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What Are You Smoking? GM 4.3L Analyzed

Friday, November 1, 2013

Have you ever had a customer with a dirty environment? Have you ever seen a forklift that uses the GM 4.3L engine? Only if you’re in the forklift business! You may also have had experience with dirt and debris dusting a customer’s engine. Some engines and accessories are more prone to air leaks which can be the killer of any new or remanufactured engine. When an engine is dusted it creates a serious liability for the party that installed the engine. Since topics regarding the GM 4.3L engine have been a huge success I thought I would outline several critical areas that are prone to ingesting dirt and how smoke testing an engine after installation can solve this problem.

What is DUSTED? It is the failure of an engine due to dirt ingestion. When an engine has an air leak on the intake side of the engine it can turn your engine into a vacuum cleaner. Any air leak after the air filter will allow dirt to enter the engine and rapidly wear out the engine’s core components.

What is SMOKE TESTING? It is a smoke diagnostic machine that fills the intake system with pressurized smoke. When performed with the engine off, it is as simple as looking for smoke to find your leaks. Smoke diagnostic machines come in many different makes and models. Ask your local tool guy for a price and opinion as to which machine is best for you.

I know what you’re thinking – “If I need to find an air leak I’ll just spray 17 cans of carb clean, brake clean or ether around the intake areas and listen carefully. I don’t need some fancy machine” Just to remind everyone – the new tier 1,2,3,4,5,6,7,8,9,10 GM 4.3L engines are computer controlled with fancy mixers and throttle bodies that have more areas to seal and leak. The computer also compensates for so many different variables that you may never notice a small leak that could completely destroy your engine.

We have recently worked with a customer who has a large fleet of forklifts that run the GM 4.3L engines. They have several areas in their facility where there is a super fine abrasive powder constantly in the air. By using a smoke tester on several different units we have learned volumes as to where the GM 4.3L engines are capable of ingesting dirt and debris. The following is a list of our findings in no particular order:

  • We have found leaks around the EGR valves across all tier level configurations.
  • Trucks with the big fancy Cyclone Super-Duty - High Velocity – Extra Volume Pre-Cleaners mounted at the top of the overhead guard (OHG) can still have problems. We have found smoke coming out of the taillights, filter sealing surface to OHG and even tapped holes in the side of the OHG that are left open from the factory. Doesn’t it seem strange to have a $4 million dollar pre-cleaner and immediately after that have direct paths to the filter? Remember that most OHG’s are used to channel the air into the filter because this is the highest point away from the ground to intake air.
  • We witnessed air cleaner hoses and PCV connections that were pressed on good and tight but would leak if they were not properly clamped.
  • Here is a good one – a brand new mixer out of the box had loose internal bolts. These are blind holes between the plates that hold the mixer together. It was obviously leaking and smoke came pouring out of the sealing area.
  • The tier 2 o-ring and sleeve that seal the mixer base and throttle body have also been found to leak at the seam. Be sure to replace both the bushing and o-ring after disassembling these items.



  • The tier 3 mixer doesn’t come with the fitting - only a plug on the air horn side. This customer’s technician removed the plug and forgot to move the plug to the open hole on the other side. This completely destroyed a new engine in 24 hours. So remember to re-install the plug when you swap your fittings.
  • This customer also believes that over changing the air filter in harsh environments is a bad idea. He runs an air flow gauge on all of his trucks and feels that some restriction of the filter is actually a good thing. Only when the air flow gauge indicates a restriction will they change the air filter. I cannot confirm this as a best practice but I thought it was interesting to at least mention and could be something for everyone to consider.

Engine failures due to dirt ingestion are easy to diagnose. The cylinder walls will have a ridge or sometimes in severe cases one ridge for each piston ring. When looking at the lower portion of the cylinder bore you will see the exact area where the oil control ring stops. It will look like the cylinder wall has been glass beaded and below the line will be the perfect cross hatch. The other sure sign of dirt ingestion can be found on the valve stems. Swirl like patterns and or wear ridges could be seen on most all of the valve stems. Dirt does not discriminate – once it gets into the manifold it is distributed evenly in each cylinder depending on the manifold design.

Customers find it hard to believe that one simple air leak can completely wipe out a brand new or reman engine. For this reason we are strong advocates of smoke testing all engines after installation. There is no better way to make sure that everything is air tight and that your profit on the job is protected from future dirt ingestion liability.

If you have a customer that is experiencing dirt ingestion failures – consider the smoke tester – you’ll be shocked at what you find. The GM 4.3L engine will be around for many years to come and you are bound to eventually run in to these types of problems. Our job at All Industrial Engine isn’t to just sell reman engines but to assist customers in solving their engine related service problems. We are the specialists – specialist!

If you have any questions regarding this article or any other Tech Talk article please feel free to give me a call at any time – we are always here to help (877) 303-LIFT.

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