View Full Version : Rebuilt 5.7: Pinging and Piston Slap

10-16-09, 10:14 PM
I finally had my 5.7 rebuilt in March. Ever since, the engine pings, especially when the car is cold, whenever light acceleration is applied. I have taken it back to the mechanic who did the rebuild, as it is still under warranty, but he says that everything seems fine. Recently, the problem has progressed so that it pings all the time, regardless of what octane fuel I put in, or whether it is Ethanol free or not. It pings whenever light to moderate acceleration occurs, like holding speed going up a slight hill.

I took it to my mechanic, and he said that's all he can hear is a little piston slap, which he says is normal. I even drove it with the engine pinging, with him with me, and he claimed he couldn't hear the noise. So he has said theres nothing he can do since he can't identify the problem. He also tried blaming the problem on a bad fuel pump, which I have replaced, and now on the transmission.

I am fed up getting the runaround. I want to know what I have to do to get this dealt with. I should think that a newly rebuilt engine should not have either pinging or piston slap, and I want to know what steps to take to deal with the problem, especially while the engine is in warranty. I would just as soon not have him work on the engine again if he can't diagnose something so simple, but I have already doled out a significant amount of money getting the engine rebuilt.

10-21-09, 07:11 AM
It's been a long time since I heard an engine ping. Maybe I'm going deaf like your mechanic. I have mistaken body squeaks and exhaust leaks for pinging in the past. Are you positive it isn't an exhaust leak that is only noticeable under pressure like part throttle or lugging up a hill? A rebuilt engine should definitely not have piston slap unless it was a glaze breaking re-ring job. You should learn to adjust the timing yourself so you don't have to depend on paying somebody for this simple procedure. If you play with the timing you should be able to get rid of the pinging. I don't know if your distributor is stock or what. Is your car still computer controlled TBI? It may be the knock sensor or the incorrect knock sensor for the 350. I'm not sure what engine was in the 90 Broughm because they changed engines every couple years during that time. If it came with the 350 then it should have the correct knock sensor and distributer.

10-25-09, 01:39 AM
Your car has the Chevrolet LO5 350 engine.

Piston Slap is an assembly problem, and indicates that the cylinder bore is too wide, which is allowing the piston to jiggle back and fourth in the cylinder. As the engine warms up, the metal expands and the bore gets tighter, which prevents the piston from slapping. To repair the problem, the engine will have to be disassembled and any bores that are out of specification will have to be re-bored to fit an over sized piston, or re-bored and sleeved to fit the stock sized piston. But piston slap is not overly harmful to the engine, and does not need immediate correction; it's just annoying.

Engine ping is caused by improper timing, too low octane fuel, or high altitude driving. Rebuilding the engine should not have changed it's octane requirements. The timing could have been set incorrectly when the engine was reassembled. Your, car's MAP sensor doubles as a Barometric sensor, to gauge to operating altitude. If the MAP was damaged, then the BARO sensor cannot get a reading of the vehicles hight above sea level, and the computer will operate the engine incorrectly based on default settings.