ep-jb

Thanks millball - might as well while I'm that close
You all are great

coltonstewart

Im also having issues with a very poor running engine with a code 52. Im not sure what to believe about the ECU role with the knock sensor because Ive seen other people saying that a faulty knock sensor will just keep a "ping" signal from occuring (from the KS to the ECU), which shouldnt retard the timing at all. So if that were the case then running no knock sensor shouldnt affect the way the engine is running, only keep the ECU from doing its job in the event of a ping.

But it seems the consensus here is that the ECU is constantly retarding the timing when there is a shorted or open knock sensor circuit (code 52), right? Is that what I should believe? cause if thats my cure-all then fantastic

scope103

And then what would happen? When the ecu receives a knock signal, it retards the timing. If it "didn't do its job" (because it no longer received the knock signal), would it just keep advancing the timing? Until the knocking blew a hole in a piston? (That might take as much as one second after the knock signal disappeared.)

Since the ECU doesn't "want" to do that, it knows that when the knock signal disappears it is "flying blind." And it does the only safe thing: dramatically retard timing, just to be sure.

[Since you seem to doubt this, I tried to find one of my usual web references to Toyota publications, but in the few seconds I worked on it I couldn't find it. Later.]

coltonstewart

Scope- I definitely appreciate all your help and your timely responses, as youve been the primary help for me. I do trust that you have extensive yota experience. I didnt mean any offense I just want to be sure. There are alot of opinions on the internet and this is the page that threw me off - and the guy is supposedly a certified toyota master technician - but not sure about him now:

http://www.justanswer.com/toyota/1nm...993-model.html

Check out his second and last responses must be wrong?

Has every 3vze that youve ever heard of with a code 52 run like crap?

ep-jb

G'Morning, and thank you,
I'm guessing that my 54Code (and the rich mixture it provides) is the primary problem for my occasional flooded starts. Makes a little sense at least

scope103

"Disabling a knock sensor will do absolutely nothing good or bad." http://www.justanswer.com/toyota/1nm...993-model.html Wow. That's just about all I can say. Except that Skyvisions really doesn't understand how a knock sensor works, or what its purpose is.

First, I have no professional qualification, unlike our ASE Certified (??) friend. Second, my direct hands-on experience with Toyota Trucks is limited to my '94. And third, I've never had code 52 myself, or driven one with that code. So my experience is limited to what those on Yotatech describe (and reading about it.). I believe that a truck with code 52 SHOULD run like crap (due to retarded timing), but of course it might be possible to advance the BASE timing so far that the truck will run "okay" at RPM (though it should be hard to start and idle poorly) So I can't say that all trucks with code 52 run poorly.

At the risk of being pedantic (feel free to stop reading here), let's take a tour of ignition timing. If you look at those cute animations of 4-cycle engines, the spark plug fires right at TDC, and the flame spreads throughout the power stroke. But over 100 years ago, automotive engineers determined that at higher rpms, the flame wouldn't burn all the fuel before the exhaust valves opened at the bottom of the power stroke, unless you fired the spark plug a little BEFORE TDC. So for good performance, the spark plug had to fire earlier at higher rpms. But not too much, as the expansion of the burning fuel was pushing the piston the wrong way until it got past TDC. So for good performance, the spark plug had to fire earlier at higher rpms.

On the Ford Model T, the ignition timing was adjusted by hand, as you drove! http://www.mtfca.com/discus/messages...tml?1321457711 http://www.mtfca.com/books/1926Inst.htm You would advance the timing until you could hear some knocking, then back off. (fun fact: you started a Model T with the ignition set about 15̊ after TDC, and advanced the timing as you opened the throttle. If you tried to crank it with the ignition timing left in the advanced position, the plug would fire before the piston was all the way up, it would push the piston down, turning the crank backwards, breaking your wrist!)

Time marched on, and the public wanted the timing adjusted automatically. Centrifugal weights could sense rpm and adjust the timing, but didn't detect changes in engine load (like driving up a hill). Adding vacuum advance could react to load changes. But all of these pre-planned settings were all very approximate. And they couldn't know anything if you filled up with slightly lower octane gasoline. Running the vehicle with slightly retarded timing would hurt performance, but running it with slightly advanced timing would cause knocking, which was very bad, up to blowing a hole in a piston. So the designers played it safe, with the pre-planned ignition timing always a little retarded from optimal. All this because a centrifugal or vacuum advance can't "listen" for knocking.

Or can it? In the last third of the 20th Century, the need for better fuel economy and reduced emissions meant that setting timing approximately just wouldn't do. So they gave the ECU the ability to listen to the engine, just like a Model T driver could. The Knock Sensor is just a microphone, tuned to be specially sensitive to about 7kHz. http://www.cygnusx1.net/Media/Supra/...taTech/h38.pdf The ECU demodulates the microphone signal to detect the onset of knocking Then, the ECU constantly advances the timing until it "hears" knocking, then retards the timing until it just stops. (the sensor is so sensitive that you will never hear knocking yourself). You are always driving with the timing set just perfectly! http://www.cygnusx1.net/Media/Supra/...taTech/h40.pdf

What if someone disconnects the "microphone"? As it advances the timing, the ECU never hears knocking; it never hears anything. Knowing that isn't right, it throws code 52. But where does the ECU leave the timing? It doesn't have centrifugal weights or a vacuum diaphragm, so it can't fall back to early-20th-Century approximate methods of setting timing. Leaving the timing set too far advanced would mean you could damage the engine as soon as you loaded it. So the ECU sets the timing where you can still drive it (limp), but where it shouldn't damage the engine no matter what is going on.

Note that the knock sensor is NOT a switch (like an oil pressure switch), nor is it a rheostat (like a temperature sensor). That's why the pigtail and the rest of wiring is electrically shielded, and why any damage to the shielding can introduce enough electrical noise that the ECU can't HEAR the sensor. Shorting the sensor to ground will wipe out the signal, just as shorting it to 12v or 6v or anything else. So thinking that shorting it to ground will cause severe timing retardation, while shorting it to 12v will not, just shows a lack of understanding of this type of sensor.

307Yota

Thanks for the explanation Scope. Very well written.

ep-jb

Sorry that it took forever for me to 'keep you posted' on this project -

Got 'er done - signal wire was birdcaged and running on 2 strands - replaced
changed the KS while I was there (already had it, so what the heck)
replaced every gasket I disturbed - all were showing their age, although very few minor leaks before I disturbed them (wasn't going to find out they didn't like being disturbed the hard way)
very few vacuum lines were softened, but I had a roll so I replaced a lot of them
set valves (thanks for the reminder)
found 5 connectors that had broken strands at the connector - repaired
replaced TPS, PCV (yes, great time to do it), Air Intake Cleaner box (blew it up from backfire pressure), plugs and wires since they were so easy to get to

Runs real good now - very satisfied with the results vs time and money spent
I had a stretch after KS change where TPS caused a lot of problems - It took a while to narrow it down - I tried all the 'quick fixes', but it all kept pointing back to it.

I like the little bugger - it seems as though it's definitely going to be a project for a while - age is showing
next project - get my big hands into the drivers door because my ds window seems to have jumped a track

Thanks again for the help - you guys got me started and pointed in the right way