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2000 Jimmy (4.3) loses voltage to the fuel pump

  #1  
Old 02-14-2010, 09:17 AM
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Exclamation 2000 Jimmy (4.3) loses voltage to the fuel pump

I've done the following:
Replaced the fuel pump (twice)
Replaced the fuel pump wiring harness
Checked the ground to the fuel pump (checked out okay)
Replaced the crank sensor
Replaced the distributor, cap and rotor
Replaced the fuel pump relay
Checked all power supply wires from the battery to the relays
Replaced the oil pressure sending unit
I always have spark just lose fuel pressure (all of it)

Occasionally the Jimmy will start and run for a few minutes and then shut off. Most of the time, however, the vehicle simply doesn't have fuel pressure. When it does, it's around 60 lbs. I know it's not the fuel pump because it just started this morning, ran for about 5 minutes and then just shut off losing voltage to the fuel pump. Now it won't cycle the pump. I've done all the passkey checks and it seems to working properly. I'm out of ideas. Anyone have something else to check or replace? And exactly where is the BCM?

Thanks,
Randy
 
  #2  
Old 02-16-2010, 02:20 AM
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The BCM is located to the right of the accelerator pedal below the radio. The plugs on the BCM face towards the drivers side.

There is a connector near the under hood fuse box that you can use to send power directly to the pump for further testing purposes. It is usually a gray single plug connector that sticks out a few inches from the main wiring harness and isn't connected to anything.
From that connector you can send 12v directly to the pump bypassing all the other stuff in the truck that might be interrupting power to your fuel pump and allowing you to verify the pump and the wiring harness to it is good. (I know someone who got 3 bad fuel pumps in a row from the auto parts store so it's not out of the realm of possibility)
Be sure to use a fused connection when you do this (15 amp)

The only other thing that I can see that you haven't already tried is that you may have a bad ignition switch. A bad ignition switch has been known to cause the problem of not turning on the fuel pump in these trucks.
There is a full writeup in the DIY section on ignition switch replacement should you need it.

Good luck and let us know how it goes.
 
  #3  
Old 02-19-2010, 12:01 PM
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Default Can't find the wire to test the fuel pump

I can't seem to locate the gray wire to test the fuel pump. I did exactly as suggested. In the main underhood harness near the relay box, there is a gray wire with the conduit but it goes into the relay box. Thanks for the help, however and the link to the ignition replacement instructions.

Randy
 
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Old 02-20-2010, 04:01 AM
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I did a bit of looking and apparently on the jimmy the location and color of the fuel pump test connector is slightly different then on the blazer.

I will see if I can locate a picture of it on the jimmy but it should be a red wire with a black connector or red and black wire in a green connector. (95-01 supposedly) The location should be either off the main harness near the ABS system or off the main harness near the center of the firewall.

Hopefully you can find it. I just wish that I had a jimmy handy so I could locate it and take a picture for ya. It is a lot easier to find small stuff like this from a pic of a real engine compared to a wiring diagram.

(edit) I have just been informed that for some reason some models/years of the jimmy after 1995 do not have this test connector. Though most of them do.
 

Last edited by awe341; 02-20-2010 at 04:07 AM.
  #5  
Old 02-16-2019, 09:10 AM
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Have you confirmed no voltage to the fuel pump with a voltmeter or test light during a no start condition and if so, where did you measure it?

What brand was was the replacement fuel pump. Store brands are notorious for early failures.



George
 
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Old 02-16-2019, 07:24 PM
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I don't think it is a BCM or VCM problem, but can't say for sure, since it all goes back to low fuel pressure causing the no start condition it seems,, I believe it is pointing to the fuel pressure regulator inside the Fuel injection Spider Assy. When I relieve pressure from the fuel line, which of course goes to the Spider and fuel pressure regulator, it will start right up, think what's happen there is the fuel pressure may reset itself by way of computer perhaps, but still strange that it does not want to start with pressure in the line, seems to want to see "no pressure in the line as it will start right up with that being said.
 
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Old 02-16-2019, 08:01 PM
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Don't know that I understand relieving the rail pressure and the truck starts. What is the pressure before you relieve it? Have you done the fuel pressure test in the sticky yet?

George
 
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Old 02-17-2019, 10:04 AM
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Usually the pressure will be only around 45 psi when it won't start,,,just cranks,,,if I relieve pressure from the rail, take pressure to 0, then it starts right up as if nothing is wrong...I believe it may be the fuel pressure regulagtor inside Spider Assy...what u think? The fuel pump will give me a healthy 60 or 61 psi if I use the prime terminal on the under the hood fuse block prime terminal,, by applying battery voltage to it,, you probably already know that using his prime terminal on a 2000 GMC Jimmy will bypass everything else and it goes directly go the fuel pump.
 
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Old 02-17-2019, 07:32 PM
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You really should do this entire test:

https://blazerforum.com/forum/2nd-ge...eakdown-88305/

45 psi may be a problem. As you will see in the sticky, you need to develop 60+ at prime and hold 55 psi at key off. It may be that when you relieve pressure it forces the system to repressurize with a running start from 0 for the next start and that gets you over the hump. You will need the unregulated pump pressure as the final piece of the puzzle and then we will know what the problem is.

If you leave the fuel rail charged at around 45 psi and turn the key on, do you hear the pump energize and does the pressure head back up to 60+?

If you open the butterfly valve do you smell gas from leaking?

Are your fuel trims off at idle or 2500 rpm?

George
 
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