Car Starts, then shuts off as if i took out the key

[twinturbo3k]

I own a 1991 TSi AWD
Mods: 3" gm maf, maft 2.02, dejon upper intercooler pipe, evo 3 16g, walbro 255, mbc, stock 450s,down pipe, test pipe, intake, act 2600, and poly mounts.

The car normally runs like a champ, with minimal issues other than a 1100 rpm idle sometimes, usually it will idle around 750-800ish. After doing a boost leak test, and replacing my alternator/waterpump belt i drove the car around the break in the belt, easy driving, minimal boosting. The next day i start the car and the belt squeels, as i was expecting. After tightening the belt i started the car and noticed some issues. Upon start up my tach went to about 600, the car was obviously idling at about 1200 (idle was very rough), i let it idle for a few seconds and it became smooth, although relativly high at about 2200rpms. While running like complete ass before it smoothed out i could smell that it was running pig rich. Anyhow, everything was hunky dory and i went to the gas station put a few bucks in just to drive the car and do a data log. The log came up perfectly normal. Went home, picked up my wallet and went the start the car, started up perfectly and after about 2-4 seconds just shuts off like i pulled my key out of the ignition, no sputtering or anything, just a smooth shut off. I can start the car but it will onlyrun for about 2-4 seconds before shutting off. I changed out the coil pack last night with the same results. Not sure where to begin with a diagnosis though, the CEL was only on for a little while when it was idling weird, then the light shut off. Any suggestions would be awsome.
Thanks, Mark

ps. i have been on the site for a while, usually searching will find me the answers i need, and my sig car the 1992 tsi fwd is my daily driver, so theres no confusion.

 

[95talon_in_ma]

When you turn the key on, before starting, does the CEL light come on? If not it could be the ECU. I had the same type of thing happen on another car.
Other than that, I'd unplug the battery and plug it back in to see if it resets.

weird though....

 

[DarkSwatCobra]

Yea hes right, id try poppin the battery cables n see what happens...i dunno..but good luck to ya bro..

 

[ddavisaf]

I've encountered the same problem before. My turned out to be a combination of bad gas and a massive boost leak. How long were you holding 20 psi for during your boost leak?

 

[twinturbo3k]

I kept at least 20 psi for around 10 seconds before it started falling into the teens, I replaced some dry rotted vacuum lines and it held 20 steady for ten seconds, then i took it to 25psi and the valve cap on the turbo popped off .

When the key is in before starting the CEL pops on breifly then shuts off.

I disconnected and reconnectred the battery, didnt change anything really.

Also, i pulled out my translator and leaned it out a little bit at idle, that did not do anything, so then i richened it up, and that didnt help the problem either.

I wish i didnt just sell my spare ecu on ebay.


Also, my car has ABS and i noticed that the GM maf is rubbing on it slightly- im not sure how durable GMs sensors are so maybe a slight amount of vibration against my ABS which is like a solid aluminum block could have killed it.

Thanks for the advice guys

 

[92awddsm]

Check the power transistor and make sure it is plugged in good. Just unplg it and plug it back in to be safe. If th tach ever does anything stupid as far as false readings, it is usually associated to a problem with the transistor.