slinkyeleven

I keep getting a code 12 on my pickup. This DTC definition is for the knock sensor. I have a hesitation off idle or when the throttle is snapped wide open in neutral or in any manual gear. This is most noticable at light throttle / cracked to less than 1/4 opened. At WOT or 1/2 + it has full power. Timing is at 5 degrees with the connector shorted, tps replaced with a new Denso unit and has been set multiple times with a feeler gauge, the knock sensor has been swapped and the coaxial cable to it from the ecm has been replaced with the ground being repaired. With a timing light connected and the ecu in timing mode at 2-2500 rpm the timing intermittently jumps from 40 degress to near zero momentarily then back again? An new coil, tune up components, fuel filter have been installed. The EGR main vacuum supply has been plugged with a screw to test if this was the issue but now change exists. I am stuck any ideas?
Thanks
David

85 toy pickup 2.4 fi code 12 issue

thook

How's the TPS wiring look? Old/brittle at all?

slinkyeleven

I have wiggled the tps harness and not been able to create any runnings issues in doing so

David

thook

That's good. But, how do the wires "look"? What I mean is with age the copper and the wire jackets oxidize and become brittle. Then, they don't conduct as well and eventually break. Anyhow, it may not be part of your problem, but you can atleast rule that out.

slinkyeleven

I have checked these wires while wiggling them back to the ecm with a dvom and readings stay constant. No luck still. What is the name of the sensor that is located on top of the thermostat. This is a single wire sensor on top of the tstat housing but I cannot find the application in the service manual.

David

Zealot

If you are pinging under partial load and the knock sensor isn't the problem, I would think it might be a lack of fuel. A lean burn will ping and cause hesitation (until your O2 sensor picks up the lean burn and runs the injectors open longer) How many miles does it have? You might want to look into having the injectors checked. I use Dr. Injector. They will actually flow your injectors and tell you how plugged they are. If they need to be cleaned, they "rebuild" them and recalibrate them to the same flow.

shaeff

fix the KS code. chances are that the wire is simply shorted out. rewire it directly from the sensor to the ECU. follow these directions (sortof, these are for a supra, but it's the same basic jist)

http://www.supras.com/06/techcenter/display.php?QID=69

-shaeff

thook

That's the sending unit for your temp gauge.

slinkyeleven

With a dvom connected on the frequency (HZ) scale I have tapped / hit the intake manifold with a hammer to generate a "knock". A Frequency is generated by the knock sensor when connected directly to the sensor. Originally I wired this with a solid wire RG58 coax thin wire. Today I rewired the sensor with RG58 coax strand interior wire. We will see in the am. Also with a timing light connected at 2500rpm, when the similar tap / hit with a hammer is applied to the intake, the ignition timing does not retard on the balancer. If it is not the wire replaced today? I took apart the ecu and did not find and burns or damaged components. Has anyone replaced an ecu on a 85 2.4 fi as I heard these were bulletproof.

David

slinkyeleven

Very nice article on addressing code 12 on early toys and code 52 on later models,

Thank you

slinkyeleven

I have replaced the wire with RG58 COAX and still get a code 12. I am stuck and do not know what to do next.

How much is a 1985 4WD solid axle shortbed 2.4L FI with original paint and original condition worth? NO RUST, but code 12

thook

Giving up, eh? Before you do, try asking someone directly. Like a pm or email. Roger Brown of http://www.4crawler.com/4x4/CheapTricks/index.shtml knows quite a bit. So does quite a few of the folks at http://www.4x4wire.com/. It's just a thought...and what I do sometimes. They're really helpful when they can be. Expanding your knowledge resources helps a lot...that is if you're not the getting the answers you need in one source.

Sorry I can't help you more myself, but this is not familiar territory for me. I would be interested to know what you find, though, if you don't sell it first. If it were me, I'd hang on to it and fix it. But, then I like the early model Toys.

BTW, IF...and that's a big if...it's something serious and requiring a rebuild, they're aren't worth a whole lot....relatively.

Bigblock

This could just as easily be a computer problem.especially if you've replaced ks all the way to the ecm.Do you have a good fsm?

slinkyeleven

I have AllData, Mitchell, Identifix and IATN. I have not heard of many finding issues with this model year of ECU. I tool of the covers and did not see any physical damage but?? This ECU is one year only and is $700 at the dealer

thook

Do you have a lot of valve train noise, then? When's the last time your timing chain was done? Do you have a miss in any of the cylinders?

Flash319

If you can see the timing retard and you get a code 12 I would assume that the ECU is seeing a knock. My understanding of the knock sensor is that it is a switch that opens when it senses a knock. It is one wire to the sensor so it is using the main ground of the engine as the circuit. I would try checking the resistance from the sensor wire connection on the sensor to the ground terminal on your battery. It should be low as the switch would be closed with no knock condition. This was my understanding of how the Chevy knock sensor worked so I am making an assumption here. There will be a specific resistance that it must hold to let the computer know that it is there. The only other thing is as mentioned before, you do have a knock in the engine. More then likely a lean knock as mine does it all the time when I start climbing a hill and get on it a bit.

slinkyeleven

Thanks Flash. With a timing light installed I am not able to get a retard to display when simulating a knock with a small hammer tap / whack on the intake. Does anyone have a ecu for a 1985 Toyota Part # 89661-35020

slinkyeleven

Replaced the ECU with another unit from a Furmann's Salvage in Santa Ana, CA and have yet to see the MIL illuminate since then. I have never replaced an ECU in all the time I have worked on vehicles but this one fixed it. If you have this code 12 follow these steps first.

-Backprobe the ECU KNK pin with the pos. lead and ground the other lead of the DVOM. Start the vehicle and with the meter on the Freqency / Hz scale. The readings I had with both the old ecu and the new are 0 at idle and ranging between 1 - 2/3 K Hz. A lower reading is found off idle rpm and at full throttle 2-3 thousand (K) Hz are displayed.
-If you do not get this reading you either have an issue with the wiring to the sensor or the sensor itself. Measure continuity from the terminal on the sensor connecter to the KNK pin at the ECU. If you clear this code and it still resets, just repair the wire with RG58 coax cable and solder / secure the ends.
-Checking the sensor - Use a DVOM and measure the Hz output with the pos. lead on the knk sensor terminal when installed in the engine and the other lead to ground. Tap on the intake manifold with a hammer to generate a knock / vibration. The meter should show a frequency. These sensors are quite reliable and unless the engine has been severely overheated generally do not fail.
If the wire has been repaired, the knock sensor test ok and a signal is generated to the ECU while running, the ECU is the remaining component for this code 12.

Thanks for all of your help

David