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K. Wiggins
K. Wiggins, ASE Certified Technician
Category: Chevy
Satisfied Customers: 2993
Experience:  ASE Certified Technician, Associates Degree in Automotive Technology, 15+ years in the trade
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1995 Chevy 1500 Ground question. Shouldn't all ground read

Customer Question

1995 Chevy 1500 Ground question.
Shouldn't all ground read the same resistance throughout the entire vehicle to the battery?
I have more detailed information regarding my situation, just cannot fit it all in this column.
Submitted: 2 years ago.
Category: Chevy
Customer: replied 2 years ago.
1: Get a call from my brother, he stated he let his truck run too low on fuel and it wouldnt restart when he filled it up.
2: Got over, he had a fuel filter that he wanted put in, installed it for him (Yes i put it in the correct direction as directed with the dummy arrow) lol
3: After changing the fuel filter he attempted to start the vehicle and it wouldnt turn, at that time i went to go listen for the fuel pump. Nothing.
4: Popped the fuse cover and checked voltage at the fuse feeding the power to the relay which was the orange wire for pin 87 on the relay i believe, we were good there.
5: Had him put the key in the run position to see if the relay was switching and no go, 85 was getting voltage (Coil wire) but the coil was not energizing.
6: For fun i decided to just verify the pump was at least able to run so i jumped pin 87 to pin 30 (Orange to grey wire) which would send 12V to fuel pump, it ran.
7: Checked resistance from ground terminal on fuse block to ecm ground as well as battery ground and resistance was .4 Ohms which i consider acceptable.
8: The relay still would not pull in, so i installed a temporary ground to energize the coil thinking that maybe the ground was compromised by corrosion somewhere. The relay began to pull in when the key was in the ON position every time. This led to the belief that the ground was bad.
9: Checked all grounds, Cleaned up all grounds around the engine area that i considered important. (Battery to engine, ecm to engine, frame strap to engine, frame strap to cab.) No go.
10: Took apart wire harness which led from the fuse block, behind the motor, behind the distributor and ultimately came upon a ground splice on the left hand side of the distributor just before the harness clamp on the passenger side firewall.
11: I took this connection apart and verified all wired ohmed to ground and they all did with .1-.3 ohm. At this point i reconnected all everything properly and used plenty of heat shrink tubing to verify no moisture or contaminants made there way into the new connection.
12: Put everything back together and verified operation of relay and all was good.
13: Time for pressure test, Hooked up fuel pressure gauge to the TBI side of the fuel filter, pinched off the hose feeding the TBI to deadhead pressure on the line to verify i would build pressure properly and get a good reading right off the pump. The test showed 3 PSI. Of course i was very shy of what i need for this truck so i just wanted to verify a couple of things before i gave my brother the ultimate diagnoses.
14: I check voltage on the 3 prong quick connect which is bolted to the frame by the fuel pump, using the ground on plug and not the frame i got 12V to the grey wire which according to my prints feeds power to the pump. I also checked to the ground on the frame of the truck which gave me 12V as well to the grey wire.
15: Just to humor myself (Should not have done this but now i am curious) I ohmed out the ground on the 3 prong plug to the battery. Got 24 Ohms resistance. Ok so now im confused since i already verified all the grounds in this general area.
Customer: replied 2 years ago.
16: So i traced the ground wire (Black with white tracer) from the 3 prong plug back up to under the hood, this wire goes into a 4 pin (Only 3 are used) connector, in my prints i surely do not see this connector. So when i checked the run from that plug back to the connector by the fuel pump i had good continuity @ .1 Ohms.
17: Now moving on to the opposite side of the connector which would run up to the 6 wire splice i checked and verified earlier (#10 ). I stuck some wire into that connector and made sure i had it in there good and then started checking resistance. Here is what i got which is what i need answers to. (Picture attached named as "Picture of fuel pump ground plug" ) is the plug i am reffering to when i state the below results.A: That plug to Battery negative terminal with negative lead hooked up to battery was 10.4 Ohms
B: That plug to the stud from the cab where the grounding strap from the frame is connected was 26.4 Ohms
C: That plug to the frame Ground strap was 28.5 Ohms
D: That plug to the ECM ground was 2.2 OhmsThe ground splice (6 wire connection) i spoke of in #10 ultimately all lands by the PCM. It is a multi wire plug which is behind the glovebox. Picture attached states " Ground Connection By PCM"What i really need to know before i fully diagnose this as a "Pump Issue" Which i truly believe it is because he ran the truck out of gas.Does anybody know of or have a print of the ground circuit? My prints just show a ground symbol. That may be what is confusing me, i am an experienced industrial electrician and i have worked side by side with a master electrician for 5 years but then again, high voltage 3 phase runs and 24 Vdc controlcircuits in packaging equipment is not a chevy.I am extremely confused as to why the high resistance from this plug to certain area's but not others, in my understanding ground is ground, Period!Maybe im missing something as to how this circuit works.The other question i have is regarding to the fuel pump, i have 2 ground wires by the fuel pump. 1 grounds to the frame where the 3 prong plug bolts down and the other ground is in the 3 prong plug which has the following color wires. Purple, Grey, Black with white tracer. My understanding is Purple is for the sender to show the fuel level, Grey is the 12V to run the pump and the grounds im not so sure of. As i said earlier ground to me is ground. If someone could explain this in a little more detail or has a print i would appreciate it. Spending way to much time trying to make sense of something i just dont have the experience or the working knowledge of the PCM/ Componants. I can troubleshoot all day long but if anybody has something that will help out you'll be a huge time saver.
Customer: replied 2 years ago.
I have pics attached, names of pics may vary from original post.
Expert:  K. Wiggins replied 2 years ago.
Hello, I'll post a link bellow to the fuel pump circuit. The black and white wire goes through a connector (103 the one in your first pic) and ultimately terminates at ground 103 which is located by the thermostat housing. The ground for the fuel pump relay also uses ground 103 via splice 103. It wasn't uncommon to have problems on these vehicles at splice locations leading to high resistance. Look over the diagram and let me know how I can help further.
Copy and paste link in your web browser to view.
https://dl.dropboxusercontent.com/u/103900598/chev%20fp.pdf
Expert:  K. Wiggins replied 2 years ago.
The quickest way to diagnose if the fuel pump is getting power is to simply use a volt meter with negative lead in black with white wire cavity and positive in gray wire cavity. With key on there should be power for around 3 seconds as the PCM primes the pump. Then while cranking the vehicle signal will be sent by the oil pressure switch re activating the circuit and power should be present again.
Customer: replied 2 years ago.
Please see the pictures attached, I have labeled them to correspond with each other. Picture 1 is the action and picture 2 is the result checking the ground wire on plug 103. The end I was checking was not what leads to the fuel pump, it was the ground circuit running through the wiremold on the firewall where I found the 6 ground wires spliced together. These ground wires also run into the plug which I attached in the previous question photo which was next to the PCM.The original question was not answered, though your print is much, much better than the one I have in my Haynes manual I still have un answered questions as to why I see the high resistance.As for the pump running, I have verified voltage being supplied to the pump via this ground wire and the pump does run. I do not understand the resistance issue though. This is my main concern.The questions I ultimately need answered.
1: Why the high resistance readings, also why are they different? Yes the battery was plugged in put the key was out, leaving only the lighting in the cab and under the hood to be turned on.
2: Why do I have these 2 grounds coming from the fuel pump? One bolts to the frame and the other is in the plug connector which comes from connector 103. Do they both go to the fuel pump? Your print still shows only one so at this point without pulling the bed I am just trying to verify that my path to ground is exactly where it needs to be with minimal resistance.