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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: LW on November 26, 2018, 09:28:26 am

Title: NO POWER TO FUEL PUMP LATE 80'S K5 BLAZER
Post by: LW on November 26, 2018, 09:28:26 am
Hey guys I just joined so I am new to the group, but I need some help with my late 80's K5 Blazer!

Previous owner powered the fuel pump with romex fed from a 20A ignition space in the fuse block >:(.  I am trying to use the factory brown/white wire.  I have traced it from the tank up through the bulkhead connector.  It does not go through the fuse block though, it goes from the bulkhead connector to a plug behind the instrument cluster that is not plugged into anything ???.  This doesn't seem right to me?  Where does it need to plug into to get 12V?   The pink signal wire takes the same route, but plugs into the back of the instrument panel into the printed circuit board as it should.  The fuel pump relay is new.  PLEASE HELP!
Title: Re: NO POWER TO FUEL PUMP LATE 80'S K5 BLAZER
Post by: VileZambonie on November 27, 2018, 04:56:40 pm
http://forum.73-87chevytrucks.com/smforum/index.php?topic=9072.0
Title: Re: NO POWER TO FUEL PUMP LATE 80'S K5 BLAZER
Post by: LW on November 28, 2018, 01:19:37 pm
That looks helpful.  What is a FUEL MODULE and how do I know if my truck has one?
Title: Re: NO POWER TO FUEL PUMP LATE 80'S K5 BLAZER
Post by: hatzie on November 28, 2018, 02:49:29 pm
It's a module to run the fuel pump for additional seconds after key on and after key off when the engine is at full operating temp. 
They called it a Hot Start Fuel Module.  It's to reduce fuel temps and control vapor lock.
It's buried behind the dash.
GM used them on all of the 7.4L trucks.  Some of the 5.7L had em but not all.  None of the 4.3L and 5.0L trucks had them.
Title: Re: NO POWER TO FUEL PUMP LATE 80'S K5 BLAZER
Post by: LW on November 29, 2018, 08:39:50 am
Oh ok thanks.  Could it prevent power from getting to the fuel pump?  I have a 5.7 but I am not sure what I am looking for to determine if my truck has one or not
Title: Re: NO POWER TO FUEL PUMP LATE 80'S K5 BLAZER
Post by: VileZambonie on November 29, 2018, 07:30:54 pm
Jumper B+ to the pigtail at the fuel pump relay and see if it runs.
Title: Re: NO POWER TO FUEL PUMP LATE 80'S K5 BLAZER
Post by: hatzie on November 30, 2018, 12:12:05 am
Quote from: LW on November 29, 2018, 08:39:50 am
Oh ok thanks.  Could it prevent power from getting to the fuel pump?  I have a 5.7 but I am not sure what I am looking for to determine if my truck has one or not
If your truck has one... it can prevent power to the fuel pump.
You'll find it near the headlight switch behind the instrument cluster.  The GM part number for the hot start module.  10052973
(https://static.premiersite.co.uk/24535/img/24535_5690660.jpg)

Jumper power to the fuel pump test terminal that's dangling from the fuel pump relay and do some more troubleshooting before throwing parts at it.