Hey guys! Im a newbie to this site and i just recently bought a 93 s-10 blazer with 123k miles on it. Did a tune up on it(replace plugs and wires, dist cap and rotor, ignition coil, air filter, and belt) and also cleaned the egr valve and placed a screened gasket on it.

The problem im having now is there is a buzzing sound comming from the fuel pump at all times that the truck is running. It runs and drives smooth now(was idleing rough when at a stop before i did the tune up) and has sufficent power when i punch down on the pedal so i dont think the fuel pump is bad......yet.

The PO did a hack job on some of the wiring that i think is comming from the fuel pump rely. I need to find the wiring diagram for the fuel pump relay and redo the wiring. Could the reley be sending a constant signal to the pump telling it to start up? The buzzing sound is the sound that u hear when the fuel pump turns on, but insted of lasting for 6 or so seconds its always on. ANy ideas on this will be welcome!

 

Your fuel pump runs at all times the engine is running. The relay only works on start-up, Then the power to the pump is supplied through the oil pressure sender when the relay de-energizes.

 

yes i know.......when you stat your truck or just turn the key partway the relay sends a signal to the pump. you normally hear the buzzing sound for 4 or 5 seconds and then it stops, BUT mine continues to buzz like that until i take the key out.

 

If you're sure it's the pump then you might check the relay and the O/P sender just for grins, When the relay shuts off then you have to get enough oil pressure to close the sender to supply voltage to the pump. (You probably know this already) Another way to make the pump run is to ise the "pump prime port" which is a Gray (or could be Red depending on where you look in the book) wire coming out of the wire loom that feeds the junction block in the engine compartment on the right side firewall. It has a single blade type female connector and is used to bypass the relay and O/P sender for testing purposes. It's not fused and leads directly to the pump. The relay should only engage for 2 seconds and is controlled by the PCM (or ECU - whatever you want to call it). I know that on my 94 there are two relays mounted side by side above the brake booster. One of them is the pump telay. Here is how it's set up. I'll just give you the wires and pin numbers to the relay. If you need more please just ask. This is from a factory wiring diagram for a 94.
Orange wire coming from the ECMB fuse (15 amp) goes to pin D on the fuel pump relay. Before it gets to the relay it splits off and supplies voltage to the PCM connector C211 (the red on on the PCM) at pin E16 and supplies power to the O/P sender for the pump. The PCM relay control is a Dark Green/White wire from PCM connector C210 (the blue one) at pin F6 and goes directly to the relay at pin A. Pin C at the relay is a Black/White wire and goes to the engine ground. The pump is supplied power from the relay through a Gray wire coming off of the relay at pin B. Gray wires in the pump system are power wires pump side. This is off the W/D.
Don't mean to confuse but the "Driveability and Emissions" section has a little different breakdown. It shows 5 pins at the relay that are used.
Pin 1 is a Black wire and is ground
Pin 2 is the Dark Green/White wire and ges to the PCM to pin F6
Pin 3 is the Gray wire supplying power to the pump, pin D on the O/P sender and pin B12 on the PCM.
Pin 4 is the Red wire to the pimp prime terminal (remember it could also be Gray)
Pin 5 is the Orange wire that supplies input voltage to the relay, O/P sender at pin C and PCM at pin E16.
Just depends where you look in the book but if you have all the info, you can see what you have. The prime port terminal wire on mine for instance is a gray wire not red.

 

is it a buzz or a whine? i have a 93 also. and that stupid pump has been whining for 2 years now and hasnt crapped out yet. i even asked a mechanic about that and said thats common. they can go for years. i kinda like it. that way when the truck dont start and i dont hear that whine i know why

 

yah its more of a whine then a buzz. Thank you Gimpy Blazer for the breakdown of the wiring. I highly suspect that the wiring/relay is the culprit because they are spliced at 2 diffrent points and put together with a wire twist cap thing(don't know what there called) and lots of electrical tape. gonna actually soder it when i get a chance to put it back in the garage(its freaking cold in Alaska and my roommate currently has a trans am in the garage installing a turbo)

 

Hope the breakdown on the relay wiring helped not overloaded. They're called wire nuts by the way and real common in your household wiring. Really never seen any on a car before.

 

Actually they are called MARETTES and there should never be any on your car... Take them off and solder those wires together with some heat shrink on top.

 

Whatever you call them I'll second ohsofly and tell you to get rid of them. Solder or good butt connectors with shrink tubing. Ot you could splurge and replace the whole wire. If you want to do that I can hook you up with a website where you can but the connectors. I have a couple that I'm going to replace.

 

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