electrical load and low idle

[mnstanggt]

I have started to notice my idle drops alot if i turn my headlights on or rear defrost. it doesnt drop then come back up it stays low with these on.
the car idles smooth normally but when it drops like that it i starts misfiring, all my lights seem dim lately
cant figure it out battery tested at 12.6v and alternator was 16.4v i cleaned my grounds and connections, cant find firewall to engine ground though, dont know if that would cause anything

 

[BlackVert]

do you have underdrive pulleys?

 

[mnstanggt]

nope engine is completely stock

 

[HISSIN50]

Does it happen more with a hot or cold engine?

FWIW, an alt testing at 16.4V should have failed. You're running the risk of blowing bulbs.

 

[fordtech28]

you mention the alternator giving you a reading of 16.4V if I recall thats too high and the alternator will stop charging if it goes up too high which would cause your issue somebody correct me if im wrong I think the highest I seen an alternator charge is 14.6V check all your grounds this would cause this voltage reading

 

[mnstanggt]

hot and cold actually my idle stays normal during the day when im not using the lights or anything, ill have tests done again i guess maybe the place i took it messed up or something

 

[Car Nut]

Voltage regulator maybe messed up?

There is a silly ground mesh cable that Ford installed on our cars from the frame to engine. Replace this with a short negative battery cable (check the length first) and that will improve things even if it doesn't solve this specific problem. I also ran another ground cable from the battery to the front radiator support area. No problems since.

I've had similar issues a few years ago as you mention, but cleaning all the grounds cleared it up. I did not have the high alt voltage you mention, so that may by your sole culprit.

The ground cables I mentioned above may seem like overkill or wasted time/money, but I promise those few dollars go a long way. Electrical problems are never fun for me.

Good luck.

 

[HISSIN50]

you mention the alternator giving you a reading of 16.4V if I recall thats too high and the alternator will stop charging if it goes up too high which would cause your issue somebody correct me if im wrong I think the highest I seen an alternator charge is 14.6V check all your grounds this would cause this voltage reading

The alt won't stop charging if the regulator is bad (which is why it would have such a high output). The battery light should illuminate however.

 

[mnstanggt]

something else ive noticed is the car rolls over alot slower than it use to hot or cold

 

[HISSIN50]

something else ive noticed is the car rolls over alot slower than it use to hot or cold

All the more reason to have the components tested again. Or have a dynamic test done (with the components in the car).

Your battery might have an issue (like a bad cell) so the alt is trying its best to charge it up at all times (the high output voltage), but the battery itself is deficient. This contradicts the 12.6V you saw on your battery (unless this was a freshly charged battery, in which case it is low).