bureau_c

Here's a question for the list gods, or at least the stock ECU gods. Normally, under light throttle below a particular RPM of I think under 4K or thereabouts, the stock ECU runs in closed loop mode, i.e. it monitors the O2 sensor and adjusts fuel delivery so as to keep it in a certain window. This is done for fuel economy reasons I think, and can be most easily seen on an Air/Fuel Ratio gauge when the LED cycles back and forth Knight Rider style. Now the question: What kinds of things can go wrong that will cause the ECU to abandon this behavior and run in very rich open-loop mode?

I believe loss of an O2 sensor signal will cause this. Does anyone know of any other things that can do so? My car is running extremely rich right now and not too well, and it is also not entering closed-loop operation when it should. I suspected my cheap Pep Boys plastic splice that I used to hook up my AFR gauge, but I've since removed that and spliced the wires in a more reliable manner, and the problem remains. Either I've lost the connection somewhere else (like at the ECU connector, as my AFR guage still works, i.e. the O2 sensor is not bad) or something else is happening to contribute to this. As an additional hint: I just had my primary injectors replaced. It was done by a shop that knows these cars very well, but that's the area that was recently touched.

jds

SnowmanSteiner

well if it is running rich I would assume that it is getting a signal somewhere that it is very lean(DUH Not aimed toward you but to the obvious comment I just made) or not getting a signal like you said. My first guess would be that your O2 sensor is either broken or messed up somehow. You said that you had your primary injectors replaced. Are they the same injectors, or are the upgrade, flowing more, etc. Maybe if they flow more you might be sending the wrong signals to the ecu from the injectors. Those would be my guesses. Good luck.

- Steiner

bureau_c

I should have been more specific about the injector work...I had leaky stock injectors, and they were replaced by new ones, but still the stock injectors. Also...and here's the irony...the car was running great when I took it in, it just stank of fuel and was primed to turn into a fireball at any minute :-)

I'm reasonably certain my O2 sensor is not bad, as the AFR gauge monitoring its output looks fine. Also, when in open-loop mode, which I appear to always be in right now, the ECU completely ignores the O2 sensor and runs off the maps. I imagine there are default no-02-sensor detected maps for light throttle that just assume it needs to be rich, but that's just an assumption at this point.

jds

paw140

Something else to check is your coolant temp sensor. Most cars (I think the RX7 too) will run in open loop mode until the engine reaches operating temperature. If for some reason your car is not reaching operating temperature, or the computer doesn't know the temp of the engine, it will never go to closed loop. You could have a faulty coolant temp sensor or a bad thermostat.

Have you pulled the trouble codes? If not, do that first before you go any further.

bureau_c

Good idea, I'll look into that! I'm not actually getting any ECU error codes except for knock sensor, which is a known ECU problem I have. It was doing this before (another ECU doesn't do this) and it never caused me any problems.

jds

bureau_c

Actually, that doesn't make any sense (my previous post) as if it doesn't see the O2 sensor there is a code for that, isn't there? Doh! I'm so used to getting that immediate Knock Sensor code I didn't even think about what might also be there! You're right, that should have been the first thing I checked.

jds

bureau_c

OK, I'm not getting any error codes that are relevant. As I mentioned previously, with my Pettit ECU I have a problem where it gives me a knock-sensor code. This is definitely the ECU, and has been happening for a while without preventing closed-loop operation. I also get a speedometer sensor error code sometimes when I get on the gas...this is not the ECU, as it happens on both the Pettit and stock, but again, was occurring long before my current problem.

I also verified that if I disconnect the O2 sensor from the ECU entirely, I get no error code for that. I'm not sure what is supposed to trigger the O2-related codes, but apparently its not the simple absence of a signal. I also completely revamped my splice between O2, ECU and AFR gauge...I'm definitely getting a good connection between O2 and ECU. Something else is preventing me from running closed-loop. Maybe the temperature issue, but in the absence of any error code, I'm not immediately sure how to test that.

jds

skunks

i though the O2 sensor goes in to close loop during cruise control...

bureau_c

Well, it is supposed to go in closed-loop mode while cruising...but cruise control isn't required. Basically, normal light-throttle operating conditions under 4K or so (might be closer to 3K, I forget) are done in closed-loop mode for fuel economy purposes.

jds

paw140

I would still check out the temp sensor. Just because there is no trouble code does not mean that it is working correctly. Do you have a temperature gauge? Are you reaching operating temp?

bureau_c

I have the wonderful unmodified stock gauge. It hasn't changed though :-)

Which temp sensor is the appropriate one here? Coolant temp? It does seem like, when operating properly, the car goes closed-loop much without waiting for the car to come up to operating temps. It only takes a short time for the O2 sensor to put out normal values.

jds

paw140

The sensor I am talking about is on the back of the filler neck. There are two sensors back there; it is the top one. There is a procedure for testing it in the FSM.

bureau_c

Well, you are a prophet! I took the car back to the place that did the injector work, and they just called me to tell me it was a bad temperature sensor! I'm not sure, but I'll bet its the one you're talking about. Nice call!

jds