Hey team,

I've done a bit of searching/research to try and diagnose this issue, but I'm now at the point of needing to put it out to the world to try and get some ideas/input.

Car is a 1996 series 7 JDM car with a series 8 engine and ECU. Engine/harness etc is almost entirely stock aside from catback and clutch. Has been driving fine with this setup for a number of years so not a recent swap with teething issues.

If I start the car from cold, it will run in limp mode as far as I can tell. It will rev out with light throttle, positive boost/heavy throttle will cause it to cut ignition.
If I drive it for ~30mins in this condition, and then let it sit for 20ish mins before hot starting, it will drive normally, boost normally and have regular power/behaviour and the issue clears up.

I have tried to pull codes by grounding TEN to G in the diagnostic port, and running an LED from FEN to BATT+ (S7 do not have a CEL on the dash). When I turn the key to ON the LED will be static for 4 seconds before starting to blink every 2 seconds. The LED does not do a 4 second pause at any point, just blinks every 2 seconds until key off. If I run the LED between MEN and BATT+ I get a solid LED, no blinking.

I can't find any reference to this CEL behaviour, so it leaves me at a bit of a loss as to what could be causing limp mode.
I have tried resetting the ECU by disconnecting GND and holding the brake pedal for 30seconds, reconnecting GND and running the car for 2-3 minutes. Diagnostic LED has the same behaviour.
I don't have a spare ECU to try, and I'm not in a position to fit a PFC or Haltech or similar.
Fresh fuel in the tank
Because the car does drive correctly when hot I'm inclined to think it's a sensor not quite reading correctly when cold.

Any help or suggestions are greatly appreciated!

Video of the ignition cutting with boost/revving out with light throttle -
https://youtube.com/shorts/D2Ab2kgtnK0?feature=share

Video of LED in diagnostic port blinking out code -

 

I've not had a lot of experience with doing the LED hook up on the JDM cars, but that really looks like it's just doing a 2 code.

https://www.rx7club.com/3rd-generati...-codes-851414/

2 is an issue with the crank angle sensor, this will definitely cause major problems with how the car runs. It's pretty easy to get to and check out, it would be worth going over the crank angle sensors and look for any damage.

Dale

 

Thanks Dale, I've been seeing you lend your knowledge and helping others on this forum for decades, I guess this time was my turn

I did consider it might be flashing code 2, but the lack of 'pause' was what threw me a bit. I'll look into the CAS units this weekend and see if I find anything.

 

It's a quick pause but it's there. The flash/pause sequence may need a certain amount of resistance in the circuit to slow it down.

That may not be what's going on but it's not hard to take a look at, worth doing.

Dale

 

What you said here, about it may need a certain resistance in the circuit, got me thinking about the way the LED was flashing consistently without any lengthy pauses. I replaced the resistor with another 680 ohm one and tried again, now the LED is flashing out with the expected behaviour and has flashed out code 45, with a proper pause between sequences. The first resistor must have been faulty I guess.

Anyway, 45 is Solenoid Valve, Charge Control - open or short circuit, and doing a quick search on that code shows that it is a code that will cause limp mode - so I'm pretty sure I'm on the right track now.
15 years of ownership, one engine swap after the original engine blew and never having to diagnose turbo solenoid issues. Now, my time has come.

 

Good deal! That shouldn't be too bad to fix.

Dale