Help with Transimission

[ssarmstro]

Hey guys!

I am a new to this forum. I have a 2004 with a 4.6 engine and recently the transmission has intermittently been shifting late or hangs (RPMS rev then shifts correctly)?? BUT it only occurs when the A/C is on! I have taken it to the dealer and they reset the computer but cant find the issue. Anybody have thoughts?

Again when the A/C is off the truck shifts normally....

 

[stamp11127]

The "only" difference between the two modes is one has the a/c on which is loading the engine and really shouldn't matter. Rpm's are rpms.
But if the electrical load on the system isn't being offset by the alternator then the pcm is running on lower voltage. May be enough to show up in odd shifts.
Check the ground connections also since you are in a salt in winter state.

 

[Bowesmobile]

I agree with Stamp, that's very plausible. Check your voltage at the battery first with the A/C off AND only using a Voltmeter. DO NOT DISCONNECT the battery to see if it stalls. Sigh...Sorry there's been a lot of that here lately. Then check it with the A/C on and it should still be between 13.7v - 14.4v . If not then you might want to check grounds and/or look into a alternator.

 

[ssarmstro]

Thanks guys I am def gonna try that. What amp should my alt be?? I have seen 110 and a 135.

My battery did die a couple weeks ago and truck was pretty much running off battery. I heard that was not a good practice. Running off alt.

 

[stamp11127]

At this point we don't care what the alt is rated at. We only are interested in the output voltage at idle and at 1500+ rpm.
Charging voltage should run between 13.5-14.5v depending on who you talk to. Some use slightly different numbers but you can't go over 15v and you can't charge a 12v battery with 12v.