5.3L trouble starting when HOT outside

[darikfrye91]

Hello, I have a 1999 Sierra with a 5.3L motor. This is my first post to this forum. So this is also my welcome post as well haha. I'm from Ludlow MA and I've had my truck for two years. So now onto my issue! Whenever its really hot outside the truck won't start. It still cranks over, and will fire for a split second then die. I normally have to keep hitting the throttle and cranking it over and shutting it off at the same time until it finally starts up. And whenever it does finally fire it idles very rough until it warms up so I normally have to keep the rpm around 1500-2000 rpm for a couple minutes until its finally warmed up. Any ideas of what I should be looking at or for and what to test? Any help would be great! Thanks!

[CapitalTruck]

Take a look where the air intake hose runs into the throttle body. Take the hose off and clean out the throttle body really well with throttle body cleaner (the good stuff like CRC throttle body cleaner, NOT carburetor cleaner). Have somebody step on the throttle to open the butterfly, clean it out real good in there. Also, clean out the idle air control valve next to the throttle. This is a little electronic valve that controls the amount of air that comes into the engine when idling (or anytime your foot isn't on the throttle). That could be all gunked up too. You might have to take it off to clean it up well. All my trucks have had drive by wire, so there wasn't an idle air control valve. I think yours still had a throttle cable, so that valve should be there. Does it happen after you've been driving your truck for a while, it's hot outside, and then when you go to restart it won't start (but the engine is still "warm")?

 

It seems like it's running rich (to much fuel in the air for "warm" start), once it gets going it gets balanced out.

 

This is just a guess, no bad ever comes from cleaning that gunk/carbon out of there.

[darikfrye91]

I should re-phrase, it only seems to happen when its humid out. Cuz yesterday was a hot day but wasn't has humid and it started no problem.

[anumber1]

I second the recommendation of cleaning the throttle body, IAC, and clean the MAF too (special spray, don't use TB cleaner).

 

How many miles on it?

[darikfrye91]

I second the recommendation of cleaning the throttle body, IAC, and clean the MAF too (special spray, don't use TB cleaner).

 

How many miles on it?

149k miles on the truck.

 

 

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[anumber1]

At around 180k (miles) on my truck (99 silverado 4.8l) I had hard warm starts and sluggish part throttle acceleration.

 

It got better with fresh o2 sensors and a cleaning for a while.

 

Then at about 225k the troubles came back and cleaning didn't help. Lots of headscratching later, I replaced the MAF with a new Delphi unit and all was right again.

[SouthernSilveradoGuy85]

I had similar issue in my '98 where I would have to hold the throttle for it to start. Difference is that it would only do it if it was raining or was raining. But, when it's hot and humid you can get moister in there. The problem was the distributor cap not sealing good enough to the distributor.

[CapitalTruck]

I had similar issue in my '98 where I would have to hold the throttle for it to start. Difference is that it would only do it if it was raining or was raining. But, when it's hot and humid you can get moister in there. The problem was the distributor cap not sealing good enough to the distributor.

 

I don't think he has a distributor on a 99, unless it's a V6

[darikfrye91]

 

I don't think he has a distributor on a 99, unless it's a V6

No its the 5.3L V8. Now that i'm thinking about it wouldn't run right and would pretty do the same thing in the dead of winter too. when it's really cold out. Could the same issue cause both problems?

[rjgti]

check your plug wires, I use a spray bottle and mist the wires. it will show up a bad wire right away

[darikfrye91]

Take a look where the air intake hose runs into the throttle body. Take the hose off and clean out the throttle body really well with throttle body cleaner (the good stuff like CRC throttle body cleaner, NOT carburetor cleaner). Have somebody step on the throttle to open the butterfly, clean it out real good in there. Also, clean out the idle air control valve next to the throttle. This is a little electronic valve that controls the amount of air that comes into the engine when idling (or anytime your foot isn't on the throttle). That could be all gunked up too. You might have to take it off to clean it up well. All my trucks have had drive by wire, so there wasn't an idle air control valve. I think yours still had a throttle cable, so that valve should be there. Does it happen after you've been driving your truck for a while, it's hot outside, and then when you go to restart it won't start (but the engine is still "warm")?

 

It seems like it's running rich (to much fuel in the air for "warm" start), once it gets going it gets balanced out.

 

This is just a guess, no bad ever comes from cleaning that gunk/carbon out of there.

No I drive it to work at 8am and then when I leave at 5pm it happens. I did clean everything you told me to and it's still happening.

 

 

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[CapitalTruck]

Only other thing I could thing would be fuel injector leaking:

 

http://www.clarks-garage.com/shop-manual/fuel-17.htm

 

I assume you've tried the thing where you turn the key to "on" (not start), pause 3 seconds, off, on, pause three seconds, off a few times to make sure the fuel pump isn't losing it's prime as it sits.

[darikfrye91]

Only other thing I could thing would be fuel injector leaking:

 

http://www.clarks-garage.com/shop-manual/fuel-17.htm

 

I assume you've tried the thing where you turn the key to "on" (not start), pause 3 seconds, off, on, pause three seconds, off a few times to make sure the fuel pump isn't losing it's prime as it sits.

Yes the fuel pump is good.

 

 

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[Brianibew]

I know it doesn't explain the humidity issue, but have you checked your fuel pressure regulator? Super easy to replace, and does fix a lot of throttle issues with the 5.3. Buy the Delco brand as others I have used in the past don't hold up as well. Hope you find the issue.