Well, although I don't fully understand the continuity readings the voltage readings are correct so I'll assume that sensor is good. I'll be pulling the ECU today to send it in for repair/replacement. It's the only thing left that I can think of.

 

UPDATE
It's been a few weeks so dropping in to give an update...
I sent the ECU off to SIA Electronics to have them troubleshoot/repair it. They indicated that a power chip on the board was bad so replaced it. Great news I thought. Finally found the problem. It was just returned on Thursday. I plugged it in with fingers crossed. Engine turned over fine but would not start. Tried several times with no luck. As soon as I would turn the key to the on position the radiator fan would come on. Not a good sign. I tried to see if I could read any codes with my OBDII scanner. Won't even connect. At least before I could start the car and use the OBDII scanner. The ECU isn't even powering up. The car has sat untouched since I pulled the ECU initially so I'm going to contact them on Monday to return it.
Now here's the other possibility after some additional troubleshooting. On the ECU harness, I probed the harness pins 119, 120 and 121 for power. I read online that 119 and 120 should show 12V with the key on and 121 should show 12V with the key off. Well, 119 and 120 show mV of power regardless if the key is on or off (more when it's on) and 121 shows 12V when the key is on and off. Maybe power isn't getting to the ECU but again I did nothing since the ECU was pulled before when it was at least powering up. Checked ECU fuses in the driver's panel and the box near the battery. All good. Went to the ECU relay on the IPDM and tested it. All good and functions properly when applying a 12V power source. I probed the power contacts for the ECU relay on the IPDM with the key on. I expected 12V because that is what is sent to pins 119 and 120 on the harness. I got mV of power on my DMM. Could this indicate a bad IPDM? What should I be seeing for voltage here?
Does anyone know what connector on the IPDM supplies it power? I want to check this as well and make sure the IPDM is in fact getting power. However, I can't find anywhere online that shows this.
I just told my girlfriend last night that I know way more about this car than I really want to at this point

 

I don't know but if you are testing the output without the relay in place then it won't have voltage. Make sure the relay is clicking when the key is turned on, if you tested the relay and it's not clicking then I'd look into IPDM.

 

Dark, I'll try what you said about listening for the relay click when the key is turned on. Might be hard though with all the other relays in that vicinity.
Just curious though, why do you say there would be no voltage at the relay receptacle without the relay in place? Obviously the circuit won't be closed but just like a wall receptacle I should see the power that would run through the relay to close it.

 

If you check the input to the relay you should see voltage, the output will not have voltage due to the relay not being in place. Mind you the relay can click and be bad, only way to be 100% sure is to wire it up and test it because resistance is a bad value to check for in most cases. One strand of wire will have continuity but isn't enough to transfer any significant amperage.

 

Ok, just got done running a few more checks. With the ECU removed (so I didn't damage it with power cycling), I turned the key on with the ECU relay removed from its socket on the IPDM. I then slowly inserted it to see if I could hear/feel the relay contacts close. Nothing. I then pulled the ignition relay and tried it in the ECU slot. Nothing. I inserted the original ECU relay into the ignition slot and the contacts closed and it worked fine (fan kicked on).

I also tested the ECU relay using a 12V power supply. The contacts closed and continuity checked good on the output terminals.

Is this enough to say the IPDM is bad? I assume with the ignition on I should have heard/felt the contacts of the relay close at the ECU socket on the IPDM?

 

I'd say there's a chance it's the IPDM. But I'd look to make sure there isn't something that's inhibiting that function before getting one.

 

Such as...? I plan to check the power supply to the IPDM when I pull it (asked this question above to determine the power connector). If it's getting proper power, what else could it be but the circuit board inside?

 

First, get the ECM fixed. The repair job bricked it. Second, have you replaced the throttle body with a known good one? I haven't read the entire thread. I did read that you unplugged your TB and it ran fine. This indicates to me that the position sensor in the TB is likely bad. The TB's in these cars are extremely fragile. It's possible it just went bad. Might have nothing to do with the clutch replacement.

 

I appreciate the response cobra. I know it's a long thread but I tried to document what I did throughout the process to get advice and help others. The throttle body has been ruled out as the problem. It was one of the first things I went after.
I agree, fix the ECU if it's broken. However, knowing that the IPDM isn't sending power to it I need to fix that before I decide what to do with the ECU. With no power, it doesn't matter if the ECU is broken or good.

This afternoon, I did a more thorough job with a better setup to test the power sockets for the ECU relay. I get mV level readings. To confirm my setup, I tested the ignition relay power sockets and saw the full 12V. I should see the same 12V on the ECU sockets as well, unless someone disagrees. Supposedly, this relay sends power to pins 119 and 120 on the ECU harness. I get the same mV readings there as well. If my logic is right, there is something wrong with the IPDM.

 

You check BOTH ecm fuses in the IPDM? There's two.

 

Been a little while since I've posted to this thread but I haven't found the issue yet. I'm about at the end of what I can do and plan to take it to someone this week. Trying to decide to go back to the stealership or try a local shop with 4 decades of experience.

The latest test I ran that I don't really know how to interpret is related to the Absolute Throttle Position reading from my OBDII scanner. When reading live data with key on but engine off, I get 0% without depressing the accelerator and it will gradually increase as I press it up to a max of 83.5% when the pedal is to the floor. This is what I would expect although I thought I would see 100% at WOT. Doing this with the engine running I get completely different results. At idle without depressing the pedal, it holds steady at about 6.7% even though the engine is revving in its rhythmic pattern between 2000-3500 RPMs. If I press the pedal and bring the engine to 5000 RPMs, the ATP stays around 6-8% per my BlueDriver scanner. I know that isn't what I should see but I don't know what that is telling me. Why does it work properly when the engine is off but doesn't when started? Before you say a bad TPS on the throttle body, I've replaced it with 2 different bodies (one brand new Hitachi and one OEM from another Nissan) with no change. Thoughts?

 

Two things come to mind, one are you able to see both signals from the TB (or TBs) if HR?
Two have you looked at the APP sensor signal?

Please understand that this is just my thoughts, take it with a large grain of salt.
Hope you have success with this issue
and good luck.
Please let us know how it turns out.

 

Thanks EJohn. I don't have an option to view both signals from the TB separately. I only get one readout which is what I provided above.
Regarding the APP sensor, I haven't tested the signal itself but did change it out with a new, old stock OEM sensor. No change.

 

You should see some throttle percentage at idle. With an electronic TB, you no longer have a separate idle control system. The ECM just opens the throttle a certain amount in order to idle. The amount varies with every throttle body. This is why to have to do a closed position learn and an idle control learn every time you swap throttle bodies. I assume this has been done.

 

I apologize I didn't read the entire post before I posted last night.
When I did it jumped out at me that you were having an issue with the IDPM supplying the correct voltage to pins 119 and 120.
Haven't looked at the FSM so can't say anything about on that. If it were me I'd start there and find out why not.
It seems to me you've tried everything else.
Hope you have some luck with this.

Ejohn.

BTW, electrical stuff is the worst.

 

Yes, I've done the relearn procedures more times than I wish to admit. It has never yielded any changes.

Regarding the IPDM, I actually bought another off Ebay that was tested good and swapped it out. I just went back a day or so ago to confirm that the ECU relay is closing when the key is on. It is but I didn't pull the ECU to test what voltage is going to the pins.

Here are the next options I'm considering. Let me know your thoughts if you agree...

1. Either take it back to the stealership and pay for them to continue troubleshooting at $150/hr
2. or I could buy a remanufactured ECU from Flagship One already programmed for this car for $400. I will lose the custom tune but at least I can drive the vehicle if it works.

For what they charge for labor at the stealership, I can continue to throw parts at it or at least the ECU. After that, I have no more ideas.

 

I would not go to the stealership just yet...

As far as buying an other ECU, not yet.
If it were mine, first check the fsm for the proper voltage at the IDPM if it is good, then check it at the ECU connector. If not good then it probably be a good idea to test the wiring between the IDPM and the ECU.

If it is good then time to rethink other options.
Dealership/different ECU.
BTW this is what I would do not necessarily the only way to find an answer.
I sincerely hope you will be able to get it fixed.
All of the above is just my two cents.

Let us know what you find.

 

Since this nightmare finally ended today, I wanted to close the loop on this thread in case anyone runs into this crazy issue down the road. And no, I didn't take it out into the woods and burn it to the ground although I've thought about it many times.

After a ton of troubleshooting and 2 separate visits to the dealership, the car is now running and back on the road. What did the problem end up being? Bad ECU or software on the ECU. Not sure exactly which one since I changed both but it was one of the two.

Longer story... I did suspect the ECU earlier on but was trying to troubleshoot first with the cheaper/easier components that may have been contributing to this issue. Once I finally decided to focus on the ECU, I had the existing one sent off for refurb (twice!) which was a complete waste of time and money. I think I'm going to call them and let them know it but I don't expect any refund. That never fixed the issue. I then bought an ECU off Ebay from a salvage car that proved to be defective. The dealership programmed it multiple times with no problems but the car would never start. Returned that one for a full refund. Bought another one directly from a salvage yard in Buffalo. Took it to the dealership for programming and BAM! it worked. Obviously, the dealership loaded the OEM software on the new ECU so I really don't know if the software fixed the issue or the replacement computer. We discussed previously them flashing the old ECU with the OEM software before I bought these other ECUs but chose not to do that in case it resulted in a completely dead vehicle. At least I could start and move it with the old one as is. The engineer in me would really like to know for sure but I need a break from this POS for a while.

So there you have it. If you ever see a problem like this, it may be worth skipping all the BS I did and go straight to the ECU. The only other write-up I ever saw on a similar issue ended up being the same thing. I certainly learned a lot through the process but it wasn't worth the years it shaved off my life. Total cost dealing with this issue has been about $1100. Of that, $685 was put towards either repairing the existing ECU or buying a salvage ECU and getting it reprogrammed including all the issues I ran into with bad repairs and ECUs. The rest of the money was spent on miscellaneous part swapping while troubleshooting (used IPDM, used throttle body, pedal position sensor, dealership troubleshooting, etc.).