Cranks no start issue

Tiny
LE CHEN
  • MEMBER
  • 2009 CHEVROLET COBALT
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 146,000 MILES
Thank you all for reading this post.
My car has been running flawlessly for years until two months ago. It refused to start when I parked my car at a mountain top with very low fuel. After adding two or three gallons of fuel, I managed to drive it back home. I immediately topped the gas tank then the nightmare started. It constantly stalled and struggled to start.
The local auto shop diagnosed the car then replaced the fuel filter, crankshaft sensor, and camshaft sensor. The car ran well for two days, then the same issue reappeared. The shop replaced the sensors again, as they suspect the replacement parts can be faulty. This time my car lasted for a month. Finally, the auto shop told me they could not figure out why.

So, here are symptoms of my car:

1. I managed to start the car initially, now it shut off completely.
2. The engine cranks but the car will not start.
3. When the key is on, the fuel pump does not prime, and there is no control signal on the fuel pump relay.
4. When I applied 12v to the fuel pump relay control pin, the pump runs and good fuel pressure was tested. I cranked the engine, still no start, only to smell unburned gas.
5. This indicates that the vehicle lost fuel and spark at the same time, and a bad crankshaft sensor seems to make sense.
6. But then what can make the sensor go bad frequently?
Any sort of help is greatly appreciated!
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Friday, July 5th, 2019 AT 7:22 PM

6 Replies

Tiny
SCGRANTURISMO
  • EXPERT
Hello,

The fuel pump relay ground it probably bad. This is the ground on the coil and the other side should be coming from a switched power supply. The crankshaft sensor is probably good, but did the shop check the connector and the wires going to the Power-train Control Module (PCM)? This could very well be the problem. In the diagrams down below I have included wiring diagrams for you to check the CKP wires for damage as well as instructions for checking for an open, short circuit, and ground inspections on your vehicle's CKP circuit and fuel pump relay. Also here is a link on how to test a relay properly:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Please go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros
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Saturday, July 6th, 2019 AT 12:16 AM
Tiny
LE CHEN
  • MEMBER
Hi Alex, thank you so much for this very informative response. I will let you know once I find out more information. Lots of thanks!
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Sunday, July 7th, 2019 AT 7:15 AM
Tiny
KEN
  • ADMIN
SCWICKEDSTANG is one of our best! Please let us know what you find. We are interested to see what it is.
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Tuesday, July 9th, 2019 AT 10:53 AM
Tiny
LE CHEN
  • MEMBER
Hi 2carPro friends,

Here is an update on the above issue. A mechanic helped me diagnosed the vehicle. Confirmed there was ignition spark, just fuel pump not running. So he replaced the fuel pump. Still not running. Switching fuel pump relay did not help.
Honestly, to troubleshoot circuit issues as Alex suggested requires a more advanced skill level. So he came up with a simple fix -- jumped a wire to bypass the fuel pump relay -- fuel pump shuts off when the key is off.
Yes, there is still a circuit issue which causes the fuel pump relay not getting control signal.
I asked another experienced mechanic whether he can fix the issue, he said this issue could be related to the "engine computer" which can only be reprogrammed at the dealers.
So far my vehicle runs perfectly. No engine light or any type of error codes.
Both mechanics told me it should be fine with the current solution.
What do you guys think? Any potential risk for bypassing the fuel pump relay?

Thank you for any kind of input!
Leo
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Monday, July 15th, 2019 AT 9:48 PM
Tiny
SCGRANTURISMO
  • EXPERT
Hello again,

I have done the same thing in my vehicle. I have a 1997 Ford Mustang GT and the fuel pump relay is contained in what is called the Constant Control Relay Module (CCRM) that also holds the PCM relay and both the high and low speed fan relays. So when I had an issue with the fuel pump relay, I simply ran a new relay, using the high amperage wire from the Under hood Fuse Box and a switched power line from the Instrument Panel Fuse Box via a fuse tap. Just like yours, when the ignition key is in "run" or "start" the fuel pump is getting power and is running, and as soon as the ignition switch is turned off, the relay also turns off. Works great.

Thanks,
Alex
2CarPros
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Tuesday, July 16th, 2019 AT 1:47 AM
Tiny
LE CHEN
  • MEMBER
Hi Alex, what you've shared is really helpful. Lots of thanks!
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Tuesday, July 16th, 2019 AT 9:33 PM

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