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Engine won't start?

Tiny
VAUGHN58
  • MEMBER
  • 3 POSTS
Battery is good so I am going to check the alternator.
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Wednesday, July 29th, 2020 AT 12:30 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Here is a guide that will help you:

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Please let us know what happens.

Cheers, Ken
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
JERRY STENGER
  • MEMBER
  • 3 POSTS
  • 2005 CHEVROLET COBALT
  • 2.2L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 186,000 MILES
Car had been running rough and stalling at stoplights. Check engine light came on as driving home. Stalled as parking, will cranks but will not start. Got scanner. Here are codes. P0030, p0135, p0300, p0446, p0451, p0461 and p2176.
Replaced O2 sensor. I have changed spark plugs as they needed it. Checked for spark at the plug. Tested fuel pressure at the rail, 57lbs. I was told by a friend that there should be 5V at the mass air flow sensor. I used voltmeter and get nothing. Any ideas where to look next?
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
AL514
  • MECHANIC
  • 4,793 POSTS
Hello,

So to start off with, did any codes come back after replacing the oxygen sensor? The P0030 and P0135 are for the Oxygen Heater Control Circuit (Bank 1 Sensor 1). I am going to take you through the codes one by one because they are all for different circuits on the car. P0446 and P0451 is an EVAP system Vent control and pressure sensor circuit malfunction. To start with, and a wiring diagram for the Mass air flow sensor. It sounds like you may have a serious wiring harness problem or maybe a bad ECM.
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
AL514
  • MECHANIC
  • 4,793 POSTS
So to start with here is a wiring diagram for the Mass air flow sensor, there should be 12 volt (battery power) on the Pink/Black wire with the key in the on or run position. This is fed by a 10 amp Emission fuse that is powered by the Power-train relay. So lets start there. Here is 2 wiring diagrams for the mass air flow and its fuse that's powering it. And did you have spark when you checked it?
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
JERRY STENGER
  • MEMBER
  • 3 POSTS
Car will not start. I erased the codes and now show no codes. Yes I have spark at the coil, and the nubs and at the plugs themselves. Might be overkill but I wanted to check all the way down. Rather than backtracking. Will be climbing back under the hood tomorrow. Thank you for the reply, talk to you soon.
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
AL514
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Okay, after you check the mass air flow for power, I am only assuming right now that you don't have power there because of the first check you did. I want you to check for power at these 3 fuses with the key in the on position. As you can see from the diagram they are all powered up from the power train relay with is located in the engine compartment.
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
JERRY STENGER
  • MEMBER
  • 3 POSTS
Okay, I was being too nice to the connector and upon further testing: I do have 12v at MAS. All 3 fuses check out. Rechecked all fuses, and in the on position my fuel pump fuse shows negative voltage. But pressure test showed 57 lbs still.
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
AL514
  • MECHANIC
  • 4,793 POSTS
If you're reading -12 volts on your meter you leads are just backwards. No biggie. You're going to want to check power to the injectors and injector pulse next. You can do this with a test light. First check for power with the key on. Then hook the test light to battery positive and one of the two injector wires should have a pulse while cranking. You may have a shorted oxygen sensor due the previous codes you pulled. The p2176 is a throttle body actuator code, if the drive by wire system has failed this will cause all kinds of issues too but we'll deal with that next.
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
TROY TRAVIS
  • MEMBER
  • 1 POST
  • 2005 CHEVROLET COBALT
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
I had the alternator replaced about a year ago. Not long after, my car started to sputter and or shut off when slowing down or stopping and the headlights would dim. Yesterday it wouldn't start unless I pumped the gas pedal while starting it but would shut off instantly even with the gas pedal to the floor.
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
SEVAG P
  • MECHANIC
  • 405 POSTS
Hello, thanks for using 2CarPros.

i do not believe your problem is related to alternator because your battery can keep you engine running.
It sounds like fuel pressure problem. It is better to check for fault codes for proper diagnosis. here is our guide some tips for engine does not start problem:

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

Check the attached table for trouble shooting fuel system for your car.
Let us know what happens with you.
Thank you.
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
It sounds like you have a battery that can be shorting out intermittently and the car is in limp mode. here are two guide you can run through to see what's going on:

https://www.2carpros.com/articles/car-battery-load-test

and

https://www.2carpros.com/articles/reduced-power-limp-mode

We should run the codes as well:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run down these guides and report back.
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Wednesday, July 29th, 2020 AT 12:31 PM (Merged)

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