Please read the entire post before you reply! Yes I've searched. Yes I've been through the flowchart.

-1999 B20
-1994 B18B Throttle Body, Intake manifold, Fuel rail, Injectors etc.
-1991 Civic EX
-Rywire OBD0-OBD1
-4 wire o2 sensor wiring was ran with a factory spliced in harness with the shielded wire run all the way back into the passenger compartment (didn't want any finicky 02 sensor codes)
-chipped OBD1 computer w/Phearable basemap

The car runs pretty well overall. Gas mileage is terrible (29mpg no matter how lightly I drive it). I realize this is probably partially because it's only on a basemap right now. This could also be because the B20 is a gas hog. Maybe a little of both.

With that said, I plan on getting it tuned, BUT I cannot get it tuned until it's free and clear of CEL's! the tuner will not touch it until then!

The problem is I can beat on the car all day long at WOT and never get a CEL.

But the minute I start partial throttle cruising, assuming the engine is up to operating temperature, I'll get a code 43.

The oxygen sensor tests out fine.

I've been all through the code 43 flowchart. Everything checks out.

Questions:

Does a code 43 put the computer into safe/limp mode, and will it cause terrible gas mileage?

Or is the gas mileage a result of whatever issue is causing the code 43?

When I unplug the 02 sensor, should I immediately get a CEL? I do not. In fact, I never get a CEL regardless of how long I drive or what style of driving I do with the 02 sensor unplugged, not even a code 43. This seems very peculiar to me.

I've replaced the 02 several times with brand new units of different brands just to rule it out. Plugs and wires have been changed. Timing is good.

So with o2 sensor plugged in, I can beat on it at WOT and never get a CEL. Partial throttle cruising gives me a code 43. Driving the car any style with NO 02 sensor hooked up gives me no CEL.

Can a "rich" basemap trigger a code 43?

Can bad injectors trigger a code 43? If so, why don't they trigger the code at WOT or beating on the car? Why do they only trigger it at partial throttle cruising?

Any ideas? I see many B20 swaps get code 43's - but hardly any seem to get the issue resolved. Or if they do get it resolved they never update the thread.

Please don't just throw a blanket statement out there like "replace the 02 sensor".

Thanks for any help guys.

 

What's your fuel pressure?

 

Haven't checked it.

The flow chart only says to check fuel system if code 43 is on AND poor drivability is present.

Drivability is excellent throughout the rev range.

Should I check it anyway?

If fuel pressure was the problem wouldn't I get the CEL all the time and not just at partial throttle steady cruising?

 

Had the same problem but Code "41"
I used obd0-obd1 jumper harness
Ran the wires straight to the jumper.
Tried what you did. use different o2 sensor, replaced fuel filter, did any cleaning thats fuel related.

Until this day i got irritated and just left it alone.Hope you find your solution

 

It's only a few things a bad o2 sensor, fuel pump,fuel filter, fuel pressure regulator, a shorted or broken white wire from the sensor to the Ecu, or the Ecu itself. Nothing else will cause this code

 

The flow chart does say what you said but it also says to check fuel pressure and if it's not within spec to change the regulator. My money is on the regulator or the Ecu .

 

I've got a 100% stock p75 computer on the way that I'm going to try in order to rule the ECU out.

I'm getting the injectors cleaned and flow checked this week just as preventative maintenance and I'll change the fuel pump too as I've got a spare new one.

I'll check fuel pressure Thursday.

 

Only change the fuel pump if the pressure is wrong and the regulator does not fix the pressure.

 

code 43 can be bad O2 wiring...normally the ground side

 

Update - swapped in a 100% bone stock P75 and the CEL went away and has stayed away for nearly a thousand miles now.

Fuel economy went up maybe 1-2MPG highway to 31 mpg (still awful IMO)

Performance is noticeably worse with the stock p75. Rougher idle, revs less smoothly etc etc.

Why would a chipped ecu run better/smoother but throw a CEL and a stock p75 get rid of the CEL but appear to run worse?

I made no other changes to the car - haven't even put in the flow-tested injectors yet.

 

No 1 cause of this code is wiring issue. Intermittent open, connector(s) not crimped down all the way or slightly opening up.

 

Do an idle learn, set ignition timing, calibrate tps if it's adjustable.

 

a fuel pressure regulates fuel....... pressure?

you need to get a gage on your fuel system. easy diagnosing, easy monitoring.