2013 Silverado mystery no start

Juan Technician California Posted   Latest  
Resolved
Driveability
2013 Chevrolet Silverado 1500 LS 5.3L (0 LMG) 4-spd (4L60-E)
Starts Then Dies

Hello Everyone!

Have this 2013 Silverado that has me stumped! Was called over by my friends shop to take a look at this truck. Initially the truck will crank & start, but immediately die… just like security feature. There are no codes, exept P0621 - Generator L circuit … truck alternator is charging. Unplugged MAF, then MAP no start. After a while, I reconnected MAF & MAP, then the truck started like nothing wrong! I started & stopped the truck several times with no problem. Then all of a sudden it won't start anymore. After checking all the data in engine & theft, I put in a A/C Delco computer… initially it won't start either…. then after disconnecting the MAF, it ran for about an hour, like nothing wrong!! I reconnected the MAF & it ran again!! I replaced the MAF, now the truck won't run again. No codes. The pids look fine!

This is a flex fuel truck, so I thought about the fuel… but why would it start fine sometimes? When it was running with the new computer & old MAF, I saw the fuel trims climb to 29%. When I would reset the fuel trims, it would die out & hard to start until the fuel trims climbed back up to 29%

After replacing the MAF, the fuel trims started going negative !!! Then it started to misfire some. After going back & forth with the new MAF & new ECM, now the truck won't start anymore. 

At this point, I'm at a loss to what I'm looking at. System wide code scan show no codes except the P0621 sometimes.

I'm asking for some direction, thank you.

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Interesting
Milos Technician
Ontario
Milos
   

I've had GM's with 5 volt ref problems/shorting causing a no start but they threw codes specifically for 5v ref from what I remember. The symptom of it running with the MAF unplugged would make me wanna check 5v otherwise I would just go back to basics and treat it like a regular no crank no start (or cranking no start?) Edit: Reading it again I don't think it has anything to do with MAF/MAP/5V…

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Keith Diagnostician
New York
Keith
 

Tell me more about what was checked during the time that it would not start please

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Juan Technician
California
Juan
 

Fuel pressure 50+ psi. Got spark. Doesn't make a difference if I spray carb. cleaner into the intake. Feels more like someone turning off the key after starting. When it runs, runs like nothing is wrong… then it won't start again. Got good signals from all the pids as far as I can tell. No 5V ref problems.

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Keith Diagnostician
New York
Keith
 

If you are adding alternate fuel and it has spark , does it even attempt to chuggle and sputter ?

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Joel Diagnostician
California
Joel
 

Do you have a pressure transducer ? Yoncan do 3 channels 1- incylinder , 2 injector ,3spark , all of them in the same cylinder , there you will find the reason why does not start . What is missing or out time

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Todd Diagnostician
Michigan
Todd
 

Juan, I recently had a 2012 with similar symptoms, and found an intermittent high voltage drop across the 175-amp mega fuse between the battery and the UBEC. When I finally caught it, the drop was almost 2 volts. Replaced the fuse and cleaned the connections and no more issues.

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Juan Technician
California
Juan
 

OK, checked for voltage drop across 175A fuse, none found. I'm kind of at a home disadvantage because I don't have any room @ my shop at the moment & went to check it at my friend's shop Of course, I didn't take everything I need to check it out properly. Today, I returned with more of my equipment & rechecked what I could. When you turn the key to crank, the computer takes over &…

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Todd Diagnostician
Michigan
Todd
 

Juan, Another thing I've seen with GM trucks is mis-timed ignition switch when its replaced. If the SES light is off after the engine stalls, that is likely your issue.

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Agree
Juan Technician
California
Juan
 

One of my checks was the pids on the POWER MODE screen. The pids match the switch position. I've also seen mis-timed ignition switches, learned to check the POWER MODE of the ignition switch to verify this. Also verify the pids after ignition switch replacement.

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Harm Technician
Ontario
Harm
 

I have had this a few years ago. The starting / ignition switch circuit. not excactly sure how i came to the conclusion but it ended up being the front fuse panel. these panels corrode badly and have giving us a lot of grief. we keep a spare / old at the shop for testing purpose. we dont like to throw them out and always write on them what kind of an issue they had. example dodge front module -…

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Juan Technician
California
Juan
 

I have a feeling something like this may be possible. I've read in the ALLDATA that the starting/ignition is dependent on 3 power sources/relay. I have bypassed the starter relay to crank the truck (because you need 2 people: one to crank the car & one to check the circuits while cranking). The starter spins, but never a spark or injector pulse when doing this, so the crank signal has to…

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Gib Owner/Technician
California
Gib
 

Did you check the cam & crank sensors to see if they're consistent?

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Juan Technician
California
Juan Resolution
 

HELLO & HAPPY FRIDAY! The sky looks blue again & I can enjoy the birds singing & watch the butterflies dancing with a smile! I couldn't spend anymore time on this truck out of my shop, so I caught up with my jobs & had the truck towed to me. By that time, my friend had installed a new ignition switch. I had check all the pids already & was convinced that wasn't the problem…

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