What are some of the common issues that can cause knocking (rattling of the engine)?

[Newhart111]

When I first got my car new, I was using premium gasoline because it seemed to run better. It was getting expensive and so I tried using regular gas for a while. However when I did, I noticed that I would get knocking/rattling sounds, especially when I was driving up a hill.

It progressively got worse with regular gas and I would get the rattling sound in even more situations. I learned that engine carbonization can cause this knocking and learned about cleaning it off with Seafoam (through the brake booster hose into the engine). It actually worked! After I did the treatment the engine knocked less and decided to go back to premium gasoline to avoid this happening again.

I haven’t had much problem (for the most part) with knocking ever since. The only time the knocking would come back is when I got bad gasoline. I notice that the gas station I use would get good gasoline for the most part but once in a while get a delivery of a gas that would cause knocking. Once I fill up with a good gas, it would go away. The engine would feel perkier also.

My understanding is that the engine should correct itself for the octane level and prevent knocking. I believe the specification for my car (2016 Lexus ES350) allows for 87 octane but my car doesn’t seem to run well on it. It seems many other cars also do not, judging by how often I hear them knocking/rattling.

Is there a component failure, or a common problem that can prevent my car from working with regular 87 octane gas without knocking? Maybe there is a sensor that can go bad?

 

[Boomer]

I would say that in many ways it depends on the compression ratio of the engine. With a high ratio, there is only so much that pulling the timing can do.

The All Track in my signature is a GDI turbo engine and I feed it only Top Tier premium gas. Runs like a champ on that....climbs local steep hills at speed with nary a ping or rattle.

 

[PontiacHO]

Not sure about any sensor that could be bad but downloading stored codes may help discern that. Fuel octane ratings are allowed a + or - minus variable that is deceiving. 87 octane may only be 84 in reality.

 

[bullwinkle]

Do you do any long drives or full throttle runs (fully warmed up)? The old Italian tune-up is good for keeping the carbon down, that's what the blackish-green cloud of smoke comes from on full acceleration. It's a Toyota at heart, it can take it!

 

[b_b]

I have the same problem with my f150, it has 12:1 compression and it does not like regular fuel. I just run premium and suck it up.

 

[John105]

It’s predetonation. The octane is lower than called for, most likely. However, cars have knock sensors to adjust the timing.

I ran my Maxima 1998-2023 on regular. It knocked all those years. The only time I used premium is when I knew my knock sensor was not functioning (it’s the VQ job where knuckles are necessarily skinned and unpleasant).

The downside? All those years I didn’t achieve the 190/205 in the brochure when using 87.

My .02

 

[Newhart111]

Do you do any long drives or full throttle runs (fully warmed up)? The old Italian tune-up is good for keeping the carbon down, that's what the blackish-green cloud of smoke comes from on full acceleration. It's a Toyota at heart, it can take it!

You know, you may have put your finger on the problem - nowadays I hardly do any long highway runs especially at 70 mph and even at 60 mph I go maybe 10-14 miles.

 

[Newhart111]

It’s predetonation. The octane is lower than called for, most likely. However, cars have knock sensors to adjust the timing.

I ran my Maxima 1998-2023 on regular. It knocked all those years. The only time I used premium is when I knew my knock sensor was not functioning (it’s the VQ job where knuckles are necessarily skinned and unpleasant).

The downside? All those years I didn’t achieve the 190/205 in the brochure when using 87.

My .02

It’s amazing your car lasted so long.

 

[zrxkawboy]

Common causes are carbon buildup, stuck EGR valve (if your car has one), or bad knock sensors.

Also, check your owner's manual to verify the octane requirement.

 

[SHOZ]

They sell E15 gas around here (85 they call it), cheaper than regular and I bet it would fix your knocking.

I had a 1979 4 cyl Mustang that knocked bad under load on regular. That was the year they went to E10 gas in Illinois. Just using E10 fixed that issue.

 

[Newhart111]

Prior to my recent ignition coil change it wasn’t knocking, but now I notice that after the change that it is knocking when going uphill or accelerating hard enough. What can cause that? I’m still using premium.

 

[Newhart111]

Common causes are carbon buildup, stuck EGR valve (if your car has one), or bad knock sensors.

Also, check your owner's manual to verify the octane requirement.

Is it common or possible for knock sensors to go bad? Can you test them?

 

[Astro14]

What does your owner’s manual say about octane?

Most modern engines, in which category I would place yours, have at least two “knock sensors“. If the engine detects knocking, it retards the timing to compensate.

If your engine is knocking, there are two explanations, the first is that the knock sensor is bad, and the second is that the engine has enough junk in it so that the need for timing reduction exceeds the engine’s ability to reduce timing.

 

[zrxkawboy]

Prior to my recent ignition coil change it wasn’t knocking, but now I notice that after the change that it is knocking when going uphill or accelerating hard enough. What can cause that? I’m still using premium.

I don't believe a coil replacement could cause it. I think sometimes after a repair, we are watching/listening more closely, and notice things that maybe we didn't notice before. If your engine is still knocking on premium, I'd suspect a bad knock sensor.

 

[Newhart111]

What does your owner’s manual say about octane?

Most modern engines, in which category I would place yours, have at least two “knock sensors“. If the engine detects knocking, it retards the timing to compensate.

If your engine is knocking, there are two explanations, the first is that the knock sensor is bad, and the second is that the engine has enough junk in it so that the need for timing reduction exceeds the engine’s ability to reduce timing.

I’ll have to look for my manual but pretty sure it included 87 octane.

Are knock sensors known to go bad?

Maybe it’s time to Seafoam my engine again.

 

[SHOZ]

Is it common or possible for knock sensors to go bad? Can you test them?

You can if you can see the timing with OBD. Find the knock sensor and tap on the block while it's running. It should reduce the timing. I'm sure there is some sort of electrical test too.

 

[Kira]

And remember, after everything mentioned here, heat adds to an engine's propensity to knock. It's just another factor.
I was always under the assumption that the retained heat in the carbon buildup contributed to preignition.

On a Ranger forum I follow, a guru claims knock sensors rarely fail.

 

[Astro14]

Knock sensors can go bad, but it is very rare. Much more likely that your engine is carboned up, or has a vacuum leak, or is running hot.

This is not something that can be diagnosed by posting a couple of words on the Internet.

You are going to have to talk to the car via a scan tool, and see where the timing is, and where the fuel trims are, and what other operating conditions exist.

A vacuum leak makes your engine much more susceptible to knocking, because it introduces a lean condition. Your fuel trims will tell you if you’ve got a vacuum leak.

Your timing will tell you if the knock sensor is working.

And finally, no, the temperature gauge on your dashboard does not tell you if your engine is running hot. That is a glorified idiot light, it sits in the middle over a wide range of temperatures. Your scan tool will tell you the actual temperature of the engine.

 

[John105]

Do you do any long drives or full throttle runs (fully warmed up)? The old Italian tune-up is good for keeping the carbon down, that's what the blackish-green cloud of smoke comes from on full acceleration. It's a Toyota at heart, it can take it!

I respectfully disagree. Maybe in the days when vehicles had carburetors. I think this is a myth in 2024.

 

[kschachn]

Not all knocks are the same. Please post a video of what it sounds like.