Rx300 Gas Knock

[bowtie3]

My wife's 2000 RX300 [ 49,000 miles ] has a slight gas gas knock under acceleration. Dealer says it's no problem, maybe bad gas. We always use 93 octane, as recommended by dealer. Since taking it to the dealer for a rear main oil seal fix about a month ago we've tried BP, Citgo, and Shell. It still has a periodic gas knock. Is this a problem with the RX300 or is it something that the dealer can solve? Also, is 93 octane really necessary for the RX300? Any advise on this would really be appreciated. Thanks.

[SKperformance]

lots of discussion on the gas grade in general maintance

[SKperformance]

lots of discussion on the gas grade in general maintance

[SW03ES]

The 3liter V6 is sensitive to the type of gas and it will knock from time to time. Mine knocked once and the dealer told me the same thing. I switched gas brands and it hasn't knocked since.

Just for fun, try going down a grade in gas from 93 to 89 and see what happens with the knock. I've heard some people say that actually going DOWN a grade remedies the intermittant knocking.

[RX in NC]

My wife's 2000 AWD RX300 runs just fine on 89 octane. The only concession I make to the fuel system is to add a bottle of generic fuel injector cleaner to the tank at every oil and filter change. That's been a habit of mine for decades across many different vehicles, and I've never had one knock or ping.

Keep in mind that different areas of the country require different fuel formulas at different times of the year. You might have to do some experimenting before you find a solution that works for you.

You may also want to pull a couple of your more easily-accessible spark plugs (the three front ones) and ensure that you indeed have the iridium spark plugs from either NGK or Nippondenso as called for in your owner's manual. They truly are a requirement for this engine to operate at peak efficiency, and they are rated to go 120,000 miles in this vehicle. At about $10 apiece from NAPA or a similar auto parts store, they're expensive but mandatory.

[SW03ES]

Yeah theres really no reason to put 93 octane in the car, thats true of all Lexus engines.

[mikey00]

My wife's 2000 RX300 [ 49,000 miles ] has a slight gas gas knock under acceleration.  Dealer says it's no problem, maybe bad gas.  We always use 93 octane, as recommended by dealer.  Since taking it to the dealer for a rear main oil seal fix about a month ago we've tried BP, Citgo, and Shell.  It still has a periodic gas knock.  Is this a problem with the RX300 or is it something that the dealer can solve?  Also, is 93 octane really necessary for the RX300?  Any advise on this would really be appreciated.  Thanks.

←

Both my former 2000 RX and current 2001 RX both run fine on regular 87 octane. Only time I didn't use 87 was for a small trial period. If you find your RX doesn't run as well on 87 then you have some kind of problem that the higher octane is masking. Get it fixed.

[92Lex]

Octane doesn't mask any problems. Your car was designed to run on premium...Lexus doesn't make money off of that.

[mikey00]

Octane doesn't mask any problems. Your car was designed to run on premium...Lexus doesn't make money off of that.

←

Yes octane does mask a problem. It happend to more than a few owners that the engine begins to ping on regular which they have been using all along without problem. Moving up to higher octane stops the ping (masks the problem). Eventually the check engine light will come on revealing which sensor has failed. After the sensor is replaced everything is fine with regular again.

[SW03ES]

Lex- Newer engines have adaptive ECUs and are much more forgiving when it comes to using lower grades of fuel.

[92Lex]

SW, I'm sure you're right about that but I'm just saying vehicles using lower octane than they were designed to run on are likely to "ping"...I'm not saying every single vehicle will ping on 87 octane but it's not uncommon.

mikey, are you refering to vehicles made to run on premium or made to run on regular unleaded? 87 octane burns faster than 91...the ECU can only !Removed! the timing to a certain point, if it's already retarding the timing all it can but the mixture is still "pre-ignited" because of the added heat, wouldn't you get pinging because of the extreme combustion temperature?

I've seen vehicles come into the shop that fail for NOx, they've been running 87 octane in vehicles made to run on 91 octane. I'll tell ya, those vehicles usually ping under acceleration.

[SW03ES]

If you look all over the Lexus forums though plenty of owners are using 87 with no problems...

*I* do still use 93 though...

[92Lex]

Seems to be a 50/50 thing.

I'm not going to say that using 87 will cause pinging in every vehicle...but how does premium mask any problems? Tell me if I'm wrong cause I'll throw out some of my schooling and I'll absorb the knowledge.

[mikey00]

Seems to be a 50/50 thing.

I'm not going to say that using 87 will cause pinging in every vehicle...but how does premium mask any problems? Tell me if I'm wrong cause I'll throw out some of my schooling and I'll absorb the knowledge.

←

OK. I will try this on more time. It looks like most, not all, RX owners are using 87 octane. I don't know this for a fact but am basing it on the small surveys on the various RX sites. A small number of these owners have posted that after years of no problems a slight pinging has developed. If you move up to a higher octane the pinging is gone. But why does a car that only requires 87 and runs for years ok suddenly develop a ping. The dealer’s usual quick answer is to use the higher octane. In most of these cases, a few thousand miles later the check engine light comes on indicating which sensor has failed. Once the sensor is changed and light reset, you can use 87 again and everything is fine. The reason the engine began to ping on 87 was due to a sensor failing. If you move up to a higher octane you can get the pinging to stop but you are not fixing the failed sensor, only masking the problem by getting the problem to stop. The check engine light will eventually come on. After owning RXs and being on the various sites for a few years now, I can see that this scenario is not that uncommon.

Let me use another masking example. An older GM engine designed for regular runs many years on regular ok. Over the last few years it begins to develop a ping due to carbon buildup. Running a higher octane gas stops the pinging but is only masking the real problem of carbon buildup. Once the engine is dissembled and carbon removed you no longer require a higher octane and the engine once again runs on the fuel it was designed for.

[92Lex]

87 was the culprit of the "ping" because it caused the carbon build up. Exactly what sensor are you refering to? Was it carbon fouled? Is your RX designed to run on premium or regular?

[mikey00]

87 was the culprit of the "ping" because it caused the carbon build up. Exactly what sensor are you refering to? Was it carbon fouled? Is your RX designed to run on premium or regular?

←

I was refering to the oxygen sensor ( diag code P0171). And the carbon buildup example I used was a GM engine designed to run on 87. And yes my RX is designed to run on regular.

[92Lex]

Bank 1- system lean? Contaminated MAF, low fuel pressure...maybe even a vacuum leak. O2S isn't the only reason for this code...there's NO direct monitor that tells you of a failed O2 sensor. Maybe once they develop OBD3 you'll see this but there isn't a monitor that tells you of a failed O2S as of right now.

Are you trying to say that premium fuel somehow tricks the O2 sensor into thinking that the air/fuel ratio is richer? Or are you saying that premium fuel causes a vehicle to run richer? It doesn't matter what fuel you run...if your O2S is bad then it's bad. I'm sure if you drove another thousand or more miles with the regular fuel the computer would of thrown the same trouble code.

(I was under the impression that RX's require premium unleaded...sorry about that one).

[mikey00]

Bank 1- system lean? Contaminated MAF, low fuel pressure...maybe even a vacuum leak. O2S isn't the only reason for this code...there's NO direct monitor that tells you of a failed O2 sensor. Maybe once they develop OBD3 you'll see this but there isn't a monitor that tells you of a failed O2S as of right now.

Are you trying to say that premium fuel somehow tricks the O2 sensor into thinking that the air/fuel ratio is richer? Or are you saying that premium fuel causes a vehicle to run richer? It doesn't matter what fuel you run...if your O2S is bad then it's bad. I'm sure if you drove another thousand or more miles with the regular fuel the computer would of thrown the same trouble code.

(I was under the impression that RX's require premium unleaded...sorry about that one).

←

I agree with your line 100%: "I'm sure if you drove another thousand or more miles with the regular fuel the computer would of thrown the same trouble code."

The sequence of events which did happen to certain number of RXs:

1. Engine starts to ping on regular. Owner switches to premium which stops the pinging but is really only masking the problem of the bad sensor because the bad sensor is still there but not evident because the pinging has stopped.

2. A few thousand miles later the check engine light comes on (P0171) which is usually the oxygen sensor in the case of the RX. Might even come on sooner if pinging continued with regular. I don't think anyone really knows the answer to that part. Once the sensor is replaced you can go back to regular without pinging.

[92Lex]

Okay.

[jgr7]

I borrowed this from another forum. The author is a powertrain engineer for GM.

There is a big difference between a phenomenon called pre-ignition and another , related but different phenomenon called spark knock or detonation.

If the end gas in the chamber spontaneously combusts due to heat and compression from the normally burning mixture that is called detonation or spark knock. Key here is that it occurs AFTER the spark plug ignites the mixture normally. The mixture ignites, burns and if the end gas gets too hot or too compressed it spontaneously combusts. The octane rating of the fuel tells how well it resists this spontaneous combustion. Detonation or spark knock makes the characteristic "pinging" or "knocking" marbley noise from the engine.

If the fuel/air mixture ignites BEFORE the spark plug arcs as suggested then that is called preignition. The mixture will NOT just spontaneously combust under those conditions...it needs an ignition source such as an overheated spark plug electrode or glowing carbon deposits in the chamber to ignite it before the spark. There is simply not enough compression in a gasoline passenger car engine to spontaneously ignite or combust the mixture. Since the phenomenon of pre-ignition requires an alternate ignition source increasing the octane rating of the fuel will not prevent pre-igntion. Octane rating has virtually no affect on pure preignition. Also, you cannot hear pre-ignition and if preignition occurs it is almost a guaranteed engine destroying event. Holes in pistons most likely.

[jgr7]

sorry for the long posts but I think you guys will like it. Also from the same GM guy.

The octane rating of the fuel simply indicates the resistence to detonation that the fuel has. It really has nothing to do with "quality" of the fuel or anything else.

When the spark is ignited in the combustion chamber the fuel/air mixture starts to burn in an orderly fashion across the chamber...much like the ripples in a pond from a stone dropped in. As the burn progresses the heat and pressure in the combustion chamber builds. If the end gas (the unburned gas) in the farthest reaches of the combustion chamber gets too hot and under too much pressure it can spontaneously combust. That is called detonation or spark knock. It is the rattling sound that you hear in some cars when you run low octane fuel. It is not good. The octane rating of the fuel indicates how "good" the fuel is at resisting that detonation or spontaneous combustion of the end gas.

The spontaneous combustion of the end gas is potentially damaging to the engine and creates the noise that you hear because the normal "gradual" pressure rise is suddenly changed due to the high pressure spike in the chamber caused by the spontaneous combustion of the end gas and the rapid, sudden expansion of the gases at more than one flame front. That sudden pressure rise "rings" the structure of the engine much like hitting it with a hammer would and the resonance of the engine structure is what you hear as spark knock.

(The higher the octane, the slower burning the fuel. The slower burn produces a more even combustion, preventing hot spots and making a little more power.)

This statement is a common misconception about octane ratings of fuel. There is no difference in the burn rate of the fuel whether it is regular or premium. All gasoline burns at the same rate (within practical reason..at least close enough for this discussion). The only difference in the fuel is it's resistence to that spontaneous combustion in the end gas that is being heated and pressurized by the normal burn in the chamber. No difference in burn rate.

This is easy to prove as , if there WAS a difference in burn rate between fuels, an engine would make different power levels on different fuels and/or the spark timing would have to be adjusted to account for the change in burn rates. This doesn't happen. On an engine dyno, the engine will make the same power regardless of the octane rating of the fuel at the same , fixed spark advance. If the engine starts to knock due to the lower octane rating then the spark would have to be retarded to stop the detonation and the power would drop...but...the power is dropping due to the change in spark advance...not a change in the burn rate of the fuel.

This issue gets really confusing, leading to the idea of different burn rates, etc... because there are many different ways to increase the octane rating of commercial gasoline. If the gasoline is pure gasoline the gasoline that is higher octane rating will be blended differently and will have a higher percentage of...octane in it. But, adding lead to fuel increases the octane rating. Adding alcohol increases the octane rating. MMTBE and other compounds increase the octane rating. Alcohol burns slower than gasoline....so...a "premium" fuel spiked with 10% alcohol to get the octane rating (common) will burn a little slower. Not because of the octane rating....but because of the alcohol in the fuel. This also leads to the myth that regular fuel will "make more power" ... someone must have run regular and premium on an engine on a dyno that was jetted perfectly and when they put the premium in (spiked presumably with alcohol 10%) the engine ran a little lean (10% alcohol will make it 5% lean) and made less power. So...the old wives tale of regular making more power is born....

[92Lex]

All that information is very credible...it's the same stuff I learned. The burn rate of fuel is fixed....premium is just a little harder to ignite.

Thanks for taking the time to research that, that post was way better at explaining it than I was.

[APN]

My wife's 2000 AWD RX300 runs just fine on 89 octane. The only concession I make to the fuel system is to add a bottle of generic fuel injector cleaner to the tank at every oil and filter change. That's been a habit of mine for decades across many different vehicles, and I've never had one knock or ping.

Keep in mind that different areas of the country require different fuel formulas at different times of the year. You might have to do some experimenting before you find a solution that works for you.

You may also want to pull a couple of your more easily-accessible spark plugs (the three front ones) and ensure that you indeed have the iridium spark plugs from either NGK or Nippondenso as called for in your owner's manual. They truly are a requirement for this engine to operate at peak efficiency, and they are rated to go 120,000 miles in this vehicle. At about $10 apiece from NAPA or a similar auto parts store, they're expensive but mandatory.

Hi

My wife has a 99 AWD RX300, we use 87 octane from the start with no problem. Last few days she told me, and I confirmed, about a rattling noise coming from th eengine when the car is revved to around 1800RPM, above and below that it has no noise. Does anyone have any advise as to where I can look for the source of this noise. The noise sound like metal tapping at fast rate.

Also can the spark plugs be changed at home or one has to bring the car to the shop for special tools ?

Thanks.