loftygoals Posted January 20, 2011 Share Posted January 20, 2011 Does anyone know the truth about running a US Spec DME in open loop (aka O2 Sensor unplugged)? I've read that US open loop mode goes into a "fuel enrichment" setting and runs richer. The other thing I've read is that w/o the O2 sensor that it falls back to the ROW map. What's the truth? I've added a narrow band gauge to my car. Here's what I know about my early (1982 build date) car: When running on the O2 Sensor the car bounces between very lean and just under rich with the gauge spending most of it's time in the "ideal" (.4-.6 Volts from the O2 sensor) range. It seems to never go rich. With the O2 sensor unplugged, it runs extremely lean. It rarely will even register on the gauge. If I unplug the FPR (and cap the vacuum line) with the O2 sensor plugged in the car will run a little richer actually making it into the rich part of the dial. With the FPR unplugged and the O2 Sensor disconnected, the car again runs richer, but still stays very lean. Is what I am experiencing normal? Or is it a result of my near 10.5:1 compression, late head, late cam, 1.6 degrees retarded cam timing, on all early electronics? -bj Quote Link to comment Share on other sites More sharing options...
944-Spec#94 Posted January 20, 2011 Share Posted January 20, 2011 Sounds like you may need to tune the AFM. I run have run in open loop or closed loop. No difference in noticeable engine output, but idle was better with O2 plugged in. My advice is to run with the O2 and then put the car on a dyno to tune the AFM to make sure you are in safe fuel mixture. The reason we allow AFM adjustment is most cars seem to be off and adjusting brings power back to stock while preventing lean burn detonation. Quote Link to comment Share on other sites More sharing options...
loftygoals Posted January 20, 2011 Author Share Posted January 20, 2011 Sounds like you may need to tune the AFM. Tune? The only adjustment I'm aware of on the AFM is the CO adjustment screw. I was under the impression that this only alters the fuel mix at idle. Having any more info on the adjustments you are speaking of? Thanks, -bj Quote Link to comment Share on other sites More sharing options...
krystar Posted January 20, 2011 Share Posted January 20, 2011 not sure how the 944 DME operates, but working with other ECU's and when you're WOT, it's in open loop anyway. the closed loop feedback mechanism just isn't quick enough for the DME to make adjustments. so only time you're in closed loop is when you start to exit a corner or feathering the throttle Quote Link to comment Share on other sites More sharing options...
loftygoals Posted January 20, 2011 Author Share Posted January 20, 2011 not sure how the 944 DME operates, but working with other ECU's and when you're WOT, it's in open loop anyway. the closed loop feedback mechanism just isn't quick enough for the DME to make adjustments. so only time you're in closed loop is when you start to exit a corner or feathering the throttle The 944 DME operates the say way--WOT=Open Loop. -bj Quote Link to comment Share on other sites More sharing options...
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