Where is fuel pump fuse for TBI 5.7?

[Daveo91Burb]

I am trying to do a compression test, but don't want the fuel pump running while I'm doing it! I've tried pulling the connector at the relay on the firewall as well as a 5 amp fuse that is mounted to the side of the A/C box, but the fuel pump still runs when I turn the key. Is there an actual fuse somewhere for the pump? Or is there another way to get it to not run so I can do a comp test? I've got all the plugs out right now waiting to do it. Thanks!

 

[chengny]

It probably is powered by the ECM. Try pulling the ECM B fuse.

 

[Daveo91Burb]

Cool. Didn't think of that, but it makes sense since the ECM tells the pump when to pump so it might as well get its power from it, too. Didn't get a chance to try it tonight -- will tomorrow. Thanks!

 

[HotRodPC]

You can kill the fuel pump relay on the firewall near the AC box. Simply unplug it.
@89Suburban prolly has a pic of it he can post. I'm on a different computer and don't have my pic file.

 

[Daveo91Burb]

Relay was the first thing I tried and fuel pump still operates when I turned the key. I also tried pulling both ECM fuses at fuse block and still no luck. I saw a pic online of a '93 with 5.7 TBI and it had the relay as well as a fuse near it on the firewall. Any other idears??

 

[89Suburban]

Some trucks have a 2nd "Hot Fuel Relay" whatever the hell that is. Check out these diagrams.

http://www.gmsquarebody.com/forum/showthread.php?t=9975

 

[kleedus]

unhook your oil pressure switch it feeds the fuel pump
also unhook the fuel pump relay

 

[chengny]

Pull your ECM fuse and wait a bit.

If your truck is over 8500 lbs GVW, it has an override module that is intended to help with hot start/vapor lock conditions. It will power the fuel pump independently of the ECM and keep it running for 20 seconds after the key is turned on:

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[Daveo91Burb]

Thanks for the great info, guys. The secondary system makes sense. I should be able to get this figured out now!