How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Clayso Your Own Question
Clayso
Clayso, Master Automobile Technician
Category: GMC
Satisfied Customers: 880
Experience:  ASE Master Certified Automobile Technician. 30 Years Experience.
77147243
Type Your GMC Question Here...
Clayso is online now
A new question is answered every 9 seconds

GMC 1500 (5.7 engine Sierra: I have a 1992 GMC Sierra Truck..My

Customer Question

I have a 1992 GMC Sierra Truck..My fuel pump went out..So I thought..Come to find out that there is no power to the fuel pump..( At the fuel tank )All my fuses look good..There are four wires total on the fuel pump remote switch on the firewall..All four have power running thru them..( I'm using a test light BTW )..I also do not hear the remote switch click when I turn the Key..I'm stumped..Please help..Thanks, Mark
Submitted: 1 year ago.
Category: GMC
Expert:  Clayso replied 1 year ago.
Hi Mark, I'm Clayso a certified master automobile technician with 30 years of automotive repair and diagnostic experience and I'm here to help with this problem. Additional services may be offered for detailed information.
Glad to see you are using a test light for this circuit. On fuel pump circuits I normally use a sealed low beam headlamp to verify the circuits integrity. I use the lamp just like a test light. Ground one side and verify power with the other. Low amp test lights and voltmeters will show power, but not under a load.
From your description it sounds like there are a couple of things going on. Check the ground at the thermostat housing, make sure it's there and it's not corroded and the connection is clean and tight. The ground on the thermostat housing should be a black wire with a white stripe, this is the same blk/wht wire on the fuel pump switch aka. fuel pump relay. If this ground is bad the relay will not close/click. To check the fuel pump relay itself, swap it out with the horn relay and see if the horn still works. The relays are the same.
The four wires on the fuel pump relay should be:
Dark Green/White == Fuel pump relay control, from the ECM
Black/White == Relay control ground
Orange == Power from gray fusible link
Gray == Power to fuel pump
With the relay disconnected you should now only have power on two connections. The dk grn/wht with the key on and orange should be hot at all times. The orange wire is power from the gray fusible link on the passenger side firewall. The link below is the fusible links, fuel pump relay and an inline fuse to the fuel pump. (When the key is turned on the inline fuse should power the fuel pump when the relay clicks). Check these fusible links and make sure they are not rubbery feeling.
Inline Fuse & Fusible Links
http://tinyurl.com/orptj7r
A fuse link is a short length of wire, integral with the engine compartment wiring harness and should not be confused with standard wire. The fusible link wire gauge is smaller than the circuit which it protects. Fusible link wire is covered with a special thick, non-flammable insulation. An overload condition causes the insulation to blister. If the overall condition continues, the wire will melt. To check a fusible link, look for blistering insulation. If the insulation is okay, pull gently on the wire. If the fusible link stretches, the wire has melted.
I can also offer additional services for 5 bucks and continue this conversation on the phone and or through private email with diagrams and technical information specific to this vehicle. Let me know if you're interested.
I hope this information is helpful to you.
Should you have any questions please let me know.
Positive ratings are greatly appreciated.
Thanks so much.