Suspected Knock Sensor Failure - Corolland: the Toyota Corolla Forums

In my 2001 Toyota Corolla, the performance was getting abysmal, and the mileage was extremely poor (28-32mpg highway, low 20s city), even on a straight highway trip. I noticed that on some hills, the engine would rev up a little and then it would downshift out of overdrive, and that it seemed to do it more and more on hills that it used to never have a problem on.

As my '95 Previa S/C doesn't do that (and it has a much worse power to weight ratio), it occured to me that the knock sensor was just too sensitive and the timing was getting retarded more than it should have been. What seems to have confirmed it is that when I run 89 octane fuel (rather than the 87 the manual calls for) the performance is much better, and the mileage jumped from about 31mpg highway to over 36mpg (very nearly the original mpg I used to get).

So, either the engine is way carboned-up, or the knock sensor is just too sensitive.

Does anyone have any ideas on this?

possible carbon issue, do some things to clear that out and see if it gets better.

I'll probably do a Seafoam treatment and let it soak a few hours and see how that does. It's certainly cheaper than a knock sensor, but I just can't help but feel it's still related to that. I guess after 81Kmi it might have a little carbon in there.

Definitely need a datalogger to measure what the timing does, atleast something with real-time data display, when you put the engine under load. Scangauge, CarChip, DashHawk are a few - many more out there.

There are "overly" sensitive knock sensors out there (good example, LS3 egnine in the 2009 Corvette) just that the 1ZZ-FE is not one of them.

I would suspect that you might have a VVTi system that is acting up on you. Not very common, but it does happen. Might try a tankful of premium to see how the car behaves. It is seems to run better - you have some heavy carbon deposits in there. If it runs about the same - possible VVTi issue or a faulty knock sensor (picking up false knocks).

Might try a tankful of premium to see how the car behaves. It is seems to run better - you have some heavy carbon deposits in there. If it runs about the same - possible VVTi issue or a faulty knock sensor (picking up false knocks).

I'm on my second tank of 89 (mid-grade here), and it still seems to be running much better than on 87 (but it is pretty unscientific right now, as it could just be the weather or something). One thing I've really noticed is that on 87, it has strange hesitation/surging right off idle when the car is just getting warmed up, but it doesn't seem to do it on 89 (this tells me it's something with knocking and timing being retarded rather than a VVT-i failure). I've not tried 91 (what they call premium here) yet, as that's $.20 more a gallon than 87 ($.10 higher is bad enough, but it's ostensibly worth it as my MPG and MP$ has gone up considerably).

While I don't doubt that I'll get some knocking at the car's age, it still seems that the knock sensor is just overreporting. I know they're tuned to about 7KHz, so it should screen out other rattles and bangs, but maybe it's just some sort of oddball failure.

Someday, I'll have an ODB-II scanner, maybe a ScanGauge II...

Even a small bump in octane, resulting with a better drive - points at carbon build up inside (carbon build up leads to "hot spots" in the engine, that would eventually lead to knocking).

My 2002 does the same thing (150K miles) - though not the surging/hesitation that your experiencing - that's what led me to believe a possible VVTi issue at first. Mine also gets considerably greater fuel economy as I increase octane rating - all point to carbon buildup so far. I might try and clear it up later - but for now, it is just a nuisance more than a serious issue. Mileage is still pretty good on the highway - 35MPG+

If you get a piggyback ECM - might be able to "tune" the knock sensor a bit - but I would chase after some other know 1ZZ-FE "features" before I chalk it up to an overly sensitive knock sensor.

Definitely need a datalogger to measure what the timing does, atleast something with real-time data display, when you put the engine under load. Scangauge, CarChip, DashHawk are a few - many more out there.
There are "overly" sensitive knock sensors out there (good example, LS3 egnine in the 2009 Corvette) just that the 1ZZ-FE is not one of them.
I would suspect that you might have a VVTi system that is acting up on you. Not very common, but it does happen. Might try a tankful of premium to see how the car behaves. It is seems to run better - you have some heavy carbon deposits in there. If it runs about the same - possible VVTi issue or a faulty knock sensor (picking up false knocks).

HEY! speaking of that! you just reminded me. hunt down your local mac tools dealer, they have a sweet little hand held obd2 scanner with live graphing data and all the normal bells and whistles for $150 with lifetime updates online.

I was just thinking that that could be a type of failure -- instead of not working at all, just sending false signals or overreacting in general.

I'll have to check out that Mac Tools scanner. I like the idea of logging and graphing and all that.

I'll probably do a short-soak Seafoam treatment this afternoon. I plan on mowing today, so when I get home I'll do the initial Seafoaming and let it soak for as long as it takes to mow the lawn before starting it up. That should probably clean quite a bit out...

I did a Seafoam treatment last night, and let it soak for about an hour before restarting it.

All the YouTube videos I've seen on the subject did not prepare me for how much smoke I'd see come out the tailpipe. I let it idle for about 10 minutes with periodic romps on the throttle, and then drove it around the block and returned to the driveway. It was like a James Bond smokescreen. After that, I took it to a dirt road not far from the house and drove it in 1st and 2nd gear with periodic runs to redline and it finally cleared up.

It's hard to tell, but my butt dynamometer seems to say that things have improved. It idles much more quietly, too.

I'll just have to keep an eye on the gas gauge over the next few tanks and see if it's helped at all.

awesome, i really think that the amount of smoke is proportional to the amount of grunky buildup it's soaked into. i say this because my car hardly smoked any and i knew it was already pretty clean, other cars i've done have smoked MUCH less the 2nd time around.

OK, its a Mac Tools ET97. hunt down your local mac tools dealer and buy one Fish!