I just completed a a cam change, and the addition of a C&L 76mm MAF with 24lb injectors and now I get code 41 (O2 sensor not switching, reading lean) consistantly.
I have a '91 GT convertible 347 with twisted wedge heads, GT40 intake, BBK long tube headers, 1.7 rockers, BBK adj fuel pressure regulator and 70mm MAC TB & spacer.
My cam change involved switching back to the stock cam.
At the same time, I installed a C&L 76mm MAF calibrated fro 24# injectors. I installed new 24# injectors at the same time.
I tuned this setup according to C&L's advice: Fuel pressure is 37PSI (set with vacuum detached from regulator) and timing is 18 degrees BTDC (set with plug next to distributor removed).
I have taken the meter to the O2 sensors and they appear to be producing reasonable voltages, and to be switching back and forth. I also checked the wiring to both sensors and it seems OK.
They car runs great! Do all my changes require a new chip to fix this problem? If I do upgrade, can I buy a chip or an ECM that will allow me to monitor sensor outputs in real time?
Bill Temple

 

did you have the ecu burned with previous cam and maf/injectors or is it stock

 

ECU is and has always been stock.

 

sound like your in need of a tune , the long tubes move the o2 musch furthere away from the combustion chamber. im will look into the code in my emmissions manual . </P>


</P>

 

The funny thing is that I did not get the code before the cam/maf/injector change, and I had the same long tube headers. Here are some other facts that occurred to me:
1]I also changed the thermostat at the same time. The old thermostat was a 195 degree, but the car always seemed to run around 210 degrees. The new thermostat is a 180. Now the car takes forever to warm up. The temperature very slowly creeps up to about 175 degrees. I do not get the code 41 until the temp reches about 175. Then it stays on continuously.

 

you might have to move the bungs for the o2 sensor closer. their are severals ways to go as chips..Tweecer.tweecer rt, diablo etc..all will help..I'm curious about going back to stock cam with that 347

 

As far as the cam goes, I had a Trick Flow stage 1 cam (TFS-51402000). It did seem to produce a lot of power above 2000 RPMs, but it had absolutely nothing below 2000 RPMs. Both my wife and I found the car to take a great deal of attention to drive. I do not deny that I could have done more tune for this cam, but in the end, we decided that we did not want to sacrifice the top end by going to lower gears. We swapped back in the stock cam with 1.7 rockers and it runs great. It has tons of torque around town and it cruises effortlessly at 90mph on the freeway. The fact that the car runs so well makes it even harder to understand why I an getting the code 41.

 

well I think when you combined the long tube hearders, colder 'stat and a big maf and injectors the exhuast temp has been lowered to a point you might need to move the 02 sensor closer toward the engine..as for your cam all you need was to put 1.6 rockers on it and advance the cam 2 degree..the 1.7 will great help lift but do nothing for duration on the exhaust side

 

Would a set of MIL Eliminators help?</P>

 

not appl. on a 91