Car will start, run for 8 seconds, then die. It doesn't sputter, just dies. All connections are fine. Battery and alternator are good. Fuel pump primes and at least delivers for 8 seconds oil pressure is good. New vacuum lines from intake manifold to fuel pressure regulator. So......what do I do?

No codes either....

I just installed a VATS bypass module right before this startup. So, what to do? I'm trying to sell this, but I can't till it runs right. I don't want to sell a half-working beast to someone, I wanna sell the real deal! This car has been great till now....I don't want it to end like this!

This video is on a weak battery from sitting for a few weeks, ignore the hard-to-start. That's not normal when battery is fully charged.
http://www.youtube.com/watch?v=ix5j_Ip5Is0

 

It seems like a fuel problem from the way it dies. Check your fuel pressure...

 

the alt is dead which in tern is killing the battery check volts at alt and see if its puting out volts

 

mmmm, if your battery is good you can run for 30 minutes or more without an alternator. that's dying after a few seconds. seems fuel related. perhaps the pump is cutting out.

 

You are losing ignition signal it looks and sounds like, fuel issues will usually sputter a little.


It shuts off just like you are turning the key back. Check the ignition switch.

What light is flashing on the left?

 

I had this problem too. Would die at random like yours.. Except mine turned out that the coil had broke the little plastic piece that holds the connector on.. Might wanna check that too.

 

IMO your VATs bypass is wrong. If it was running fine until you did the bypass, then that would be my guess. The compuer is reading that its not the right signal then it kills the pump. You need to look at it again and make sure you have the right resister reading on the bypass.

 

If it's not fuel or inginton, Some where I just read about how the inital start works before you get to open loop or closed loop and it runs off a preset table and looks at the MAF MAP TPS and RPM. I just cant remember how long it runs in that pre open or closed loop for. had a outboard that would do the same thing run for a few seconds and then die. ended up being the magnetic timing pickup. don't know on that one.

 

Takes longer then 8 seconds to reach Closed loop, that is not the problem. Seems ignition to me as well, double check your VATS bypass.

BTW - Is that your "Security" light I see on the entire time and if so - there you go - VATS?

 

Is your fuel pump stock?

I have the exact same car with the exact same problem. My car does this some days and others its fine. I believe it to be my old fuel pump dying.

 

If the Vats is wrong it shouldnt even crank, am I correct?

What else did you do recently at the same time, maybe some of the plugs under the dash by the vats are loosely put back together?

 

If it wasn't shutting down before installing the bypass then all roads lead to something wrong with the bypass install.

 

deffinetly a vats problem. my buddy with a 55 chevy LS7 was having this same problem and it was vats. you can wire in a resitor to bypass the vats thats what i did but they are specific to the resitance in the key.

 

No, the car will still run at start. The VATs will allow it to run for about a 8-10 secs, then shut down if the signal is wrong or unreadable. This was GMs way to prevent the car from being stolen if the factory alarm was bypassed or the car was broken into and was able to start without the key. Here is a site with the VATs bypass info that may help.

http://vats.likeabigdog.com/

 

The car was doing this pre-VATS bypass. I did the bypass so that it would run right. I failed.

So many people are telling me it is fuel pump related, but if that is the case, the car wouldn't start EVERY SINGLE TIME and THEN die. It just wouldn't start. Right?

 

On my 94 if the VATS signal is wrong it wont do SQUAT, turn the key and nothing happens at all. The security light flashes.


I bypassed my switch recently when mine started acting up.

 

Highly doubt it's fuel pump. Normally when a fuel pump acts up it can stay running and will start acting up when the engine is under load or it's difficult to start and will sputter, snort, burp and die or it won't start at all.

 

Some people responding to this thread don't seem to know there are two parts to the VATS system- the resistance in the key and the fuel enable signal from the VATS to the computer. Two different things and different things happen when one or the other is the issue.

http://shbox.com/1/pass_key.html

 

but where between the ignition which is most likely ok to the fuel pump which is most likely not messed up?

 

Well thats simple, put a test light on the fuel pump power wire or ground, whichever turns the pump on and watch it when this occurs.

What year car is this?