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" SOMETIMES GOING BELOW 14 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.

- Unplugged the IAT while the truck was doing it, nothing changed.

- Checked all grounds.

- Put my hand on the grid heater while it was doing it, and there was no warmth at all, so I know its NOT the grids.

- 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.

 

Bump...
Help

 

have you replaced the headlight relays and checked for corosion where they plug in and the wire terminals where they connect to the wire for the relay ?

also i saw some had headlight switch problems?

get the regulator tested ?

just some things i would look at doing !

 

I have seen this with another type vehicles charging system. First thing to do is check the grounds on the batteries. Make sure they are clean and tight. Should be a ground going to the (motor) somewhere also. I had one that was loose causing this issue. I have also had a alternator go bad doing the same thing. It's regualtor was in the alternator so I don't know for sure if it was the regulator or alternator itself. If one of the above is bad yes a bench test will pass. Darndest thing I have ever found on 2 different vehciles. Also, the problem can be intermittent. Somtimes happens other times dosen't. So it is either a bad ground or a bad alternator/regulator( I would think regulator).

This brings back some memories!!!!!!! What fun!!!!!!

 

Find a friend, swap alternators, give him a beer to drink, see if it goes away, keep drinking till it does. I'm going with a regulator. Does the problem persist while both driving and sitting still? AC on or off? Interior lights too, or just driving lamps?

 

From what I have experienced you mainly notice it with the lights on. It still may do it without the lights on it is just not as noticable. Hope this helps.

 

Thanks guys! Look in the HELP section for the final nail in the coffin.

 

Had the same problem over the weekend. Another website said check grid heater connections if problem is above 18mph? I went a little further and tightened all grid heater connections (at heater and relays and battery) and also checked my grounds. Got a flat or more out of all connections but mainly at my battery. Connection was loose and dirty. Voltmeter and lights are now rock solid.

 

I fixed it...

It was the connection to the solenoid...

 

Throw us a bone here.. I searched the Help section looking for a recent post on your behalf with nothing recent... What solenoid were you fixing?

I have had similar problems so I would really like to see what you did.

 

On the 2 solenoids there are 4 90* elbows that plug on the studs...

Over time the 90's will wiggle loose a bit...

Take em all off, use some pliers and squeeze 'em a little then shove 'em back on...

Make sure they have 0 play on the studs or it will make the solenoid engage kinda like a short...

 

Digital Bullet you are talking about the solenoids for the grid heaters, correct? That is also where I found loose connections. It was loose on the power connections for the heaters, and everywhere else in the power circuit.

 

Yeppers!

 

I thought we talked about driving it with the grid solenoids unplugged? Maybe it was another thread. I could be wrong...............hard to keep them all straight in my head with all the voices too. I hate to listen to them all the time, but every now and again they have some good ideas!

 

I have had this very same problem on my 97 as well. Never have figured out what it is.