LS3 Hot start issue

Vipergts662

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For about a year and a half the engine when heat soaked after a drive has a good knock like a diesel. After the initial start everything is fine on a cold start it sounds like a 6.2 liter V8 should. I have also had blackstone do an oil analysis after every change with the latest analysis coming back above average for an LS3 with 33,5XX miles from a wear standpoint it is in good shape.

Interestingly enough another guy with an SS in town is having a similar issue and has taken the car to two different dealers. The first dealer looked at the car at least five times and even flew down an engineer from Michigan to look at it with his analysis being its normal for an LS3. The other dealer has replaced his fuel injectors twice and three months after the last replacement the issue is coming back. I took my car to the first dealer last week to document the car had been looked at basically knowing what they were going to say. My angle is if the engine craps out before the power train warranty expires in the next two years I have it on record I took it in with them giving it a clean bill of health. BTW car is bone stock outside of the wheels and 6 pot brembos on the front, I have also added one of the DEI insulation blankets to the starter to minimize the infamous starter heat soak the LS3 is known for.

Is it normal for an engine to knock like that on a hot start and what can I do from my end to try and chase down this issue? Of all the different engine configurations and brands I have had this is the only one that behaves like this. Has anyone ever heard of this being normal for an LS3 the engineer calls it an "echo".

Thanks,

Andy
 

ScarFace88

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My gut suspicion is something to do with the valvetrain where the lifters aren't pumping up or something like that. What oil are you running?
 

Vipergts662

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Castrol Edge 5W-30, fuel comes from chevron, shell and sunoco 93 octane and I use techron maybe two or three times a year.

Here is the latest oil analysis the wear really cleaned up between 22-27k miles. If the injectors were leaking like the one dealer thinks wouldn't you expect to see some fuel in the oil?
 

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73GMCSprint

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Get a mechanic's stethoscope and see if you tell exactly where on the engine the noise is coming from. That will greatly narrow down what it is. There are many things it could be, but probably not a bad bearing; that should make noise whether the engine is hot or cold.
Could be a lifter going flat as the oil gets thinner with heat, or an exhaust leak, or even a cracked flywheel, among other things.
 

Spectre

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I'm wondering if you're having heat soak issues with the injectors. That wasn't an uncommon cause of vapor lock and knocking on a hot start with 80s fuel injection and it continues to show up as a cause every so often even these days.

Could you possibly insulate your injectors (after cleaning/flow benching) and fuel rails and see if the problem goes away?
 

Vipergts662

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That is an idea, the fuel rails would be easy to insulate I need to see what would be required to insulate the injectors.

This is a short interesting read, my commute is 20 miles each way when I drive it to work the rest of the time I drive it within 10 miles of the house doing errands and running the kids around.....


"3. Heat Soak
When the engine is shut off, the injectors undergo heat soak. Fuel residue evaporates in the injector nozzles, leaving the waxy olefins behind. Because the engine is off, there is no cooling airflow moving through the ports and no fuel flowing through the injectors to wash it away, so heat bakes the olefins into hard varnish deposits. Over time, these deposits can build up and clog the injectors. A vehicle may have low mileage, but short drive cycles and increased heat soaks can clog the injector.

Since the formation of these deposits is a normal consequence of engine operation, detergents are added to gasoline to help keep the injectors clean. But if a vehicle is used primarily for short-trip driving, the deposits may build up faster than the detergents can wash them away. On four-cylinder engines, the No. 2 and No. 3 injectors are in the hottest location and tend to clog up faster than the end injectors on cylinders No. 1 and No. 4. The same applies to the injectors in the middle cylinders in six- and eight-cylinder engines. The hotter the location, the more vulnerable the injector is to clogging from heat soak. Throttle body injectors are less vulnerable to heat soak because of their location high above the intake manifold plenum.

Heat soak can affect direct-injection injectors due to their placement in the head. Even with the higher pressures, the orifices can become clogged over time."
 

Vipergts662

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I wrapped the drivers side fuel rail in thermo tape and the passenger side that has the coolant lines which lay on top of the fuel rail with left other DEI starter blanket and enclosed it with more thermo tape. The injectors are doable with starter blanket scraps but since they are sitting in a massive hunk of hot metal wouldn't they heat soak from their chamber?

I am taking my temp gun with me to work in the morning to see what the temps look like after driving for 20 miles, I found a few videos that show the fuel rails on the LS3 around 160° with no insulation I am hoping for something lower than that.

Thank you Spectre for the idea hopefully it minimizes the issue.
 

Spectre

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I wrapped the drivers side fuel rail in thermo tape and the passenger side that has the coolant lines which lay on top of the fuel rail with left other DEI starter blanket and enclosed it with more thermo tape. The injectors are doable with starter blanket scraps but since they are sitting in a massive hunk of hot metal wouldn't they heat soak from their chamber?

I am taking my temp gun with me to work in the morning to see what the temps look like after driving for 20 miles, I found a few videos that show the fuel rails on the LS3 around 160° with no insulation I am hoping for something lower than that.

Thank you Spectre for the idea hopefully it minimizes the issue.
You can get some heat shield tubing to go over each injector but you generally have to take the injectors and rail off to fit it. Yes, they do sit in the intake manifold (isn't the one on the LS3 plastic?) but what you want to do is keep the heat from getting to the injectors from any angle but one, the bottom. If the fuel cokes at the tip of the injector, that's the easiest point for the fuel to blow the residue off of at your next restart. If it cokes up in the body of the injector, it can take a lot longer for the residue to wash off/be powered out. Also, the less surface area exposed to heat, the slower the injectors, rail and fuel will heat up.

Some modern vehicles avoid heat soak issues by allowing their main cooling fans to fire up periodically with the engine off until it cools down (I do this myself when doing electric fan conversions because it's a good idea). Older vehicles with mechanical cooling fans would sometimes have an auxiliary electric fan just to cool the injectors by blowing air through the vee or across the injector bank/fuel rail.


Here's one from a 4.9L I6 powered Ford F-150 - this one was needed because the 4.9L does not have a crossflow head and both intake and exhaust are on the passenger side. The exhaust being right next to the injectors tended to make it a bit warm...

These were often of dubious effectiveness, but some were actually worthwhile - the OEM injector cooling fan went away with advances in heat shielding, injector construction (the change from metal to plastic bodies) and additional engineering improvements not least of which were electric fans that ran on after shutdown. :p However, in some troublesome individual cases, people have resurrected the injector cooling fan idea with modern technology and found it can help. Lots of ways to do this.
 

Vipergts662

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Initial findings show a 20° drop, I misspoke last night I wrapped the coolant lines with the blanket and thermo tape not the passenger side fuel rail. It still started rough today. I will take the extra material I have and wrap the injectors and the passenger side rail as well and see what happens.
 

Spectre

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You may have to have the injectors cleaned of existing residue then reinstall them with insulation to get results, FYI.
 
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