No fuel pressure

Friedhouse

Friedhouse

Member
Donor: 2007 Chevy Cobalt SS LSJ 3.0 pulley.

Finally just finished up the car, I have taken it out for small drives and pulls throughout the last 10% of the build, but nothing long. I went out today for a longer drive down the highway and started getting some misfiring. I immediately pulled over, turned around and started back home. Stayed in a low gear and limped back to my garage. Lean engine code p0171 was popped. After the car sat overnight, the engine will only crank over, but not run or idle.

  • I pulled the plugs and compression checked w/ all cylinders @180.
  • Checked the fuel pump relay in the fuse box and they were good.
  • Turning the car to acc I could hear the fuel pump start up to prime/run.
  • Went and bought a fuel pressure test kit, installed it on the fuel rail, turned acc on and the fuel rail only reads 10psi for a few seconds, then drops to 0.
Solution: There is a fuel pressure issue. So now I narrow this down to fuel pressure sensor, or pump?

If its a pump what do you all think is my best fix? Just a new stock pump, a ZZP or AEM fuel pump?

Are there any other diagnostics I can do to help me figure out what might be bad?

I was pretty **** depressed to take it out on my first full drive just to cut it short....
 
G

Gtstorey

Goblin Guru
Why only turn to acc? That is likely just a pump prime although that truly isn’t accessory setting, it’s probably the run not crank. Go ahead and confirm what it is doing when cranking. It should hold pressure at 58 psi ( I thing that is correct for your donor). If it doesn’t hold pressure, there is a good chance that it’s the fuel pump, but would need to do additional test to confirm. A bad connection in the wiring might allow voltage but not enough amperage. Or vats may be causing a problem. If it doesn’t hold pressure I would confirm voltage at the. Pump to rule outs vats being an issue.
 
Friedhouse

Friedhouse

Member
Just tried to crank the car over and its not cranking so I can't check fuel pressure. Only hearing the starter doing single clicks. I checked voltage on the battery and its at 12.4 Do you think this is now a separate issue with the starter, or an electrical gremlin I have to track down? This seems very odd to me given the car has run 100% before this longer drive.

Edit: I just put the battery on a drip charger. I'm going to try and give the car a jump start to increase voltage when I have a chance. A weak battery that has sat quite a bit could be this problem.
 
G

Gtstorey

Goblin Guru
If it won’t crank, I would definitely troubleshoot that before fuel pump. Definitely sounds like an electrical problem at first but could be separate issues.

Been a while since we had a problem with a ground as a post, but that is often the problem when you have multiple electric problems.
 
Rttoys

Rttoys

Goblin Guru
It’s always a ground.

load test the battery to make sure it’s good. If you are hearing a click. Could be a loose connection, bad starter or a number of things.

to the original problem
you said you are hearing the pump run, not seeing any leaks and low or no fuel pressure? Make sure you have gas. also, might pull the fuel pump and make sure the connections inside are still attached. never know when things got moved around.

when you pulled the plugs for the compression test, what did the plugs look like?

jist a few things to look at.
 
Friedhouse

Friedhouse

Member
I have the car cranking now, but 0psi as far as fuel pressure. I can hear the fuel pump humming, but it sounds like its not doing its job. What fuel pump replacement solution would you all suggest? Just a new stock pump? or a ZZP or AEM fuel pump?
 
Ross

Ross

Goblin Guru
Stock engine? Just run a stock pump. If you plan on making big HP, then maybe it is time to invest in a bigger fuel pump.
 
Desert Sasqwatch

Desert Sasqwatch

Bigfoot Goblin
Enough fuel? Is the fuel filter plugged? Are the hoses from the fuel pump connected to the correct ports on the fuel filter? Are all of the correct electrical plugs connected to the fuel pump and fuel injectors? Are the fuses all good?
You don't have your donor listed in your signature, makes it more difficult to help. EDIT: nevermind, see it in the first post of this thread.
 
95Blitz

95Blitz

Goblin Guru
If going with more power down the line, I would suggest a boost referenced style fuel system.
dfkitcar.com

LSJ boost referenced fuel system

I have been over thinking this boost referenced fuel system for a while now. After looking at OTTP and ZZP systems and reading through ZZP's install, I think I have worked it out. Please check the diagram and make sure I am looking at this correctly. I did leave out the vacuum/boost side of...
dfkitcar.com dfkitcar.com
 
Rauq

Rauq

Goblin Guru
On my LSJ, the pump will only run for 5 seconds when you turn the key to the on position, then won't run again until the engine cranks or until you wait with the engine off for about 10 minutes. You can't make it run continuously with the engine off or with quick consecutive key cycles. I never ran a fuel pressure gauge on a stock fuel system but my setup now builds pressure with the pump running (albeit 42psi vs 58) and drops by about 10-15psi when the pump finishes its prime (with the engine still off).
 
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