Rattling Sound when engine under load or uphill


I have a 96 GMC yukon with 160k miles and I hear a rattling sound whenever I go uphill or accellerate quickly (i.e. getting on to the highway). These are the only times it happens. I can rev the engine in park or neutral and cannot hear the rattling. Anyone know what’s causing this?


160K? Congratulations! You must take really good care of this vehicle.

It’s called “Knocking,” or “Pinging,” depending upon whom you ask. Also known as pre-ignition, I believe. It could be caused by incorrect octane rating (too low) of gasoline, incorrect ignition timing, deposits on the cylinder heads and/or pistons, or a malfunctioning knock sensor.

It will only happen under load, which is why you don’t hear it when you rev the engine in neutral.

Thanks for the reply. Yes, she’s my pride and joy. I’ll check my timing, and add a fuel system cleaner and see how that goes. And maybe its time to switch to the good stuff as far as gasoline goes. I can hear my wallet moaning at the thought.

Thanks again for the info.

Agree with the previous posting.

My 05 Wrangler 4.0 with 51K miles, religious maintenance, has pinged when towing our tent trailer uphill since it was new. Regular is the only fuel recommended in the owner’s manual. Premium fuel and downshifting mitigates the pinging some, but not completely. The dealer’s service department did not reckon that this was a significant problem and just said use premium. I’ve read on this site that the 4.0 is an “anvil” and I’m not terribly concerned about it since it performs great under other conditions. Am I right that this is not a big deal if the pinging is not loud? It’s pretty subtle - you only really notice it if you are driving alongside a cut in the hillside.

You might want to try decorbonizing the engine. And it’s easy.

Purchase a can of SeaFoam Engine Tuneup. Remove the vacuum hose from the brake booster. Adapt a hose that fits between the brake booster hose and into the bottom of the can of SeaFoam. Squeeze the hose shut with a pair of pliers. Have someone start the engine and get the RPM"s up to about 2,000. Now slowly loosen the pliers from the hose so the Seafoam is drawn into the engine. The idea is to keep the RPM’s up, and allow the SeaFoam to enter the engine without stalling it.

When all the SeaFoam is sucked out of the can, shut the engine down, and let it sit for a half hour. Restart the engine, and get the RPM’s back up to 2,000 RPM’s until the smoke clears. And it will smoke when doing this!

Do this, and see if it gets rid of the pinging problem.


Thanks. Will try the SeaFoam. Any ideas why this would occur in a new Jeep 4.0 engine? It’s been driven primarily freeway with two round trips to Texas and back to California. Daily short trips in area with extreme temp variation beween Summer and Winter. Near Death Valley

You can also decarbonize parts of the combustion chamber by starting up the hill, slamming the pedal to the floor and shifting to second gear and wringing it out, If you see a cloud of black smoke the problem will go away for a few days. If you do that often, there will be a new motor or car in your future. Everything has drawbacks. Dumb things have more.

You probably have a fault in the EGR system.

Wouldn’t I have a CEL? Thanks.

Not necessarily. A code can be present even with the CEL off. AutoZone, Advance, Checkers, etc. will check the codes for you free.
It’s also possible for the EGR passages to be mostly clogged due to the high mileage and have no CEL.

Try the SeaFoam as mentioned and see if by some chance it may clear up. In some cases the EGR must be removed and the deposits scraped out.