[SOLVED!!!] What's the strangest reason your truck wouldn't start? (Yes, I need help)

I think you are right. If I remember correctly, my '92 and '93 PU both had CSC buttons, and without pressing them, you turn the key and nothing happens at all.

 

Yep. That’s exactly how it works, but you can still bump start the truck so it’s not stopping the ECU from firing spark or fuel

 

If it has different logic circuits it will be a different part number. You can't flash one and turn it into another. At least Toyota doesn't give a way to do this in the repair manual.

And I wouldn't trust a company when they say they test used ECUs and all this. My friend needed a computer for an old Dodge van and the company said they thoroughly test, replace components, etc, but it was obvious they just repainted the outside and shipped it out. It's a lot cheaper for them to get used ECUs and send them out without testing and if they don't work send another one than have people that can actually fix the computer. The ECU he received didn't work.

Just make sure the ECU is the correct part number for your engine.

The repair manual has specific instructions to diagnose spark problems working backward from the distributor to igniter to ECU. This procedure would eventually lead to the wrong harness or ECU pinout if that were the problem.

 

I've got the correct part number ECU (#89661-04050), and I've worked through the FSM until it says to test the igniter. I tested it using a procedure I found on Youtube, providing the 12v power and 5v reference signals needed to actuate the firing signal, and it tested fine. The FSM has this as the last 2 steps with "Try another igniter" as the next step, and then check the wiring between ECU and distributor and igniter, and finally "Try another ECM" as the final step in the Ignition system troubleshooting section (Page IG-3).

I understand what you're saying about scam companies offering to repair ECU/ECMs. If everything points towards the computer, I'd rather not spend the $600+ to replace it. So, if a company is offering "repaired/refurbished" computers and they send me a used one that works, I'd be fine with it. But if they just replace the paint over the screws and send mine back to me, that's another story. I'd be pissed off. If you can't tell, I'm getting desperate over here, lol.

 

I've seen pictures of Toyota ECU boards and they generally have letters printed on the circuit board near the output pins, so that is a way to verify the pins match correctly to the wires.

The igniter sends an IG- signal to the tachometer, so if it's receiving the signal from the ECU you should see some RPMs on the tachometer while cranking. Without a tachometer in the cluster you could hook a tachometer to the IG- terminal in the diagnostic port under the hood.

But it sounds like the ECU isn't even outputing the IGT signal to the igniter. That seems to leave the crank and cam signals not reaching the computer or the computer itself.

I wonder if a live data reader on the OBD2 port would show anything unusual while cranking. I'm not even sure if it would work while cranking.

It sounds like you've gone through everything in the repair manual, so I'm not sure I'm adding much. I hope you figure it out.

 

I don't notice a significant movement in the tach when I'm cranking it. That being said, I've been told that it is sometimes imperceptible anyway, so I don't know how reliable that is as a diagnostic tool on my rig. I have had a forum member who lives nearby offer to come by with diagnostic tools to help me figure it out. My OBDII scanner is nothing special and only tells me that the ECU is connected, and that there are no stored or pending codes. Like you said, hopefully a more useful diagnostic tool could tell me more.

I haven't tried the suggestion of swapping the +/- wires to the crank position sensor yet. Seems like a quick fix if those were somehow mixed up during harness construction. I just don't know if swapping them would cause damage to a properly wired sensor. My instinct says no, since the sensor seems to be a simple inductance pickup. Swapping them shouldn't matter, but I am only smart enough to know what an inductor is, and not how it works!

And yes, you are adding quite a bit, as is everyone else. Thank you so much for your time and insight!

 

I still think your issue is somewhere in your distributor since you're getting power in, but not out.

 

Are you getting a pulse on a test light at the IG- terminal in the diagnostic socket? If not then test the inputs to the pcm like cam sensor and crank sensor, kinda need a lab scope to do it correctly.

If the inputs look good and still no pulse at IG- check all the powers and grounds for the pcm. if power/ground is good then the pcm is bad

 

Quick update, but nothing earth shattering: I swapped the wires on the Crank Pos sensor, with no effect. The ORS guys asked for some pics and I should hear back from them again tomorrow. I'm relly thinking I got a crap ECU from Ebay (*surprise*, *surprise*), and FS1 screwed up my order and sent me the wrong replacement ECU. Have you all seen the prices for used ECUs on Ebay lately? You can't tell me a microchip shortage is affecting ECUs built 25 years ago, lol. Anyway, next time I'm outside of San Diego and see a decent pick-n-pull, I'm going to see what I can find. And if it turns out that it is an issue with the harness, I'll have a small fortune in ECUs sitting in my garage that I can sell myself.

 

I got no light at the fuel injector connector. I haven't messed with the diagnostic port. I will see if that yields any results. There is a guy on here who may be coming by in the near future with something better than my 20+ year old Fluke that can give better info than simple voltages and continuity.

 

Forgot to add: The power(s) in and the grounds at the ECU are all good. I did test those, at the connectors while connected to the ECU. Soooo...probably a bad ECU. I've got an offer in on #3. We will see if it is accepted.

 

Today's update: ORS (Who have been amazing, BTW) agrees that it's likely the ECU. So, I ordered my 3rd ECU for this project. The first came from Ebay, and while it looked clean and undamaged, including the circuit board and all resistors (checked them all), I think it was a dud. ECU #2 came from Flagship One out of New York, which is a company I will not be doing business with again. They sent me an ECU for an automatic transmission, which if anyone now or in the future wasn't aware, has an additional (for a total of 4) port on it. And, it turns out, unless that ECU was also bad, an auto tranny ECU will not work with a manual transmission 3RZ. It will be returned tomorrow for a refund (minus their ridiculous $90 "restocking fee"). ECU #3 is coming from a wrecker out of Eugene, OR and has a warranty that comes with it.

ORS has offered to take their custom harness back and do a complete end-to-end continuity test and circuit check, which I appreciate. I'm really hoping it doesn't come to that because of the effort that will be required to remove the thing intact without removing the engine. It was so easy to install with the engine on the hoist. But, if the ECU doesn't fix it, and the guy who offered to help with the diagnostic tools determines it's not the ECU, then this will be the next step.

Unless some new info comes out, I won't update again until the new ECU gets here and I have something to update. Again, thanks for all of your help and suggestions thus far.

 

Starter full of sand.....

 

That’s a good one. Was out wheeling in WA state a while back and a friend went through a frozen puddle in his Jeep.he somehow managed to get ice (and probably mud too) up in his clutch and couldn’t get it into gear. Had to be pulled out and waited for it to warm up enough to shift. Can’t imagine how scratched up that flywheel and clutch disc were.

 

Quick update:
A bunch more tests and checks, another new ECU, and no change. Still no spark or injector pulse.

Yesterday I removed the entire engine wiring harness. Today it is being shipped back to the manufacturer for testing and repair.

Update once I get it back and reinstalled. Hopefully I get the truck started finally!

 

FWIW I spoke to my buddy who has been doing toyota builds and swaps for many years this week and asked if he was familiar with ORS. He actually has a bad ORS harness on the shelf with the same symptoms. He gave up on having them repair/replace after they stopped responding to his calls and emails. Hopefully you have better luck.

 

ORS has been great with troubleshooting thus far. Pretty prompt with emails and I think we exhausted all other options before shipping the harness back. Sorry to hear about your buddy. I hope mine gets fixed because I couldn’t imagine trying to figure out how to build a harness on my own!

 

UPDATE: Recent troubleshooting results and still...all crank, no spark.

Anyone still listening - I sent the wiring harness back to ORS, and they checked it end-to-end, pin-to-pin and it checked out good. I pop-tested #1 fuel injector, and it is opening as expected, just not on the igniter pulse like it is supposed to. So, I've still got no fuel into the cylinders and no spark to ignite it. Igniter, plugs, wires, injectors, distributor, coils, crank position sensor, ECU and anything else you can think of that could be easily replaced has been replaced. Here is the current mystery that may provide some leads: When cranking, the tachometer reads ZERO. All of the time. I double-checked the connections this morning and even tried cranking it without the gage cluster hooked up, and still nothing.

I still have all of the proper voltages and grounds into the igniter, distributor and ECU. OBDII hooks up fine and provides real-time readings of ECT, IAT, MAF, TPS, O2 sensor. However, engine RPM reads zero when cranking, on the scanner and the tach. I have installed the recommended resistor on the tach circuit board, using alligator clips to mitigate the heat. Install verified correct by the wiring harness folks. I could remove the resistor I suppose but that shouldn't make any difference, since I get the same results whether the gage cluster is hooked up or not.

Next steps...??? Anything you all can suggest before I start saving $$ to begin replacing parts all over again. I think I would start with the crank pos sensor (even though it is new). I just don't understand why if I have everything needed, no fuel/spark occurs. I'm on my 3rd ECU and have a hard time believing that they are all bad, when everything else works that the ECU controls.

Still looking for that crazy suggestion that magically makes it all work. It's been 8 months now since I started the swap. I have too much $$ into this thing to just scrap the project. Thanks for your help thus far.

Gabe

 

What provides the reference signal to the tachometer? Crank pos sensor? Knock sensor? Keep in mind, this year of engine (95-96 3RZ, w/distributor) does not have a cam sensor...maybe another crank pos sensor is the answer. I just don't know.

 

Without scanning the whole thread again, have you checked the circuit opening relay? And here’s a screenshot from a quick google search which I’m sure you’ve already done.