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Discussion Starter #1
2004 Chevy Silverado Z71 4wd 5.3L. Truck has never had a starting problem until I got it back from the transmission shop who replaced rear main seal, the plate the seal is installed in and the camshaft sensor. Now this transmission shop is one of the best in the business and honest to a fault, so I have no problem with them. Here's the problem. Turn the key and the engine turns but does not start. Try it again and it starts as usual. And it does this probably 95% of the time now. Sometimes if you keep the engine spinning long enough (5 secs) it will backfire or what sounds like backfiring. When I confronted them with this problem they thought it was the camshaft sensor. They explained that on initial start the camshaft sensor is in play and if a no start happens and crankshaft sensor takes over, or something to that effect. They wound up replacing it to no avail and put a known good one from another truck in,same result.They also replaced the pigtail the sensor plugs into. It's odd that this problem just happened after work was performed but I guess it could happen. They gave me a automotive shop's number and they'll pick up the charges if it's anything they did but I'd like to fix this myself if anyone has an idea what could be causing this.
 

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A backfire sound is generally caused by timing but with sensors all around controlled by the computer, it could be anything. You didn't state the mileage but the timing chain could be worn throwing off the timing. At least you have a good offer from the trans shop.
 

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I would think of two things. a bad camshaft sensor. or maybe a bad connection to the neutral safety switch.
 

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Discussion Starter #5
Thanks guys, this gives me a starting point. I’ll start checking these out in the morning.
 

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Discussion Starter #6
Fuel pressure is good, sensor is good. Just won’t fire on first try. Second try, fires fight up!
 

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K2500 might have a point but I would think that a bad neutral safety switch it would not crank at all.

Between the starts, is the key turned to off or just to the run position and back to start?
This is with both a hot or cold engine?

On the next attempt before turning the key, wiggle the shift selector or move the key a few times from lock to the run position.
 

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WF, I’ll try that tomorrow, thanks!
so the repair shop replaced the rear main seal .. that tells me the crank shaft sensor under the starter motor was messed with or the wiring/connector . common problem like you have no start or erratic starts and many had no codes. the sensor has a encoder wheel in the location when the seal was worked on.

why did they mess with the cam sensor ? if they messed with it then it needs a GM program re-due ..
 
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