Hello I am new to this forum and new to rotaries in general so please be patient. Ive got a 94 rx7 and have been troubleshooting the fueling for a while now. I’ve read a bunch of different threads and what I’m experiencing seems to be slightly unique. I have just replaced the FPD, FPR, and fuel filter. I have a new fuel pump otw because I don't think its ever been replaced. When I have the ignition on, the AFR will read rich and then go lean point by point until it is unreadable. When I go to fire the car up the AFR would be perfect but after a few seconds it would become unreadably lean and the car would run rough and stall out. Still have a few more tests to run such as injectors and the noid lights. I’m not seeing or feeling any leaks when I run the system via the diagnostic box. When I go to check fuel pressure should I go to the schrader valve on the secondary rail?

 

Key on, you're watching the wideband go through its heating cycle. It's doing exactly what it's supposed to. Depending on how you have it wired, it repeats this process post start. This why it's best to wire your wideband to a power source that maintains when cranking. So post start you are not seeing actual afr readings, you are seeing the wideband go through its heating cycle.

What ecu are you using and what Schrader valve are you talking about? What rails do you have?

 

How many miles are on the car? I'm asking because the issue could be related to the engine (emission) wiring harness.

I'd see if the car will stay running on bursts of starting fluid. Your pump could be failing and only running enough to prime but not maintain the pressure needed for the car to stay running. It's worth replacing after 31 years and I wouldn't troubleshoot too much more until it's done since you have one on order already. Alternatively, you could have a power issue to the pump which you could check now. Ground the "FP" pin on the diagnostic connector and listen for the fuel pump running, if it does try to start the car. If the car stays running your issue is related to the power circuit, probably ECU relay triggers.

Another thing you can do, which is generally a good idea on any stock FD, is to bypass the "Fuel Pump" relay in the box that is mounted to the radiator support. Put a 10AWG jumper between the two load terminals to bypass the fuel pump resistor pack to ensure your pump gets full voltage while the car is running. The factory setup for the car turns the pump on with the circuit opening relay, which sends fuel pump power to the "fuel pump" relay and the resistor pack, the resistor pack reduces the voltage to the pump so it runs at a lower speed. When the ECU sees a satisfactory amount of engine load it triggers the "fuel pump" relay which bypasses the resistor pack and sends full voltage t the pump to speed it up.

 

Aaah okay that makes sense. I’m running stock ecu with a PFC. My bad meant the banjo bolt on the secondary rail, and I am still running stock rails.

Jake

 

Thank you for this! the speedo says 48k but its aftermarket so Its gotta be close to 100k maybe. I’ll try this out sometime after work this week and check back in!

Jake

 

Stock ecu OR a power fc? You can't use both

 

Apexi PFC, my bad.

 

cool... post a picture of your sensor check screen with key on. a fuel pressure check is definitely something you should do but as suggested, jump the pump at the diag box and see if that helps. it can steer troubleshooting in a different direction depending on the result

 

Just tried jumping the pump and it did seem to start up a tad bit better and tad bit better idle but still rough. Give it a bit of gas and then the AFR goes from rich to unreadably lean. Im starting to think it might be the UIM gasket, even though its metal it was a bit warped and not very flat. Almost seems like a big vacuum leak.

 

What's the story on the engine- is it a rebuild you installed?

 

The running OK on startup and then rough to the point of stalling out as it gets warmed up phenomenon on a PFC (or really any ECU with a functional fuel temp compensation such as the stock ECU) has been a case of the owner mistakenly plugging the water temp connector into the fuel temp sensor and vice versa after a botched 'rats nest cleanup' more times than I think they'd like to admit. I can't tell you how many cars people would bring to me in that state when I used to do maintenance and street stuff.

 

If you are going to replace the fuel pump, I would also get a relay kit to make sure it has constant power. There are a few to choose from, but Sakebomb is local to you.

 

So I bought the car in September and the pilot bearing grenaded and so I had the pilot bearing, throughout bearing etc. replaced. When I got the car back. I was running leaner, but still okay. fast forward a couple months and started running way lean so I replaced the parts I mentioned in the first part of the thread. The guy who I bought the car from didn’t do anything other than maintenance. Whoever originally had the car did a rebuild, street ported, seals, apex seals, and slapped on the turbo setup from the ‘99 models. Thats about all I know. What was interesting when I had the UIM off I noticed there was no rats nest and there were plenty of plugs with nothing to plug into. Not sure if this is common or not ideal.

 

Just tried switching them and ended starting up but dying immediately. Makes complete sense though being the same color and connector. Thank you!

 

you are absolutely correct about this. the plugs are the same and they reach lol very common mistake and people spin their heads backwards trying to figure this out

 

This means they set your car up for non-sequential. It makes your car feel like it has a larger single turbo and you lose the benefits of the sequential system like instant boost pretty much whenever you want.

 

My bet is on the fuel pump.

 

Just replaced the fuel pump and now the car will start up but is still running lean. When it got a lil warmer it started to get richer and then as soon as I gave it a bit of gas it leaned out. I have the relay kit but at this point Im waiting to install until I have it running correctly and have time to get it retuned. When I start it up the AFR goes from 13s to unreadable.

 

heres one video

 

and another

 

It's not pulling much vacuum, and without the tacho I'm only guessing but it sounds like it's idling too low if the engine was cold during those videos.
If you've confirmed it has fuel pressure, my best guess is a vacuum leak causing the ECU to use the wrong cells in the fuel map. Or the ECU just needs to be calibrated better; getting a standalone ECU car to idle well both cold and warm can be harder than most people think. The IACV needs to be allowing the right amount of air, the fuel and spark maps need to be calibrated well enough to keep the engine happy, and the system needs to respond to disturbances well. The extra load from fans or lights or the AC compressor activating is very significant compared to what the engine is usually experiencing at idle.

Have you tried a smoke test to check for vacuum leaks?
Does it have the Idle Air Control Solenoid Valve still? Can you check that the IACV has 12V power at one of its two wires when the key is on?

 

Have you checked your fuel pressure yet? With a gauge