Vortec hard start when warm

[luconi]

Yep sounds like the pump, time to check fuel pressure.

I'm leaning into that it is not a fuel pressure issue. I just checked the fuel pressure hot and cold and it would pop up to 60 psi and run at around 55psi. Also the Delphi MPFI spider is new so i can rule out the FPR since it was part of the kit.

could be fuel pump going. I had similar issue. Only when hot summer temps above 80 and engine hot I would have hard starts and occasionally have cutout in rpm range. Cold start and warmup runs like a top.

Turned out I needed a new Ignition control module. You can see the heat mark on the original one that lasted 210k miles. Make sure you use the paste it comes with or some computer CPU thermal paste.

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I am going to check this. thanks!

Check all your connections and terminals. I had this issue early this year, and it was fixed by 3 things.
#1: the longer positive cable (the one that goes across the fan shroud and over to the back of the computer)was corroded where I couldn't see it. This is a common problem on the vortecs. This cable is expensive and hard to find at the parts store, but if you have access to a shop that can make cables, they can make you one. Be sure that it's 4 gauge copper cable, and the ends are properly installed. This cable cost me $11 at a battery shop.
#2: the starter was dirty and needed a good cleaning. Oily grime is not something starters like to have in them. Brake cleaner is a good thing to use, just don't get much of it on painted surfaces because it does melt paint.
#3: the small terminal on the starter solenoid was loose. It has a metal speed nut that I tightened up with my vise grips. This wire goes to the ignition and it is what activates the solenoid to magnetically pull the plunger, this shoves the starter drive gear into the flywheel to spin the engine.
All of these things combined can cause this problem, or any of them separately. It can also be the ignition module or the fuel pump or fuel pressure regulator. But on my 99 5.7 vortec Burb, I fixed these 3 things that I found, and fixed the hot no--start issue.
My Burb is stock, but I've always used a larger cold cranking amperage battery than the catalog calls for. That's something that 35+ years of experience with cars and trucks in the gulf coast heat and humidity has taught me; buy the best battery that will fit.

I checked the connections and everything seems to be good. I will report back swapping out the ICM.

 

[luconi]

Yep sounds like the pump, time to check fuel pressure.

I'm leaning into that it is not a fuel pressure issue. I just checked the fuel pressure hot and cold and it would pop up to 60 psi and run at around 55psi. Also the Delphi MPFI spider is new so i can rule out the FPR since it was part of the kit.

could be fuel pump going. I had similar issue. Only when hot summer temps above 80 and engine hot I would have hard starts and occasionally have cutout in rpm range. Cold start and warmup runs like a top.

Turned out I needed a new Ignition control module. You can see the heat mark on the original one that lasted 210k miles. Make sure you use the paste it comes with or some computer CPU thermal paste.

You must be registered for see images attach

I am going to check this. thanks!

Check all your connections and terminals. I had this issue early this year, and it was fixed by 3 things.
#1: the longer positive cable (the one that goes across the fan shroud and over to the back of the computer)was corroded where I couldn't see it. This is a common problem on the vortecs. This cable is expensive and hard to find at the parts store, but if you have access to a shop that can make cables, they can make you one. Be sure that it's 4 gauge copper cable, and the ends are properly installed. This cable cost me $11 at a battery shop.
#2: the starter was dirty and needed a good cleaning. Oily grime is not something starters like to have in them. Brake cleaner is a good thing to use, just don't get much of it on painted surfaces because it does melt paint.
#3: the small terminal on the starter solenoid was loose. It has a metal speed nut that I tightened up with my vise grips. This wire goes to the ignition and it is what activates the solenoid to magnetically pull the plunger, this shoves the starter drive gear into the flywheel to spin the engine.
All of these things combined can cause this problem, or any of them separately. It can also be the ignition module or the fuel pump or fuel pressure regulator. But on my 99 5.7 vortec Burb, I fixed these 3 things that I found, and fixed the hot no--start issue.
My Burb is stock, but I've always used a larger cold cranking amperage battery than the catalog calls for. That's something that 35+ years of experience with cars and trucks in the gulf coast heat and humidity has taught me; buy the best battery that will fit.

I checked the connections and everything seems to be good. I will report back swapping out the ICM.

 

[stutaeng]

Don't rule out "new" parts, as they can also fail. Yes, not likely, but can't rule it out until you check. Did the fuel pressure hold steady with key on the run position, engine off?

Gotta check all the basics. Checking for injector pulse at that big connector on top is easy enough and that will rule out crank sensor. ICM would also be culprit, but not likely if you are getting spark. Can't remember if you stated spark was checked already.

 

[gabe_97]

hello everyone, i also have this issue. trucks starts right away when its cold but really struggles when we started getting warmer weather. also noticed that after starting when its warm theres a pretty loud ringing/whine while its running. i asked around thinking it was the fuel pump but everyone said it was probably just the idler pulley or a bearing in one of the pulleys. unfortunately cant put a video in but im almost certain its the fuel pump after reading through here

 

[HotWheelsBurban]

I was having a similar problem with the Burb ( 99 C1500, 5.7) where if it was sitting more than an hour or so, I'd have to hold the key in Start for a few more seconds. When it was in the shop getting the oil pressure sending unit replaced, it wouldn't start at all when they went to move it out of the bay. New battery and starter got it going again, and made me realize how much stronger the new starter sounds.