In our last installment, you may recall a recurring high-rpm misfire that prevented my LT1 Formula project car from making a clean dyno pull, despite our brand-new LTCC ignition and MSD LS1 Blaster Coils. At this point, it was time to exhaust all possible causes, beginning with the crusty stock optispark. Though the LTCC ignition system takes away the opti's role in distributing spark to the plugs, it still relies on the optical eye of the distributor-which if dirty is known to cause a misfire. This seemed the most likely scenario, so after first checking the simple things, like vacuum and electrical connections, I took the Formula back to Ron's Custom Auto and had head technician Junior Perez order up a fresh opti.
When that failed to fix the misfire, we hooked up a scan tool again (as well as a fuel pressure gauge), and did some road testing. What we discovered was that the car was pulling timing like crazy, though there was no audible knock; however, the good news was that our fuel pump seemed to be in fine shape. Fuel pressure was constant and well within spec, so that turned our attention toward some of the electrical devices feeding information to the computer, like the MAF, O2 sensors, knock sensor, and knock module. GM Performance Parts was happy to furnish us with these products, which are good ideas for any LT1 owners looking to increase reliability, gas mileage, and performance. A tank full of Sunoco 104 was utilized to separate false and real knock, but the problems remained.
These tricks still yielded no successful results, so we looked at the mechanical side. We were planning to replace the stock 13-year-old valve-springs and timing chain anyway, and now was as good a time as any. COMP Cams was sourced for a stock replacement-style single-roller timing chain, as well as new valvesprings and everything needed to complete the install (including seats, retainers, and locks).
Even after Ed Wright at Fastchip sent over another tune to turn off the knock retard at wide-open throttle, the problems persisted in the low-rpm range with the V-8 out of balance. In the end, a trip over to TT Performance Parts in Passaic Park, New Jersey, to scrutinize the underdrive crank pulley and harmonic balancer solved the problem. Three new bolts and a little patience later, and we were good to go
In order to read the PCM in...
In order to read the PCM in the hopes of gaining some clue as to what is going on, a call was placed to tuning whiz Craig Moates at Moates.net, who suggested picking up a couple of his cables to link the ALDL port to a laptop via the USB port. Moates.net's ALDU1 USB-to-ALDL Converter and Cable combo retails for $80, which can provide valuable insight into your OBD-I LT1 with the help of data logging software like TTS DataMaster or EFI Live V4. As a quick fix, we used a free trial of TTS DataMaster, which revealed 6.0 degrees of knock at WOT and an astronomical knock count. Meanwhile, the fuel system and other functions seemed to check out.
Though unnecessary, since...
Though unnecessary, since Ed Wright at Fastchip tuned the PCM (and desensitizes the knock sensor through his tuning software), we'd ordered the LT4 Knock Module (PN 16214681) and Knock Sensor (PN 10456126) to combat the noise from our roller rockers, so we installed them anyway....
...We also picked up a brand-new...
...We also picked up a brand-new MAF, MAP sensor, and O2 sensors from GMPP (not pictured), which made a noticeable, albeit small, increase in gas mileage, and seemed to make the car idle a touch smoother.