ROCKN SS

I have a '97 SS with 15,000 miles on the odometer and believe that it is not staying in closed loop when it should. I have a Cyberdyne Air/Fuel gauge and on a recent trip I noticed that when cruising sometimes the gauge would just show constant rich instead of fluctuating around like normal. This was occuring under minimal load conditions.

I have AutoTap so I hooked it up and first checked for error codes and had none. I ran a log looking at the O2's and the commanded Air/Fuel ratio. When just cruising the commanded Air/Fuel ratio would randomly change from 14.7 to 13.8. When I accelerated hard the commanded Air/Fuel ratio would go to around 12 (correct I think). When the command Air/Fuel ratio is 14.7 the O2 logs fluctuate as expected and when it is 13.8 the O2 log holds at around .9XX.

I thought that there was a parameter to tell weather the computer was in open or closed loop but I couldn't find it. However, by the commanded Air/Fuel ratio I believe that it is going in and out of closed loop.

Does anyone have any ideas what to look for?

carl97ss

Autotap does have a command that shows you if and when your car goes into closed loop. look some more.

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'97SS, More Performance 396, AS&M cold air, Grotyohann LT, SLP 2ODL muffler, Magnacor, PCMFORLESS PCM, LS1 twin piston calipers, KVR crossdrilled and coated rotors, SLP stage II w/ KYB AGX, 6M, Star Stage II.

Injuneer

There should be a "closed loop" flag that indicates you are in closed loop. This simply means the O2 sensors are hot and working, the coolant temp has met the minimum, and the timer from startup has timed out. When you go into "enrichment mode" the flag will still inidcate "closed loop enabled". So it might not help you much, unless either the coolant temp or O2 sensor activity has fallen off. You would see that in your logs.

At exactly what combination of throttle position and RPM are you seeing the target A/F ratio depart from 14.7:1? The point at which enrichment mode is enabled is set by a table of RPM vs. TPP. Conceivably, you are exceeding the TPP threshold at some cruise conditions???

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Fred
94 Formula A3+1: 381/TH400+OD/N2O

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ROCKN SS

When it goes from 14.7 to 13.8 seems random. I'm looking at it when I get up to speed and back off the throttle to just maintane my speed. The TPS is anywhere from 10% to 25% and the RPMs are in the range of 2500 to 3200.

Shouldn't there be a code thrown if there is a problem with the O2 sensors. At first I thought that it might of been because of the coolant temp since I have a 160 deg thermostat and it does seem to go to 13.8 more when I am up at speed (more air across radiator) and then go back to 14.7 when I stop. However, AutoTap reports the coolant temp to be pretty stable in the 180 to 185 deg range.

I do have long tubes and extended the O2 sensors myself (soldered connections), however that was over two years ago and this is the first that I have had this problem.

I thought that AutoTap had the closed loop parameter when I used it in the past but I could not find it now. I upgraded to the windows software before I used it this time, maybe I will have to go back to the dos software.