i have a 96 12 valve cummins and after its warmed up it runs great, but when its cold out, and its not warm, i start it and the idle stays down at like 3500-5000rpm, then wen it warms up, it goes back to 7500rpm. the battery gauge also shows that it isnt at full power yet., its like it warms up and then puts out enough juice for the battery to go up to operating volts. sometimes ill start it and its at 7500, then it will drop to 7100 or so, and it cycles like that for awhile? wtf is it? please help, idk if it hurts it or if its normal? do i need a new alternator? whats the deal?

 

The fluctuations in the RPM's are due to the grid heater cycling on and off. The grid heater is the whole reason you have 2 batteries, it has a HUGE current draw on the system.

What it does is requires more amperage than the alternator actually produces, which is why you see the voltage drop off and the engine lugs a bit.

It's just cold, nothing out of the norm.

 

anotherthing, some of these trucks have a battery temp sensor, that limits the ammount that the altinator can put out when its cold, the grid heaters are the reason for the idle drop and voltage drop, but if you have it on defrost, that will also cycle the a/c clutch and pull the idle down some too

 

cool, thank you guys. so i guess putting in 1 batt instead of 2 is out of the picture huh? lol, jk, my buddies idea, i like my 2 batts. but anyways, so nothing wrong then? sounds good to me. also, since im running straight pipe dumped right under the passenger door, should i be worried about sucking up cold air and maybe bending the valves? just something someone warned me about

 

Someone filled ya with false fears brother.

You're good, nothing to worry about there. I'd be more concerned about ingesting a wayward elf on Christmas Eve than I would be about bending a valve from cold air.

 

thats what i was thinking too, the elf and all. lol, yea, especially when people are putting hood stacks on there trucks. cant get much colder then that, huh, lolhow hard would it be to do 5" from the turbo back? what would it do to my power and or sound?

 

Really, until you start touching 500 - 600 HP, you don't really need the 5" exhaust.

Start going bigger than a 66/71 turbo or putting twins on, then you need it.

Otherwise, you won't see any real benefit from it.

 

i just like the size and look, i wanted to go 7" but figured that was a bit much, but i just want to make sure i wont lose power or ruin anything by putting the 5" on.

 

I just put a 5" on a pretty much stock truck earlier this week.

It felt stronger all the way through the RPM range to me.

Some guys say they feel like it has less bottom end when they straight pipe or go to a big exhaust, but I'm more inclined to say that what you're really experiencing is a stronger top end and that makes the bottom end seem weaker.

Now, only way to really prove it is on a dyno.

 

true. i think i will just go 5" untill i go bigger on the hp. i was told that i could adjust the valves and something else to get a lil extra out of it? wat else? we need a how to forum section. lol i feel like im annoing cause i ask so many questions and i dont know much about my own truck. but the way i learn is by asking and doing,