Poor idle/rich(?) on stock ECU
 

I need to smog my car, which means I need to run it on the stock ECU. I've smogged it a few times in the past this way and it hasn't been an issue. I basically I just put the OEM DP/cat on, revert some of the beefed-up fuel pump wiring (disconnect 12 gauge bulkhead through fuel hanger, swap 1ohm low-speed resister with OEM resister, connect power back through the ignition switch instead of directly to battery), put the stock IC and airbox in, connect at AWS hose, hide the AI hose/nozzle, and put the stock ECU in. Other than that it's got BNR stage 2's, stock primaries, 2200 secondaries, and IGN-1As. The smog guys either don't notice or don't care about the rail/secondaries and IGN-1As, and the car runs fine with the stock ECU under low load on the stock primary injectors.

This time around, after doing all the above, when I install the stock ECU, the car starts idling poorly. Plug the PFC in and it runs perfectly. The precat will glow red hot if you drive at very low speeds for a few minutes with the stock ECU in. Although it idles poorly, it runs well above idle with the stock ECU.

At idle the CO emissions are at 3% -- they need to be under 1%. HC is also elevated at idle. At 2,500 RPM both the CO and HC emissions clean up to almost zero and the car runs smoothly.

Cold idle is very rough and smells bad, and warm idle bumps around in the 600-800 range. The smog guys tell me it's running rich because of the 3% CO.

So, PFC runs perfectly, stock ECU does not. Here is what I have looked at/tested:

- Swapped air pump. Both work/suck air. No change.
- Checked all plugs are sparking.
- Plugs are fowled.
- Checked TPS voltages: VTA1 = .55, VTA2 = 1.23 - both in-spec according to FSM.
- Checked fuel pressure at ~1,400 RPM (warm-up idle): ~26-27psi.
- Checked fuel pressure engine off/ignition on: ~36.8psi.
- Checked for leaking injectors by cutting the engine and monitoring fuel pressure for a few minutes: no leaks.
- Checked battery voltage engine off: 12v.
- Checked battery voltage @ ~1,400 RPM: 14.1v.
- Checked PIM/MAP sensor reading engine off: ~9260 PIM ~= -1.5psi/-3inHG (?)
- Checked PIM/MAP sensor reading @ ~1,400 RPM: 4000 PIM ~= -9psi/-18inHG
- Checked CAS-to-plate spacing: ~1.5mm - in-spec according to FSM.

What could be causing the vehicle to idle poorly at idle/well off-idle with stock ECU, but run well all the time with PFC?

Uh..... the stock ECU isn't tuned properly for your engine?

What are your AFRs.

Did they actually look at the ECU? Did you really need to do all that?

I have done this before with the same setup and it ran very well with the stock ECU. The exhaust system is stock, intake is stock, the primary injectors are stock. It should idle almost exactly like a stock car with the stock ECU, as it has in the past.

Don't know AFRs because the stock DP is in, as stated.

Yes I have to run the stock ECU. There are several issues with running the PFC for smog: no CEL at key-on is an instant fail, the PFC doesn't operate the AWS or ACV.

When I lived in California, the smog techs never looked under panels to check if the ECU was stock. They did look on the dash to make sure the Check Engine Light operated like normal: lights up at key on engine off, and then turns off with the engine on. There's no guarantee your car would pass with an aftermarket ECU, and it is technically illegal because you could tune it to run dirtier than the stock ECU. But it's not a guaranteed fail either, in theory an aftermarket ECU should be able to run the engine at the correct AFR and operate the air pump and ACV if you have enough flexibility in the output configuration.

a cursory google search indicates there is a way to make the CEL work with the PFC.

AWS shouldn't be needed for a smog test when the engine is already warm, but ACV is probably important. There are a lot of suggestions in this old thread: https://www.rx7club.com/3rd-generati...hread-1087637/

Thanks for the info and link. PFC is no-go because of the CEL alone. And it can't run the ACV.

I'm starting to think you must not know how to read.

the PFC does run the ACV, it runs it the same as stock, not sure why you think it wouldn't.

the PFC is from a Japanese market car, and those didn't have a check engine light, however what they did have in that place was an exhaust overheat light, so if you run the exhaust over heat pin to the CEL, then the CEL will work the way the smog guy expects.

if you want to keep trying with the stock ecu, you should start by setting the base idle

I have in fact wired my PFC through the ELD box and the CEL does do things, just not the same things a normal USDM CEL does. It does not light, for example, at key-on.