7MGTE Ignition system functionality breakdown and questions. PLEASE HELP

the t3d

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I've done so much reading and testing over the last month on my 7M's ignition system to try and diagnose an issue of just random cutting out of the engine, but I can honestly say that I have learned a whole lot. My supra has been down for a couple of months now, and now that the semester is finally over, I have had much more time to do more reading and testing. To keep the long story short, initially, the car would sometimes just cut off like you turned the key off randomly. Sometimes it would start right back up with no issues or symptoms, and other times it would just crank but not turn over. I knew it was an ignition issue because when this happened, I would not get an RPM signal to the tachometer. When it wasn't acting up, the tach would work just fine. Anyways, this went from a intermittent problem to a constant problem where the car will not start at all now, just crank. This is definitely much more preferred with electrical issues, I know that. When she is running though, she runs goooood. No mechanical issues at all. It's beautiful.

I have tested the CPS thoroughly, both with the DVOM and feeler gauges, and it tested out right within spec. I have even cleaned up some of the wiring as well. There are no codes that lead me any direction. I tested ground, continuity, and resistance of all three coils, and they checked out okay. All fuses and wiring has been inspected and passes with the proper voltage and grounds as they should. I tested the igniter carefully, and even made some fancy jumper wires to make the process a little easier. All tested okay. I thought maybe the ground for the igniter was the issue, so I did the Jetjock igniter ground mod, as well as the extra ground from the 02 sensor to the head and body. I cleaned and smoothed out all ground contacts to where they are grounded as well. The ignition wires and spark plugs are all new, as well as the harness to the coils.

I finally went to the ECU and identified any and all wires related to the ignition system. I checked all basic power and ground points the ECU just to rule them out, and they all checked out. I read Jetjock's very thorough explanation of what the igniter does and how it communicates with the ECU, and from I understood, there are 3 wires that are signals FROM the ECU, and then one that communicates back to the ECU (IGf, I believe). They are 5-volt signal wires that are either on or off, depending on which coils are to be fired on, but no in between voltage values should be read or sent from the ECU to the igniter. My problem is that I am reading a voltage of 1.1 volts at the IGf wire and 0.1 volts at the IGt wire. The other 2 wires, I am getting 0.0 volts. This is with just the key in the on position. I'm assuming I should be reading 0.0 volts across the board? I also wanted to measure the voltage if any at the IG check connector location. With key-on, I am measuring a ground signal and 0.0 volts. When I crank the car, I am reading a consistent 0.3 volts at the IG check connector, which is coming from the igniter. I don't know what numbers I should be reading there, but I shouldn't be reading any voltage amount with any ground locations, correct? My igniter and the one that I bought to replace and retest have made no difference at all with this problem. I know the timing and positioning of the CPS is correct, and the ECU numbers seem to be the only thing that isn't making sense to me. I am going to remove the ECU tomorrow and I am tempted to open her up and see if anything is roasted inside. Those voltage numbers just seem odd to me. SOMEBODY, PLEASE HELP.

Also, if I am looking at a new JDM ECU, if anyone has one for sale for a pre-89 7MGTE, please let me know! Thank you so much!
 

Piratetip

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Just based on the issues I have had with mine.
I would primarily look into the CPS/ coilpack and ignitor wiring and connectors/ pins ect...
I've had similar issues where it would be running fine then go to start again...nothing. crank and no start.
I've pretty much narrowed it down to connectors at this point but it needs to happen a few more times for me to diagnose properly.
If I unplug and re- plug the cps / coilpack and ignitor everything works fine again.

My bet is you are loosing a signal or connection somewhere.

I have to methodically go through each individual part the next times(s) I happens.
Though will take some time with an intermittent issue.
 
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plaaya69

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I know when I got my 1st remain CPS unit from A1 Cardone a wire inside the unit would short out and touch the CPS metal housing. It would only cause problems when the engine warmed up which was the weird part then the Supra would turn off and just crank over and not start when fully warmed up till it cooled down again. When I got my 2nd remain CPS unit, I had some old o2 sensor high temp wire sleeve and I used that inside the CPS unit to protect the wires a little more so they are not pinched on the hot metal CPS housing. I would take a double look and inspect those wires and the insulation on them inside the CPS unit.
 

Piratetip

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Yeah I think part of it is the weak signal from the CPS under idle rpm (cranking rpm).
If there is a short or weak connection somewhere it won't start.
I've only had issues during cranking, never while driving.
 

figgie

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Inspect the wire going to the 4 pin connector on the cps housing. With age, the protective covering of the wire deteriorates and then the wires short or ground out.
 

the t3d

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Just based on the issues I have had with mine.
I would primarily look into the CPS/ coilpack and ignitor wiring and connectors/ pins ect...
I've had similar issues where it would be running fine then go to start again...nothing. crank and no start.
I've pretty much narrowed it down to connectors at this point but it needs to happen a few more times for me to diagnose properly.
If I unplug and re- plug the cps / coilpack and ignitor everything works fine again.

My bet is you are loosing a signal or connection somewhere.

I have to methodically go through each individual part the next times(s) I happens.
Though will take some time with an intermittent issue.
All good tips, but I have connected and disconnected, shook, wiggled, and tapped on every connector tied to the ignition components. When I was first noticing this issue, I went through the connection and connectors, unplugged and reconnected them, and then sometimes it would start up with no problem. This time now, there are no changes with messing with any connectors or wiring. There is just a constant no RPM signal when cranking. Every component has tested okay as far as measuring voltage where it is supposed to be, resistance levels, and also the gaps within CPS measured right where it should be. I have cut and heatshrinked any exposed wires going to the CPS as well. Any thoughts on the measured voltages I found at the ECU with the ignition wires? I wish I had another CPS to swap in just to see. I have the ECU removed and I'm going to open it up to see if there is anything noticeable around those connections.
 

the t3d

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Inspect the wire going to the 4 pin connector on the cps housing. With age, the protective covering of the wire deteriorates and then the wires short or ground out.
While I was getting power where I am supposed on all ignition connectors, I am going to start peeling back all the wire loom and tape and inspecting the wiring closer to the main harness.
 

figgie

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Umm. The cps is it's own power source, 1 ground wire and the rest feeding the tccs/standalone.

The ignitor does have power going to it. If you get rpm on dash, ignitor is not the issue.
 

A70nut

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Not sure if the 7m system is the same basic principal when it comes to the igniter, but on a jz the rpm signal is acquired from igf for coil 1, so if the first coil isnt firing you wont get an rpm signal, which would mean in your case unless you are seeing electrical noise, you have at least one pair being fired. I noticed that you say you have 1.1 volts on igf though, is this constant? Is the 1.1 volts coming from the ecu side of the harness or the igniter? Does it happen with both igniters? Does voltage stay the same on the circuit no matter of engine position? What if the ecu is unplugged?