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david craig
david craig, Auto Mechanic
Category: Chevy
Satisfied Customers: 905
Experience:  owner/mechanic at 3D Automotive
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Changed the sending unit, but it still won't come on. The

Customer Question

Changed the sending unit, but it still won't come on. The relay clicks though.
JA: How many miles are on the car? Has the car been starting normally?
Customer: 127,000 ish. It was running fine up until about 2 weeks ago and it just quit while driving.
JA: What is the model/year of your Chevy?
Customer: 2003 S10
JA: Are you fixing your S10 yourself? What have you tried so far?
Customer: Yes. Made sure the relay was working (the clicks) but no sound coming from the fuel pump. So I changed the sending unit . Still can't hear the fuel pump engaging. Also noticed the fuel gauge is showing empty, but there's over a half tank of fuel.
JA: Anything else you want the mechanic to know before I connect you?
Customer: Not that i can think of right away.
Submitted: 3 months ago.
Category: Chevy
Customer: replied 3 months ago.
Also checked the ECM-B fuse and it is intact.
Expert:  Gary replied 3 months ago.

at the fuel tank connector when cranking it over with a meter does the grey wire show 12 volts at the tank ?

Customer: replied 3 months ago.
I can't crank it and check the voltage at the same time by myself. No one else available to assist today and perhaps tomorrow.
Customer: replied 3 months ago.
I'll try to come up with a plan for a one-person test.
Expert:  Gary replied 3 months ago.

if that has 12 volts at it can you be sure the big black at the pump connector is a confirmed good ground

if not run a new ground from the frame to the connector

Going to work

He said what your describing and what you sent is exactly what he thought. Something wasn't getting enough air or fuel.

Customer: replied 3 months ago.
Made three test leads with 12 ga wire and alligator clips to bring multimeter out to where I could see it and crank engine at the same time. Tested leads to the battery to make sure they worked (12.04 V) with multimeter. Unplugged the terminal connector (white - 4 pin) on the fuel sending unit and inserted pins in the terminals for the large grey and large black wires then clipped the test leads to the pins and the leads of the multimeter. Cranked the engine and got a 0 V reading. Took another lead and clipped it to the chassis and the pin in the large black wire terminal. Cranked the engine and still got 0 volts.
Expert:  Gary replied 3 months ago.

so the grey does NOT have 12 volts cranking it over ?

if that is correct pull the fuel pump relay out and with the key OFF how many terminals in the box show 12 volts that the relay plugs into ?

Customer: replied 3 months ago.
Correct. Grey did not have 12V. Tested 4 terminals at relay with ignition off. No. 30 shows 1.41 V decreasing. All others are 0 V.
Expert:  Gary replied 3 months ago.

# 30 should be 12 volts all the time then it is jumped through 87 which is the grey wire and sends the volts from 30 to the fuel pump

does the ECMB fuse show 12 volts on both sides of it testing that fuse in place through the little openings in the tops of that fuse ?

Customer: replied 3 months ago.
Realized I didn't have a good ground when testing no. 30. Clamped ground lead to chassis, put a pin in no. 30 and got 12.14 V. Are you saying no. 87 is negative? 12.16 V on the fuse.
Expert:  Gary replied 3 months ago.

no 87 is the grey wire that goes to the fuel pump

if you jump 30 to 87 in the box will the truck run and the fuel pump run ?

Customer: replied 3 months ago.
no. 30 is ground?
Expert:  Gary replied 3 months ago.

no 30 is supposed to be 12 volts which you tested it showing 12 volts

jump 30 to 87 will the truck and fuel pump run ?

Customer: replied 3 months ago.
No.
Customer: replied 3 months ago.
But the jumper started getting warmer.
Expert:  Gary replied 3 months ago.

with it jumped does the grey show 12 volts at the tank connector ?

Customer: replied 3 months ago.
I couldn't get a good voltage connection for a reading, but the fuel pump started running.
Customer: replied 3 months ago.
It still won't start.
Expert:  david craig replied 3 months ago.

Hi Im David, so you can get the fuel pump to run by jumpering the fuel pump relay? correct?

Customer: replied 3 months ago.
Correct and was also able to get a 12 V reading on the multimeter after I unplugged the terminal connector from the fuel pump.
Expert:  david craig replied 3 months ago.

with the relay jumped you had 12 volts at the pump? or without the relay jumped and the key on?

Customer: replied 3 months ago.
With the relay jumped, key off, I was able to get 12V at the pump.
Expert:  david craig replied 3 months ago.

ok pull the jumper , turn key on and check for 12vdc on another pin on the relay base. you should have 2 positions that get voltage (one will have it all the time, 1 will have it with key on) make sure that happens

Expert:  david craig replied 3 months ago.

what engine you have?4.3?

Expert:  david craig replied 3 months ago.

heres a print for us to work from

Customer: replied 3 months ago.
I'll check tomorrow. I have a 2.2.
Customer: replied 3 months ago.
Would the other position be 83 or 87?
Expert:  david craig replied 3 months ago.

should be 83. theres 4 positions. correct?

Customer: replied 3 months ago.
Correct.
Expert:  david craig replied 3 months ago.

so 30 87 83 85?

Expert:  david craig replied 3 months ago.

let me know tomorrow when you're ready

Customer: replied 3 months ago.
Correct. 30 tested 12V with key off and I jumped to 87 to get the 12 V reading at the fuel pump connector.That leaves 83 and 85 untested but I guessed 85 since it was on the same side as 87.
Expert:  david craig replied 3 months ago.

youll know, when you have 12 volts with the key on. if you dont then we got issues to look into

Customer: replied 3 months ago.
0 V on all three terminals, 86, 85, and 87.
Customer: replied 3 months ago.
with key on
Expert:  david craig replied 3 months ago.

ok then thats a problem...... let me look into it

Customer: replied 3 months ago.
Thanks so much
Expert:  david craig replied 3 months ago.

you bet

Expert:  david craig replied 3 months ago.

you have either an open wire from the fuel pump relay (dark green/white wire to the PCM or possible a problem with the ignition switch, im trying to find the wiring for the ignition switch tie in.

Customer: replied 3 months ago.
Would a problem with the ignition switch also be causing the fuel gauge to be showing empty?
Expert:  david craig replied 3 months ago.

sure, if its bad.

Expert:  david craig replied 3 months ago.

gimme a few to find that wiring print

Customer: replied 3 months ago.
The voltmeter still works when the key is turned on so it isn't all of the gauges.
Expert:  david craig replied 3 months ago.

ok... im still looking

Customer: replied 3 months ago.
Take your time. It isn't going anywhere soon.
Expert:  david craig replied 3 months ago.

check the black wire at the relay to ground. make sure its a good ground

Expert:  david craig replied 3 months ago.

just checking in to see how its going

Customer: replied 3 months ago.
I've been real busy and it's too hot to work in the garage. There's a break in the temperatures soon so I hope to tackle it again on Friday evening. Thank you.
Expert:  david craig replied 3 months ago.

ok

Expert:  david craig replied 2 months ago.

any update?

Customer: replied 2 months ago.
I got a bit of time to do some more testing on the truck. I wasn't sure which wire was ground to the relay, so I pierced the largest black wire under the fuse block and ran it to the chassis. Nothing new transpired. I discovered in a youtube video that pin 86 is constant ground. For the heck of it I connected a lead directly to the positive terminal on the battery. Pin 30 = 11.97 V, pin 86 = 11.64 V, pin 87 = 10.70 V and pin 85 = 10.76.
Expert:  david craig replied 2 months ago.

ok. let me go back over our notes

Expert:  david craig replied 2 months ago.

so we still have no pump operation correct?

Customer: replied 2 months ago.
The aforementioned test results were with the key off. I tested again with a test wire connected to the battery and the key on. These were the results: pin 30 = 0.04 V, pin 85 = 9.10 V., pin 87 = 0.01 V, pin 86 (-) = 10.59 V. Correct, in that the pump still isn't working.
Expert:  david craig replied 2 months ago.

jump 86 to 30. key on

Customer: replied 2 months ago.
Nothing happened. I tested pin 30 again immediately after and got 8.65 V (with test wire connected to battery).
Expert:  david craig replied 2 months ago.

you going to have to check continuity from the relay to the pcm.

Expert:  david craig replied 2 months ago.

that pcm isnt putting out the control voltage to the relay.

Customer: replied 2 months ago.
Okay. I'll follow up when completed.
Expert:  david craig replied 2 months ago.

ok my friend