I have a 2004 that has been knocking under load excessively (or at least more than I'm used to). I changed the plugs (that was overdue) and I tried some hi-test fuel just for kicks, no difference. I'm not getting any codes on the scanner.
I tested continuity on the knock sensor (terminal to body) and that didn't exist (normal I think).

I tried driving with the knock sensor unplugged and I didn't perceive any difference. I'm about to order a new sensor, but I just thought I shoot out this post in case there in anyone who has further advice for diagnostics. I'd hate to spend 140$ on a sensor and find no improvement.

 

you need to share some more info, is an an xa or an xb, mileage, manual or automatic, any modifications at all. are you using a top tier gas company like shell, chevron, exxon etc?

when you say under load, do you mean under wide open throttle (WOT) does it happen around a certain RPM. have you tried resetting the ECU (disconnect the battery)

before you shell out 140 dollars for a new part that won't fix the problem, why not go and get it diagnosed so that then you can just spend the money repairing you need to instead of just replacing parts that had nothing to do with the problem in the first place.

 

Opps sorry. I thought I was posting in a specific xB Engine forum. I have a 2004 xB all stock. I use 87octane fuel (Tesoro). Mileage is around 60k. When I say "under load" I mean low gear (1st and 2nd primarily) just before upshift (auto trans). I don't notice pinging at high speed, but with the added noise at higher speed, I suppose it could be happening then as well.

I haven't tried resetting the ecu. If it was as simple as that I would be shocked (and happy).

There are no Scion or Toyota mechanics within two hours drive of my location, so I was hoping to diagnose this problem myself. The repair manual only states the continuity test for evaluating sensor.

 

well, you are in the xa/xb drivetrain and power section, since they have very common drivetrains

are you sure it isn't the VSC/TRAC system intervening?

also, what kind of spark plugs did you replace them with, cuz some work better with toyotas than others apparently. like bosch platinum plus 4's aren't very good apparently, while NGK and denso's are pretty good.

 

The [original] stock Densos were definately spent- and the pinging started before I swapped them out. I put in Bosch std Plats, no change, then I read Bosch Plats aren't good in Toyotas, so I swapped them out for NGK GPWR, no perceptible difference in any case.

 

I can try disabling the VSC/TRAC- never experimented with that control before.

 

Two things could be happening . . . carbon fouling in the cylinders which raises compression and makes hot spots that can cause some nasty knocking and pre-ignition and the bad knock sensor. If you had a ScanGauge you could monitor the ignition timing as you drove and see if it was retarding and advancing when it was supposed to. Check for carbon on the plugs that you took out and when was your last oil change and with what weight oil did you use . . . if you say 5w20 then bing bing bing it's summer time and it is too light a weight oil.

 

Plugs showed normal wear and no carbonizing.
I use Mobil 1 5W-30, And summers in Alaska aren't all that hot (at least where I live)

 

It surprised me not to get any percetible change when I left the knock sensor unplugged. (Or any warning lights for that matter)

I don't have a scanner capable of monitoring timing under-way.

 

Wow yeah I guess you don't have a heating problem unless your water temp is way too hot. Mobile 1 5w30 should be good too. I guess if you have a bad knock sensor that could really do a number even with high test gas. I would not think that it would read open circuit with an ohm meter unless it is a crystal type device that outputs a high impedance signal to the ECU. Only way to tell for sure is to monitor engine timing like with a ScanGuauge - you might try to borrow one if you can find someone locally that has one.

 

If I can get my hands on a ScanGauge, what should I look for to know the operation is either flawed or correct? Would I expect timing to retard if ping/knock is happening? If it stays the same under that scenario, would that mean the sensor is bad?

 

I think the knock sensor just tweeks the timing a little when a knock occurs and is generally not needed because the timing adjustments are already very close to perfect under the usual engine operating conditions. The only thing it is supposed to do is to compensate for unusual events like low octane gas or hot intake air temps carbon buildup in the engine or faulty injectors causing lean burn conditions would would cause knock. Like I said a ScanGauge would do the trick.

 

Timing display on the ScanGauge should retard when you apply throttle and advance when you back off or touch the pedal lightly. Normal timing is in the 30's at cruising speeds and I would have to check to see how low it gets but I think around 8 degrees under heavy load is close. The thing to check is at the RPM and throttle that it knocks, what is the timing then.

 

The trouble code scanner that I *do* have doesn't indicate any issues, nor have I ever had any trouble lights.
I guess I'm just not sure what a new (better) scanner will tell me at this point.

 

Thanks for the advice.

If I can get my hands on a borrowed scanner I'll put it to use. Otherwise the 150$ to buy one is probably just as well spent on a visit to a pro garage!

 

Well a ScanGauge would tell you coolent temp, intake air temp, fuel burn rate, mileage, peak readings for RPM TEMP etc, digital speed, rpm, mpg, gallons used, trip mileage, throttle position, engine load in % of available power at present rpm and TIMING. It is more than just a test instrument.

 

You might want to check your oil pressure too. Kind of rare to get an oil pressure failure but it can be bad if that is the problem. Only problem is getting to the oil pressure switch under the intake manifold to connect an oil gauge.

 

Yeah, the knock sensor is quite difficult to reach under there as well.
If the oil pressure is an issue, I would assume a dumby light would come on, unless that sensor is bad too.

 

The light come on at about 6psi - pretty low and at that pressure you already have a problem. You could stall it and see how quickly the light comes on that would show a little about have fast the pressure drops at least. Or crank it and see how fast the light goes out - but reading the pressure is more better.