I'm trying to get this wrapped up today. My close friend is a single mom and she has a 94 Blazer with the Vortec in it. Last night it wouldn't start for her. Cranked over fine but wouldn't run. I checked for spark and it's good. I got as far as putting a little gas down the vaccuum hose to the brake booster and I can get it to run off of the gas put through the hose but it wont stay running.

My thoughts would naturally be fuel pump, fuel pressure regulator, fuel filter or possibly something in the injection system?

Anyone know what I can do to narrow down the culprit? I don't want to replace anything unless I know it's needed. Thanks

 

Yup, borrow or buy a FUEL INJECTION PRESSURE TESTER and thread it on the test port behind the manifold where the fuel lines enter it. The tool costs about 50 bucks, but you may be able to rent or borrow one from autozone or places like that. You should get about 58-60 psi on the gauge if its the "W" engine which I think she has. The 8th digit in the VIN number will be a W or Z... W is a Central port injection motor 58-60psi, Z is a Throttle Body injection motor 12psi.

You hook up the gauge and turn the key but dont start - whats it read?
Turn off the key - Does it drop at all?
5 minutes later - Has it dropped any yet?

If all is good you should hold around 58psi for longer than you want to wait.

If you get ZERO then its not pumping. There is a test wire by the brake booster with a female plug just hanging there, if you run a "Hot" lead from your battery + to this plug, it bypasses your fuel pump relay, does it give pressure now? Yes? Then you have a bad relay... If no pressure, then you can go with a bad pump.

You should be able to hear the pump buzzing back by the fuel filler for a couple seconds when you turn on the key.

If you get pressure, but it drops off, then there is a fuel leak. It wont run because the injectors wont fire without the proper pressure. Then you have to take the plenum off and find the leak.

If you would like to do some reading on this, then search the forums for "CPI injection" and you will find a wealth of discussions on this problem, its quite common for us on these older trucks.

 

Excellent advice! Thank you. Could I get just a little more specifics on where that test wire is by the booster? What does it look like?

 

Sure, no problem, allow me to go grab my camera. I guess its not really by the booster, this is where mine is located at, its a white wire.

http://sphotos.ak.fbcdn.net/hphotos-..._1972585_n.jpg

And this is where the test port that you thread the pressure gauge onto is

http://sphotos.ak.fbcdn.net/hphotos-..._6783736_n.jpg

Post your results in here and we will help you out.