94 Chevy S10 LS not getting gas


untal3nted1
06-06-2006, 02:20 PM
Motor: 4.3L Vortec TBI (~180,000 miles)

Fuel Pump and Sending unit replaced ~8-10 months ago.
Spark Plug and Wires replaced ~4-5months ago.
Air Filter replaced ~1month ago.
Wires going to Fuel Pump/Brake lights were apparently smashed during fuel tank reinstall and had been all repaired/replaced, this was also around ~5months ago.

Something I have noticed, is when I am trying to start it, the fuel gauge has gone up now WAY past the F line (tank is 3/4 full), now facing about perfectly horizontal towards the passenger side.

This has happened one other time, but after playing with it, it suddently started & gauge went back to normal. Now a month or so later, it has happened again, and we have tried about everything to get this thing started. Dumping gas directly in will make it start, but obviously dies shortly after.

I was thinking maybe its the fuel filter, but I was talking to a mechanic buddy of mine, and he said that shouldn't cause it to not start at all, especially if this has happened before, and then suddently started. He was said that its probably a bad sending unit with the gas gauge being screwy, but I really dont want to drop the tank again without being sure. I just dont see how a new sending unit can go bad so soon.

Thanks for your help.

busa4
06-06-2006, 02:45 PM
a bad fuel sending unit is not going to cause you to have no fuel supply. check the fuel pressure at the shrader valve on the fuel supply line next to the throttle body. if you have no fuel pressure check the fuse first, then check the fuel pump relay, then check the fuel pump. dont forget to check the filter. do you hear the fuel pump running when you turn the key to the on position?

untal3nted1
06-06-2006, 03:09 PM
a bad fuel sending unit is not going to cause you to have no fuel supply. check the fuel pressure at the shrader valve on the fuel supply line next to the throttle body. if you have no fuel pressure check the fuse first, then check the fuel pump relay, then check the fuel pump. dont forget to check the filter. do you hear the fuel pump running when you turn the key to the on position?

The fuse is good, my bet has been on the relay, which I have no been able to find. Its very hard to find info on locations of things. Some say driver side firewall, others say somewhere under the dash. I found what I THINK may be it on the driver said dash, looks like wires head back towards tank, so I was going to try to jump the pump to see if that works, but none of the wire colors match up to what I found to be the wires to test/jump. There was also a red wire with a connector on it just hanging there not plugged into anything right next to what I THINK may be the relay.

I did not hear the pump running with the key in the 'ON' position, but I dont think I ever have been able to hear it even with it running. These pumps are pretty quiet to what im used to hearing in my performance car.

Where is the FP Relay located? How can I test it/jump it? I do have a multimeter.

busa4
06-06-2006, 03:37 PM
the relay could be anywhere. check in the engine compartment and under the dash. its a 4 pin relay. when you find it jump terminals 30 and 87a. remember these numbers are on the relay so it is going to be backwards on the relay socket. dont jump the wrong terminals or you might fry something. my haynes manual also shows an oil pressure switch that controls the pump. if this switch is defective it will cut of your fuel pump and injectors.

untal3nted1
06-07-2006, 11:57 AM
the relay could be anywhere. check in the engine compartment and under the dash. its a 4 pin relay. when you find it jump terminals 30 and 87a. remember these numbers are on the relay so it is going to be backwards on the relay socket. dont jump the wrong terminals or you might fry something. my haynes manual also shows an oil pressure switch that controls the pump. if this switch is defective it will cut of your fuel pump and injectors.

Ok, under the center dash, under the radio behind some panels, I found 2 relays next to a big box (the alarm buzzer thing). These 2 relays are EXACTLY the same, same number, same layout, everything. All these relays have marked on them is 1-5 for the connections. Getting behind this litte 'center' is a PITA also, kinda hard to see whats going on. These is also a circular silver 12volt fuse looking thing on the other end of this.

Both of these relays are 5-pin relays, but, only 1 of the connectors the relays plug into uses all 5 pins, the other one you can see only uses 4.

addon- ok after searching around, I believe I found the correct set of relays. I searched on google 1 of the numbers found on both relays, '12065125' and came up with this: http://www.rockauto.com/catalog/catalog.php?carcode=1061020&parttype=3380&a=FRc1061020k97364

FP relay for 94S10, now to figure out how to test this and jump the FP to infact see if this is the problem.

busa4
06-07-2006, 12:23 PM
look on the relay. there should be a diagram on the relay about the internal layout of the relay. at the relay terminals you should see the terminal numbers as follows: 30, 87a, 85, and 86. terminal 85 and 86 activate the relay. terminal 30 is a fused power source going into the relay. terminal 87a is the component the relay is controlling. when the relay is activated terminal 30 supplies voltage to terminal 87a and thus turning on whatever component is connected to terminal 87a. in your case it the fuel pump.
if you jump terminal 30 and 87a in the relay connector you will bypass the relay and power up the fuel pump. make sure you remember that the relay terminals are reversed on the relay connector. so dont jump the wrong connectors in the relay socket.

untal3nted1
06-07-2006, 01:12 PM
look on the relay. there should be a diagram on the relay about the internal layout of the relay. at the relay terminals you should see the terminal numbers as follows: 30, 87a, 85, and 86. terminal 85 and 86 activate the relay. terminal 30 is a fused power source going into the relay. terminal 87a is the component the relay is controlling. when the relay is activated terminal 30 supplies voltage to terminal 87a and thus turning on whatever component is connected to terminal 87a. in your case it the fuel pump.
if you jump terminal 30 and 87a in the relay connector you will bypass the relay and power up the fuel pump. make sure you remember that the relay terminals are reversed on the relay connector. so dont jump the wrong connectors in the relay socket.

The diagram does show the internal layout, and all the pins as 1-5. This is also the same for where you plug the relay into, 1-5. The bottom of the relay itself has no markings, but also looks like some black glue or adhesive on them to keep it together could be covering it. Ill try getting it off and see if there is anything, but all other markings just have each pin numbered as 1-5.

Edit, This black crap on the bottom is hard as a rock, its not going to come off easy, even once it is off, it just scratches the plastic on the bottom so even if there are true pin marking there besides 1,2,3,4,5 they would be lost. I think im just going to get my multimeter out and try to figure out whats what and doing what heh.

busa4
06-07-2006, 02:02 PM
http://www.autoshop101.com/trainmodules/relays/relimages/iso12relay2.gif

as long as there is a picture of the relay layout your good. some relays use 1-5 and other relays use 85,86,30,87a,87b .

you should have a layout that looks like this (see posted pic).

busa4
06-07-2006, 02:04 PM
if this is what your relay layout looks like then you will need to jump terminals
4 and 3 or terminal 5 and 3.

untal3nted1
06-07-2006, 04:17 PM
Yeah thats pretty close, I scanned a pic of the relay just for clarification. Sorry the brightness is bad. If you need a better scan I can do one, I just did this quickly.

http://shellsx.zoidial.com/~untal3nted1/relay.jpg

busa4
06-07-2006, 04:21 PM
looks like you have to jump terminal 4 and 5. terminal 3 shouldnt be used. is there only 4 pins in the relay socket?

untal3nted1
06-07-2006, 04:41 PM
looks like you have to jump terminal 4 and 5. terminal 3 shouldnt be used. is there only 4 pins in the relay socket?

There are 2 of these relays directly next to each other. One only uses 4 pins, while the other next to it uses all 5. But I believe that #4 is the one which is NOT used in the socket which only uses 4 of the pins.

busa4
06-07-2006, 04:54 PM
yep thats what i figured. jump terminals 4 and 5 and see/listen to what comes on. if your pump is good you should hear the pump.

untal3nted1
06-07-2006, 05:11 PM
yep thats what i figured. jump terminals 4 and 5 and see/listen to what comes on. if your pump is good you should hear the pump.

The relay socket that only uses 4 of the pins though, it is pin #4 that is not in use... still jump pin #4 to #5 on the relay? on the socket only using the 4 pins (not pin #4)? (kinda confusing all the 4s :P hope it makes sense)

To clarify, on the socket that only uses 4 of the 5 relay pins, #1,2,3,5 are in use, and #4 is not (but still plugs into the empty connector).
The relay socket next to it, uses all 5 of the relay pins.

untal3nted1
06-07-2006, 05:56 PM
The relay socket that only uses 4 of the pins though, it is pin #4 that is not in use... still jump pin #4 to #5 on the relay? on the socket only using the 4 pins (not pin #4)? (kinda confusing all the 4s :P hope it makes sense)

To clarify, on the socket that only uses 4 of the 5 relay pins, #1,2,3,5 are in use, and #4 is not (but still plugs into the empty connector).
The relay socket next to it, uses all 5 of the relay pins.

Ok well nevermind that, this relay is definently used for the horn... the other one im not really sure, so its the wrong relay. I think im just going to drop the tank or pull the bed back and see whats going on, or try to trace the wiring coming from the pump is I can get to it.

I have ripped this truck apart looking for this '4 pin/4 wire relay, and just cant find it anywhere.

busa4
06-07-2006, 09:26 PM
your going to be pissed. i was looking at the wrong diagram. i was looking at a cpi wiring diagram. i went back and checked the wiring on the tbi diagram and the fuel pump relay is a 5 pin relay not a 4 pin relay. S%$T! sorry man. i completely missed that other terminal in the wiring diagram. terminal 3 on that relay goes to a fuel pump prime connectorwhich allows you to activate the pump with a machine instead of cycling the key when doing a fuel pressure leak down test. sorry.......i am working with a haynes manual here. it gives me 7 model years and 4 different injection systems to work with. wish i had a factory wiring diagram.

is the 5 pin relay the same internal layout? if it is, jump terminals 4 and 5 and listen for the fuel pump.

untal3nted1
06-08-2006, 10:11 AM
your going to be pissed. i was looking at the wrong diagram. i was looking at a cpi wiring diagram. i went back and checked the wiring on the tbi diagram and the fuel pump relay is a 5 pin relay not a 4 pin relay. S%$T! sorry man. i completely missed that other terminal in the wiring diagram. terminal 3 on that relay goes to a fuel pump prime connectorwhich allows you to activate the pump with a machine instead of cycling the key when doing a fuel pressure leak down test. sorry.......i am working with a haynes manual here. it gives me 7 model years and 4 different injection systems to work with. wish i had a factory wiring diagram.

is the 5 pin relay the same internal layout? if it is, jump terminals 4 and 5 and listen for the fuel pump.

haha thanks man.. ill have to go out ina bit and try it out. It was kinda funny with the other relay.. I first tested all the connections, then jumped power to the one which appeared to be waiting to get power, and WHAAAAAA freakin horn starts blaring... I was like WTF OOOPS.

busa4
06-08-2006, 11:08 AM
yep!!!! ooops...my mistake... lol!

untal3nted1
06-08-2006, 03:34 PM
Well everything looked good with both relays, both worked, both exactly the same. So I directed my attention to the pump iteslf. Still saying the pump is not bad since its so new (even though every one keeps telling me the pump is bad just change it), I direct my attention to the wiring at the back of the pump. I was able to see, access some of the wiring without pulling anything off. Guess what? Bad ground connection to the pump ;-) The bolt for the ground wire was like 1/2 off, and the connections all rusted, but it was probably the fact that it wasnt a secure connection. Im just going to take it completely off, sand the connections, and reconnect it.

Thanks for all the help and the horn scare busa! :smokin:

busa4
06-08-2006, 03:39 PM
let me know how it turns out.

untal3nted1
06-14-2006, 01:36 PM
let me know how it turns out.

I actually have not touched it yet. The truck has been running fine since I just jiggled that lose wire around. This actually reminds me I need to go and actually fix it, cause I know if I dont, it will fail me again at the worst possible time. Dont you hate that?

seanfriddle
06-17-2006, 05:07 AM
There is a splice in the wiring loom on the passenger side, it's below the AC and inside the plastic wire wrap. Its red awith 5 or so other wires (all red) with one that goes to the oil pressure sending unit. It's a saftey shut down and prevents fuel from being delivered if there isn't any oil press. At the splice is where moisture gathers (especially if pressure washed) and the soldered connection becomes corroded and breaks. Your dash instruments will jump erraticly also. This will happen to alot of s10's.

ritalz
10-03-2006, 10:24 AM
The fuel pump relay on my 94 s10 blazer is under the hood between the brake booster and the left fender attached to the firewall. There are two relays mounted together and I don't know what the second one is for.

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