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Hey gents. Working on the GF's car again. We were driving the other night and I noticed the headlights were pulsing,like a voltage fluctuation or something.

Read it could be a few things

- Checked all the fuses, under the hood and under the steering wheel. Nothin. Unless there is another fusebox somewhere.

- Pulled off the ground strap between the engine and the radiator core. Cleaned it with a wire brush (didn't look horrible), put it back on with dielectric grease. Also, pulled off the battery ground at the fender well and the transmission body. Cleaned those off and put some grease on those. Was still pulsing, so I tried grounding the engine block to the battery negative terminal. Didn't seem to fix the issue.


Where do I go now? Alt seems fine, it was tested not too long ago. Also the voltage was above 14 volts, and I could not see any fluctuations in the voltage.

 
Rep Power: 242

It could still be your alternator. Does it get worse when you load the engine down? Turn your ac radio and defroster on and see if it gets worse.

 
Rep Power: 517

Could be normal, or maybe not. Depends.


So what exactly was the voltage at, and where was this measured?

What other electrical consumers were being used at the same time?

Y/M/M of the car?


Alternator mounting bolts tight?

Could be normal action of an ELD controlled charging system?

 
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I'd have to check again but it was around 14.25 at the battery.

It was running the Defrost (blower) and headlights.

2004 Honda Civic LX

 
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Normal. The electrical load of the defrost will include not only the load of the interior fan, but will also include the load of the AC compressor and radiator fans. The compressor and radiator fans all cycle on and off during operation, so the headlights will dim and brighten as the other electrical loads change.



You should also notice the headlights dim a little bit if you try to operate the power windows all at once, or have the window motors stalled out.

 
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Plus these alternators are not the best, at least thats what my car shows.

 
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Happens to my car often, though usually not a big difference but I can still notice it pulse.

 
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mine never pulses even with high electrical loads, but i have a napa alternator. cant remember what the oem was like cause it went out two years after buying the car new. but ive noticed quite a few honda and acura that have this pulsing problem. it seems to be normal, but not something i would like to have.

 
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My interior map lights pulse as well. I notice the problem was more apparent after I bought a cheap Autozone alternator. No pulsing unless the engine is running so I know it's an alternator issue.

 
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Varying brightness, depending on rate of charging, is one thing. Normal, if the PCM is controlling it. Many people can SEE a 1-1.5 volt change in the brightness of the lights

Rhythmic pulsation is another. Lowest cost parts went inside at the low-rent rebuilder. You get what you pay for!

 
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yeah by pulsing i mean the lights get brighter for a half second, then get dimmer the next half second, and repeat like this forever as the car is sitting at idle. almost like when a subwoofer is constantly bumping and the lights dim with each bass note (except there is no sub when this is happening). ive seen it on a stock acura rsx alternator and was pretty surprised. that would drive me nuts.

the dimming is normal due to using accessories, but that is only a one time event when the accessory is first turned on and the voltage drops.

 
Rep Power: 517

I have never noticed this half-second pulse thing on OE. Then again, I don't drive customer cars at night, either.

I have seen it in low cost reman alternators, even a couple from a local rebuilder that tends to use low cost internals.

 
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yeah most parts at the auto store are junk. even higher end aftermarket can be tricky. i had brembo blank rotors at one time and they were terrible. noisy and wouldnt stop nearly as well. went back to new oem last year and cant believe how hard they grab. same with rims, aftermarkets seem to vibrate quite a bit even with centering rings. i later found out oems are all matched to the honda hubs and using a generic can cause all sorts of issues. there are certain things that arent worth the problem of going aftermarket.

 
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The only reason why it should be pulsing in a rythm/pattern is if the load is changing rythmically as well, like turn signals/hazards being on. I can hear the engine lug down a tiny bit each time they turn on and from my cigarette voltmeter voltage lowers by about 0.1v when on vs off. This is with an Ebay hi output alt.

It shouldn't pulse rythmically unless your flashing lights or something or your engine RPMs are changing rythmically.

The ELD shouldn't be the problem but you could always take it out of the fuse box in the engine compartment and see if there are any changes.

Monitor system voltage with it's pulsing to see what's up and maybe borrow a ammeter.

 
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You might check the serpentine belt and the tensioner assembly. If these are good as well, i suggest checking your voltage regulator.

 
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9 year old thread.