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.
 

Vipergts662

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Some what of an update, one of the guys on the SS forum had a few of us with this problem start the car with the throttle pinned to the floor. When the engine is cold all I heard was the starter ticking when the engine has heat soaked for 20-30 minutes the car started and of course the revs shot up.

I am assuming the car should behave the same when it is hot and cold?
 

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Yes it should behave the same. Namely, it shouldn't start unless the engine is flooded. Pushing the pedal to the floor shuts down the injectors.

I want to know where he's going with this.
 
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Vipergts662

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As do I, one of the guys with this issue is on this third set of injectors and is getting ready for his fourth set. This article showed up a few days ago talking about the Aussie vehicles https://www.caradvice.com.au/768453/holden-commodore-ls3-v8-fuel-injector-dramas/

I have a very hard time believing the entire Australian continent is getting bad fuel along with random pockets in the US that are only destroying the Bosch injectors in the LS3....

If the injectors are leaking could there be enough fuel in the cylinders to cause the rough start hours after the car is shut off?
 

Spectre

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Yes, it's entirely possible that this is the case, where coked fuel is holding one or more of the injectors open. It's rather rare, though, and I've never heard of it happening in a modern car with less than hundreds of thousands of miles on the clock. Remember that when you turn the key, the car pressurizes the rail (or tries to) and then opens the injectors at the appropriate time for the appropriate duration. If you try to start with the pedal matted, the car will still pressurize the rail, it just won't command the injectors to open. If the injectors are sticking open, you will get fuel entering the cylinders without the computer commanding the injectors to open and the car will likely start.

Might be worth finding out what else (if anything) used those same fuel injectors and see if they have the same problems.

That said, I would have the injectors cleaned and flowbenched (off the car with the proper rig) before replacing them. The supermajority of troublesome injectors do not need replacing; however finding places that perform this service is getting harder and harder as the industry moves to simple parts replacement instead of parts servicing.
 

Vipergts662

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Yes, it's entirely possible that this is the case, where coked fuel is holding one or more of the injectors open. It's rather rare, though, and I've never heard of it happening in a modern car with less than hundreds of thousands of miles on the clock. Remember that when you turn the key, the car pressurizes the rail (or tries to) and then opens the injectors at the appropriate time for the appropriate duration. If you try to start with the pedal matted, the car will still pressurize the rail, it just won't command the injectors to open. If the injectors are sticking open, you will get fuel entering the cylinders without the computer commanding the injectors to open and the car will likely start.

Might be worth finding out what else (if anything) used those same fuel injectors and see if they have the same problems.

That said, I would have the injectors cleaned and flowbenched (off the car with the proper rig) before replacing them. The supermajority of troublesome injectors do not need replacing; however finding places that perform this service is getting harder and harder as the industry moves to simple parts replacement instead of parts servicing.
Got any recommendations in Houston? Do performance shops generally do this?

Googling the Bosch part number only shows use in GM LS engines

http://www.showmetheparts.com/bosch-parts/bosch-62647.html
 

Spectre

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Got any recommendations in Houston? Do performance shops generally do this?
Some performance shops do, but the last contact I had in Houston from years and years ago retired recently and closed his shop. Therefore I don't have any personal recommendations but here's some listings (again, not recommendations) from some EFI forums I'm on:

https://www.injectorrx.com/
https://theshophouston.com/
https://injector911.com/

If you want to ship them up here to DFW or plan on coming up here for some reason, Mister Carburetor in Cedar Hill has one of the original Bosch-endorsed cleaning/flowbench machines and I've had good luck with him over the years (and I've posted pics of his rig here on the forum before, I believe.) He's one of the last people in the DFW area that can do this in house.
 

Vipergts662

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We have friends in Flower Mound but we are not planning anything in the near future to head up that way.

I asked a guy in our neighborhood who owns a shop and they clean them in the car "injectors are cleaned in the car and pulse width diagnostic is done via computer . Also you can do fp test and cold soak test as well ."

Worth the 5 minute drive to his shop or better to take them out and cleaned that way?
 

Spectre

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We have friends in Flower Mound but we are not planning anything in the near future to head up that way.

I asked a guy in our neighborhood who owns a shop and they clean them in the car "injectors are cleaned in the car and pulse width diagnostic is done via computer . Also you can do fp test and cold soak test as well ."

Worth the 5 minute drive to his shop or better to take them out and cleaned that way?
Take them out and have them cleaned - part of that is testing them on a flowbench. Here's a video on how this is done:



You cannot tell how well an injector is flowing in situ.
 

Vipergts662

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I will be taking the car over to Powerfab Autosports, they have one of the best LS reps/tuners in Texas with a pretty good following around the country as well to have the injectors looked at and probably talk about some other go fast things, for some reason I miss the blower the XFR had.......
 
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