Hard start to no start

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I have a 2011 Silverado with the 5.3L. This last week I was having issues with hard starts after sitting 8+ hours. It would stumble, but start and after a few seconds it would straighten out. I read elsewhere on this site where others were having very similar issues and letting the tank get close to empty and then filling the tank seemed to fix the issue for several people, so I tried this too. I just filled the tank last night and when I went out to go to work this morning, it wouldn't start at all. The first time I tried to start it this morning, it acted like it was going to do the same thing, but then didn't start. Since then it doesn't even seem to fire. I did a test of the fuel pressure, thinking maybe a fuel pump, but I had 62 LBS of pressure at the rail. Tried hooking up a code reader but there were no codes. I don't really have the funds to take to a dealer, but I am running out of ideas. Hoping maybe someone on here might be able to at least have some suggestions to help diagnose this issue. I have had this truck since last April. It has 62,000 miles

[sefiroxx]

I have a 2011 Silverado with the 5.3L. This last week I was having issues with hard starts after sitting 8+ hours. It would stumble, but start and after a few seconds it would straighten out. I read elsewhere on this site where others were having very similar issues and letting the tank get close to empty and then filling the tank seemed to fix the issue for several people, so I tried this too. I just filled the tank last night and when I went out to go to work this morning, it wouldn't start at all. The first time I tried to start it this morning, it acted like it was going to do the same thing, but then didn't start. Since then it doesn't even seem to fire. I did a test of the fuel pressure, thinking maybe a fuel pump, but I had 62 LBS of pressure at the rail. Tried hooking up a code reader but there were no codes. I don't really have the funds to take to a dealer, but I am running out of ideas. Hoping maybe someone on here might be able to at least have some suggestions to help diagnose this issue. I have had this truck since last April. It has 62,000 miles

Does it work better with more gas at startup?

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[Mike GMC]

Have you tried pressing on the gas pedal while cranking?  If that works, it's the IAC.  If not, it's something else.  But it's an easy way to eliminate one possibility. 

Edited October 26, 2017 by Mike GMC

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If I press on the accelerator while cranking, it will start. It runs rough for a few seconds, then smooths out. Only does it after sitting long periods (overnight/8+ hours at work). Otherwise it really runs great. Battery was bad. Replaced it thinking maybe I just wasn't getting enough voltage, but still have the same issue this morning. Very strong smell of gas when it does start (very rich).

[Mike GMC]

I'd replace the IAC valve and clean the throttle body.  Particularly the port for the idle air control valve.  When you put the new one in, you may have,a very high idle at first until it figures out what to do with the new valve.

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23 hours ago, Mike GMC said:

I'd replace the IAC valve and clean the throttle body.  Particularly the port for the idle air control valve.  When you put the new one in, you may have,a very high idle at first until it figures out what to do with the new valve.

From the research I have done, it doesn't have a replaceable IAC valve. It is all incorporated into the throttle body. You have to replace the entire throttle body, unless I am missing something. I can't find a IAC valve listed on any of the parts sites (Autozone, Oreillys, etc.) past 2002. Similarly, the fuel pressure regulator is part of the fuel pump assembly. I am sure the engineers had a reason for moving this from right up on top of the motor to in the fuel tank in an assembly, but I really am not a fan right now. I am going to check the fuel pressure again and see what the bleed off is after half an hour. I have looked at the throttle body and with 62,000 miles and running injector cleaner through it regularly, it is really pretty clean. I believe that it is narrowed down now to either the throttle body ($100+) or fuel pump($300). I am actually leaning more toward the fuel pump only because I turned the ignition on for ~10-15 seconds this morning and I didn't have to put my foot on the accelerator to get it to start. I still idled rough for a few seconds, but it was an improvement, like it was able to build up a little pressure.

[Mike GMC]

I knew the integrated the pressure regulator on new models, but I did not know about the IAC.  The more I learn about the newer trucks, the more I like my 2000.

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Put the fuel pressure gauge on again. Turned the key to on, had 63lbs. Waited 30 minutes and it was down to 45lbs. I don't think it should drop off that much in 30 minutes, should it?

 

[Mike GMC]

Don't know what an acceptable bleed rate is.  But before I replaced my reg, it would bleed down from 55 to 0 in less than 30 seconds.  Mine would start and run fine if I waited a couple seconds between on and start with the key.  With no hesitation to pump up the system, it was hard to start cold and impossible to start hot.