97 d1 pulsing lights

[pdXDisco97]

My headlights and interior lights are pulsing while the truck is running. It started a while back after a gasket job. I just put a new battery in which solved the start up issue, but the pulse remains. Could it be a loose ground? Or is my alternator dying? Troubleshooting tips are appreciated!

97 d1, 120k miles

 

[singingcamel]

check your connections on the alt.

 

[Levi]

I had an alternator do this when the voltage regulator went out in it.

 

[pdXDisco97]

Thanks for the tip, I checked the connections and the main lead had about a half turn of give. After that the lights have only a very slight pulse, never notice it if I wasn't looking for it. Last night it was very obvious. Ill keep my eye on it, and in the meantime, I'll save up for the new alternator!

 

[pdXDisco97]

Digging this thread back up as I still have this issue, and I'm a bit stumped.

I tested my alt output with my cheap multimeter, it read 18-19 V. Obviously, too high. So I bought an alt from Will Tillery, a 120Amp P38 unit. In the process of waiting for it to arrive, I had the oil changed, and while they changed it, they read 14.4v, but said my 3 yr old battery was very low, which explains the sluggish starts. I had the battery tested where I bought it, and sure enough, it was toast. So, I purchased a better battery, and now it starts up crisp again. While the battery was being changed, my negative cable broke, so the shop replaced the connection, but mentioned that there is some corrosion on the negative cable.

I was going to change the alt today, and I wanted to double check the reading, so I used a better multimeter, and it's reading 14.4V, but I still have the flicker.

Do I need a new negative cable?
Should I swap alternators even though the current one is putting out correct voltage?
Should I do both?

 

[helievacpilot]

Digging this thread back up as I still have this issue, and I'm a bit stumped.

I tested my alt output with my cheap multimeter, it read 18-19 V. Obviously, too high. So I bought an alt from Will Tillery, a 120Amp P38 unit. In the process of waiting for it to arrive, I had the oil changed, and while they changed it, they read 14.4v, but said my 3 yr old battery was very low, which explains the sluggish starts. I had the battery tested where I bought it, and sure enough, it was toast. So, I purchased a better battery, and now it starts up crisp again. While the battery was being changed, my negative cable broke, so the shop replaced the connection, but mentioned that there is some corrosion on the negative cable.

I was going to change the alt today, and I wanted to double check the reading, so I used a better multimeter, and it's reading 14.4V, but I still have the flicker.

Do I need a new negative cable?
Should I swap alternators even though the current one is putting out correct voltage?
Should I do both?

New cable for sure. If issue goes away, your done. If not, replace the alternator.
Also, voltage alone is not entirely indicitive of alternator health. Current flow is also a factor. Would need an inductive pick-up to measure that.

 

[pdXDisco97]

Ok, so I replaced the cable. Still flickering lights.

I decided to swap the alternator... done. Good reading on the multi, but the lights are still flickering! The headlights and interior don't seem as pronounced (maybe it's psychological...) but the rack lights are flickering for sure.

thoughts?

 

[Levi]

Is it possible you have the same issue with the other alternator? When I had this issue my headlights and dash lights slowly pulsed bright/dim but never went off, I swapped the regulator off one I had that needed rebuilt and it's worked fine since. When you say flickering are they going completely off and on like a xenon going out?

 

[pdXDisco97]

No, they do the bright/dim, but never off.

I do notice that when I turn on my dome light, and shut off my headlights, the pulsing slows down. So, faster pulse with more lights on.

 

[ptschram]

Switch your meter to AC and the millivolt scale.

the pulsing you're seeing is ripple-AC leaking through the diodes.

It will get worse and eventually, it will kill your battery overnight as the diodes leak to ground.

 

[pdXDisco97]

"the pulsing you're seeing is ripple-AC leaking through the diodes."

PT, you think it's in the alternator?

 

[ptschram]

"the pulsing you're seeing is ripple-AC leaking through the diodes."

PT, you think it's in the alternator?

Yes

 

[ptschram]

A way to find out is to disconnect the big wire to the alternator, start the truck and look for the pulsing.

My money is on the pulsing being absent with the alternator disconnected.

Don't disconnect while the engine is running.

 

[pdXDisco97]

Thanks, I'll give that a try tonight!

 

[pdXDisco97]

Ok, here's the synopsis of my troubleshooting. And I think I'm more confused than before:

1. I disconnected the alt, and the flickering was minimal. I was probably only notice it because I was really looking for it. I notice most in my rack lights, maybe they are vibrating from the idle of the truck?

2. I reconnected the alt, and the flickering seemed to be gone. Then I rev'd the engine, and on release the pulsing picked up again. It stayed during idle, and increased frequency when I gave it more gas. At about 3500 rpm, the pulsing settled down. At this point, I check the output at the battery at it read at 13.8V, which is a little lower than before.

3. I disconnected again, just to check, and the flickering/pulsing again was minimal. I let it run for about 3 minutes, rev'ing the engine a few times with no change.

4. Reconnected, and the pulsing was back, but much less noticeable. Here's where it gets confusing; I rev'd the engine, the flickering almost stopped (to the point where probably no one else would notice it) and it stayed at a very minimal level. I let it run for 7-10 minutes while I put my tools away, and it stayed steady with very minimal pulsing, to the point where I could only see it in my rack lights during idle. As soon as I touched the gas pedal (applying so little pressure that the RPMs didn't even go up) any trace of flickering went away completely. So, it seems that the pulsing has gone away, for now.

I'll be taking it up to the PCRC meet on Saturday, which is about a 2 hour drive. Hopefully, I'll be able to determine if it's gone, or just a temporary quirk.

 

[Injuhneer]

I have been seeing this on my '97 D1. It is just a pulsing of the lighting; mostly visible in the instruments at night.

I replaced the regulator assembly because the brushes were worn out. It helped but did not eliminate. I am changing out a cracked exhaust manifold today but when done I am going to check again for AC ripple in the system.

Are diodes or a bridge available for these alternators? I assume so because re-mans are available.

 

[ptschram]

I have been seeing this on my '97 D1. It is just a pulsing of the lighting; mostly visible in the instruments at night.

I replaced the regulator assembly because the brushes were worn out. It helped but did not eliminate. I am changing out a cracked exhaust manifold today but when done I am going to check again for AC ripple in the system.

Are diodes or a bridge available for these alternators? I assume so because re-mans are available.

They are but the cost rivals that of another alternator.

 

[disco baboon]

Hi, Duty disco,

First thing that comes to my mind is: There are TWO main negative cables, and I hope you checked em both:

one black running from the battery to the chassis, and
one from the starter to the chassis , directly below the starter motor, little hard to see.

If this last one is corroded or not tight, you could get things like you describe.

hope it's of little help

grtz Jasper

 

[Injuhneer]

They are but the cost rivals that of another alternator.

Part number?

Or maybe a dead bridge laying around? If it uses the regular automotive diodes it may be possible to cross to a common diode and repair them inexpensively.

 

[Injuhneer]

I also recently purchased what is ostensibly a better BT ODBII bridge. The prior ELM 327 put system voltage at 13.6. The new one indicates 12.7.

Time to break out the DMM.