H/O 270amp mechman alternator voltage issues

[triassic]

I recently installed a 270amp alt from mechman onto a 2005 grandmarquis and have ran into some issues. Shortly after starting the car my battery light turns on, when put into gear serious voltage drop occurs and car idles roughly untill i hit the gas.I checked the voltage at idle which reads about 13.5-13.8 but when i raise the rpms it only goes up by roughly .3 never even reaches 14.0v....i understand low idle dramatically reduces output but shouldn't it read into the 14's when rpms are raised atleast?Big 3 is installed with Knukonceptz ofc 0 guage and i have checked all grounds. I can post pics of wiring or anything else to help resolve my issue if needed. This occurs with all electronics off

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[negolien]

Meh sounds jacked to me Mine never dips below 14 :

 

[boxpunch]

You charged all batteries before installing alt?

Alternator output isn't going to affect the rough idle.

 

[triassic]

You charged all batteries before installing alt? Alternator output isn't going to affect the rough idle.

Yes i charged overnight and checked the voltage before starting car battery, read 12.4 volts.

 

[triassic]

Meh sounds jacked to me Mine never dips below 14 :Any suggestions on how to test if its the alt?

 

[juanmgarza26 10+ year member]

Could be a ford thing? I charge cold at 14-14.2 and once hot I charge at 13.7-13.9. I have had the alternator tested before and batteries as well. ICould also be the charging the alt is set at if it's not pcm controlled.

 

[boxpunch]

Any suggestions on how to test if its the alt?

In order to test the alt you must put a 270a load on the charging system and measure the dc current output (dc clamp meter) from the alternator.

 

[yogegoy]

Did you use a 1/0 ground wire directly from neg post of battery to one mounting bolt of the alternator as highly advised by Mechman? Did you wire the included harness correctly to your wire harness?

 

[fatboytyler]

What kind of battery? Alternators don't charge at a full 14.4V the whole time. Only when the regulator reads that the battery voltage is low enough. Also, you live in Dallas, where I'm sure it is quite hot, this will also affect voltages.

 

[kylerwyler]

I had the same alternator in my old truck. literally just sent it back to mechman last week to get it rechecked (it is 4 years old) and sent back to me. when I spoke to him I was having a few issues, (put it in my new truck)

I was told to get 1/2 inch shorter best.

Try that. evidently it is common and there is slippage.

I havn't gotten mine back yet but it has been only a few days.

Once I get it back, im going to get a shorter belt and that should handle the random slight voltage issues I was having.