A few weeks ago my 00 f150 H.D. w/5.4 started to show the battery light at hi RPM's. I replaced the alt because I've seen this happen before to my buddy's truck and I searched this site. The problem went away for a few hours and then started to do it again, only this time when the battery light came on the ABS light came on as well and went right back off once the RPM's dropped. I have a brief video I shot with my cell phone, its crappy but you can see it:



As you see when I back off the throttle the battery light AND the ABS light go back off. What makes it worse is now I have a intermittent stutter too, feels like a bad coil. The coils are all new, they have roughly 12k on them. They are Accel coils. The battery is a Walmart special and is 4 years old. I replaced the pcv valve yesterday because it was making a strange noise, and I went over the entire engine bay's vacuum hoses and replaced 2 small pieces that were cracked. I've checked the ground and cleaned that up as well. The problem is getting worse and hasn't triggered a SES light. Any ideas?

 

Sounds like the alternator is failing

 

A dying alternator would explain the battery light...but the ABS issue seems like it would be something else. Don't know for sure, but that is kind of strange. Any other symptoms? Flickering headlights/dashlights, volt gauge moving around, etc...?

I understand you replaced the alternator...what did you replace it with? OEM Ford part, or a reman from Napa, Autozone, etc...? You might have swapped out a bad part for a bad brand new part. It's happened to me before.

Also, did you replace your belt? If it is in really poor condition I suppose it could be slipping at high rpm's, but I would think you could hear that. Who knows?

One additional thing. I just replaced my alternator a couple of weeks ago, and all my problems went away. When I bought my truck used with 78,000mi on it three years ago I had the same issue you are seeing, minus the ABS light. As time went by, the rpm that the battery light would come on became lower and lower. When the light began coming on below 3000rpms (this was around the 100,000mi mark, so 22000mi after I bought the truck) I started to notice my head lights/dash lights flickering, my volt gauge started randomly dropping low, and the motor started to start REAL slow. Also, the blower motor on my HVAC started to fluctuate in speed when I would slow down/speed up. None of this was happening, with the exception of the battery light when I first got the truck, so it might be a long time before your symptoms become more than just a warning light.

Again, I have no idea whatsoever as to why this would cause your ABS light to come and go.

Mike

 

Looks like the brushes are sticking in the alternator as far as that goes. Has it got wet recently? If new , they could be sticking as well.

BUT - That might not be the problem considering the other problems your having. Something just may be loose. Like the harness bolt on the alternator itself or the other end of it.

Does this always accure at those RPMs - What about stop and go ?

Yea, I would have to go with jethat's reply below as being the problem. At least rule that out first.

 

I've had a simular problem and it was bad connections. Recheck them.

 

Thanks for the quick replies. I ran out of daylight so I'll recheck the connections tomorrow. The belt is new, and the alt came from Napa, remanufactured. It has lifetime warranty on it. The ABS light is the thing that has me stumped, as it only comes on with the battery light lol. Tomorrow I'll also have the battery tested. Oh another thing I forgot to add is when I come to a stop sign with the radio on and the blower motor running, everything dims down for a second then perks back up.

 

A faulty alternator can cause other warning lights to come on as the truck is not getting the proper voltages to power things. You have to get the alternator issue resolved before going any further.

 

The abs is coming on because the pre-ignition test mode is defaulting. Just like the battery light - it comes on before ignition momentarily.

This supports a connection problem IMO. Having the battery tested is a good idea as well. These trucks do goofy things when that starts going out.

Lots of good info posted - You should be able to find the problem.

 

I checked voltage of the battery with a micrometer and it showed 13.00 V even. I didn't get to check the alt today, I'll have to pull it back off and do a bench test tomorrow. I rechecked the connections and everything was tight and clean. I drove the truck today and it didn't act up and ran fine.. Its such a weird intermittent problem....

 

I would try my voltage regulater or replace the alternater it comes on it or you can buy it seperate my brother had a similar problem

 

Did you have 13 Volts when the truck was running or when it was off?

 

ABS light probably due to an under, or overcharge condition resulting from the alternator. Some aftermarket alternators have different sized pulleys from stock which would alter how fast they turn. Hope this helps, good luck

 

The truck was not running at the time of the test and the battery measured 920 CCA. I'm going to pull the alt off in a few hours and take it to be bench tested, rule out the possibility that the reman alt is faulty.

 

Yea Bench testing is better - I think it may be important to explain to the individual testing it what's going on and that the problem is intermittent. That it doesn't happen all the time. That way they may run it thru the procedure more than once. You know what - just tell them you want another. This is the type of problem that could pass bench testing - being intermittent. You've done everything els, use the warranty - demand a swap, you don't want to mess with this anymore.

You could also check the regulator brushes - maybe one is hanging - Both of these were and the battery light was on, cleaned them up and all was good. But still, like I said, in your position, I would just demand a new one and be done with it. This type of problem sucks.

 

If the alt test ok check the battery ground where it goes to the chassis. Also check the block to ground wire also. I've seen those two cause similar problems on a tractor. It should be the same as a truck I would think.