1UZ no sparks issue?

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Got my harness back and needed to redo the sub harness that connects to the Cam and Crank Sensors in the front of the motor. It was brittle and waiting to snap. After the rewiring that part, my motor would not start. It cranks only. I recheck my connection with 3 different wiring diagrams and everything is correct.

I test a few things and this is what I found:

I have no IGT1 & IGT2 voltage. Cam and Crank Sensors are in specs. Did a continuity check back to the ECU and there are no shorts found on those wires. Also continuity check the wires back to both ignitors. Both ignitors were also grounded. No issues found there.. IGF1 & IGF2 has 5.0V when ignition on. Fuel pump is turning on when cranking. Driver side coil resistance is a little high by 2 points. Didnt think that could be a problem since both head are not sparking up and no signal from ECU to trigger it.

What could I be doing wrong? Is there something I'm NOT checking?
 
Do you get spark when you manually trigger the ignitors? Which ECU are you using? Did you wire it or did you get someone else to do the loom? Have you checked the Caps in the ECU are OK?
 
Thank you for your reply.. I have not try to manually trigger the igniters. I will have to give that a try. My ECU # 89661-24240 from a 1992 SC400 40/40/40. The wire harness was sent to Tweak'd Performance where at 1st had many mistakes. I had rewire a few wires, and jump a few wires and trace a few wires to get it running. Totally not PNP. It was sent back to Tweak'd Performance the 2nd time. This will be the first possible start up with the new revision of that harness. I have checked the CAPs in the ECU and everything there is good. Im not sure if this "no sparks" is part of a another bad wiring job from Tweak'd..
 
Well that's a step forward.
Is the fuel pump wired through the ECU or via an external system? The SC400 ECU needs to run the fuel pump ECU to trigger the fuel pump via the ECU so it's most likely externally triggered.
I would quickly check the ECU is powered up correctly. Constant battery voltage all the time at BATT E9-Pin33 , Key on IGN E9-pin 1 , then power from the main relay, if wired correctly at +B and +B1 E9-pin31 and pin32.
Here's hopeing the ECU isn't powered up correctly.

From there I would be scopeing the Cam and crank triggers and then plugging in my spare ECU.

Good luck
 
thanks for helping. i've been trying to get a hold of a scope. my buddy has a snap on scanner that has a scope setup on it but im not sure if it needs to be connected to the DLC1, which i dont have wire up. i've also read using a multimeter and setting it on AC voltage and then cranking the engine can tell me if the cam and crank are working? im assuming its not that accurate but it might tell me just what i need to know...i also order a 93 ECU with NO TRAC, since before i was having TPS & AFM issues..so we'll see how everything turns out in the next few days or so. thanks again...
 
A scope need not be connected to DLC1. It just shows you waveform of any signal source you connect it to. It just needs AC outlet or battery to run, and 2 signal wires (signal itself and some reference, which is usually earth/chassis body).

A multimeter will show you the presence of some AC signal and ballpark figure of its RMS voltage. In fact, any LED would give you the same level of info while being more handy
 
George_R said:
A scope need not be connected to DLC1. It just shows you waveform of any signal source you connect it to. It just needs AC outlet or battery to run, and 2 signal wires (signal itself and some reference, which is usually earth/chassis body).

A multimeter will show you the presence of some AC signal and ballpark figure of its RMS voltage. In fact, any LED would give you the same level of info while being more handy
Click to expand...

Thank you. I've been trying to borrow the scope and he is extremely busy at his shop. His wife as I type this is in labor as well..

Some progress, I order a 93 ECU w/o TRAC and plugged it in, same deal, no signal to IGT1 or 2. NO trouble codes are found. I went through the wiring schematics for the 2 cams sensor and crank sensor and they are correct. I even by pass the igniters and found i have sparks on both head. Ran the volt meter under AC voltages and tested it and all 3 sensors are responding. I am in a complete lost now until I can borrow a scope. What other avenues have I not explore? Please help direct me? Thank you guys.
 
If there were no earth he wouldn't have got the spark when manually triggering the igniters

fourstars I once experimented with a 1UZ to find out what's the minimum requirement to get spark. There will be one as long as crank position sensor is fine and getting the proper pulses, and there's no need for any other sensor, even those getting the cam position.

Of course you must check the IGSW, +B, BATT, E1 terminals of ECU. Better do it with a 20Wt bulb to see if the power wires can deliver enough current. Then after the power is triple checked I would inspect the cam sensor pulses with an oscilloscope. You can in fact arrange a laptop's sound card to do that. Check that there's enough amplitude *at the ECU pins* and that there's the proper teeth per crankshaft rev.
 
Last edited:
There are 12V found on when IGN is ON @ IGSW, B+, & MREL. BATT is constant 12V. 12V is also present at the injectors and both coils. Both IGF1 & IGF2 has the 5v reference when the ignition is ON.

I will be checking the grounds today. And possibly adding more grounds just in case.

I also changed out the crank sensor for a known working one.
 
I somehow suspected Tweak’D Performance has done another mistake on the wiring harness. Is there anything in the wiring harness that needs to be look at?
 
still too little info currently, suspect anything. Start with the 2 wires from the sensor to the ECU though
 
Just to confirm you have power to both the +B and +B1 pins?

These older looms are also a bit prone to poor contacts on the terminals at the ECU. I've had a with this issue lately. You get the input signal at the outside of the ECU but it doesn't go into the ECU. Opposite with outputs. I have been lucky in finding these most of the time but sometimes scope from inside the ECU.

George only the ignitors need to be earthed to trigger them. The ECU can still lack earths. 5 earths in total on these ECUs. I do like my bulb type test light for testing this stuff. I'm often surprised what isn't needed to make a engine start.
 
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