Knock Sensor Problem - Toyota Nation Forum : Toyota Car and Truck Forums

cwc418 · 08-12-2007, 08:45 PM

I recently purchased a 1993 Camry V6 XLE w/275K beater to drive back and forth to work for $500. I the previous owner took pretty good care of the car but it does have one issue that I cant figure out related to the knock sensors and a power lag. The check engine light comes on after about 3K rpms and its always code 52 and 55 (knock sensors). I thought it might just be fuel related so I put 93 octane in it and did some PM (plugs, wires, cap, rotor, fuel filter, air filter, timing belt, water pump, coolant and tranny service) but non of this fixed the problem of the power lag. It recently became apparent that something needs to be done because after about 2 hours of driving on a short trip the car started bogging down on me really really bad. It was like it was stalling particularly up hills. I pulled the car over a couple times and let it cool down and it seems to get better after that but it always comes back. My question is, would knock sensors cause my car to bog down like this or is it another issue? What should labor cost to replace these? Sorry for the long post but I would like to get this resolved.

BTW, the car never overheated and no smoke. I also did a compression test and it seems to have good compression.

***Eye8Pussies*** · 08-12-2007, 09:06 PM

one question- so is the light ALWAYS on now? basically, after you reset the light and drive the car, the light just pops back on?

and yes, a blown/malfunctioning knock sensor will do exactly as you're describing.

At this point, there are two possiblities- either there is something wrong with one of the wires or both wires (you have 2 knock sensors), oryou have a blown knock sensor or two blown knock sensors.

Due to the age of the car, the wires can easily be damaged due to the heat and conditions in the engine bay, and the knock sensors can also be blown since they are sensitive acoustic sensors

your knock sensors are located under your intake manifold- take a look. your ecu needs 2 good signals from your knock sensors to run properly.

If you find that one of the sensors is blown, you can always wire both signals to one sensor. take a look at your haynes manual for instructions on how to check your knock sensors.

cwc418 · 08-12-2007, 10:17 PM

I guess I dont understand how blown knock sensors will cause it to bog down/stall intermittently? I downloaded the service manual from the sticky and apparently you have to take the intake off to test them?

***Eye8Pussies*** · 08-12-2007, 10:50 PM

yeah, that's the down side...you'll need to remove the intake plenum and then the intake manifold just to get to them and really see....

a blown knock sensor wouldn't cause intermittent problems if it is fully not functioning, but in most cases, it seems that knock sensors as they get up in age/mileage/use, etc. can just function erratically and send bad signals (or bad wiring, etc.)

basically, when the ecu doesn't receive a clean and "good/all-clear" signal from the knock sensor (which is a constant changing signal) the ecu will then both dump fuel as well as retard timing to save your motor from what the ecu thinks is knocking motor

if the ecu thinks things are really bad, then it will dump an excess amount of fuel and retard timing- which can easily stall your car. it also is different with different ecu's.

when I had knock sensor problems, I could still drive my car- as can you right now. but it just ran really REALLY badly and the car had no power at all. others, can't even drive the car and it will basically roll and then stall out.

check those sensors, and good luck

give it a try yourself before taking it to the mechanic's as they will rape you on labor

Toysrme · 08-13-2007, 10:07 AM

it takes the ECU alittlebit to give codes 52 & 55. it won't do it at a high idle, or a low cruise rpm until it notices the sensor grounded out, the wiring is intermittant, or the shielding is bad so the ignition system interffers with it.

it will, however throw the code immediately between (if memory serves me correct) 3800-5200rpm. which is the rpm range the knock sensors actually work at. replace both sensors & the wiring. they're pain in the asses to troubleshoot. don't waste the time.

***Eye8Pussies*** · 08-13-2007, 11:00 AM

^ really? that's good to know

on the 1mz, the knock sensors pretty much go off immediately if you touch the throttle regardless of what rpm you are at

cwc418 · 08-13-2007, 05:24 PM

Ok, so is there a way to see if its frayed wires before I spend a bazillion dollars on knock sensors? Could it be a bad ECU?

***Eye8Pussies*** · 08-13-2007, 06:59 PM

there isn't much of a way to check hte wires either since most of the wiring is off the rear wiring harness which is located under the intake plenum and the rest of the wiring then runs to the knock sensors themselees under the intake manifold

one thing that you can try though, is splicing the wiring together at the ecu so that both signals from hte ecu share the same signal from one knock sensor. you can try splicing the wiring so that the ecu runs off of one knock sensor and then the other and one of them may work, since I highly doubt that both are blown at once, or the wiring for both went bad at the same time. It's a trick that a lot of the supercharged 1mz-fe's do since they have a habit of blowing a knock sensor.

I can't help you with the wiring though, but you could try asking toysrme since he is the 3vzfe expert

Toysrme · 08-13-2007, 11:15 PM

you can do that sometimes, but the simple thing is that he's throwing 52 and 55, meaning both bank knock sensors. you can test the sensors for continuity from the terminal to the metal body, but you may as well replace them both along with the wiring as said before.
the wiring can be a bitch. it's old & crumbly, but EMI from the ignition system can cause them to get finiky if the shielded portion of the wire.
there's no reason to do the work & not replace it all less you want to DIY and risk having to do it 2, 3 or 4 times to get a resolution.

ya eye8 only modern, fairly rescent knock sensors & management do full-time knock monitoring. before that knock sensors were only calibrated to detect know at certain smaller, specific rpm ranges. for toyota it's normally the high 3000rpm to low 5000rpm range, and sometimes even smaller.

normally if the problem is the ECU sensing ground/bad knock sensor grounding out, itll throw a code ASAP. otherwise if it's intermittant, or interfferance. you may be able to drive & cruise around until later on at night.