Wont start unless cause vacuum leak
 

Im obviously new to tuning...
I cant get it to start unless I remove a few vacuum caps and cause a vacuum leak.
This is an s4 tII w/microtech lt10s.
New rebuild.
If I pull 2 or 3 vacuum caps off, it'll start, but if I cap everything it tries to start, kicks over for a second, then dies.

What happens when you get it started then put the caps back on?

And what has been removed?

If I put the caps back on it imediated shuts off. Rats nest removed. no bac.

That could be a good portion of your issue, since you removed the BAC, have you upped the idle?

Y, I upped the idle.

The BAC is an integral part of the idling process. It's possible that your AFM is not letting in enough air to allow the car to stay running given that the fuel amount is dialed in correctly. Maybe you'll want to check the flapper door to see if it is operating properly. And less fuel might be a thing to work with if the AFM appears to be okay.

The AFM is also removed as it's running a Microtech. If it's too much fuel, can initial start fuel be adjusted via one of the throttle body screws?

I don't know aftermarket ECUs very well, but as far as i know, almost any type of fuel injection needs a measure of airflow. You may need to ask over on the microtech sub forum

Did you replace the vac line to the pressure sensor and if so, did you retain the restrictor pellet?

The air pressure sensor is disconnected. Im not using the stock ecu.

It must use some kind of MAP sensor though right?

Y. Theres a vacuum line that connects it to the intake manifold. Is it possible that I dont have the throttle body setup correctly?

The computer has to mesausre SOME type of air flow or air pressure

It sounds like your computer is dumping so much fuel that when you give it a vacuum leak, it then has enough air to ignite the fuel

There is, the microtech uses speed density(map signal and iat) and the map sensor is built into the unit itself so you only have to run a vacuum line to the LT10.

As far as this issue, I would try to adjust the TB to be cracked open slightly farther and reset to tps afterwards so you can make some fixes to the tune. I know it says new rebuild but what about the microtech, was that installed and working before hand?

I got the microtech as part of a parts car I purchased. It was running on that car previously. It is new to my car.

Well, I capped everything up, connected the microtech and go it started today. Thanks for the info.

Please, can you tell us how you fixed it?

Per SpikedDerailed's comment, I started thinking more in terms of providing the correct a/f ratio in order to get it to run right(I know should be obvious, but I'm new to tuning-used to taking that for granted).

So, I assumed that since it ran with no caps and alotta air, and didn't run with caps on and less air, then I needed less fuel. So, I figured out how to adjust fuel via the water map for on the microtech for the water temperature it was at while attempting to start.

I kept adjusting down incrementally until it fired up with caps on.

You're in Boston, this coming winter will be fun to get all the cold start maps fine tuned. Since you wont see cold enough temps to do it this summer, just remember as it starts to get colder you'll likely have to make some adjustments as you go or you'll run into another no start situation.