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This would make sense as to why the AFM, TPS, and THW would all ohm out correctly when checked individually and the truck would fire up and drive on initial start up. Once the engine is heat soaked E2 sees high resistance and none of these three sensors work in conjunction with each other (they all work, just send erratic input). The truck starts with the AFM unplugged because you have completely removed enough ECU INPUT that the ECU goes into a base map. That's my guess.
My truck is a 1986 but I do not see a 4WD temp sensor. Maybe an auto transmission one may have i
Only the temp sensor on top of tstat housing, and definitely does not affect dash gage, so more likely a sensor to do with AC. Maybe to shut AC down when engine's too hot?
Yeah if you have the short one its the AC cut off switch, it differs from the temp sensor by a stamp on the housing (nut) and I think color of the "cap".
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It is a very safe bet that the "4wd" annotation is an error, if it was intended to say something else or shouldn't be there at all who knows..
Oddly the ECU knows the exact coolant temperature but there is a separate switch used for this fpu activation. Perhaps it is interrupt driven to save on calculation time..
There is a TSB for the 4y used in the van (previa) to combat "heat soak" startup issues, it calls for a switch with a lower temp activation among other parts and modification.
...
There is a completely different sensor for the auto trans temp.
It's been awhile since I've dug into it but if I recall correctly, the ect and ECU communication is one way (ect->tccs)..
We need to be clear an reference the tall sensor (rear most in my photo) with its proper signal name TSW.
AC cutoff is a short sensor, no weather resistant connection, and the wire is part of the forward body harness not the engine harness.
FPU, black-yellow (b-y), pin 9 on the large ECU connector (W).
This vsv is switched ground (ECU switches to ground to activate)
Ok so the wires I found after I took off the Intake and dug into the EFI harness was a dark green one that might have originally gone to the top of the coolant housing(like an idiot i clipped this earlier because i thought this was a diagnostic wire) Rest assured i spent all night soldering in a new wire and running it to hopefully the right spot.
I also clipped the yellow wire with the Blue clip as shown above and tied it together with the green one, connecting it to the top upper coolant intake sensor.
Update: this morning, I was driving into work and it died at idle in the MIDDLE OF THE ROAD lucky for me it was dumping snow and there was a line of cars behind me..... so I asked the guy behind me to unplug and plug back in the AFM while I mess with the gas pedal to get it back and running..very frustrating, but from what I'm seeing is the dark green wire is the only one I should have plugged into the top of the coolant housing? If so I'm going to cut the Yellow wire and leave it because if it's for 4WD or a/c either does not concern me at the moment. Just getting the truck running right is my main concern.
Last edited by YotaRick27; 02-08-2018 at 08:15 AM.
pretty sure your TSW wire is AWOL, its the one that needs hooked up, but that's the wrong sensor for it.
(From memory, the AC switch closes when hot, the TSW temp switch closs when cold, again not sure off hand. Either way it won't be set for the correct temperature)
In one of these threads is the diagram from an 86 FSM (see I've done gone and forgot if this is an 88 or 86). You want to verify you have the fpu vsv, and what signal it received under which circumstances.
The redneck fix is to put a toggle switch. In the air sensor line, at the ECU for TSW, or for the fpu vsv..
A simple test would be temporarily bypass the vsv to trigger the higher vacuum in the regulator.
Please elaborate how I can both test this and put in a switch. Aslo where is the TSW located? I see it in the ECU And what is the correct sensor. I don't understand why this would randomly happen if it was never connected before maybe because of the cold weather he have been having lately?
Also I very much so appreciate all the help with pictures.
Last edited by YotaRick27; 02-08-2018 at 07:02 AM.
Ok so just now I had to run a errand but I wanted to test the theory that the dark green and yellow wires tied together was a bad idea, so I cut the Yellow wire away from it. Dark green wire was extended with white wire so don't lose your minds thinking im colorblind(which I actually am). Here is a pic of the cut wire and the freezing conditions im fighting as trying to figure this out. It seemed to have started better even warm so.....Im not going to celebrate just quite yet because I've done that once before already and was very let down....
Please elaborate how I can both test this and put in a switch. Aslo where is the TSW located? I see it in the ECU And what is the correct sensor. I don't understand why this would randomly happen if it was never connected before maybe because of the cold weather he have been having lately?
Also I very much so appreciate all the help with pictures.
why does it happen now? You moved from draught ville California to soggy cold South dakota and you have loose wires flopping around in the harness.
First things first disconnect the wires you attached from each other and the sensor.
You have a multimeter right, do you have aligator clips? You can pick up clips from the local napa, i think a pair is under 2$. You need to trace those wires back to the ECU.
Set the meter to diode/continuity (triangle with lines on either side) if it has one, this mode will sound a tone when you touch the test leads together. If yours doesn't have this mode you want to set it to a low ohm reading range.
Attach either end of the leads to the wire in the engine bay. If you can clip it on to the metal lug great, if you can put the probe/lead between the plastic housing and the metal lug good, you may need a straight pin (t-pin) between the housing and lug then attach the clip to this.
Now inside the kick panel you unplug the computer. You will insert the meter lead into the back side of the connector (side the wire enters) and touch the top/side of the metal wire lug. If you get a tone, or zero ohms (note, not 0L this is open circuit/no connection), make a note of the wire color, its position, and which signal name (three letters).
Leave the computer unplugged for now.
The next process is to verify you have the fpu vacuum switch, that it has the vacuum lines plumbed, and signal wires attached.
Locate the fuel pressure regulator at the firewall end of the fuel rail, follow its vacuum hose to the VSV, there should be a second vacuum hose to the intake. Make sure the hoses are firmly attached (require some effort to twist on the hose barbs), if these are sloppy/loose you need new hose.
Unplug the harness from the vsv. Test the wires at the VSV with the ignition switch in the run position, you should have voltage on one side (meter on 20v DC, one lead on battery negative with the clip, other lead touching the lug), the other wire should connect to the ECU connector (same test as the earlier, continuity, either meter lead at the VSV to) the top left of the large center connector.
Plug the VSV wires back in. Test for voltage at the ECU connector now, you should have battery voltage at that same top left corner (again these are from the wire entry side). Leave the t-pin in this one well use it later, or the ECU unbolted.
Key off, plug the computer back in.
Set the meter to continuity/ohm, one lead on ground and one on that FPU wire. It should read oL/0L. When you put the key to start you will get a tone (zero ohm) if it is activating the fuel pressure up vsv. Make a note of if it does or not.
At this point it will probably start right up. Close the hood and let it heat up, you need it in the no start condition next.
Ok so now it won't start, hopefully it does this in the driveway with out hassles. Does the FPU trigger this time? Use the vafm unplug trick and note if the FPU activates.
Now with the no start condition, remove the VSV from the equation, take the regulator hose directly to the intake. Does it start now, if so the FPU is your problem and we can hack around it untill you can get the right sensor.
that tape wrapped bundle of wires below you blue notes, is that just laying there with nothing connected if so you want to use the same check as the other mystery (green) wire. Please continuity check those (battery positive disconnected also on these ones) like described above to the ECU plugs.
Ok I will start on this as soon as I get it back im my garage this evening, I do however have to pick up T-pins and Alligator crimps. It might be a good time to pick up a better multi-meter as well, anything is better than my harbor freight freebee.
I appreciate the step by step that is a huge help thank you.
Ok I will start on this as soon as I get it back im my garage this evening, I do however have to pick up T-pins and Alligator crimps. It might be a good time to pick up a better multi-meter as well, anything is better than my harbor freight freebee.
I appreciate the step by step that is a huge help thank you.
that tape wrapped bundle of wires below you blue notes, is that just laying there with nothing connected if so you want to use the same check as the other mystery (green) wire. Please continuity check those (battery positive disconnected also on these ones) like described above to the ECU plugs.
Those are the 3 wires that run to the Ignitor control module. I was planning on putting some plastic heat protectant around it this evening.
Coolant Thermal Switch (TSW) ON top of T-Stat Housing.
Hi guys,
Thanks, Co, for the detailed test procedure.
I finally swabbed 31 years worth of dust off the wire on the Coolant Thermo Switch on top of the t-stat housing (22RE), and verified against 1986 (print) and 1988 (PDF) FSM's. That is a green wire with black stripe. Yes, it is the Coolant Thermo Switch (TSW-4WD only). Same on 1986 as in 1988 22RE so safe to assume same on 1987.
Rick, Looks like you have an after-market switch on there. However, I don't believe that affects operation under normal conditions. Truck start with it disconnected. I think it only comes into play when coolant gets to certain temp limit.
This morning I printed off the tests and step by step to work through it. No work today so once the roads get cleared I will stop by and pick up some t-pin and alligator clips
So this morning I heated up the garage after shoveling the driveway, Went to lowes and picked up a multimeter that will beep at me when contacts touch. First thing I did was the efi system check with the key on
EFI system check was under 11 volts with key on si that ok?What is the fix? bad ground? Here is the VSV connector volt check(key on)
And lastly... the other pin to the VSV
odd that is has 1.97 volts? maybe this is normal(key on)
All these checks have been under cold conditions both engine and outside. (battery is reading above 12v)
Last edited by YotaRick27; 02-10-2018 at 09:40 AM.
So this morning I heated up the garage after shoveling the driveway, Went to lowes and picked up a multimeter that will beep at me when contacts touch. First thing I did was the efi system check with the key on
EFI system check was under 11 volts with key on si that ok?What is the fix? bad ground? Here is the VSV connector volt check(key on)
And lastly... the other pin to the VSV
odd that is has 1.97 volts? maybe this is normal(key on)
All these checks have been under cold conditions both engine and outside. (battery is reading above 12v)
You need to tell us what pins you are probing, it is not clear in the images. Also the post to post battery voltage.
Those weren't my instructions.. Which vsv is that, how do you know its the FPU signal wire (hint just cause it's plugged into a FPU vsv doesn't mean it's the FPU signal wire, not damaged or shorted to something else.).. You need to do those continuity checks from the engine bay to the ECU plugs, it should only sound on the one wire otherwise it indicates a short..
Extra credit, voltage drop test the ground wires. Key on, tpin and clamp on the ECU ground pins, measure voltage to the efi ground strap under the intake, measure voltage to the bolt that attaches the strap, measure voltage to the intake, at the negative battery lug, and finally the battery post itself. Yes at each junction is important, and just at each junction but on each side of the junction.. This is how you identify bad grounds. Also it may not seem prudent to check voltage from one point of a ground wire to the next, but this is how voltage drop testing works, an ideal reading is zero.
Gotta head to work soon, will check back around 4.
Go thru those steps to identify those wires.
Watch some scannerdanner YouTube until he flogs testing your test ground versus known good source into you. He also describes voltage drop testing pretty well, and voltage drop on a bad ground.
the spec for connector V pins 1,2 & 8 is 10-14 (is actually good down to about 9.5, but it starts to throw off other measurements.
You have to double and triple check that reading is legit. Take the negative lead to the battery post, anything less than the post to post voltage is voltage drop, or a bad test. Or.. Leave the negative probe there and take the positive probe to the battery, again voltage drop on the ground wire or a bad test.. With no load you should have battery (post to post) voltage pretty much everywhere, voltage drop only.happens under load (while it is passing current).
Bottom line always check your probe hookups are good and clean signals. They don't fluctuate when you wiggle the probe leads ect. Then check them again, and again to be sure, because a bad probe connection will have you chasing your tail.
02-07-2018, 07:54 PM
