I have a 98 Toyota 4Runner, which just started what I’m told is pinging or knocking on “hard accelerations”, like accelerating on the merge lane when I see cars coming up behind me in the lane I want to merge into, or going uphill. i have 258,000 miles, and have the SUV serviced regularly and get things fixed when they need it. I told the dealer about it a month ago when I had regular servicing, and he did something to clean the fuel injector, and suggested I try 89 octane (he specifically recommended Sunoco), and if that worked I could try going back to 87 octane (Sunoco was his recommendation again). I did as he suggested, and the pinging/knocking seemed to get better with 89, but returned with 87. I read the Q&A on this, but still have questions. Why did this just start after 14 years? Should I do anything about, in other words is it harmful? If so, what should I do? Does the brand of gasoline have anything to do with this, or anything else for that matter? I am hoping to keep the SUV for a couple more years (300,000 miles), maybe longer. Thanks.

Your engine has a knock sensor on it that is one of the inputs to control the ignition timing. It looks like yours has failed or is failing. You do need to get it fixed if you plan on keeping the vehicle.

There are several possible causes for “pre-ignition”… “detonation”… “pinging”… “spark knock”… Hot spots in the combustion chamber, defective timing control, overly lean fuel-air ration and low rpm lugging. If your driving pattern is unchanged the first place to look would be carbon deposits and incorrect spark plugs. If the plugs are OE, adding Techron or similar products may help eliminate carbon deposits. I am unfamiliar with any special advantages of Sunoco but it may be an excellent product and may have a Techron type additive in it. If excessive,the pinging can break pistons and virtually destroy the engine. It may be worth the cost of removing the head and de-carboning the combustion chamber. Fifty years ago that was a very common maintenance chore.An experienced driveability mechanic might test drive your 4-Runner with a lap top linked to the system and give you some insight. And a boro-scope might show the cause. Long ago I used a water pistol to clean carbon from engines but that method would be difficult these days.

As Keith suggested, have the knock sensor replaced. This critical component moderates ignition timing when necessary to suppress ping and knock…

“Why did this just start after 14 years? Should I do anything about, in other words is it harmful?”

It started after 14 years because some 14 year old part has failed, probably, as Keith and Caddyman have suggested, the knock sensor. And, YES, it’s very harmful. Get it fixed or you’ll be replacing the engine before you get to 300,00 miles.

There is a difference between harmless light pinging and destructive heavy detonation, another word for pinging. Yes, something may have changed or deteriorated over the life of your vehicle but it is possible that the pinging is at a low level where it is not harmful. Someone who knows the difference needs to hear your engine. Your mechanic may know but may not want to turn away easy work if it is the knock sensor that has drifted in its performance. It is possible that you can delay spending money on this vehicle until the pinging gets worse, if it ever does.

I can’t imagine why your dealer would want you to go back to 87 octane if 89 helped your engine eliminate the pinging. It will cost you far less money to run mid-grade than to get a repair. If the pinging gets worse, then you can temporarily switch to premium gas and then get repairs.

If you demand perfection from your vehicle, then you may want repairs now.

As has been noted, there are lots of things that can lead to pinging and most of those are easily from age/high mileage. Several of those have been mentioned and I am just adding an EGR system issue to the list. I would check it & pull it all apart & clean it all up.

I would keep running the higher octane gas until its figured out. If you do the math it really doesn’t come out to as much $$ as people seem to think.

My vote is with cigroller about an EGR fault. It’s a common fault and at that mileage it can be expected.

If it’s not the knock sensor it can be deposits in the EGR ports.
Exhaust gas to one or more cylinders could be blocked, causing spark knock, even though total EGR flow is OK.

If the EGR system is plugged up, it usually throws a fault code…The EGR is normally closed anyway during acceleration…

Thanks to all who responded. What is an EGR system (what does EGR stand for)?

Exhaust Gas Recirculation. It recycles exhaust gases through the combustion chambers to contaminate the incoming air / fuel mixture, thus reducing combustion chamber pressure when the fuel burns. This reduces exhaust emissions.

The EGR only closes under full throttle acceleration.
Again, if the cylinders don’t get equal amounts of exhaust gas some cylinders can ping, even though the overall amount of exhaust gas is OK (and thus no fault code).

The valve is also closed at idle…It is usually only open during state state cruising. It feeds exhaust gas (no oxygen to support combustion) back into the engine which lowers combustion temperature and limits the amount of NOx produced.

Most engines only have one EGR port feeding the intake manifold. What can plug up is the supply tube from the exhaust manifold or supply port…The EGR valve regulates the flow…It is always closed during serious acceleration so maximum power is available. If your engine knocks or pings under hard acceleration, it’s NOT the EGR system causing it…

Let me add one more little thing here. The knock sensor itself is a pretty robust item, but there is a possibility that the connector is not as conductive as it used to be. You might have someone unplug and re-plug the connector to see if it restores the connection and starts working again.

Does your car require timing adjustment as part of a tune-up? Most newer cars don’t. In the early 1990’s they did. If a timing check and adjustment is recommended as part of routine service, that’d be the first place I’d start.

Not sure where you are located. Here in California we have a different mix in the gasoline in the winter than we do in the summer. I get a little minor pinging sometimes w/my 1990’s Toyota Corolla with the summer gasoline, but never with the winter mix.

EGR is PROBABLY the problem.

Timing is another possible problem. Could be ignition timing…or if you have a timing chain…there’s a possibility the timing chain slipped a tooth.

I too would look to the EGR system first. Its whole purpose in lilfe is to prevent pinging (and excessive NOx production) by adding a bit of inert exhaust gas to the intake to prevent cylinder tems from spiking and causing pinging.

I’m curious, however. This being a '98, it should be storing a fault code. Got codes?

I suppose it will vary with programming and all, but my personal experience tells me that an EGR system can get fairly out of whack for a decent period of time without the computer ever “thinking” there’s a problem.

That said, I wouldn’t be surprised if we don’t eventually get one of those “Oh, yeah, the check engine light has been on for years…”

Thanks for all the suggestions. It sounds like the things to check out are the EGR system first and knock sensor second. The check engine light is not on. It has only come on twice that I can remember, and both times it was an O2 sensor that needed to be replaced, which I did. Regarding the question about a timing chain, I think the 98 4 Runner has a timing belt, rather than a timing chain. I don’t know if that makes a difference in the suggestion about timing. Regarding the question of a fault code, how would I know if have a fault code? Regarding the question of summer vs. winter gas, I live in the mid-Atlantic, and I don’t know when gas switches to winter mix, but I started noticing the pinging/knocking sometime in the fall (Oct. or Nov.)