The 2016 "Freedom Sprints" SCCA Majors race at High Plains Raceway was completed over the Fourth of July weekend. Saturday was a DISASTER as the Z would go into limp mode at various points around the 2.55-mile circuit. That meant checking the mirrors, pulling off-line and attempting to manually clear the codes. Of course, this screwed up my morning qualifying session and had me scrambling the rest of the day.
The key to understanding the issue was the two codes that continued to show up in my Cipher scans: P2101 and P1233. Both relate to malfunctions with the "electronic throttle control function" and are ones I've never seen before on the HR. But it was the bullet I'd feared: a malfunction from the installation of the 40mm restrictor plates. After checking and rechecking the installation, and multiple "test runs", it was obvious this was not a problem that would be easily solved.
The key to this mystery was checking with Bob Schader, my loyal opposition (and defending T3 National Champ) who also had to run the restrictor plates. The ones on his HR were much thicker- closer to 3/8" and had been fabricated by his chassis and engine builder. It wasn't until Bob recalled what Jesse Prather had told him that the light bulbs went off: the sweep of the butterfly plates had been interfering with the restrictor plates. Seeing this, the fabricator carefully built spacers to fit over the plates and allow the throttle bodies to fully open. BTW- no spare spacers were sent with the engine...
Bob Schader's T3 Championship winning Z
Slapping your forehead in the paddock is never pleasant. We went back to my Z and examined the throttle bodies (intake tube removed) with a screwdriver blade to confirm the hypotheses. Pushing the butterfly inward from the bottom, it only opened halfway before hitting the plate itself. Since all Z33's use a fly-by-wire throttle, the signal to WOT was being interrupted and the ECM would assume a problem had occurred and used limp mode as a safety measure. But with no spares available and no way to access a machine shop to built a proper spacer before the afternoon race, I was left with either withdrawing or trying to limp the car to a finish. I chose the latter.
We installed a padded throttle stop under the gas pedal and I'd have to limit how much input I gave to the pedal itself to prevent the butterfly from opening and striking the restrictor plate, but I chose to look at this as a driving challenge: could I drive the Z like a Spec Miata? Despite some hopeful signs, this race was a disaster: starting from the rear and completing the pace lap, I was sloooowly accelerating onto the back straight when limp mode hot at only 4500 RPM! With no one to avoid, I pulled off line and desperately tried to clear the codes with the manual on-off method. It took three full cycles before I got it restarted and was lapped in the process--but worse yet and despite my best efforts to be easy and progressive on the gas--the Z continued to go into limp mode at various points around the circuit.
Eventually, I pulled off onto an escape road and was told by the race stewards (via the ES crew) to retire the car, rather than risk a huge shunt with the car being stuck in the wrong place on this hilly track. It was the first DNF the Z had suffered in several years and meant an end to any Majors title aspirations I had. Schader took the Mid-States T3 title that day, and I was left to ponder what would have happened if I'd found some dyno time or spent the money for a short track test. This was the price for being ill-prepared.
Despite being tired and sweat soaked from a bitterly fought DNF, I had to think about the following Majors race the next day. Should I just give up and pack up? What were my options? Not being able to fabricate the necessary spacer to compete in T3, I decided to just remove it completely and change classes. While I'd be badly outgunned in a full T1 field, at least I'd stay in the same run group and find out if the throttle bodies were damaged in this restrictor plate debacle. The positive news is without the restrictor plates, everything went back to normal and the Z was happily screaming down straights again. Using older tires and finding a significant exhaust leak were not ideal, but I still finished fourth in T1 after one Vette retired with a blown engine. So, a bit of redemption from what I can only describe as a disasterous weekend racing the Z.