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.
Tuesday, November 22nd, 2022 AT 6:26 PM

40 Replies

Tiny
SQM
  • MECHANIC
  • 6,383 POSTS
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
  • 486 POSTS
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
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  • 486 POSTS
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
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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
  • 486 POSTS
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
  • 486 POSTS
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
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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
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  • 486 POSTS
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
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  • 486 POSTS
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
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So, if you have good pressure from the pump but not at the injectors, the issue could be a bad regulator. As you have also said, the pressure tends to fall off at the port.
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Sunday, November 27th, 2022 AT 4:27 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 486 POSTS
I'll be trying a replacement known to be working regulator tomorrow and I'll keep you posted. Thanks for the help.
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Sunday, November 27th, 2022 AT 6:52 PM
Tiny
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Sounds good. I will look out for it.
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Sunday, November 27th, 2022 AT 7:09 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 486 POSTS
There seems to be adequate pressure at the rail I haven't tested it but it squirts forcefully out of the Schrider. But still no fire unless I feed it gas through the throttle body. Could it be a TPS?
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Monday, November 28th, 2022 AT 10:18 AM
Tiny
JEFF HERMAN
  • MEMBER
  • 486 POSTS
Rail pressure 60 pounds but falls off and stabilizes low. Also checked injector pulse which is good on all 8 cylinders. Also checked to see if I have 3 second fuel prime and more fuel delivered while cranking. Everything checks out. Clogged injectors? Engine tried to fire even with all 8 injectors unplugged.
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Tuesday, November 29th, 2022 AT 11:55 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi Jeff,

I noticed you haven't been contacted in a couple of days. Have you been able to make any progress? Also, I read through the conversation you had. Based on everything you indicated, it sounds like it may be an injector issue. If you remove the fuel pump fuse, see if it starts for a couple of seconds and then stalls. If so, it may actually be flooding.

Also, here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Let us know your status and what we can do to help.

Take care,

Joe
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Thursday, December 1st, 2022 AT 2:21 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 486 POSTS
Engine did not fire. Proceeded to remove plugs. All 8 black, several were wet. Not sure gas or oil. Hoping gas. Majority of wires broke off connectors even when leveraging on boot or heat shield. Haven't tested spray or no spray from injectors. 20 degrees today. Is it necessary to use the heat shields?
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Saturday, December 3rd, 2022 AT 4:57 PM
Tiny
JACOBANDNICKOLAS
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Hi,

Wow, the plugs aren't in good shape. As far as the ones that were wet, chances are it was fuel. Which wires were broken? Was it the wiring to the injectors?

I just went back through your conversations. The idea that the fuel pressure reached specification and then dropped before it stabilized leads me to think you have injectors leaking or a faulty fuel pressure regulator. If you remove the vacuum hose from the regulator, is there any evidence of fuel in the vacuum hose?

Also, yes, reinstall the heat shield or you could end up with a hydrostatic lock in the fuel system.

Let me know what I can do to help.

Take care,

Joe
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Saturday, December 3rd, 2022 AT 9:01 PM
Tiny
JEFF HERMAN
  • MEMBER
  • 486 POSTS
Spark plug leads to torn off connectors when removing. No other wires are broken. Regulator was bad, put a used one in from a running engine. Falloff may have been due to gauge connection, was seeping fuel. No fuel in vacuum line. Old regulator only gave 30 psi at the rail. Will be replacing plugs, wires. Also, will check injectors and clean them. Weather depending.
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Saturday, December 3rd, 2022 AT 9:18 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Thanks for the update. Before you even try starting it, confirm spark at the plugs. That will prevent you from having to remove them again if it doesn't start.

Take care and I'll be here when you get it done. I'm interested in knowing what you find.

Joe
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Saturday, December 3rd, 2022 AT 9:27 PM
Tiny
JEFF HERMAN
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  • 486 POSTS
Truck would run when gas was poured into the throttle body so spark must be present as well as crank sensor must be okay. Engine sounded great for 250,000.
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Saturday, December 3rd, 2022 AT 9:31 PM

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