Installing a Custom Eprom
The engine in my 93 is
basically stock, and I do not foresee my going into the motor in the near
future. The main reason I wanted to change the Eprom was to lower the
temperature at which the cooling fans turned on, I did not like the
factory setting of 226�, and to raise the MPH at which the transmission
shifted into overdrive. I did not like the extra wear on the transmission
as it shifted into and out of OD when driving around town.
met Shalin on the corvetteforum about a year ago. He drives a 93 that is
blown with a 14 PSI Vortec and dynos at 576 RWHP. Shalin told me he has
probably burned over 100 EPROM\’s as of this writing. Since he has done
most of the work on his car, including the custom EPROM, I decided to get
a chip from him. I had spoke to him about 8 months before, but at that
time hadn\’t convinced my wife that a new chip was a necessity, not a
luxury. Shalin lives about 90 miles from me. I contacted him and set up an
appointment for a Friday afternoon.
My engine only has the
following minor modifications: Open air lid, K & N air filter, 160�
thermostat, and Borla performance mufflers. The first order of business
was to connect the notebook computer to the diagnostic plug under the dash
on the drives side and get a baseline reading of how my engine was
running. I drove the car under WOT while Shalin watched the Diacom
software record the data. The initial run showed that the engine was
running slightly rich at WOT, the automatic transmission was shifting at
approximately 5200 RPMs and there was some spark knock and the knock
sensors were telling the computer to retard the ignition.
at Shalin\’s he removed the three bolts that held the computer in place.
Shalin disconnected the power to the computer by pulling the fuse located
behind the battery. On another notebook CPU he first loaded the
information from my stock Eprom into the software. He then made the
following changes: The rev limiter was raised from 5,600 RPMs to 6,200
RPMs. The timing was retarded 2� at WOT. The fuel was leaned out at WOT.
The cooling fans were set to turn on at 85� and 86�C respectively (185�F
and 187�F with a 2� differential). The torque converter lock up was raised
to 48 MPH in third gear and the transmission is now set not shift into
overdrive until 48 MPH instead of the factory 42 MPH. The piggy back
circuit board with the new custom Eprom was attached to my stock Eprom and
the EPROM assembly was reinstalled in the computer. We then took the car
for another test run at WOT while Shalin monitored the engine with the
Diacom software. Since Shalin has a fair amount of experience at the drag
strip, I appreciated him saying I would get better performance if I
manually held the transmission in each gear, and shifted it at 5,600-5,800
RPMs. Doing this, and taking into account the slight lag in the
transmission shifting, the actual shift would occur at approximately
6,000-6,100 . The Diacom software showed that actually to be the case.
IMHO this is the only way to install a custom Eprom. Without a
baseline run to analyze exactly what your engine is doing, you are just
adding a generic chip that will do an average job for most engines. I feel
it is even more important to have a chip custom programmed for your engine
if you have more extensive modifications.