SCCA Camaro

I really wanted the A/F ratio meter on the dash of my ‘68 Camaro for my next SCCA Solo II outing, so I decided to buy the third generation WBO2 and controller from Holley.  Since my first generation controller had the more desirable NTK controller but didn’t work with the only gauge commercially available and nobody on the message board at www.chevytalk.org had a wiring diagram to attempt a hack, I was torn between ponying up $600 for a new third generation NTK sensor (PN 534-188) or the $300 for the Bosch sensor (PN 534-197).  The main difference seemed to be the NTKs ability to withstand leaded gas a little better (although it’s not recommended for either sensor) and because I wasn’t intending to run any leaded gas I decided to go with the Bosch.  I picked it up from the Car Shop Inc, who again had the best prices I could find.  I pulled the NTK sensor out of the O2 sensor bung I had put in the exhaust system but this time ran the wires for the Bosch sensor up through the shifter boot and into the console, where I decided to mount the Holley Commander 950.  I had room in the center console in front of the shifter lever for the Commander 950 ECU and the WBO2 controller box, both of which I mounted with industrial Velcro.  Now the Holley in-dash A/F gauge (PN 534-200) was a simple plug and play affair, after I sourced the PDF document from the Holley help desk.  Unfortunately no amount of searching their web site or inquiring on the forums was able to turn it up, but after a few emails to Holley they sent it to me electronically.  I snipped a little piece of sheet metal and fit it in a hole in my dash and drilled a hole in it to mount my gauge.  In addition to the plug to the controller, it needs switched 12 V and ground.  It has an optional connection for dimming at night time which I didn’t worry about for now.  Now I could see my A/F ratio right on the dash in real time.  Cool!  I cable tied everything down and got all of my tools out of the car, because it was time to autocross again!

In March I got around to wiring the Holley Commander 950, following the supplied instructions, which called for a ground wire, positive 12 volt supply, and switched 12 volt.  These were easy to hook up with my American Autowire first generation Camaro wiring harness that I had already installed.  I uploaded a program to the C950 ECU from the base maps which seemed to fit roughly what I was running, which was Wbmp3008, described as: 355 small block Chevy, 30 lb./hr. injectors, Stealth Ram intake, 58mm throttle body, 20 degree Holley heads, Lunati 30142 cam (235/245 @ .050, .507/.534, 112 LC), 9.5:1 compression, 43 PSI fuel pressure, 418 HP @5500 RPM, 422 ft./lbs. @ 4700 RPM.  For now I just had the C950 ECU sitting on the passenger side floor so I could easily see what was going on and troubleshoot without laying on my back.  Although my gauge was supposed to be plug and play with my WBO2 sensor controller, the gauge didn’t plug in.  Another thorough read of Holley’s document on their WBO2 sensors indicated that the NTK WBO2 sensor and controller I had purchased off eBay was their first generation controller, and was not compatible with the Holley digital A/F gauge (PN 534-200).  The document indicates that a digital A/F gauge is from another company, FJO Racing Electronics, but a quick internet search and question at www.chevytalk.org confirmed this company was no longer in business.  I was still determined to get the WBO2 sensor hooked up and with a readable output before race day, so I decided to attempt to hook it up so that I could at least read the output from the sensor on my laptop.

I confirmed that I had the latest firmware (version 3.6) and software (3.0.7), and started the car up.  The WBO2 sensor was showing 5 V initially, then going to a very low voltage, about 0.35 V, after a few seconds.  The set-up at this point was pretty simple, being a ground wire, 12V, and switched 12V, and the controller for the WBO2 and the sensor itself plugged into the controller.  After much gnashing of teeth I found that although I had grounded the ECU through the wiring harness ground per the instructions, I had failed to ground the ECU case.  Unfortunately, this did not fix my problem, and I had to keep searching for a solution to my bad WBO2 signal.  The fellows at the www.chevytalk.org forum warned that running the car with the WBO2 installed but not functional can wreck the WBO2 so I started testing with the ignition on but car not running, which is when I noticed that there was an audible click just as the voltage on the WBO2 sensor went down to 0.35 V.  This was the last clue the guys at www.chevytalk.org forum needed to diagnose my problem.  Because I had not connected a tach signal to the C950, the ECU was shutting down shortly after cranking, because it didn’t receive a signal indicating that the car started properly and was running.  The audible click I heard was the relay shutting down the voltage.  Although I was running a regular HEI distributor, I was able to tap into the tachometer wire, keeping the tach on my Dakota Digital dash running fine while also supplying the necessary signal to the C950 ECU. 

Now I could read air/fuel ratio on the laptop.  The Edelbrock carb is a 750 CFM Webber design (model 1407 with a manual choke) was tuned surprisingly well, but was on the rich side everywhere in the map, which is of course the best way to tune conservatively.  At this point I hooked up the MAP sensor as well since it was simple plug into the C950 wiring harness and run a vacuum line from the carb over to the sensor, which I just cable-tied into the engine bay for now.  I varied the RPMs and tried to see as much of the A/F map as possible sitting in the carport, and found the A/F read from about 14:1 to about 10:1 throughout the range.  I leaned out the idle a little to a bit richer than stoichiometric from where it was around 12:1 to about 14:1, which seemed to make the car a little more responsive around town.  I did not otherwise mess with the carb tune.  Since I had a big cam with a lot of overlap in the car, I knew that the WBO2 would be providing a signal that was a little bit richer than what the actual cylinder sees because some of the gas flows right through the cylinder during the overlap period.