I have a 2000 F150 with 5.4l that the lights have begun flickering a little until about 1500 rpm and then it goes away or not as noticeable.

I had engine issues where the alternator seized and I essentially put new alternator, idler pulley, belt tensioner, front engine cover and etc on last month. I also replaced a very old battery with a new Diehard model 2 weeks ago as I had points to use up. I also put new Goodyear gatorback on since old one was considerably old and had some cracked teeth but not many.

I noticed flickering late last night and went to Advance auto and they hooked up to machine but all showed good. Since alternator was less than 45 days old they gave me another new one ( Not reman ) 130 watt one to swap it out. Got done with swap today and its still doing it. Battery readings running is 14.52-14.53 almost constantly but drops 14.45 under higher rpms. With headlights all on it reads 14.55-14.56 so about the same .

Grounds were all cleaned when I was doing top end of engine work
Starter wires were cleaned since I had it off for manifold replacement and pulling broken stud out.
Ground on front frame rail cleaned and reinstalled.

Guy at store mentioned that if the new tensioner is bad it will allow tension to slack and grab possibly causing this also?? Also said old belt could be slipping but its also brand new so doubt its that. I have no light coming on telling me of issue or gauge for what its worth registering low or flickering reading.

Any ideas since the major two of Alternator and battery have both been changed and alternator twice. I dont run anything major in truck except small alpine amp that powers 4 speakers and its a small one at that. Its been in the truck since 2004 or so with no problems. No light bars or anything else to draw current.

Hit 1500 rpm range and I really dont notice it anymore like I do at idle or idle in drive going slow.

Any ideas on what to look at? I would think if tensioner was bad it would also make voltage at battery rise and drop unless my DMM isn't catching it fast enough

 

I am having the same issue on my 2007. I repalced the alt and battery not to long ago. My entire dash will go out sometimes. I recently cleaned my battery posts and cable and reattached to the post pretty firmly. I haven't had my dash go out yet and I don't notice the flickering as much as I did before. I'm about to replace my belt and tensioner just to see if that makes a diffrence as well. Someone mentioned belt slippage could be an issue. So I fgured for the cheap cost to replace I might as well. My transmission seems to have a hard time shifting sometimes and I was told that could be from voltage issues as well. If you figure something out please let me know and I will as well.

 

I have 2003 with the same issue.
New alternator last May (2014) that fall I noticed the interior lights flickering then the headlights flicker at the same rate.
Any update?

 

Sorry I had not updated. I did take the belt tensioner back and they gave m a new one to replace it and it solved the issue. I guess it wasn't creating the tension required and was allowing belt slip even though it was a new one. I have no more flickering of lights at idle or otherwise.

 

Beauty!

Thanks fer the update - will help any folks reading this thread in future.


MGD

 

I like that fix.
I have cleaned the grounding wires I can see, and I forgot to post I also changed the alternator a second time with no help.
I have never replaced the tensioner-and at 124K it could be due.
Thanks again

 

Well, replaced belt, tensioner and idler puller.
No help, still flickering.
Going to pull kick panels and look for grounding wires there.

 

No help there either.
Did find one ground corroded and when I loosened bolt, the door locks went up/down.
Might be time to take it to the stealer (dealer).