Crank no start?

Tiny
JEFF HERMAN
  • MEMBER
  • 2004 CHEVROLET TRAILBLAZER
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 250,000 MILES
Just replaced fuel pump, hear it run, fuel at rail. No codes. I'm going to test fuel pressure tomorrow. Popped once but no start. Only about 3.5 gallons of gas in the tank. Battery was out of vehicle for several weeks. No security light flashing so I don't think anti-theft is activated. If crank sensor was bad wouldn't there be a code? Would all codes have cleared with the battery out that long? Had spark before I put the pump in, I don't know about now, will check tomorrow. Also going to see if throttle body plate is stuck. That's about all I have for you for now.
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Tuesday, November 22nd, 2022 AT 6:26 PM

9 Replies

Tiny
SQM
  • EXPERT
Hello,

A good first step would be to check the fuel pressure you plan to do.
With the key on and engine off it should have 55-62 PSI of fuel pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

One thing you can do is to spray starting fluid into the intake and try to start. If it starts and runs for a little bit, then you will know the issue is fuel delivery.

https://www.2carpros.com/articles/car-cranks-but-wont-start

It is not impossible to have a faulty crank sensor, but you want to rule out the fuel first before taking a deeper dive.

Let me know what you find with the fuel pressure or if you have any questions.

Thank you.
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Tuesday, November 22nd, 2022 AT 9:11 PM
Tiny
JEFF HERMAN
  • MEMBER
The good news is it won't be a crank sensor. The bad news is the new fuel pump is only producing 30 pounds of pressure at the rail. Tried to test it at the filter because there's a fitting there but the tester wouldn't connect solidly enough to test it. Runs good on gasoline poured directly into the throttle body. I want to check the fuel filter before I go ahead and assume I have a bad pump since its brand new. Any thoughts on this?
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Wednesday, November 23rd, 2022 AT 2:53 PM
Tiny
JEFF HERMAN
  • MEMBER
Just a little more information it pumps to 30 pounds but then falls off so I think it's a weak pump not a filter.
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Wednesday, November 23rd, 2022 AT 3:07 PM
Tiny
SQM
  • EXPERT
It could be a weak pump or bad fuel pressure regulator. If you were able to test the pressure at the filter or anywhere before the regulator, it can help you determine if it is the regulator or a weak pump.
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Thursday, November 24th, 2022 AT 4:49 PM
Tiny
JEFF HERMAN
  • MEMBER
I'm going to rig up something so I can test straight out of pump.
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Thursday, November 24th, 2022 AT 6:39 PM
Tiny
JEFF HERMAN
  • MEMBER
The pressure directly off the pump is over 100 pounds. Here are some pictures and a video. I believe it falls off was my fitting was leaking.
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Friday, November 25th, 2022 AT 10:12 AM
Tiny
SQM
  • EXPERT
Right the pressure from the pump would be higher than what it supposed to be, that is why the regulator brings it to the correct pressure.
So if the pressure is stable at the pump the regulator could be the culprit.
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Friday, November 25th, 2022 AT 10:52 AM
Tiny
JEFF HERMAN
  • MEMBER
I don't know about stable but it sure is strong I didn't try with cranking because I didn't have the feed line hooked up to the engine tested directly off pump.
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Friday, November 25th, 2022 AT 11:01 AM
Tiny
JEFF HERMAN
  • MEMBER
I don't know about stable but it sure is strong I didn't try with cranking because I didn't have the feed line hooked up to the engine tested directly off pump
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Friday, November 25th, 2022 AT 11:01 AM

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