Cluster LCD pulsing

[Stingray1967]

Hey gang,
So I was sitting at a stop light the other day and noticed that the center square LCD (the one that has the speed on it) was pulsing. It doesn't seem to be in line with the turn signal clicking. I tried taking a video of it, but the camera can't really pick it up.

Battery was fully charged up two days ago (trickle charger for 8 hours), and the battery is only 6 months old anyway.

Initial thoughts? Anything I need to worry about?

[viper107]

check charging system?

[IM28702]

My 97 Suburban does that as well, I'm positive it's the alternator in mine.

[Young1]

My 91 did the pulse. Then the alternator rotor came apart at high rpm. New alternator no more pulse.

[Stingray1967]

I did a little reading online, as it has been a bit since I have done any alternator testing on my own. Is the process still this?

1. Start car
2. Disconnect battery
3. Car should run with alternator and not die?

[32valvZ]

I did a little reading online, as it has been a bit since I have done any alternator testing on my own. Is the process still this?

1. Start car
2. Disconnect battery
3. Car should run with alternator and not die?

NO!
Here is a simple procedure to follow... I found this in my first search...

https://www.wikihow.com/Check-an-Alternator

:cheers:

[Stingray1967]

I checked the voltage across the battery prior to starting the car. I had driven it twice the day before, no issues. The voltage was 12.5. I started the car and backed it out of the garage and tested the voltage again with the car running. It was steady at 15. I'm assuming this is ok.

[32valvZ]

I checked the voltage across the battery prior to starting the car. I had driven it twice the day before, no issues. The voltage was 12.5. I started the car and backed it out of the garage and tested the voltage again with the car running. It was steady at 15. I'm assuming this is ok.

Sounds like its ok. Another easy way to determine if the alternator is full fielding, put on all your accessories with the car running and see if the volts increase and hold. My cluster does the same as yours, not real bad, but my alternator is brand new and my battery is a dry cell about a year old... I know my grounds are clean and tight, cause I cleaned and tightened them... My car always starts and I never have an issue... I chalk it up to age of the car at 30 years old...

[Stingray1967]

Ok thanks. I'm heading on a three hour trip with the car in a couple weeks and just wanted to make sure everything was OK.

[Paul Workman]

No secrets surrounding lead acid batteries (including AGMs). But, to your fluctuating illumination question:

Fluctuation of the dash (LCD) screen is due to fluctuating current which can be detected indirectly by monitoring voltage.

Some facts about (car) batteries:

Each of the 6 cells at rest and fully charged produce 2.1 volts and are series connected to produce 12.6 volts at rest when fully charged.

A 12 volt car battery that measures 12.1 volts at rest is fully discharged, far as working to capacity goes. NOTE: A 12 (car) battery with a shorted cell will read ~ 10.5 volts, even after having been charged sufficiently to normally charge the battery fully. However, a battery can read much lower too if allowed to become severely discharged, e.g., leaving the headlights on over night. A battery discharged (I've seen some as low as 1 or 2 volts after the headlights ran the battery down over night. The battery's capacity to be restored to full (current load)

With the engine running and the headlights OFF, normal charging voltage is 14.6 volts, when the engine bay is cold, i.e., engine is first started and will recede to approx 13.8 after the engine bay heats up and the battery capacity if fully recovered after starting the engine is complete.

The capacity of a battery can only be done once it is fully charged and then the voltage measured after a specific time while a specific load has been applied to the battery. (Even a fully discharged "dead" battery will read 12 volts!)

So! with all that in mind, onto the fluctuating LCD (dash) light...


If the LCD fluctuations are do not seem to be in coincidence with the turn signals, i.e., they're on a different circuit, that would suggest to me that the circuit for the dash is experiencing voltage fluctuations that are related to a poor connection, either a source or a ground path connection affecting only the (LCD) dash circuit.

Just to eliminate the source for that circuit, I'd want to shine up the fusible link connections (behind the battery) first, and coat them with a film of dielectric grease against future corrosion/oxidation (these are old cars...).

Then, I'd want to service the ground buss connections, paying particular attention to the dash ground connections. Again, dielectric grease.

If the problem isn't fixed by now (and there are no voltage fluctuations at the battery terminals), pulling the dash cluster out and servicing the bulk connector on the back of the cluster assembly. (Mine were "frosted" with oxidation.) But, a quick wire brushing and scraping with a knife blade and (again) dielectric grease was the solution to my random fluctuation issue.

If all that fails, then the cluster board might need to be pulled apart and the ground points shined up. But, too, before going that far, also pay attention to the LCD board connector.

Chances are 99%(?) that you'll have fixed the fluctuation issue before getting this far! Beyond that and it is starting to look like maybe a component failure (the LCD board itself?) may be in question. That being the case, then perhaps BANTEE.com may be your solution. (And, if you haven't already replaced the tach voltage divider board, having them also do that while they're in there my be well worth the few bucks to kill two birds with one stone!)

Good Luck!

P.

[Stingray1967]

Paul, wow. THANKS!! One more thing to add. I had to replace my antenna on the radio a few months ago because the old one wouldn't go all the way down anymore. Yes I tried the ribbon cable only first, and that didn't work, so I bought the whole unit. I did that buy purchasing a replacement antenna from Mirrock. When I put that in, started the car, and turned on the radio, there was a significant buzzing over the speakers. I believe that a ground somewhere got screwed up, but I was VERY careful putting it back together. I haven't spent the time yet to put the rear wheel well out again and check the grounds. The LCD pulsing happens with the radio on or off. When I select the voltage display on the LCD screen, the NUMBER moves around quite a bit. From 13.0 to 14.5. Maybe that's ok, I've never really looked at the voltage this closely. The analog gauge needle doesn't move an inch. And the pulsing is not related to the turn signal or stepping on the brakes, or any other "driver input" electrical load I can think of.

[rush91]

Mine did this about a month ago...Sitting at a light, if the fans would kick on the volts would drop and the LCD screen flickered. I cleaned the wire connections on the battery cables with a wire brush, pulsing / flickering gone. And my connections looked just fine before cleaning them.

[Paul Workman]

Mine did this about a month ago...Sitting at a light, if the fans would kick on the volts would drop and the LCD screen flickered. I cleaned the wire connections on the battery cables with a wire brush, pulsing / flickering gone. And my connections looked just fine before cleaning them.

Yes! Very good point! The corrosion film on the connectors starts out as almost CLEAR. One cannot always see the film, but once the connector is wire brushed, suddenly all is well!

Another tip to keep in mind: Next time you start your car - especially if it acts like the battery my be low, feel the battery terminals with the palm of you hand. If the battery connector is warm to the touch, that is a dead giveaway that the connector needs to be serviced* asap.

* wire brushing followed by smearing some dielectric grease on the connector contacts (which will retard the further formation of corrosion).

[Stingray1967]

I'm happy to report that I checked the battery terminals and one of them was only finger tight. I swapped the connecting hardware and tightened it up, and the pulsing is gone. Also the voltage display number is MUCH more stable. The car seems to start easier too. Thanks rush91 for the suggestion to check the battery connection. I wire brushed the connections prior to reassembly too, but they looked fantastic.