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

[Astro14]

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

Every modern engine* has carbon on top of the pistons. FI isn’t magical. Depending on how the engine is operated, excess carbon could easily build up - it’s already present.

*Well, every one that I have borescoped. That includes a variety, but not all.

 

[John105]

Every modern engine* has carbon on top of the pistons. FI isn’t magical. Depending on how the engine is operated, excess carbon could easily build up - it’s already present.

*Well, every one that I have borescoped. That includes a variety, but not all.

Example, with DI flooring the vehicle, driving on the highway, pouring Techron in the tank, these do nothing at all for the intake valves which are likely caked with carbon from ordinary use.

Imho it makes a huge difference if one owns, or leases, a vehicle. Since the latter is so prevalent today, a lot of advice comes from that standpoint imho.

 

[Astro14]

Example, with DI flooring the vehicle, driving on the highway, pouring Techron in the tank, these do nothing at all for the intake valves which are likely caked with carbon from ordinary use.

Imho it makes a huge difference if one owns, or leases, a vehicle. Since the latter is so prevalent today, a lot of advice comes from that standpoint imho.

That is true about intake valves. So, if the problem is deposits on those valves, then, sure, the “Italian tuneup” won’t help.

In those cases, a proper valve cleaning is the only remedy.

But I am not certain what afflicts the OP’s car - and it costs little to take it out and floor it.

 

[Jetronic]

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?

The car compensates for knocking, but that doesn't mean you won't get any knock. The way this works is, when knock is detected, ignition timing gets reduced by quite a lot, and then gradually advanced again until knocking starts again, and the cycle repeats.

 

[Jetronic]

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.

gdi are inherently less susceptible to classic knocking as the fuel being injected into the cylinder means the charge gets significantly cooled down. port injection, not so much, most fuel has evaporated in the intake already. This also adds power, as you only need to suck (or push) in air and not a mixture so you can get more in. But the downside is well known: fuel dilution is more likely, and another type knock can occur: Low Speed Pre-Ignition.

 

[Newhart111]

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.

Ok, I wonder if an air / vacuum leak on one of my hoses can be my problem? I mentioned earlier that my knocking returned after changing my ignition coils. In order to change my rear plugs, I had to remove my intake plenum and all the hoses attached to it. Also I had to remove the brake booster hose. I notice that one came off easily without having to open the clamp with pliers. Also, the hose from the PVC valve to the intake plenum had some small cracks on the ends due to being hardened. I kept the same hose because they want $50 for the insulated hose. I also re-used the same gaskets on the intake plenum because I changed them on my first spark plug change and they looked good. I wonder if any of those could be it? I’ll have to go through all the hose connections now and replace anything suspect.

I don’t think my problem is carbon buildup because like I said, the knocking (with premium gas) started right after I changed my ignition coils. With regular it always knocked. That might be another problem too I’ve always had.

 

[Newhart111]

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

I will do that when I get a chance.

 

[Newhart111]

gdi are inherently less susceptible to classic knocking as the fuel being injected into the cylinder means the charge gets significantly cooled down. port injection, not so much, most fuel has evaporated in the intake already. This also adds power, as you only need to suck (or push) in air and not a mixture so you can get more in. But the downside is well known: fuel dilution is more likely, and another type knock can occur: Low Speed Pre-Ignition.

When you say fuel dilution, do you refer to the ethanol they are adding to our fuel? Or that they may be diluting it with something else?

I only go to one gas station because so many sell crappy fuel as premium. I can tell by how my car runs. Even in this one gas station, I can tell they get delivery of bad gasoline from time to time. When they do, my car runs a little worse until they run out of that gas and get a new delivery. Sometimes that gas will cause my car to knock.

 

[kschachn]

Ok, I wonder if an air / vacuum leak on one of my hoses can be my problem? I mentioned earlier that my knocking returned after changing my ignition coils. In order to change my rear plugs, I had to remove my intake plenum and all the hoses attached to it. Also I had to remove the brake booster hose. I notice that one came off easily without having to open the clamp with pliers. Also, the hose from the PVC valve to the intake plenum had some small cracks on the ends due to being hardened. I kept the same hose because they want $50 for the insulated hose. I also re-used the same gaskets on the intake plenum because I changed them on my first spark plug change and they looked good. I wonder if any of those could be it? I’ll have to got through all the hose connections now and replace anything suspect.

I don’t think my problem is carbon buildup because like I said, the knocking (with premium gas) started right after I changed my ignition coils. With regular it always knocked. That might be another problem too I’ve always had.

You're compiling an impressive list of potential but previously undisclosed problems.

 

[Astro14]

It would be helpful, to those still interested in trying to help, if you told us everything you did up front, instead of dribbling out details in subsequent posts. You may not think the facts are relevant but clearly, they are.

OK, first you never reuse gaskets.

That is the worst possible kind of fix, because you didn’t actually fix it and there’s a very good chance you introduced the vacuum leak there. You get to do that job over again, with proper, new, gaskets.

Next, you don’t put cracked hoses back on, that’s just as bad as reusing gaskets, and you probably introduced the leak there.

Finally, fuel dilution refers to what happens to the oil when it gets fuel in it - either wash down from a gasoline direct injected engine, or an engine that’s running incorrectly.

 

[Exhaustgases]

Sounds like this is a Hyundai or Toyota ready to poke some holes in the block !

 

[Newhart111]

It would be helpful, to those still interested in trying to help, if you told us everything you did up front, instead of dribbling out details in subsequent posts. You may not think the facts are relevant but clearly, they are.

OK, first you never reuse gaskets.

That is the worst possible kind of fix, because you didn’t actually fix it and there’s a very good chance you introduced the vacuum leak there. You get to do that job over again, with proper, new, gaskets.

Next, you don’t put cracked hoses back on, that’s just as bad as reusing gaskets, and you probably introduced the leak there.

Finally, fuel dilution refers to what happens to the oil when it gets fuel in it - either wash down from a gasoline direct injected engine, or an engine that’s running incorrectly.

I’ve mentioned everything - I changed all my ignition coils and regapped the plugs, but to get to the rear ones you have to remove the air intake plenum.



I understand w the grommets /gaskets but nowadays I’m barely scraping by and thought I could save on the ones on the plenum since they look good - not compressed. Also the hose didn’t look too bad - just some tiny cracks which I didn’t think would cause a problem. I’d say the hardening on the ends is more of a concern. Since I have the knocking I may end up getting the plenum gaskets and installing them. It’s fairly easy.

I didn’t get any knocking this morning driving up the hill and I haven’t done anything.

 

[Astro14]

I’ve mentioned everything - I changed all my ignition coils and regapped the plugs, but to get to the rear ones you have to remove the air intake plenum.



I understand w the grommets /gaskets but nowadays I’m barely scraping by and thought I could save on the ones on the plenum since they look good - not compressed. Also the hose didn’t look too bad - just some tiny cracks which I didn’t think would cause a problem. I’d say the hardening on the ends is more of a concern. Since I have the knocking I may end up getting the plenum gaskets and installing them. It’s fairly easy.

I didn’t get any knocking this morning driving up the hill and I haven’t done anything.

“Up front” means in the first post.

You didn’t get all the details, like coil change, plenum gasket, and others, until much later in your thread.

 

[Newhart111]

“Up front” means in the first post.

You didn’t get all the details, like coil change, plenum gasket, and others, until much later in your thread.

I see. My apologies.

 

[Newhart111]

Update on this issue:

So I went back and changed the air intake plenum gaskets, throttle body gaskets. Changed some hoses that hardened or had little cracks on the end - hose from PVC valve to intake plenum and temperature sensor to intake plenum. I also put zip ties on the ends.

Wow what a difference. Knocking is gone going uphill. Car is much more responsive and feels like I have more power and torque. Car hasn’t felt this good in years.

I thought I could reuse the gaskets because they are not flat gaskets; they’re pretty tall and stick out quite a bit -

That’s the old ones. However if you compare the new ones, they have a sharp ridge. These are rounded out. I didn’t think that would make a difference but it made a huge difference. It was the same case w throttle body gasket. I also cleaned where it seals really well this time.