Q: I have a well-maintained 1998 Toyota 4Runner Limited with 239,000 miles. The truck has been awesome, no more than normal maintenance issues. The problem is one of the lifters is knocking. I hear it in the cabin and can isolate the noise from the back of the driver’s side valve cover. Mechanics want to rebuild the engine, of course, but I tried Lucas fuel additive, which made the knock go away. Is this an issue I need to be concerned about? I love having no car payments, so I am willing to put a little money into it.
A: There’s an interesting contrast in your question. A fuel injector additive should not affect a lifter knock. A noisy lifter is a caused by mechanical wear and/or a lack of oil pressure pumping the hydraulic lifter up to eliminate the clearance between lifter and valve train.
So what else could be causing the noise? Injector cleaner would tend to help reduce noise from CCDI — combustion chamber deposit interference. This knocking sound is due to carbon buildup on the piston crown and the combustion chamber roof causing a very slight physical interference between piston and chamber roof at startup. It usually only lasts until heat is generated in the components, expanding the clearance slightly and eliminating the nonharmful knock. Injector cleaner would also help reduce the audible clicking noise from a noisy fuel injector. Either way, periodic use of a decarbonizing/injector-cleaning fuel additive is good maintenance.
If the knock is from a lifter, you could try this: With the engine warm, remove the valve cover on that side and pour Sea Foam directly onto the rocker arm/lifter. Add half the can to the oil. Let it sit overnight and see if this treatment cleans the lifter’s hydraulics enough to restore oil pressure and stop the noise.
Q: I have a 2002 Saturn. For a few weeks now, the “service engine soon” light has been on. My owner’s manual says to reinstall the gas cap, which I tried several times with no effect. I understand from the book that it may be an emission control system malfunction, which sounds very serious. Since Saturn has gone out of business, should I take my car to a service provider to check the vehicle?
A: Yes, take your vehicle to a GM dealer or independent shop. They will connect a scan tool to the diagnostic link on your Saturn and determine which specific DTC fault code triggered the light. There are hundreds of DTCs that can be recorded and downloaded for diagnostics. You won’t know whether it’s minor or serious until you check. If the vehicle runs well, it’s more likely not a serious issue.