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Old August 18th, 2009, 06:20 PM   #1
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Default Mystery of the 5.7L HELP!

My parents have a 1999 GMC Sierra Classic K1500 with the 5.7L Vortec. Over the past couple months we have been having problems with it. It will run for a few days then it wont then we replace something and it will run for a few more days then it wont. It will run until it gets warmed up and then it will die out and you have to let it cool down then it will start back up and drive for a few more feet where it will die again. we have replaced several parts including:
-fuel pump
-fuel filter
-fuel relay
-egr valve
-spark plugs and wires
-mass air flow sensor
-O2 sensors
-throttle position sensor
-distributor cap

The list goes on..... and its like it will start running then all of a sudden the same exact thing will start happening again... Is there something we are missing?
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Old August 18th, 2009, 06:47 PM   #2
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IAC (idle air control modual) or the TPS, also check the engine temp sensor, there's two temp sensors, one for the gauge and one for the computer, the one for the computer should be next to or close to the thermostat housing
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Old August 18th, 2009, 07:03 PM   #3
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lets look at it from another angle. Have you found it runs better when the tank is under 1/4 tank and it runs longer till it quits? or does a full tank of fuel take it out in short order? if so then pop the gas cap and run it. if its running normal then you found the problem. the tank is not venting. if its new enough it would set an evap code, I don't think yours is new enough though.

if the cap cure the issue then check your charcoal canister for a kinked or plugged line or plugged purge muffler.
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Old August 18th, 2009, 07:18 PM   #4
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replace the gas tank cap had gmc did the same thing vented gas cap was not working or go loosen it and see if it still dies
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Old August 18th, 2009, 07:20 PM   #5
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You may have a bad ignition module or pick-up coil.
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Old August 18th, 2009, 07:25 PM   #6
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didn't the 99 silverado's come with the 5.3,not the 5.7????
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Old August 18th, 2009, 07:33 PM   #7
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didn't the 99 silverado's come with the 5.3,not the 5.7????
I thought that was the change over year 5.3 and 6.0 but autozone shows 5.0 and 5.7.

Anywho this is what is probably your problem http://www.autozone.com/autozone/cat...&parentId=62-0

Or this http://www.autozone.com/autozone/cat...&parentId=62-0
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Old August 18th, 2009, 07:35 PM   #8
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In this case, classic = old style.
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Old August 18th, 2009, 08:40 PM   #9
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Yes it is a 99 CLASSIC which means its an old body style... and it does have a 5.7L Vortec motor in just so there is no confusion about that.

We did replace the throttle position sensor, and engine temp sensor.
I just had the ignition module tested at autozone and their machine says its fine. We are going to go ahead and try out the gas cap idea and see if that solves our problem... Didnt think of that bc i thought it would throw a code for that..

Thank you every1 for your help. Hopefully it will get us back up and running over here.
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Old August 18th, 2009, 09:31 PM   #10
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the other thing to look at is the fuel pump relay in the power distribution box. i know you replaced the relay but did you look at the wiring that connects it? i had a 98 that would die all the time. after the owner decided to take it to the dealer to get checked out they said the wiring under the box was bad and wanted 500 bucks to replace it. apparently moisture will collect in the bottom of the box and cause the wiring for the fuel pump relay to corrode causing intermittent shorting out which caused the truck to stall and not restart. only way to restart was to wiggle the relay until it made contact.
i replaced the wiring and problem was fixed.
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Old August 18th, 2009, 09:45 PM   #11
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Just replace the Ignition Module with a good AC Delco module and It will fix your problem. I have seen this problem many times. You can't always trust the Auto Zone module testers. The air in the store is 78 degrees. Under the hood when it fails the temp is about 180 degrees.
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Old August 19th, 2009, 12:33 AM   #12
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Just replace the Ignition Module with a good AC Delco module and It will fix your problem. I have seen this problem many times. You can't always trust the Auto Zone module testers. The air in the store is 78 degrees. Under the hood when it fails the temp is about 180 degrees.
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Old August 19th, 2009, 09:57 AM   #13
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H'mm lots of good info..

If none of this works, you should get an obd2 reader and keep it in the truck for when it happens again, or just keep it plugged in and monitor readings.

Lastly, most any of those electrical items could have a "green" wire causing problems.
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Old August 20th, 2009, 04:56 PM   #14
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well we replaced the fuel pump AGAIN and it seems to be running for now we will see what happens in week or two.. if it starts messing up again we r going to try these other things.

Thank you all for your help
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Old August 20th, 2009, 07:26 PM   #15
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Have you checked for spark when it quits running? I had a coil fail on my old '98 1500. I ran, then didn't, then ran, then didn't, then died all together = bad coil.
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Old August 20th, 2009, 10:54 PM   #16
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Quote:
Originally Posted by ChevyGirl View Post
well we replaced the fuel pump AGAIN and it seems to be running for now we will see what happens in week or two.. if it starts messing up again we r going to try these other things.

Thank you all for your help
we had are fair share of bad fuel pumps for 99 chevy 3500 work vans. what we have found is that the pick up in the tank do not flow very good and tend to burn up the pumps.also make sure you are getting a good walbro pump.
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Old August 22nd, 2009, 12:55 AM   #17
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Quote:
Originally Posted by ChevyGirl View Post
well we replaced the fuel pump AGAIN and it seems to be running for now we will see what happens in week or two.. if it starts messing up again we r going to try these other things.

Thank you all for your help
if it acts up again them you probably have sediment in your gas tank which is clogging up the filter/pump and causing it to out. you might have to flush the tank
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