I put a 250 amp alt on my 2006 6.0. Well I left work and the battery light was on and it only had 11 volts for about 5 miles then went back to normal. If I let it idle the volts never come back up til I drive it. Put 2 new batteries in same thing. I put the stock one in today and it idle at 12.5 and goes up to 13.5 when driving which is still inadequate. Had the 250amp alt bench tested and they said it was good. So, could my stock alt be weak and the 250 amp be bad or could it be something drawing and lot of power?

 

So I assume you have cleaned all of your battery connections both at the batteries AND the frame/engine side of the ground cables. The problem exists when the aftermarket alternator is on your truck? Or when the factory alt. is on your truck? It sounds like the alternator is not turning fast enough to excite the circuitry. What pulley did you use with the aftermarket alternator? B.

 

Terminals are all clean and with the 250amp alternator the battery light stays on for about 5-10 minutes which isnt good for the ficm. With the stock alternator the battery light never comes on but the voltage only goes up when driving. Im usung whatever pulley came on the aftermarket alternator.

 

If the battery light is coming on, there is an issue. Period.

Are you running auxiliary battery wiring to help out the 250 amp alternator deliver the electrons it is capable of? Even more importantly, are you still running the factory charge cable on the back stud of the alternator? Have you checked the two fusible links downstream of the alternator?

Just some early ideas. Of course, if you need a replacement unit, we offer those as well - but I'm not at all sure that that's your issue quite yet.

Alternators

 

i upgraded all my cables with 1/0. The battery light only comes on with the 250amp alt and goes out and it runs fine after 5-10 minutes but thats not right and can ruin my ficm. With my stock alternator the voltage is low but the battery light never comes on. What else could it be?

 

When you say that your upgraded all of your cables, did you retain and use your factory cables or did you replace them with he 1/0 cables?

 

Yes all factory cables were retained. I did use dielectric grease on the terminals, you think this could cause a weak connection?

 

Absolutely not. The use of dielectric grease is fine - not necessary, but fine.

It sounds like something is happening with the excite wire on the alternator - that it is not turning on when it should. Check the signal plug.

 

Your talking about the plug that goes to the alternator right? How do I check that?

 

Yes, that's the plug I'm referring to. I'd try GENTLY bending the pins in as a first step. That failing, you can try using a digital volt meter to check for both continuity and voltage.