So, my truck is a '98 Z71, 5.7L auto. I took it in to get the ignition switch replaced, and now they are telling me that the truck will not run. It will start but then die immediatly. I was thinking that it might be the fuel pump, but the mechaninc says that if it was the pump then the truck wouldn't even fire up. He says he thinks it's the security system. They have had my truck for 4 days now and still don't know what is wrong. Anyone have any suggestions?

-Sean

Edit: I do have an aftermarket alarm as well, but I don't have any remotes for it and don't use it.

 

For starters I'd throw a pressure gauge on the fuel rail and see what the fuel pressure is. I'm not sure what it's supposed to be at, but I'm guessing at least 40+psi. The main thing will be what the pressure does when the engine starts.

 

i'm having the same problem with a 98 gmc 7.4L. i suspect your problem has to deal with the ingnition being changed, but i would try to disconnect the battery for at least ten seconds. than give it a try. my will then start and run fine until i cut it off then it starts and dies. there are some security issues that will cause the same problem but i think it should throw a code for you. did you ever have hard starting before this? good luck.

 

If the key switch was replaced I think you have to do a security relearn. http://www.nelsonperformance.com/passkey.htm

 

Hmmm... You kinda fall in between two differnt types of security systems... Do you still have the old key? If so for ***** and giggles tape it to the stearing colum and try to start it. That should work if not, let me know a simple resitor from radio shack will work but you have to have the old key and measure it with an ohms meter and get the right one.

 

1998 and newer GM trucks use the PAsslock 2 security system.

I copied this from another site,

""The 98-2000 OBS trucks use Passlock II for the anti theft system so there is no chip. I believe how it works is as you turn the igniton with the key the ignition generates a resistance value that the Passlock module reconiginizes and then sends a signal to the VCM disableing the anti theft and letting you start the truck. The Passlock system is designed to disable the fuel system, so the truck will fire over and then sputter out and die if Passlock is not disabled"""

Sounds like you need to do the security relearn. the Passkey 2 relearn is on page 2 of this link.
http://www.bsecorp.com/files/techtips/ST9303l.pdf

peace
hog

 

some call it a chip some call it a resitor but a naked key will not work doing a pass key. There is a responder in the key. Call a keyshop most of them do responders now and will let you know your options. They can take a new key and make it match the resitance of the old key and no relearn will be necesarry.