You mentioned that you removed and had the fuel injectors serviced. Judging by your codes and issue you may have a loose ground or a broken wire to the factory ground in your emission harness (the one from the ECU to the engine.
Check ground points 3 and 4 on the engine block (emissions harness) and ensure you have the ground strap from the firewall to the engine (UIM) in place. Ground point 4 should be on top of the front or rear rotor housing and ground point 3 should be back by the lift bracket/UIM bolt. Also make sure your ground wire from the left strut tower to the engine block and starter is tight.

If all of those check out pull out your DMM and check ECU pins 4A, 4B, and 4C for continuity to the engine block, A & B go to ground point 4 and C goes to ground point 3. If your emission harness is original and baked you could have a broken wire.

 

Thank you this is a lot of good info, I will check as much this as I can when I get off work until I run out of daylight. Some of those codes exist because those emission solenoids are completely gone but they’ve always been gone. My harness is indeed baked. I’d love to buy a new one but they’re so expensive. I think I saw a thread somewhere about making your own. I might look into that in the future.

 

I just had the exact same issue with the exact same symptom where my pump would run only if I jumped F/P to GND in the diagnostic port.

My fuel pump resistor went bad.
Like you, I ruled out every other fuel electrical component first. The 2 FP relays, the fuel pump, the fuel pump connector & ground all tested fine.
When I tested the resistor with a continuity test, it tested fine.

What fixed the issue for me is jumping the fuel pump resistor connector to bypass it. The resistor appears to have continuity and let voltage through but only a tiny amount. (For me it was something like 200mv)

If I were you I'd try jumping it and then voltage test the fuel pump pins at the rear of the car while cranking. Takes 5 minutes
If you want to preserve the speed control used fuel pump resistors are available on ebay but most people bypass the system.
If you want a newer resistor the rx8 probably uses the same part (don't quote me on that)
If it's a harness or ground issue just rewire the pump like everyone else does and then track down all the rest of your electrical gremlins separately.

 

just tested the resistor by bridging it, no luck

 

I inspected the rub in the front harness. All wires intact. This happened a year ago and I forgot to cover it back up. I heard rubbing and I pulled over quick and ziptied the harness up out of the way. My date was not impressed by my emergency zip ties in the glove box or me laying on the ground to get them in. I was pretty proud of myself though.

 

godspeed with your deep dark hole of ecu & harness diagnostic.
i have a USDM ecu lying around lmk if you need it and we can work something out.
part # n3a1 18 881a

 

I think the wire to the resistor is "L/W". Can you see it among those exposed wires?

Also even if the wires do not seem damaged, water will get in there and move through the loom by capillary action, perhaps find an exposed metal wire somewhere.

I picked up a new OEM resistor for about US$75 on Buyee.

 

https://buyee.jp/item/yahoo/auction/...n_DirectSearch

If you are not comfortable with Buyee try Jesse Streeter.

https://jessestreeter.com/

 

If you jumper the F/P and GND can you start the car?

It's possible the fuel pump driver in the ECU was cooked. I know that has happened on some PFC's. Could be worth swapping another ECU in if you have access to one.

The missing emissions solenoids should not make the fuel pump not run. All the codes you listed are all emissions.

Also you just said that you did get power back to the top of the fuel pump hanger. The pins on that connector are known to melt with bigger fuel pumps. May need to check continuity/resistance across that connection - pull the hanger, unplug the fuel pump harness from underneath the side plastics, and test all the wiring for continuity/resistance from the external plug to the fuel pump itself.

Dale

 

I didn’t try actually starting the car because I didn’t know if it was safe to do so, but I did get power to the pump. Also i haven’t adjusted the fuel pressure on the aeromotive yet. When I bridged fp the first time I saw 60 psi on my fuel pressure gauge.

The only other ECU I have is a power FC I bought but I wanted to make sure the car was running good before I installed it so I wasn’t masking any problems.

At the moment I have the fuel harness depinned and I put alligator clips on it so I can test for power from the drivers seat, I ordered extensions for my multimeter. I’m considering doing some pass thru studs on the fuel hanger so I don’t have to worry about the factory harness anymore. The pins in the fuel pump harness that I depinned look to be in rough shape so I’m wondering if they’re not making good contact when I plug it it. I will check the little blue harness inside the tank when I get a chance that usually burns out but I connected the battery to the outside top of the hanger and the pump did run.

 

I don’t think it’s the resistor because I bridged the connector to bypass it and still nothing. Also the car hasn’t moved in a least two months while I was waiting for parts I can’t imagine other than humidity much water if any going up and under into the hole above my tire.

 

I think it's the wire from ECU 1T to the circuit relay. I pulled the ecu out, and checked for continuity between pin 1K to the fuel speed relay and that line is good. I checked the line from 1T to the F/P port and no continuity. I'm going to T a wire off 1T and run it to F/P to test it tomorrow after I get my wire and connectors from work. But I have some questions. STARTING WITH and most importantly : Is 1T used for anything else, does it connect to anything else or is it a straight shot to the relay? From what I can see it's a straight shot. Also as far as harnesses I know the emission one pretty well now. and I'm assuming each connector to the ecu is more or less a separate harness, I see each harness is numbered. But my question is which harness is 1T in and what route does it take? I won't dare open the loom and sneak this wire in there but I'd like to run it along side it.

Also when reading this, I had assumed the L/B was the color code but none of these seem to corollate to colors. I guess you just count the pins on each harness?

 

Just a sanity check since you said you havent tried starting the car,
have you actually checked for fuel pressure and signal at the fuel pump connector while turning the key to the cranking position?
On this car the fuel pump does not prime with the ignition in the accessories position.

 

I have tried while cranking. Engine would crank but no power to fuel pump, I tested voltage while someone cranked. But my pump definitely use to prime with key turned to ON.

 

What version is your car? You need to have the correct wiring plans for your specific version.


I have the Version 2 wiring manual for USDM (1994 edition).

1T connects to the front harness (F) through connector B1-01.

Wire colour is shown as L/B (Blue/Black) The wir3e from 1T runs direct through the (F) harness and connects to the fuel pump relay * through connector B1-03. It also connects directly to the data link connector.

* It seems the 1994 wiring manual may be calling the "circuit opening relay" the "Fuel pump relay", on the diagrams I'm I seeing (B-1a). It then calls the relay related to the resistor the "Fuel Pump Relay (Speed)".

 

I have a USDM 1993. Yeah I ended up seeing that 1T only goes to the relay and diagnostic port or data link connector. Is there a key to understand the colors? How is L/B blue and black?

 

 

This is exactly what I was looking for, thank you.

 

So I must have checked the wrong pin on the ecu before I knew the color code, I counted pins and I counted from the wrong side. Today before I cut into the harness to run a new wire I tested again using the color code I realized I had the connector mirrored. I checked for continuity one more time. Pin 1T to the relay is good. This leaves two options, the ecu has failed or I'm not meeting the conditions for the ecu to ground 1T. I opened the ecu up, I didnt take pictures because the boards are like a clamshell and I was trying to be careful, but it looks immaculate in there.

 

It sounds like part of the difficulty here is taking useful measurements of what's happening. Is there access to tap the relay pins on the Circuit Opening Relay while everything is connected? I would expect to see 12V at the L/B wire (blue with black stripe, lower-right relay pin according to the wiring diagram) when the relay is off, and 0V when the ECU activates it. Measure this carefully, because the ECU is not going to continually run the fuel pump when the engine is off. The fuel pump only runs for 1-2 seconds immediately after the ignition key turns on to pressurize the system. It should run the fuel pump continually when the key is in the Start position, and when the engine is running.

 

If I'm just trying to test L/B I can test it at the F/P in diagnostic port. I believe I tested it but I'll check again.

 

I ordered an ecu to test. Have to put this on pause for a couple days though because my daily driver needs a little work. Still appreciate any input anyone might have in the mean time.

 

I’m finally back to working on this. I tried another ecu, no luck. I tested most of the wires from plug 4 to the ecu. I found two bad wires.

4M - Pressure regulator solenoid
4F - Split air bypass solenoid

I wonder if these could be my culprits or just coincidence.

Does anyone know if the car will run with rats nest solenoids unplugged? I’ve heard people replace them with resistors when they remove ones that are unnecessary.

 

At this point, I would try a small jeweler's flathead screwdriver, or an icepick, or a depinning tool and carefully remove the wire from ECU pin 1T. Example here, OBD1 Honda vehicles used the same style of connectors but grey rather than yellow. The trick is prying the retaining latch out of the way, it should hardly require any pulling force on the wire at all if you have the latch pried up correctly.

Then I would get a multimeter and measure that wire's voltage with the key on. Since the ECU is not pulling it down to ground, the voltage should be 12V as long as the fuel pump relay is receiving power on its Black/LightGreen wire (from the 15A Engine Fuse). If not, remove the relay and check for 12V at that Black/Light Green wire. If that Black/Light Green wire has 12V, I would run a brand new wire in place of the original Blue/Black wire. The ECU triggers the relay by connecting the Blue/Black wire to ground, as a test you can temporarily connect the Blue/Black wire to ground which should activate the relay, which should send power to the fuel pump.

If all of that sounds scary, find someone local who is good at wiring harnesses and troubleshooting pre-OBD cars. If you're near Tampa Florida, Full Detail Automotive should be able to diagnose and fix that sort of thing. He's a member on these forums also.