Another step closer!

Dale

 

I just tested both wires. I used my old OEM wiring harness first. 4Q is incorrect, it is 4I (JDM). Tested the L/G wire on the car, resistance is OK.

The other wire gets some resistance when testing with chassis ground (I tried 2 different points and same reading).



Alright and here is the concern:

I tried what you said. I get a reading at the connector of 0.11V when key is ON (ISC unplugged).

When the engine is started, I get a reading of 0.01V at the connector (ISC unplugged).

 

Ah. Well, I imagine then that this would be a probable cause for your idle issues. Whether it's key on or engine running, you should be getting battery voltage at the power pin of the ISC. No power, no ISC of course. I remember when this happened to me the engine would start and run great as long as I kept my foot on the pedal at least a little. When I let off the throttle completely, car would die after maybe ten seconds.

What's the state of your wiring harness? Stock but modded for single turbo? New and custom? I think if you want to fix this the first step would be to unwrap the harness enough to trace back the ISC power wire and ensure it's still properly connected, and that you have power at the connection point. Its not the most fun job to do but it's not too difficult either. The power wire that powers the ISC also gives voltage to the rats nest solenoids (see page B-1b of the wiring diagram). If you have any of those left, you can also check to see if they have power to rule out the power line in its entirety.

 

Not sure on the 4I JDM thing. If that was the case you would have to re-pin that to make the PFC work in a US car. As is the PFC just plugs in to a US car and the ISC works.

Regardless it sounds like we may have an answer as to why the ISC isn't cooperating.

Dale

 

Wiring harness is new and custom.

Resistance from the wire going to IAC to PFC connector is tested and perfect (0.00Ω). Resistance from ground wire (ISC) to chassis ground shows 1.32Ω. I think I can assume that the wiring is OK.

I do not have any rat's nest solenoid left (and no connector for it anyway).

I'm not a master in electricity, but I think it is safe to assume that the problem comes directly from the Power FC... Am I right?

Before sending the Power FC for a repair ($$$), I would like to make sure that it is the problem. Is there another test i can do?

 

Well so I really want to make sure I understand first. At the power wire of the ISC connector, you do not get any voltage when the car is on right? If that is the case, then it doesn't point to the PowerFC as the issue, as the power is fed right from the EGI main relay. Until you find why there is no voltage on that pin, I would keep the PFC in the car.

 

JDM Power FC works on a USDM car!?

I looked your 4Q information by searching on here, and you are right. That is the correct pin for USDM cars. But both my old stock harness and my new single turbo custom harness show continuity with 4I pin (which is for OMP on USDM cars).

With ISC disconnected: when key is ON, I get a voltage reading of 0.11V. When the engine is started, I get a voltage reading of 0.01V (I tried both tests several times and I get a solid 0.11V and 0.01V each time).

Hmmmm. Power is fed from EGI main relay, but that pin on the ISC connector seems to be connected directly to the 4I pin connector on the ECU. So I thought power was coming from the ECU...

 

No sir. Here's how it should be (edit, this is for USDM '93)

The ISC hooks up at pin 4Q of the ECU from a blue wire with green stripe. The other pin of the ISC is black with white stripe and goes out to the EGI main relay.



Here we can follow that wire back.



Now, looks like this also gives power to pin 1B, which is listed as ignition on the power FC pinout, and since we know that's working then we know the first bit of the wire is powered. then it goes into connector X-05, then along to lots of solenoids. The thing to do here, is see if you have anything past that X-05 connector still available to test power on. If you do, and you find power, then you know the problem is past the connector, and possibly isolated to the ISC's connection to the power wire.

If it does turn out that the power pin of the ISC goes somewhere back to the ECU, then I really would be confused...

 

I took a picture of where I get continuity from ISC L/G wire. It seems like it is 4I (or is it 4Q? I'd be shocked if it is, diagram clearly seems to be showing 4I).


X-05 connector - that's the blue connector (female seems to be coming from somewhere under the dash)? At this point I would like to say that my CPU #2 is missing. Could it affect something here?

 

You're looking at the wiring diagram backwards . The pinouts are always from the wire side of the connector. That pin you have highlighted is 4Q but you have to reference the diagram from the other side of the connector.

Apex'i only made 1 PowerFC for Japan. XS Engineering initially brought them to the US and figured out the 4 wires that have to be cut on US harnesses for emissions stuff that's on US cars and not on JDM cars.

The B/W wire is 12v when the key is on (EGI relay on). The L/G wire is to the ECU, the ECU taps it to ground to activate the ISC. It's not on/off - it's a pulsewidth just like a fuel injector. There's no ground wire for the ISC per se, the ECU just grounds that pin in a certain pulse width to open and close the ISC.

CPU#2 missing won't cause any problems with the car running or idling. Had a friend with a bad CPU#2 who drove around for ages with it unplugged with no problems.

Dale

 

Why does it have to be so complicated? Well damn, okay, ISC L/G wire goes to 4Q on my JDM and resistance is perfect.

So I was reading voltage from the wrong wire. I was reading it from the L/G wire. The B/W wire shows 0.00V at all time. But keep in mind that I'm reading the voltage while the ISC is disconnected (not sure if it affects something). Good information about CPU #2, so I can continue to search for that problem without it.

So right now I know something is wrong with the ISC wiring somewhere.

 

With key on the B/W wire should show 12v. Doesn't care if the ISC is plugged in. May want to refer to the wiring above to make sure that fuse/relay is happy too but I think if the fuse/relay was a problem the PFC wouldn't turn on at all.

That wire from X-05 pretty much just feeds the OMP and the turbo control type solenoids. Makes me wonder if that custom harness has something wrong since those are all probably removed for single turbo.

Dale

 

Yes, OMP and all rat's nest solenoids are removed. Maybe there is something I do not understand, but if resistance is OK from L/G from ISC to ECU, and B/W wire shows some resistance with chassis ground, wiring should be ok? I do not know.

 

Mmmmm, if the car is on, the resistance from the B/W wire to ground would, I imagine, just show an overload on a DMM. Since the wire should be getting battery voltage, it would be the same as measuring the resistance across your battery terminals.

The simple thing here is that you've found that there's no power at the power pin. If you're not getting +12V at that B/W wire when the car is on, I'm afraid it really looks like you've got a wiring problem.

I might start simply, and find the X-05 connector, should be the blue one under the dash by the ECU
https://www.rx7club.com/3rd-generati...ctures-892648/
and make sure it's connected snugly. If at all possible, try to stick your DMM probe into the socket of the B/W wire in the X-05 and make sure you've got power there. Then move on to tracing that ISC power wire back and see where it ends up...

EDIT- Maybe you can contact the person who made the harness? I don't know if any warranty is involved, but may want to check on that first, at least before unwrapping any of the harness.

 

The L/G wire to the ECU is good. At this time it seems like the B/W wire is the problem,

Turn the meter to show voltage, and put one lead on B/W and one on a ground. You should see 12v with engine on. If not there's a problem there.

If it's showing resistance to ground it could be mis-wired or something could be wrong on that wire somewhere. That B/W needs to be 12v into the ISC for it to work.

Dale

 

I already contacted that person. He's helping me now.

It seems like you found the exact problem. There is 12V power to the B/W wire (female) that goes to X-05.

BUT, on the male side... It looks like we found something here! There is no wire at all! I found continuity to the pin just under it.

You are amazing.

0.00V B/W to ground. Stay tuned, there seems to be something wrong with the harness, I'll come back with an update later on!

 

Ok, I just spent 30 minutes with the harness builder to de-pin and re-pin one of the wires. I tested continuity with my multimeter afterwards. All good!

At this point, I was ready to rock. Was it finally over?

... not yet. Far from it.

I put the key ON. I went to check voltage to the ISC connector... Still 0.10V to the L/G cable, 0.00V to the B/W cable. Well, how is it possible... "I must have forgotten to plug something."

I went inside to see if everything is plugged in as it should... The brand new harness was burning. I have burnt one of my fingers to quickly disconnect ECU cables, put key OFF, unplug battery.

Now I need to know WHY it happened.

Is it the harness? Or is it something else?

 

Which wire is that, the one you moved? Power being grounded will catch fire like that.

 

Dang... was that the new harness? It most had been close to something very very hot.

 

X-05, under the dash. RED arrow shows before, BLUE arrow shows after.


It was floating in the air, inside the car... Yes, it is the new harness.

 

Wow! not good. Let's just try to piece this together. I see the connector looks to be the JDM style X-05 which is 12 pin rather than 10.
https://www.rx7club.com/3rd-generati...ithin-1024820/
This is not a fun connector, as (at least on the USDM version) the wire colors don't necessarily match up from the female to the male. However, the B/W wire should match in color from the female to male connectors. I see that the burned wire you show is yellow, which would indicate the 1st gear SW. Is that the wire that was relocated?

ie, assuming the harness has its wire colors correct it should go
B/W -> connector -> B/W. If you have it as B/W -> connector -> Yellow, that is a problem.

Key questions-
So was the wire that was moved the yellow wire? Was it in the position of the Red arrow before? What was in the position of the Blue arrow before, was it just blank? If this is the case, then the wiring of the yellow I think was correct, you were just missing the wire that powers the ISC and solenoids.

 

Colors on the new harness are NOT correct. I'm using my old OEM harness as a reference.

• Wire that was moved is NOT the yellow wire.
• Wire that was moved was in the position of the red arrow.
• Blue arrow: it was blank before. Now, the red arrow is blank.

I attached a picture of where the yellow wire is going. As mentioned, I used my old OEM harness for reference.

Top is male, bottom is female.

 

The wire you indicate on your stock harness is the 1st gear switch located on the X-14 connector.
Let's look at this-


Starting at the bottom and going up, the black wire with dots is ground marked B(D). It goes through the white X-14 connector and becomes white (or beige as it is faded) then through the transmission 1st switch, becomes yellow, goes through the X-05 connector, turns to violet with white stripe, then into the ECU. The thing is, the pin that it connects on the X-05 connector (yellow) is right across from the B/W +12V pin (like your blue and red arrows). So, my suspicion is that the wire you swapped was the 1st gear switch and it was in the right place, but was moved to the +12V pin which would mean it would go straight to ground if the car is in 1st gear, burning the wire.

So what were the connection colors before the swap on those two pins of the X-05? was it-
Yellow -> V/W
and on the other pin
Blank -> B/W

Or something else?

 

can you take a picture of the wiring going into your x-05 connector

 

OEM is:

Yellow -> V/W
B/W -> B/W

Before the pins swap:

B/W -> V/W
Blank -> B/W

After the pins swap:

Blank -> V/W
B/W -> B/W




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