Vortec hard start when warm

[luconi]

98' K1500 with a vortec 305.

Truck runs really great. Except I am running into an issue where it's hard starting after it warms up.

It will eventually turn if i tap the throttle only while it's warm.

It fires right up in one turn when it's cold.

I thought it could have been the fuel pressure regulator but I just did a MPFI spider conversion (delphi) 2 months ago so that's all new. Also tried swapping out the engine temp sensor in the intake with a new delphi unit and it still does it.

The distributor and cap is new and was properly adjusted with a scanner tool.
Sparkplugs and wires have 5000 miles on them.

Could it be an issue with the fuel pump itself?

 

[98 Nitro]

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

 

[97K1500Silverado]

98' K1500 with a vortec 305.

Truck runs really great. Except I am running into an issue where it's hard starting after it warms up.

It will eventually turn if i tap the throttle only while it's warm.

It fires right up in one turn when it's cold.

I thought it could have been the fuel pressure regulator but I just did a MPFI spider conversion (delphi) 2 months ago so that's all new. Also tried swapping out the engine temp sensor in the intake with a new delphi unit and it still does it.

The distributor and cap is new and was properly adjusted with a scanner tool.
Sparkplugs and wires have 5000 miles on them.

Could it be an issue with the fuel pump itself?

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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[97K1500Silverado]

FYI - I’m still rocking the original spider injection!

On my 3rd fuel pump. Original died around 100k, replacement died around 170k

 

[HotWheelsBurban]

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.

 

[SUBURBAN5]

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.

Jw what battery are you using? What cca are you buying? Think mine is 750 or 800 have to check though...

 

[HotWheelsBurban]

Jw what battery are you using? What cca are you buying? Think mine is 750 or 800 have to check though...

Duracell 78DT(dual terminal),800 CCA. From Sam's Club, 3 year free replacement warranty. Current one is from April of last year on that warranty. Usually get a little longer than the warranty period on them. We used to have a family owned auto parts store, and I've sold a lot of batteries. You also have to be sure you get a fresh one, they will try to give you an old one just to get rid of it. Ask me how I know this LOL

 

[SUBURBAN5]

Duracell 78DT(dual terminal),800 CCA. From Sam's Club, 3 year free replacement warranty. Current one is from April of last year on that warranty. Usually get a little longer than the warranty period on them. We used to have a family owned auto parts store, and I've sold a lot of batteries. You also have to be sure you get a fresh one, they will try to give you an old one just to get rid of it. Ask me how I know this LOL

Didnt know that. We used to get die hard from Sears and they lasted the longest. Every where else like autozone, oreilly I'm lucky to get 2 yrs. I heard advanced was gonna sell diehard but wasn't sure the quality.. was gonna try optimo but then I heard there quality went down the drain too..

 

[HotWheelsBurban]

Didnt know that. We used to get die hard from Sears and they lasted the longest. Every where else like autozone, oreilly I'm lucky to get 2 yrs. I heard advanced was gonna sell diehard but wasn't sure the quality.. was gonna try optimo but then I heard there quality went down the drain too..

The dual terminal ones don't sell as fast as the regular ones, but we started getting them so we could move a battery between the truck and a mopar I wasn't driving but needed to be able to move when needed. Gives a better place to jump start too, since GM didn't make much space between battery and air cleaner box. Never could afford an Optima but I've heard they're not as good as they used to be. For $200+ that shouldn't be happening.
BTW another reason to get a fresh unit is it's more likely to have most of its original charge. We always charged the batteries we sold, but a lot of places don't.

 

[PlayingWithTBI]

We always charged the batteries we sold, but a lot of places don't.

Yes, plus it's a good idea to throw a trickle charge in it every month or so. If you let the battery get weak and have to jump it, you need to put it on a charger to fully get it up to level. An alternator won't do that, they're only designed to maintain a battery.