Diagnosing And Fixing A Misfire In A High-Mileage LS Engine

A few weeks ago, we were on the market for a new tow vehicle. Of course, we had a few stipulations that needed to be met while hunting for the perfect tow rig. We wanted it to be a Chevrolet 2500, LS-powered, and within our budget. After looking at Facebook’s Marketplace for a few weeks for a truck, we changed directions slightly. Used truck prices are at an all-time high, leaving us searching for another solution. 

After digging around for a new tow rig option, we realized that GM produced Suburbans and Yukons from 2000-2014 in 3/4-ton form. These vehicles were available with eight-lug axles, a 14-bolt rearend, and either a 6.0-liter LS or the 8.1-liter big-block making it the perfect toy hauler. Soon we found a 2008 4×4 Suburban with a little over 100,000 miles on the 6.0-liter engine and 6l90E transmission. However, there was one issue. The check engine light on the dash was illuminated. However, we were confident that the vehicle could be fixed quickly, so we struck a deal with the owner.

6.0-liter L

Just your basic high-milage 6.0-liter with a common misfire.

On the two-hour road trip back home, the Suburban ran great on the highway. However, when we pulled up in the driveway, the 6.0-liter engine idled somewhat erratically, and the service StabiliTrak light illuminated the issue with the check engine light. So we plugged in our SCT X4 tuner to see the problem and read the codes. The tuner quickly told us we had a P0301, a misfire in cylinder number one.

Burnt Plug Wires

Burnt plug wires, like in this image, are a common issue with misfires. However, that was not the case with our Suburban.

Misfire Culprits

Misfires on a high-mileage LS are not uncommon and are usually a simple fix. However, we wanted to check and find the issue before throwing parts at the engine. So, with the hood popped, we immediately looked at cylinder one because that’s where the problem lies. Upon further inspection, we noticed that this cylinder already had a new coil and new plug wires all the way around. This certainly got our attention because 80 percent of the time, a misfire on an LS will be because of bad spark plugs, plug wires, or a bad coil. 

Since the engine had cooled off, we decided to check for other issues that could cause a misfire. Items like a collapsed lifter, weak valve spring, burnt valve, and clogged fuel injectors can all be an issue regarding a misfire. However, we knew it wasn’t a lifter issue because there was no valvetrain noise. So we started with a compression test on each cylinder. Forutanly, all of the cylinders checked out, meaning we were in the clear, eliminating the chance of bad piston rings or a burnt valve. 


SCT’s X4 is the perfect tool for tuning, reading, and data logging data on most modern-day OBD-II-equipped vehicles.

At this point, we were scratching our heads just a bit and decided to fire up the Suburban with the spark plug removed on the number one coil to see if it ran rougher. Much to our surprise, it did not, as it made no difference if it was hooked up. This told us we had an ignition coil problem, even with the new coil. So, we switched the number one coil with the number three coil and cleared the P0301 code. 

After we drove the Suburban around for a bit, the check engine light illuminated again, but the code was different this time. Instead of the P0301, we got a P0303, meaning the issue was now in cylinder number three. We had found our problem. 

After diagnosing the issue, we ordered a set of Performance Distributor's Sultans Of Spark coils and Liverwires.

Since one coil had already gone bad, we also decided to replace all the coils, spark plugs, and plug wires. And instead of going to a local auto parts store and buying the house brand, we reached out to Performance Distributors for a set of Sultan Of Spark (SOS) coils, and LiveWires spark plug wires. 

Performance Distributors offers coils for every make and model LS engine, including the Gen-III, Gen-IV, and Gen-V LS and LT platforms. And while that’s good to know, it’s the coil’s performance that’s important. 

SOS Coils

The SOS coils might look just like the factory units, but it’s the inside that sets these high-powered units apart.

The SOS coils are packed with performance offering more voltage than the stock coil packs. With 7,000 more volts per coil, you can expect better throttle response, quicker starting, and a smoother idle. In fact, these coils are so hot that you can open the plug gap up to .065 inch for a more significant spark, giving your engine an increased burn of the fuel mixture for better performance and fuel efficiency. What’s even more impressive is the SOS coil price point. A pack of eight coils can be purchased from Performance Distributor’s website for $399. This is a steal when you consider a far less superior coil for a parts house is about the same price, in most cases. 

Sultans Of Spark Coils

  • More voltage output over stock
  • Expand plug gaps to .065 inch
  • Increases engine performance and efficiency
  • Installs In OEM location
  • Compatible w/ flash-tuning devices & programmers

While ordering the coils, it only made sense to purchase a set of Performance Distributor’s Livewires as well. Livewires are high-quality, low-resistance spark plug wires designed to deliver all of the spark energy from the coil to the plugs making them the perfect match with the SOS coils. 

Livewires are manufactured with high-temperature sleeving that protects the plug wires from extreme heat. The unique sleeving offers heat protection up to 1,400 degrees Fahrenheit. Inside the sleeve is an 8mm spiral core wire insulated with a silicone jacket. This plug wire is extremely low resistance for optimum spark travel, and there is no electronic interference with the radio or electronic fuel injection. 



Livewires are available for numerous applications and in a variety of colors.

  • High-temperature rating
  • Numbered for each cylinder
  • No radio interference
  • Low resistance value
  • All sets are ready to install
  • Available in multiple colors

After we had the SOS coils and Livewires in our hands, it was time to fix the Suburban once and for all. Well, on the ignition side, at least. The first order of business was to remove the old plug wires and coil packs from the engine. This is a simple task that only requires an 8mm socket. With the coils and plug wires out of the way, we turned our attention to the new components. Performance Distributors includes dielectric grease, a viscous, non-conductive, waterproof lubricant used to protect electrical connections from corrosion and dirt. You apply a dab on each connection to protect the terminals on the coils and plug wires. 

Dielectic Grease

Dielectric grease is always good when working with coils and plug wires.

After we had the coils and plug wires greased up, we began the installation. First, we mounted the SOS coils on factory GM brackets and plugged the coil packs into the factory harness. Then we slid the Livewires onto the spark plugs before connecting them to the SOS coils. Be sure to take your time here and ensure a good connection. That was it! The process only took about 20 minutes, and we were ready to fire up the Suburban. 

LS coil installation

Installing a new set of coils and plug wires on an LS is a relatively simple task.

Once again, we grabbed the SCT X4 controller and cleared out the misfire code before starting the 6.0-liter. Then, with the check engine light off, we fired up the Suburban, confident that we had fixed the problem. The engine started immediately and idled as smooth as butter. Not only had we resolved the misfire issue, but the service StabiliTrak light was also gone killing two birds with one stone. 

LS coils and plug wires

We got the Suburban running like new again with the help of Performance Distributors and SCT.

We have put about 2,000 miles on the Suburban since swapping out the coils and plug wires with zero issues. And while we’re sure that we will have more problems with our Suburban down the road, we are confident that it will not be with the ignition system, thanks to Performance Distributors. 

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About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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