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Open Loop and Closed Loop

Car-specific questions and tuning advice for the 1995-1999 Turbo Talon and Eclipse cars.

Open Loop and Closed Loop

Postby da1sexmonk83 » Sun Jun 29, 2008 4:23 pm

Alright, we finally got the car down to 800ish idle (since I bought it the car has been running on 1200 rpm idle out of necessity) via tuning. We still need to set base timing, as at the moment we are artificially lowering timing to what it should be. The factory fuel trims are at 0% correction by the stock ECU and we are correcting with +10%. Aaron rebuilt the throttle body installing new seals and what not. So our horrible boost leak is gone.

The problem now is that the car will not go into closed loop (at idle). It jumps to closed loop for about a second then goes back to open. Any ideas on the reason for this?

Also, is there any way to see if its in open loop , closed loop while actually logging? I have been having to swtich back and forth between obd II information and recording.
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Re: Open Loop and Closed Loop

Postby tlcoll1 » Mon Jun 30, 2008 11:47 pm

If you don't have any check-engine codes, then maybe check OBD-II coolant temperature. The car has to be warmed up to be in closed loop mode. Once warmed up, the O2 sensor should cycle - I think the sequence is:

1. Start car, front O2 at ~0 volts since the sensor is cold.
2. Warm up, front O2 goes to ~1 volt since the car is running open loop and rich.
3. Stock ECU notices that O2 sensor has warmed up and starts running leaner to get the O2 voltage down to ~0 volts.
4. Stock ECU flip-flops between slightly lean and slightly rich and verifies that the O2 voltage is cycling. It then declares closed loop mode is active.

Also, have you looked at the service manual in this area? It usually has a flow chart for diagnosing this kind of thing.

I believe the fuel trims only apply in closed loop mode. If your car is in open loop all of the time, the reading probably doesn't mean anything.

Tom
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Re: Open Loop and Closed Loop

Postby da1sexmonk83 » Wed Jul 02, 2008 12:56 am

ugh stupid O2 sensor. It still reads really low. .02 - .09. I added fuel at idle (10%) and everything, even let the car warm up to temperature and d the timing is retarded some too. I want to say something is wrong with my O2 sensor, but It is reading at least SOME voltage and the car isn't throwing a code. I guess it could be really lean but I don't understand why.
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Re: Open Loop and Closed Loop

Postby da1sexmonk83 » Tue Oct 07, 2008 11:27 pm

Follow up, o2 was fubar. Replaced it, car ran great.
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Re: Open Loop and Closed Loop

Postby tlcoll1 » Wed Oct 08, 2008 10:04 pm

Nice.

Tom
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