck. if the issue is gone my vote goes to the alternator.

 

Just because the alternator is charging doesnt mean it is good. Several other problems other than voltage output can be caused by the alternator. I think there was a tsb for poor running caused by alternator ripple issues.

 

Following on Cheezit's good advice (that never occurred to me), it seems like you could unplug the connector and remove the battery wire from the alternator and acheive the same test without having to mess with the belt, tensioner, etc.

And matty said better what I was trying to say. It's not necessarily that the alternator is bad or not charging or anything. Just that maybe it is not putting out a consistent voltage because it's isn't working exactly right (not failed but not holding a consistent voltage).

(And it could very well be a load issue also)

 

If it's the alternator one of the diodes is probably failing. The alternator is still putting out but the failing diode is letting some AC ripple thru.

 

well it did not do it this morning. but later on it was doing it very lightly. i did check the voltage at batteries, altenator and tand at a couple of the ground wires all checked out and where showing the same reading 14.3, 14.2. so if it starts again i can just unplug the alt connections to see if it stops. will it hurt the alt to be turning without connections?

 

as odd as it sounds just set the dvom to ac volt and check the battery more then about .3v -.4v you got an issue.

 

i wondered about doing that, thanks cheezit i will update later

 

it hasn't done it at all since i posted the problem here. so which one of you all are causing this problem? just kidding, weather was warmer today around 60 degrees wonder if that is relevent?

 

It is the glow plug relay load that is probably causing the problem. The glow plugs draw about a 100 amps when they are on. The OEM alternator is rated for 110 amps. Not sure if that is continuous or intermittent load. So with the GPs on, headlights and other power requirements, you get to or exceed the alternator's rated capacity pretty quickly.

I have the same problem and it occurred this morning as it always does. About 15 to 20 seconds after I start the motor, my head lights get brighter and my fuel pressure increases. I have a fuel pressure gauge and a AD2 fuel pump with an internal pressure regulator set to 70 psi. When I turn the key on to start, the fuel pressure is 45 psi. This morning, at the same time the headlights got brighter, my fuel pressure went from 45 psi to 70 psi. With the motor hot and normal operation, it normally runs at 60 psi.

I have a 160 amp alternator that I bought aftermarket to attempt to cure this problem. But the GPs still drop the voltage below the standard 13.5 to 14.0 VDC charging voltage due to the high current draw. I have verified that because I have one of those plug in electrical monitors with the RED, YELLOW and GREEN LEDs. After I start the truck, it is a hard yellow LED indication. On real cold mornings it actually flickers between red and yellow. After the GP relay goes off, about 15 to 20 seconds later, I get a hard green LED. After the motor warms up and the alternator gets hot, I start to get a slight green/yellow LED flicker.

DSMMH

 

As I recently learned, the alternator isn't turned on until the glow plug cycle is complete. So it wouldn't matter how big an alternator you put on, you are still running solely on batteries until the glow plugs are turned off.

I don't think the glow plugs cycle on and off, though. I think they are on for as long as the PCM wants them on. This depends on oil and water temperature, at least, so when the engine is warm, the glow plug cycle is very short, if they are turned on at all.