No fuel Pressure

OIFVet0326

Original poster
Member
Aug 21, 2021
10
Florida
I'm working on my father's 07' Trailblazer. The other day he started that on his way home that his trailblazer started to spit and sputter. He pulled of to the side of the road and shut the vehicle off for a few seconds. Turned it back on and it seemed to be ok except now his speedometer started to mess up. When he turn the ignition on the speedometer would drop below O mph. While driving the speedometer would increase but ticking like the second hand on a clock. He gets home and the vehicle stalls and dies right in the drive way. Tried to start the vehicle and it ran for like 2 seconds and stalled again. Tried to start it again, only crank no start.
I check for fuel pressure on the rail, no fuel pressure whatsoever. Checked fuel pump relay by switching out relays with other relays in the underhood fuse box. Nothing, still no fuel pressure whatsoever. Dropped the tank and replaced fuel pump because it was still under warranty. Still no fuel pressure with the key in the on position or trying to crank/start it.
During these checks of turning the key to on position, on a few occasions, when I turned the vehicle to the on position (not run) the vehicle tried to start for like a split second. This definitely has me scratching my head. I heard or read that the PCM can also stop power to the fuel pump relay and cause many other problems. All ground wires look good and are tight upon inspection except that the bolts and connectors look rusty but no corrosion. Any ideas if to what my problem could be? I was leaning towards a corrupted/bad pcm but maybe a bad ignition switch. I just don't understand why everything else works when you turn the vehicle to accessorie/on but no power to fuel pump.
 

mrrsm

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Oct 22, 2015
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Welcome to GMT Nation...

One of our Sages... @MAY03LT has a Video that covers these problems very well ...including providing the Vehicle Schematics and Diagrams worth Screen Printing to refer to more than once:

This one is an Introductory Rant...


For No Crank No Start ...with MORE Diagram Analysis and Start Circuit Investigation:


Keep the issue of "Bad Grounds" here in mind as well, because uniquely with the Trailblazer and Envoys... the Fuel Pump Relay shares a Common Ground located at G-107 on the Driver's Side of the Engine Block with the Left Turn Signal AND the Left Head Light. If the Ground is poorly connected ...and ALL Three items demand power...the Fuel Relay will trip and the Engine will Die.

While you are at it.... Check whether or not the Top Galvanized Fasteners hold the Power Control Fuse Block to the Plug-In Harnesses connected to it from below. They might be getting loose enough to break electrical contacts when the vehicle is vibrating and cause the Engine to Stall.

And Last bust Not Least.... Consider Replacing your Ignition Switch with an ACDelco Brand, If the Key Switch gets even a little sketchy... so many 'pre-signals' between it and the PCM and Security can cause this Engine Suddenly Dies Problem to occur. It is a Mechanical Thing that Can and DOES Fail.
 

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OIFVet0326

Original poster
Member
Aug 21, 2021
10
Florida
Welcome to GMT Nation...

One of our Sages... @MAY03LT has a Video that covers these problems very well ...including providing the Vehicle Schematics and Diagrams worth Screen Printing to refer to more than once:

This one is an Introductory Rant...


For No Crank No Start ...with MORE Diagram Analysis and Start Circuit Investigation:


Keep the issue of "Bad Grounds" here in mind as well, because uniquely with the Trailblazer and Envoys... the Fuel Pump Relay shares a Common Ground located at G-107 on the Driver's Side of the Engine Block with the Left Turn Signal AND the Left Head Light. If the Ground is poorly connected ...and ALL Three items demand power...the Fuel Relay will trip and the Engine will Die.

While you are at it.... Check whether or not the Top Galvanized Fasteners hold the Power Control Fuse Block to the Plug-In Harnesses connected to it from below. They might be getting loose enough to break electrical contacts when the vehicle is vibrating and cause the Engine to Stall.

And Last bust Not Least.... Consider Replacing your Ignition Switch with an ACDelco Brand, If the Key Switch gets even a little sketchy... so many 'pre-signals' between it and the PCM and Security can cause this Engine Suddenly Dies Problem to occur. It is a Mechanical Thing that Can and DOES Fail.
Ok I watched the first video and another one by the same guy on you tube. Also I forgot to mention that there is no check engine light and no codes when scanned with code reader. Checked the fuel relay ports with multimeter, the battery port read 12.26V, PCM port read 12.26V when vehicle was turned to on position. Ground port read -12.26 volts, I'm assuming the ground is good from that check. Also I checked G107 and it is tight and doesn't look like anything damaged it or anything. On the pump relay port, I then took a lead wire from the battery port diagonally across to the fuel pump port to directly connect the pump to the battery. A YouTube video said this is how to test if your wiring or pump is good or bad. Is that correct? Still nothing. No fuel pressure. I should have checked to see if there was power at the pump when I dropped the tank but I never thought it would come to something like this. Definitely a lesson learned there. I am guessing that there will be no power there because the pump is brand new. Not that new pumps can't be defective but the one that I just took out was only 3 months old and was still under lifetime warranty. Is there another ground that the fuel pump is connect to near the tank or frame near the pump or something? Is there anything I might be missing. I'm going to drop the tank again tomorrow and check everything, just would like a few pointers. This has become crazy.
 
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budwich

Member
Jun 16, 2013
2,027
kanata
you just need to do a resistance measurement toward the pump at the fuel pump relay socket. That will likely tell if the pump and connections in that direction are OK.
 

OIFVet0326

Original poster
Member
Aug 21, 2021
10
Florida
I dropped the fuel tank again, today. I'm doing all this by myself no one to help turn the key on and off. I turn the key to on. I get under the vehicle and test the black and grey wire for voltage at the harness. No voltage. I take fuel relay out and straight wire the positive wire (Terminals 87 & 30) to the pump with a lead wire. Check for voltage again. This time there is voltage 12.12v. I'm not experienced with a multimeter but I tried to check for resistance at the connector to the pump and it said 1.06. On the multimeter I had it on 20M. The resistance at the fuse box before I dropped the pump it said .4 to.5 for like 1 second or so then back to zero. While I was lowering the tank I had temporary help. Before I disconnected the pump I had them turn the key to on while I had my hand on the pump I could feel it slightly turn on for like 1-2 second and then shut off. Oh and I tested the 3 prong wire to the pump for voltage and it said 5v. I feel like I'm making some progress but can't understand why I have voltage at the connector to the pump when I use a lead wire at the fuse block but no voltage with the key on using any of the 3 relays in the fuse block. Also can't under why the pump wouldn't run when straight wired it in the fuse block while I still had the tank on the vehicle. Also just to clarify, during each resistance test I made sure the vehicle was in the off position. I forgot to mention that on another site and someone got pretty bend out of shape. They thought I was checking resistance to a circuit with power. Like someone mentioned early, I guess I just have to take my fuse block apart and check that the connection there is good. It just looks like a daunting task with all that wiring. Unless a bad/failing ignition switch would cause this. Just a quick look over the wire from the fuse block to the pump and nothing looks chewed up by a rodent or any damage. I would have take the plastic protective covering off for a better inspection. Just trying to avoid that and qt this point hoping its something more simple.
 
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OIFVet0326

Original poster
Member
Aug 21, 2021
10
Florida
Yes. G305 if memory serves.

See here...

I checked the ground 305 it looked fine. I took the ground off, cleaned it up and tightened it back up. I also jumped the terminals 87 and 30. Still nothing, just a little bit of fuel came out of the rail.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
I checked the ground 305 it looked fine. I took the ground off, cleaned it up and tightened it back up. I also jumped the terminals 87 and 30. Still nothing, just a little bit of fuel came out of the rail.

If you have power where it's supposed to be at the relay, and you jumpered between terminal socket #87 to #30, and the ground is good, but your pump doesn't run, then you either have a bad pump, or a broken wire, or have missed something in the aforementioned checks.
 

mrrsm

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Oct 22, 2015
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_^_ +1

...and this VOP (Video Original Poster) runs down his Fuel Pump Electrical Issue via a DEEPER testing of Powers & Grounds trying to work through a Bad Electrical Harness Coupling:

 
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OIFVet0326

Original poster
Member
Aug 21, 2021
10
Florida
_^_ +1

...and this VOP (Video Original Poster) runs down his Fuel Pump Electrical Issue via a DEEPER testing of Powers & Grounds trying to work through a Bad Electrical Harness Coupling:

Ok so I decided to test the fuel pump while I had the tank out. With the fuel pump still in the tank. I took the vehicle battery out and manually put a positive lead wire from the battery to where the grey wire would would connect on the fuel pump and a lead wire from the negative wire on the battery to where the black wire would connect on the fuel pump. I could feel the pump come on but hardly hear it. Also no fuel was being pumped out even after holding the positive for about 10 seconds. Does this mean this new pump is also bad? Is this a proper way to manually test the pump while the tank is out of the vehicle?
 
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mrrsm

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There are only a FEW OEM Quality Fuel Pumps that can give a reliable service period of many years:

(1) ACDelco
(2) Bosch
(3) Delphi

Everything else on the Market breeds nothing but problems...

You have not mentioned the Brand-Model & Part Numbers for your Replacement Fuel Pump... but if it is NOT on this accepted OEM Quality Short List, there can only be a few other reasons for it NOT to Pump Fuel properly:

(1) The Electric Pump itself is Damaged Internally.

(2) The Limited Wiring Harness attached to the Pump is Damaged.

(3) The Wiring to the Pump is Incorrect on the Pump Side.

(4) The "New" Fuel Pump may have been a Prior Purchase, Returned to the Store, Re-Stocked and Re-Sold with Hidden Damage. This CAN occur without ever dunking the Fuel Pump in gasoline if the former pump owner "tested the pump" via hooking it up to a 12 Volt DC Bench-Top Battery while it was still Bone Dry. The Fuel Pump is only supposed to be run AFTER it becomes fully immersed and constantly cooled down inside the Fuel Tank to avoid overheating.
 
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TJBaker57

Member
Aug 16, 2015
2,897
Colorado
no fuel was being pumped out even after holding the positive for about 10 seconds. Does this mean this new pump is also bad? I

If you have a charged battery and you have hooked positive to the correct terminal shown as grey #4 in the picture here. And connected the battery negative to the correct terminal shown as black #1 in the picture (being certain you are not connecting to the level sender ground by mistake), and no fuel comes gushing out, I would say the pump is defective or the tank is empty :smile:

I would expect all brands could have a bad unit these days. I changed out a brand new Delphi pump for a friend a while ago. It did pump but failed to develop the required pressure.

Screenshot_20210823-124503.png
 
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OIFVet0326

Original poster
Member
Aug 21, 2021
10
Florida
It's a Delphi from Napa. Part# FG0515
There are only a FEW OEM Quality Fuel Pumps that can give a reliable service period of many years:

(1) ACDelco
(2) Bosch
(3) Delphi

Everything else on the Market breeds nothing but problems...

You have not mentioned the Brand-Model & Part Numbers for your Replacement Fuel Pump... but if it is NOT on this accepted OEM Quality Short List, there can only be a few other reasons for it NOT to Pump Fuel properly:

(1) The Electric Pump itself is Damaged Internally.

(2) The Limited Wiring Harness attached to the Pump is Damaged.

(3) The Wiring to the Pump is Incorrect on the Pump Side.

(4) The "New" Fuel Pump may have been a Prior Purchase, Returned to the Store, Re-Stocked and Re-Sold with Hidden Damage. This CAN occur without ever dunking the Fuel Pump in gasoline if the former pump owner "tested the pump" via hooking it up to a 12Volt Desk Top Battery when it was still Bone Dry. The Fuel Pump is only supposed to be run AFTER it becomes fully immersed and constantly cooled down inside the Fuel Tank to avoid overheating.
 
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OIFVet0326

Original poster
Member
Aug 21, 2021
10
Florida
If you have a charged battery and you have hooked positive to the correct terminal shown as grey #4 in the picture here. And connected the battery negative to the correct terminal shown as black #1 in the picture (being certain you are not connecting to the level sender ground by mistake), and no fuel comes gushing out, I would say the pump is defective or the tank is empty :smile:

I would expect all brands could have a bad unit these days. I changed out a brand new Delphi pump for a friend a while ago. It did pump butnfailed to develop the required pressure.

View attachment 101543
The battery I used said 12.8v when tested with multimeter. Yeah I hooked it up correctly. Ironically this is a Delphi pump as well but before I go bashing a reputable brand name I have another pump coming in a few hours. I will be sure to test it as well before I slap the tank back in. Just so everyone knows the tank is 3/4 full. Should be plenty of fuel to keep the pump cool for the test. Which is the same thing I did with this new pump I got a few days that seems to not be working. Learning lesson is to test the old pump before taking it back, test the new pump before putting it back in lol. Never thought you needed to do this with new stuff especially brand name products.
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Delphi is not the same company of old. It went through a bankruptcy and exchanged hands. I keep myself to only ACDelco or Bosch, who actually supply them to ACDelco.
 

Mektek

Member
May 2, 2017
656
FL
Are any of them not made in the far east today???
I'm going on 2 years with a Chinese pump - so far so good..
 

mrrsm

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Oct 22, 2015
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Tampa Bay Area
FWIW... @OIFVet0326 ... More than most, you followed sound Mechanic's Diagnostic Thinking and Investigative Procedures ...so Props to YOU and your Skill Set... Brother!
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Been burned by Chinese pumps, never again. The ACDelco/Bosch are made in Mexico.
 
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