A few weeks back I did Dale's PFC CEL mod (https://www.rx7club.com/power-fc-for...t-work-620175/) (What a pain in the ***!!)

It's cool to see the CEL light at IGN power on (maybe the reason I think it's cool is a holdover from my days trying to pass CA emissions with a JDM ECU in my MX-3...), and I can verify that the knock threshold warn works as configured in FC Edit - cool!

I have a strange issue, though: the CEL lights solid under heavy, in-gear deceleration, and stays lit until I start to apply throttle again. Literally, rev the car up to, say, 7K on the freeway, then let off the gas while leaving it in gear, and the CEL will light, just sitting there glowing solid, until you finally start applying a little gas.

What is going on with this? Does anybody know?

 

no idea, but maybe look at the TPS voltage?

 

That's an interesting idea, but if it was the TPS I would think it would happen regardless of if the car was in gear or not...

 

Chances are you’re exceeding your knock threshold number. If you have a datalogit you can see where the knock threshold number is set. Mine is set at 45 and during high rpm decel it will light until it comes back down. Pretty normal to see high knock readings during that state.


~ GW

 

This is not knock sens, because in case of detonation CEL will blink. It can be a problem with one of the sensors, probably MAP sensor (you have a huge vacuum under in gear deceleration and it can force MAP's fail). You can check this at commander's "Sensors/SW Check" menu. If there is a problem with one of the sensors, it will be blacked.

 

So I finally logged some data on the Datalogit, and it turns out the solid light on decel is the overheat exhaust warning. This would imply the motor is getting a lot of unburned fuel that is burning up in the catalytic converter...

My wideband is setup to report between 9-20 AFR, and under this deceleration, in heavy vacuum (P01), the ARF is pinned to between 19.5 and 20. That can't possibly be too rich, right?? All the FD-specifc maps I've seen range from about 12.5 - 14.7 under heavy vacuum.

Note that this is with a Bonez/RX7.com cat, with the air pump electrical connector physically unplugged and the hose physically disconnected...

Is it possible the motor is actually running way too lean and that is what is triggering the overheat exhaust sensor? This is with zero throttle input.

 

Maybe your 3 fuel cut (F/C) setting are set for making flames out of your exhaust. Some owners love to do this.
All three should be set to no higher than about 1500 rpm.

 

They're all set to PFC default.

What exactly do those settings do?

 

They are for fuel cut restore. Its at what rpm your injectors turn back on. Also, the higher the number is leaner. Off throttle decel (engine braking) will send your afr to full lean. Thats normal.

You can test a theory by changing your f/c values. Change them all to 7000 and see if you get the same thing happening with the cel

 

So it that why I get short knock spikes right when letting off throttle?

 

OK, few things here.

When you are off throttle, the injectors aren't injecting at all. The AFR gauge will peg dead lean - 20.0 is as lean as it reads. This is fine and normal. Lower numbers are richer, higher is leaner. Typically you see 13.5 at idle, 14.7 at cruise, 11.5 at full boost, and 20 when under no throttle deceleration.

JDM cars had an exhaust heat probe that was actually in the main cat, like an EGT probe. US cars had a sensor bolted to the floor under the passenger seat. JDM cars had the "exhaust overheat" light on the dash with the other idiot lights (high beam, abs, etc.) and US had exhaust overheat as a little light in the center console near the ash tray.

JDM cars also didn't have a Check Engine light.

The warning function of the PFC doesn't work on US cars since they are wired differently. A US ECU doesn't have an output that can light up the Exhaust Overheat light, that's why I made that mod to make it work - it takes that output from the PFC and taps it into the Check Engine light circuit.

If you go into the Sensor Check on the commander, there are 2 relavant items here. CAT is supposed to be the heat waring probe in the JDM cat, HWL is "heat warning light" that should show if that light is lit.

This is weird why it's doing that, you're going to have to do a little more digging to see what's up. But this should give some clues.

Dale

 

11.5 at full boost? You're a mad man. Surely you mean 10.5.

I think it's strange that it's lit solid, not a blink code like the injector or knock warning.

Since I have been poring over the FC Edit logs and feel confident in my tune I think I'll just disconnect the wire and forget about it. I am looking forward to playing with the fuel cut threshold, though. Would be cool to get some subtle snap-crackle-pop on decel. I guess I should mount the gopro and get at least one video of shooting flames though. I mean, it would be rude not to.

 

depending on what mapsensor is used it can be that the voltage on high rpm vacuum is is below something like 0.5v and then it will show up red in the datalogit and iluminate the CEL/Overheat warning.

What mapsensor are you using?

 

I'll have to check that when the car is running again. GM 3-bar.