-=j0nnyr0773n=-

I have been working on figuring out how to fix code 12 (knock sensor circuit) and I have come across a pinout for my ECU on my 86 Xtra cab 22re pickup. Here's the one I have been going by.



Now I have been mainly looking at the middle plug with 18 pins on it. I believe my knock sensor wire is going to the location that my water temp switch (TSW) is supposed to be. What is the best way to diagnose which wires are coming from where and will I totally destroy the ecu if I switch the tsw and knk wires? I am not sure what is hooked to the knk spot but it is an all black wire and the tsw one is green with a black stripe (matches the color of the wire at the plug on the knock sensor). I am placing a dmm at each end of the wire (one at the ecu and one at the sensor) and am getting a reading of 0.00, not infinite, but zero. When I put one terminal on the knock sensor end of the wire and the other end to any of the other pins on the ecu I get infinite, so I am assuming that I have located the right wire on the ecu when I get 0.00. Also my ecu says 22r on it and I have 22re, I would imagine that the 22r ecu works for 22re as well... Anyways I'm going to try and locate a new/used knock sensor and see if that helps. I read that the wire from the knock sensor is supposed to be shielded, mine is not. It is a regular stranded 14 gauge wire that looks like it was put on in 1986, but I believe it to still be making a solid connection based on my multimeter testing. Any help with my code 12 and weird ecu wiring would be great.

abecedarian

Do not switch the wires
Unplug the harness from the ECU before testing continuity of the wires - tt is not likely, but is possible that the voltage the meter uses to test for continuity could damage an ECU.
Unplug the wire from the sensor- you don't want the sensor itself affecting the reading.
ANYTHING connected to the wire could affect the reading.

Now, getting a 0 (zero) ohm reading means the conductor is electrically continuous (connected).
you need to make sure that the conductor being tested is not continuous to any other conductor as well- this will eliminate wires shorting in the harness.
Also test the wire for continuity to the chassis (ground). That should read infinite. If it doesn't, something is wrong.

And, IIRC (read about it on the 'net), the knock sensor wire, even though it doesn't look like it from the outside, is a shielded conductor, meaning there is a center conductor surrounded by some insulation, then a 'shield' conductor kind of like cable tv coax cable. The shield is supposed to be grounded (should be grounded near the ECU) in order to isolate and prevent any noise from the ignition system and fuel injectors leaking into the knock sensor signal.

-=j0nnyr0773n=-

Ya I have been testing the wire with the plug unplugged from the ecu and the sensor unplugged, I guess I forgot to mention those exact details. I'll look closer at the wire to see if the wire is shielded, but I really really don't think that it is. I was reading somewhere that before 87 a lot of trucks don't have shielded wires on the knock sensor but that may be totally wrong. Well anyways, about the knk wire being plugged into the wrong pin on the ecu harness... is that something to worry about? Otherwise, so far I am thinking the knock sensor is probably what is bad being that my wire tests good for continuity. Where is the shielding supposed to be grounded near the ecu so I can check for that?

-=j0nnyr0773n=-

After a careful inspection I found that the wire from the sensor does is not a shielded wire. There is a tube around it that looks as if it shields the wire from heat but inside the wire insulation there is not any type of shield. The wire is 14 gauge stranded wire with only one layer of insulation around it. I did test again with my multimeter and the connection is good, but again the wire is going to the wrong spot on the harness to the ecu, does anyone have any insight on this? Anyone with an 86 22re that can check to see where their knock sensor wire is connecting up on the ecu?

abecedarian

wish I could help more. I have an 88.

good luck

-=j0nnyr0773n=-

Thanks for all of your help so far

SDTrucking

I had the same problem best advice is get the info on your ecm (now installed) thats in the vehicle and then the sensor value from other ecm and test that way as long as the person (you) or previous owner set every sensor up right it will read correctly at the pins

Hadmatt54

According to my 86 wiring diagram manual the position of the knock sensor is 18p #2, it is a black wire and it is shielded. The shield seldom goes the complete length of the wire so you won't see it at the knock sensor and it is tied to ground in the harness before the ECU and ultimately it is tied to ground at the intake manifold.
Only 4Wd's have a TSW and it is in position 18p # 16 and is a green black wire. The wiring diagram book backs up the ECU pinout page in your first post.