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Ask Juan Crespo Your Own Question
Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1525
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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My truck cranks over but shuts directly back down. This is

Customer Question

My truck cranks over but shuts directly back down. This is an intermittent problem that happens every few months, or weeks, or days. It's happened about 5 or 6 times total. Usually it starts up about 20-30 min later. Sometimes its in the morning first start up and sometimes after long drive. Computer at Auto-Zone said mass air flow sensor, but my concern is if this is wrong.
JA: Does the engine stall right after starting? And what about hesitation or jerking during acceleration?
Customer: Stall no hesitation really when accelerating
JA: What is the model/year of your Chevy?
Customer: 99 Chevy Silverado. Vortec 5.7
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I am getting ready to change Mass Air Flow Sensor, but double checking that this is my problem
JA: Anything else you think the mechanic should know?
Customer: I gave a pretty detailed description
Submitted: 8 months ago.
Category: Chevy
Expert:  Juan Crespo replied 8 months ago.

Hi there.

It's very rare to see an intermittently bad MAF - they usually just go bad and, when they do, they trigger a code and turn on the check engine light. Also, when the onboard computer (PCM) detects a bad MAF, it will use substitute signals from the crank and throttle position sensors to make the engine run; all of which makes me doubt the MAF as being the cause of the no-start.

Let's try this; go ahead and disconnect the MAF, then try to start the engine. Does it start?

Customer: replied 8 months ago.
When I disconnect.l, it still starts, it just idles a little more purely
Customer: replied 8 months ago.
Poorly
Expert:  Juan Crespo replied 8 months ago.

OK. So that tells us the MAF is not the direct cause of the no-start - my advice regarding the MAF would be to erase the code, clean the sensor with the appropriate cleaner and hold off on replacing it for now.

Back to the intermittent no-start; if the engine cranks but won't start, this type of issue is usually caused by the anti-theft system (Passlock VTD) - most likely the sensor in the steering column, with the ignition lock cylinder running as a close second. Diagnosis of the Passlock VTD requires a Tech-II or equivalent scan tool that most licensed locksmiths have access to - they are also much cheaper than the dealer.

Customer: replied 8 months ago.
Ok I changed the ignition switch about a year ago. Would that effect it? Being that I use a different key now.
Expert:  Juan Crespo replied 8 months ago.

Well, not really. You see, if either the key or the switch were the cause, then the issue would happen constantly not intermittently. I'm more inclined to believe the fault lies within the Passlock sensor. Then again, to be sure, the system would have to be diagnosed with a Tech-II or equivalent scan tool.

In the mean time, you can try the auto learn procedure - see attached - and see if that takes care of it.