Ok, I just put my set up in my Evo 9... and because of short route UICP I bought a mini battery for it. Well, my car will run with the original battery, but not the mini battery. It will start but then die. When I start the car with the original battery it will stay running, but when I disconnect the battery the car dies... I have no idea how long this has been going on.. I'v been driving the car for 2 years with no issue... Alternator is reading 14.4... and it is charging battery... the car is just not running off the Alternator for some reason. Not sure if this is related I did notice about a year and a half ago when I removed the stock MR gauges my turbo timer would no longer calculate how long to stay running correctly... the timer would just climb, even at idle.

Any help is greatly appreciated.

 

you cant just disconnect the battery and expect the car to run---that can cause all kinds of issues. None the less--- at idle the alternator is likely not charging as it has a threshold ( rpm) it needs to reach to charge--likely around 1500+ rpm to trigger the charge signal. If its putting out 14v its fine--. If the battery is what you changed---why not start there.

 

My other cars you can remove battery after you start because the car should be running off the alternator... But anyway now it won't stay running with original battery either... I had mini checked and charged.... Is there anything other then the alternator I should look into ? Because when car is on I'm getting 14.4 I feel like alternator is good.

 

How about you take your battery in to be checked---I don't mean charged but tested with a load. It can show charged but not be able to support a load. I don't think you have an alternator issue, if its putting out 14v--again its fine--if anything it would show overcharging on your battery--you could tell that by a swelled battery case--. Back to my original statement-- pulling the battery cable can cause other issues with the power surge it causes--check all your fuses, check wires and grounds-- you mentioned gauges and removing them-- check the wires there as well--you could easily have a grounding issue. Did you do work on the battery cables when you did your swap? Are they soldered and sealed correctly, no corrosion? Good Luck.

 

Umm, if cars could just run off the alternator they wouldn't need a battery. If you disconnect the battery while the car is running, it will stop running. If the voltage across the battery is above 14V, then the alternator is charging the battery. Check your connections are clean and secure.

What's is the voltage on the battery when the car is off?

 

Cars use a 12v system. Up to 12.6 is acceptable. The only place you get 14v is from the alternator to the battery to charge it. Also alternator output is unsteady due to rpm change. Everything in your car needs a steady 12v to operate properly, (ecu, injectors, coils etc) Running it off just the alternator you are giving it an unsteady voltage/amperage. You are taking a risk by giving your electrical components that high of a voltage (14+v).

Mithrandir the alternator doesn't turn till the engine is running so you would still need the battery to operate the starter.

I agree with the load test idea. Your mini battery must be bad. If your issue is resolved when you swap batteries then that is your problem. No need to keep looking for a fix when you figured it out already.

 

I believe I figured it out but I have to wait till I'm back in state to confirm. Battery is fine because it's doing it on both batteries now. So unless that is because I drained the big battery too much, I believe it has to do with I threw a code for TPS then the TPS at one point stopped all together. The way it happened was kinda weird. We'll see what's up.

I was about to say... I guess my DSMs and the beater Camry are freaks cuz they only need a battery to start. But it's good to know that is not safe...