SOLVED! 2004 envoy crank wont start fuel pump not prime .

Ben4.2

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Jan 21, 2022
13
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I was driving home on the interstate and my 2004 Envoy 4.2 stopped running. I tried to start it a couple times and it still didn't start, I called tow truck to tow it home.

The first thing I knew: my fuel pump could not run. I tried circle ignition couple times and pump still not prime, I opened the FUSE box under the hood and I checked the fuse pump which was good. I removed my fuse pump relay (number 41) and checked the power with my test light. I got power battery supply on one side and the other side pcm control does not have power when I turned my ignition on.

Would you please guide me for things to look for when addressing this issue? ...or could it be that my ignition switch is bad?
 

azswiss

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May 23, 2021
861
Tempe, AZ
A shot in the dark here based on a similar experience with my 2003 5.3L Suburban. On my truck the fuel pump and the PCM share a 20A fuse ("PCM B"); the fuel pump died and blew the fuse.

Found a diagram for the 2004 4.2L Envoy and there is a 20A "PCM B" fuse (#10) listed.

external-content.duckduckgo.com.gif
 

Mooseman

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Dec 4, 2011
25,262
Ottawa, ON
I got power battery supply on one side and the other side pcm control does not have power when I turned my ignition on.
The PCM sends ground to the relay to activate it, which is why you didn't see power there.

Edit: My bad, the PCM does send + relay control as per the video. Check all the fuses to be sure another one for both the ignition and fuel pump hasn't blown.

This video explains well how to troubleshoot an inoperative fuel pump. If all the tests check out, then it's likely a bad pump.
 
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Reprise

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A shot in the dark here based on a similar experience with my 2003 5.3L Suburban. On my truck the fuel pump and the PCM share a 20A fuse ("PCM B"); the fuel pump died and blew the fuse.

Found a diagram for the 2004 4.2L Envoy and there is a 20A "PCM B" fuse (#10) listed.

I note that #10 sits right next to the pump relay (#41), as well.

I do see in my '03 Sierra owner's manual (sister to the Burb) that PCM B performs the same (so, relay + fuse). And PCM B is adjacent to the pump relay in the Sierra, as well.

I also see in my Envoy owner's manual that #10 is PCM B in both the I6 and V8 underhood boxes.
I'd pull #10, as a result, and make sure it's intact. Only takes a second.

Also, I see from the OP's profile that he has the LWB (same as me), and I don't see any reference to the fuel pump (or PCM B) in the 2nd row underseat fuse center. So the underhood box should be the only place to have to worry about the fuel pump relay / fuse.
 

mrrsm

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If jumping the relay like @MAY03LT shows still does NOT allow the Fuel Pump to run...

2008-10-12_190659_2004-Trailblazer-Underhood-Fuse-Block-Label-Late.gif

Be aware that, oddly enough... The Fuel Pump Relay...The Left Head Lamp and the Left Turn Signal ALL share a Common Ground at the G-107 Bolt Down Point on the Driver's Side of the Engine Block..Thusly:

2002GROUNDWIRES.jpg

So... if there is either a BAD or Corroded Connection there and there is High Resistance of the Ground Wire... It can Trip the Relay and keep the Fuel Pump from running. You may have noticed your Headlights Flickering... just before the Engine Died as a result.

Necessary Action:

Locate, Remove, and Clean the G-107 Ground Contact Point at the Engine Block. Then apply some Dielectric Grease in between and Bolt it carefully back in place... Thusly:

G107.jpg

Hope this Helps...

[Mod Edit: Edited for clarity]
 
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mrrsm

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I'm hoping that THIS situation involving a Hidden Broken Copper Wire Trace in between the Upper & Lower sections of the Under Hood Fuse Box are NOT involved here... but if it needs investigation, THIS particular 'One Over The World' Video from Wayne Sallee on this Unusual R&R is worth keeping in mind.

A Word of Warning...

Wayne's Shrill, Reedy Voice sounds like your Angry Social Studies Teacher dragging her Fingernails across a 50 Foot Black Board to get your attention... So either Lower the VOLUME at first until you can get used to it... or put some Cotton Balls in your Ears while trying to follow along with his well described narrative about this Oddball Repair... and NOT having to Wince in Pain:

 

JerryIrons

Member
Dec 20, 2011
434
Then apply some Dielectric Grease in between and Bolt it carefully back in place...
I've never really taken this approach before when it comes to ground bolts, putting dielectric grease in between lets say washer, frame and bolt. The assumption here is that the pressure when tightening forces out the grease so that metal touches metal ? (and left over grease forms that insulating weather sealing barrier) The grease itself is non-conductive. Usually on these grounds I will clean them up, bolt back together and spray with some of that purple battery terminal protector spray.

I get it when it comes to 2 electrical connectors, the pin fitting into the socket forces grease away from the metal contacting each other, and the grease that's left causes a "tighter" fit so to speak, and keeps out moisture.
 

mrrsm

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NP... Just understand that my reasoning is "Grounded" in my training and experience as a USCG Aviation Machinist's Mate- Helicopter Mechanic (circa 1970-1974).

This is a situation of having a "Lost Foam" AL380 Aluminum Silicate Engine Block casting being bonded together at various places with either Cadmium or Zinc Plated Mild Steel Eyelet Fasteners cinched around Copper Cables and reacting very easily with Oxygen in the atmosphere and inviting Electrolytic (Galvanic) Corrosion.

Mild Steel Rusting on compromised Fasteners and Eyelets creates the additional access to the Oxygen available in FE203 Molecules; enough so to encourage the Copper Wiring to form Cupric (Copper) Oxide and drastically increases the Electrical Resistance in the Wiring as it migrates further along under the Plastic Insulation.

This problem is often seasonally amplified by the presence of the Salty Electrolyte solutions constantly bathing that part of the underside of the Motor and Framing from abundant, "clingy" Slush and Mud heavy laden with Road Salt. Dielectric Grease is insoluble in Water and also inhibits Electrical Arcing.

FWIW... GM supports my position on the application of Dielectric Grease:

Excerpt from:


"That is what GM tells us to use nowadays inside of connectors to prevent corrosion in the terminals of the connector. It will work well to help with a ground connection on a frame as well."

This from the Silicone Grease WIKI:


Such greases are formulated to withstand the high temperature generally associated with the areas in which spark plugs are located, and can be applied to contacts as well (because the contact pressure is sufficient to penetrate the grease film).

Doing so on such high-pressure contact surfaces between different metals has the further advantage of sealing the contact area against electrolytes that might cause rapid deterioration of the metals by galvanic corrosion.[10]
 
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Ben4.2

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Jan 21, 2022
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After I check all the fuses, I got number 28 15amp pcm1 blow. I replace with new fuse and engine runs for 5 seconds until the fuse blow again and engine dies again. Is my pcm bad?
 

mrrsm

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Bounce over to THIS Thread and see What's What...

You might be looking at a "Dead Short inside of a Coil":

 
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Ben4.2

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Jan 21, 2022
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Bounce over to THIS Thread and see What's What...

You might be looking at a "Dead Short inside of a Coil":

You are 100% correct I found bad coil. thanks again
 

mrrsm

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Way Cool... BUT... ALL the Props and Credit go to @TJBaker57 and @budwich for sorting this Dead Coil issue out in the referred SOLVED! Thread. Thanks for Joining & Helping GMT Nation to "Keep The Lights ON..." Come Back and SEE Us Again... from Time to Time!
 
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