Grand National No Start problem

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edfiero

Not-quite-so-new-guy
May 2, 2022
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5
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I have an INTERMITTENT no start problem on my Grand National. It cranks, but no start. When this happens, there is NO SPARK and NO FUEL INJECTOR PULSE.
However if I just let the car sit a day or two and come back to try again and it may starts right up.

I have changed the cam sensor with a brand new one and I switched the ECU with a different one, and I still have the problem.

Suggestions on what to look at next? Crank Sensor or Ignition Module were next on my list of possibilities. But not sure which one would be more likely to produce this intermittent problem. Seems like the Crank Sensor would be bad all the time if that was a problem, but I'm not sure.

Thanks
 

Rt Jam

G-Body Guru
Mar 30, 2020
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There is not many out there that can properly diagnose these cars. Even when they were pretty new.

Have you considered fully swapping out to an aftermarket stand alone ECU?
 

Built6spdMCSS

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Jun 15, 2012
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TPS sensor controls the throttle body opening and closing properly. Could test the voltage, or, if you have a helper someone watches how the TB is behaving both at the no start, and, the later start
Negative.

Throttle Position Sensor tells the ECU how far open/closed the blade is. The cable from the gas pedal controls the opening and the spring on the throttle body controls the closing. The throttle body is mechanical.

Even in drive-by-wire stuff the Throttle Positon Sensor does the same.
 
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ck80

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Feb 18, 2014
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Negative.

Throttle Position Sensor tells the ECU how far open/closed the blade is. The cable from the gas pedal controls the opening and the spring on the throttle body controls the closing. The throttle body is mechanical.

Even in drive-by-wire stuff the Throttle Positon Sensor does the same.
Nonetheless, if the TPS is bad, which he doesn't say he checked, the ecm wouldn't be getting the proper signals as to fuel management... no?

Edit - prior comment deleted. Irrelevant info shouldn't be behind for future thread searches.
 
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Built6spdMCSS

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Jun 15, 2012
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Nonetheless, if the TPS is bad, which he doesn't say he checked, the ecm wouldn't be getting the proper signals as to fuel management... no?
I could unplug the TPS and the car would still start. His issue is something else.
 
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Built6spdMCSS

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Jun 15, 2012
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Crank Sensor
That.

Same thing with LS Engines, the Crank Sensor is the Achilles Heel. If the sensor is on the way out you will get the same exact symptoms you have now. I have like 6 spares on hand and have one in my travel tools if I take my Z06 or Truck out on a long trip.

You are getting a no-start condition. One on my truck went out while driving. Glided into a parking lot and changed that right there, had one in the glove box.
 
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edfiero

Not-quite-so-new-guy
May 2, 2022
19
5
3
That.

Same thing with LS Engines, the Crank Sensor is the Achilles Heel. If the sensor is on the way out you will get the same exact symptoms you have now. I have like 6 spares on hand and have one in my travel tools if I take my Z06 or Truck out on a long trip.

You are getting a no-start condition. One on my truck went out while driving. Glided into a parking lot and changed that right there, had one in the glove box.

Thanks. I'll see if I can get this done over the weekend. I purchased one a few months ago, when I got the cam sensor, but hadn't put it in yet.
 

edfiero

Not-quite-so-new-guy
May 2, 2022
19
5
3
Have you considered fully swapping out to an aftermarket stand alone ECU?

I do have a second ECU. The problem is exactly the same on that one. Had not thought about an aftermarket one, since my car is pretty much all stock. Not really interested in getting to a new ECU and wiring harness until I've eliminated everything else.
 
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