NOTE: I KNOW THAT ITS NOT MY GRID HEATERS CYCLING - THEY OPERATE NORMAL WHEN ITS NECESSARY

The symptoms are EXACTLY as described below:
- THE FIRST SIGNS OF THE "PROBLEM" ARE WHEN MY HEADLIGHTS "FLICKER"
BY "FLICKER" THEY ACT EXACTLY AS THEY WOULD IF THEY ARE LOSING VOLTAGE. THEY DO IT VERY INTERMITTENTLY IN SHORT BURSTS.

- AS THE HEADLIGHTS "FLICKER", THE VOLTMETER FLUCTUATES IN UNISON WITH THE "FLICKERING" NEVER GOING BELOW 12 VOLTS.

- ALSO, VERY FAINTLY YOU CAN FEEL THE ENGINE "JUMP" WITH THE FLUCTUATION AND "FLICKERING". BY "JUMP", I MEAN IT FEELS LIKE SOMEONE IS PUSHING THE OUTSIDE OF THE TRUCK NOT HARD AT ALL, AND I'D BE VERY SURPRISED IF ANYONE ELSE COULD FEEL THE "JUMPING", BUT I FELT LIKE MENTIONING IT. I'M SURE IT HAS TO DO WITH THE VOLTAGE.


Now, here is what I have done so far:.
- Load tested the alternator, passed.

- Unplugged the grid heater, and it still did it.

- Unplugged the IAT, and the problem seemed to go away, but came back very shortly (2 days) after.

- Checked all grounds.

- Batteries are NEW and the cables are nice and clean.
BOTTOM LINE:

- What would cause this?

- Could bad brushes in an alternator cause this and still pass a bench test?

- Could my ECM be bad? (voltage regulator)

- If the above could be bad, how many of them have failed?

- Can grid heaters cycle that fast? I'm talking 2-3 fluctuations per second.



Please, help me enjoy my truck and not worry about something burning up.

 

I would say the "jumping" you are describing is the culprit load releasing from your alternator.

 

I really want to find this load...

Can bad brushes cause a load?

 

No,

I would say you are on the right track. Keep disconnecting segments via. plugs or fuses until you hit the one that makes it go away.

 

So, voltage would not drop if the alternator is going bad?

Do you think my voltage regulator is bad?

How much current does the IAT draw?

This is making me sick.

 

Oh no...

This isn't going away.

We WILL find it TOGETHER as a 12v community...

 

Would an engine miss cuase anything to happen electrical wise?

 

In my 1st gen several years ago, I had a similiar problem. It was the voltage regulator, it seemed to go out on a regular basis about every year (the truck had electro hydraulic plow used HEAVILY). I'm not sure how much the electrical system changed on the 12v's over the years, but it might be worth a shot to look into it.

 

I have some similar type problems recently that have to do with the IAT, I think!!! I worked on my pump settings and had to move some plugs, soon after that I have this type of voltage drop etc, but only at WOT.. My tach doesn' t drop, I have a new Alt. So I think I may have a similar situation going on.. Hmmm, I have to look at some wiring diagrams.. I thought it might just be a bad harness plug or something feeding the engine... ??????

 

Given everything you've checked out, it sounds like a bad alt/regulator. I wouldn't suspect the grid heater anyway, given the very short cycle time (and since you understand how the grid heater normally works).

(Off the top of my head...) Battery nominal voltage is around 12.6V, depending on the temperature/etc.. When the engine is running, the alternator pulls this to somewhere around 14. The regulator controls field voltage which controls the voltage of electricity generated. The output is rectified by a set of diodes (turned from A/C into D/C). If the sense voltage was wrong, the regulator may not know how to control the alternator. If the circuit to the field coils is intermittent or of high resistance, then the regulator will also be unable to effectively control the voltage.

I would try cleaning all the alternator connections well (sand paper on the connector, the nut that holds it on, the surface it hits, etc.) Check the ground to the alternator, as well. Another potential is a damaged wire along the circuit to the regulator, which gets to be crappy to troubleshoot.

 

My vote would be for alternator brushes. It's pretty easy to remove them and have a look, you can see if the slip rings are getting chewed up and pitted. It would be handy to look at the alternator's waveform with a lab scope if available.

Another thought would be the crank sensor signal failing momentarily, but I'd think if it was bad enough to interrupt the alternator's field circuit, you'd see it in the tachometer first.

 

an alternator on its way could definatley be the cause but just hope that the regulator isnt at fault i have seen it go both ways and the crappy part is that the regulator come with a PCM and $$$ ouch! hope for the alternator, also check the alternator field relay those and the wiring to those can cause many intermittent and irritating problems.

Chris

 

i am having the same problem with my truck. this is what i have done:
NEW ALT. NO CHANGE
NEW COMPUTER NO CHANGE
NEW ESS SENSOR NO CHANGE
NEW BATTERIES NO CHANGE

this is what is going on. the lights will flicker and shut off. my tach bounces all over and goes to zero. the GEN light n CHECK ENGINE n WATER IN FUEL n WAIT TO START n TRANS TEMP lights all come on when it acts up and the TQ or OD unit unlocks and locks.

anyway have any ideas?? also the voltage jumps all over the place.

 

i am having a similar prob, but my gauges dont move, just a very faint dimming of the lights. very intermittent also. any thoughts.

 

Sounds like a gremlin behind the dash to me.. All you need to do is get some rat poison, and put it in the ash tray..that will clear the little guy right out!

On a more serious note...sounds like it could be a loose wire from the alternator to me. I had this same thing happen to me on my ol' *****'s Jeep (may it rest in peace) and I turned it on, looked under the hood and noticed there were sparks flying from one of the alternator connections. Tightened everything up, and worked like a charm!