HOW TO IDENTIFY THE CAUSE OF SPARK KNOCK ON A USED ENGINE
Used engines offer affordable replacement options when a car’s original engine goes south. However, they’re not perfect, especially the many used engines for sale listed on auctions. Sometimes, you might experience problems with a used engine – they are used, after all. And no amount of testing by the supplier is going to be able to identify every single problem that might arise. One issue you might struggle with is spark knock after replacing a car’s engine. Here’s a few handy tips to help you diagnose the problem of a spark knock on a used engine.
Look for a Simple Answer
Spark knock on a used engine can be caused by a variety of different things, ranging from the easily fixable to those requiring a lot of time and effort on your part. Start with the simplest – the EGR valve. The EGR valve (and the EGR system as a whole) is the most common culprit when there’s a problem with spark (fire). The exhaust gas recirculation valve (EGR) is part of the emissions system, but if it gets gummed up, sticks closed or has a gasket failure, some strange things can happen, including spark knock. Test the valve and see if it’s malfunctioning. If so, replace it and clean the system (make sure you replace the valve gasket as well), and you should be good to go.
Fuel Problems
Spark knock can also be caused by fuel issues. Most notably, if your customer is driving a higher performance vehicle but only putting in low-octane fuel, spark knock can result. The problem here is the octane in the fuel. Another fuel-related issue is if the engine is running “lean”. That is, it’s getting too much air and not enough fuel for combustion. This is the opposite of running rich, and will require that you dig into the fuel injection system to determine the cause (a clogged injector is the primary problem, but there are other issues, including leaking fuel rails).
Carbon, Carbon, Carbon
Carbon deposits are the bane of good engine operation. While carbon deposits are more common in higher mileage vehicles, they can show up in those with moderate mileage as well. Carbon that builds up on the piston crowns and within the combustion chambers will cause spark knock. The best option here is to clean the carbon off thoroughly (this is generally a job that must be done by hand, though a “top end engine cleaner” can also work if the deposits are not severe).
Finally, spark knock on a used engine isn’t caused by the need for a new timing belt, though it can be caused if the belt slips and the cam jumps ahead by a tooth.
