5.3L hard start when warm

[jrdecat]

Similar but not exact same problem here. Mine started after my LQ4 swap and my vehicle sat for quite a while during the process. I replaced all the sensors at that time. 70% of the time it fires up correctly when cold. The other 30% it will crank and crank and crank without ever starting and the flood clear doesn't work. If you turn and hold the key for a second and then let off, it will fire up perfectly when you try again in a couple seconds. I've checked for leaking injectors and tested FPR and I'm all good there. My fuel pressure does leak down overnight, but I don't want to get into replacing fuel pump and injectors only to find out it doesn't work. I've read a couple threads on here where people have done that.

Let me know when you figure it out, I'll buy you a beer!

 

[Bobsquatch]

Since it's my wife's car, I don't drive it enough catch every thing it's doing. I used the flood clear technique which cut the crank time in half when returning to a warm car after a few minutes. I went to show my wife how but it would not start WOT having been running seconds before. I let off and it fires right up. I repeatedly started it normally (no throttle) and it started and ran perfectly. It was not doing that before, always a long crank when warm so my problem may be intermittent. Feeling more like a leaky injector or two. I will eventually solve this and report my findings. It may be a minute though.

jrdecat, while I also look for information everywhere this thread is for warm start issues and if we ever solve the problems in a useful and common way it will be harder to find if it is diluted by different issues. Not a moderator, just food for thought.

 

[jrdecat]

Since it's my wife's car, I don't drive it enough catch every thing it's doing. I used the flood clear technique which cut the crank time in half when returning to a warm car after a few minutes. I went to show my wife how but it would not start WOT having been running seconds before. I let off and it fires right up. I repeatedly started it normally (no throttle) and it started and ran perfectly. It was not doing that before, always a long crank when warm so my problem may be intermittent. Feeling more like a leaky injector or two. I will eventually solve this and report my findings. It may be a minute though.

jrdecat, while I also look for information everywhere this thread is for warm start issues and if we ever solve the problems in a useful and common way it will be harder to find if it is diluted by different issues. Not a moderator, just food for thought.

Really? We are both having warm start issues.

 

[MassHoe04]

1) Is there any chance factory heat shields are missing between the exhaust header(s) and fuel rail(s)?

I never had the problem, but a lot of Jeep TJ owners with 4.0L experienced "heat soak" when hot.'
Fuel in the fuel rail and/or injectors vaporizes with the high heat sometimes.

Adding shields to the fuel rails to protect them from excess engine heat solved the problem for many of those people.
Jeep 4.0L had a model-specific kit to wrap the fuel rail and injectors.

I didn't see model-specific for the GM models.
Summit has this, which can be cut to fit to cover the exhaust...

Heatshield Products 177004 Heatshield Products Armor Exhaust Heat Shields | Summit Racing

Free Shipping - Heatshield Products Armor Exhaust Heat Shields with qualifying orders of $109. Shop Exhaust Heat Shields at Summit Racing.

www.summitracing.com

2) How is the catalytic converter?
Clogged converters can restrict flow of exhaust gas, which can cause excessive heat to build up in exhaust headers.
I have seen some photos of manifolds glowing cherry red as a result of a clogged cat...

 

[Bobsquatch]

Jrdecat, sorry brother I read your post as a cold start issue. I'll buy the beer!
MassHoe04, my issue is neither heat shield nor catalytic converter related as it runs beautifully once started. The raw fuel smell from the tailpipe screams fuel injectors, particularly since the flood clear method seems helpful. My wife broke her leg so my attention has been diverted but I will post my findings when solved.

 

[Schube]

I've been trying to solve this issue for the last couple years. Mine will shorten the time if I hold down the accelerator during a warm start. I've replaced the fuel pressure regulator, spark plugs, and crank position sensor. I just got a SES light for the downstream O2 sensor so I'm going to replace both this weekend. from what I've read it could be a possible cause. I came across this write up today. https://vehiclecare.in/blaze/why-car-is-hard-to-start-when-warm/ and will be checking/replacing the Coolant Temperature Sensor also.

 

[Schube]

the coolant temp sensor was only $20 so I replaced it. didn't solve my issue. I started disconnecting the fuel rail to check out the injectors and saw fuel in the vacuum line of the pressure regulator. maybe I didn't replace it before but was sure I had. either way this one is bad. getting a new one to try.

 

[Schube]

I replaced the fuel pressure regulator. problem solved!

 

[Bobsquatch]

Well, I replaced all my injectors last weekend. I primed the fuel rail with a few key on... then off, bleeding air from the Schrader valve. Engine starts with an obvious misfire on one or more cylinders. I drive around the block to let it purge any air left in the system. Still missing pretty hard when I parked it. Did a couple more key on... off bleed the air at the Schrader valve, only this time no real fuel pressure. I cranked the engine and it hydrolocked presumably with fuel. I pulled the fuel relay and let it sit. After a good bit, I cranked it and it nearly started. Replaced the fuel pump relay and it fires right away but rattles terribly. I shut it down immediately. Now I don't know if bent a rod or other significant damage or maybe just broke a timing chain guide. I'm not going to run it again until I know as it may be salvageable. Now I just need to figure out where to look first.

Darn it!

 

[afpj]

Iirc iat is part of MAF... might want to redirect fire that direction. Several posts about MAfs tending to crap out around 140k miles.