Speed density
The largest and most talked about change from 1993 to 1994 is the computer system and the way it controls the engine.
The Computer In 1993, the computer was run via Speed Density, which measured engine speed (RPM) and load (MAP in kPa) to compute airflow requirements and then use that against the VE table to get the proper fueling for conditions. An IAT (Intake Air Temperature sensor) was also used as air density changes with temperature. In 1994 however, the computer logic was changed over to a Mass Air Flow system. This system uses a Mass Air Flow Sensor placed in front of the throttle body to measure the incoming airflow into the motor. This is measured by using a heated wire in the sensor in the airstream path which has heat pulled away from it via the incoming air. This reduced heat is converted into a voltage signal which is sent to the PCM which then converts that voltage signal in to mass flow. At this point, the computer starts acting a little like the speed density computer as it uses engine sensors to judge engine conditions and provide the proper fueling off of this mass airflow reading. This was one of the main differences between the 93 and 94+ F-Body cars (and 92-93 Vette's compared to 94-96) and one of the items that makes them so unique.
Tuning Another prominent difference between the "Speed Density" 93's and the 94+ cars is how the programming of the computer takes place. In 1993, the stock computer uses a Memcal chip, which is a removeable chip from the factory computer. Contained in this chip is the program for the car to run. In the 1994+ cars, this was swapped to a non-removeable reflashable chip, which could be reprogrammed via the Auto Line Data Link, or ALDL, located underneath the driver side of the dash, next to the center console. Many people view this a more user-friendly and easier way to tune the vehicle.
Caution: A Gotcha. Be cautious whom you go with for tuning on a 94+ vehicle. There are many inexperienced people out there trying to tune vehicles, and it's easy to cut corners on a 94+ vehicle. If the tuner isn't familiar or doesn't want to, the VE tables can be bypassed and the car will be tuned for Mass Air only. But if your MAF craps out, your VE tables will still be stock, and your driveability will severely suffer. Always MAKE SURE your tuner knows what he's doing.
As for tuning the 93's, you will need a chip burner, chips, and a tuning program. Check out www.moates.net as you can get everything you need there (chips, Moates Burn1 for burning chips, and I believe he has tuning software available also). Otherwise, for programming, check out www.tunercat.com, make sure you get the $DA definition file. For chips, you want either 29C256 of 27SF512 reflashable chips. And for the burner, the PocketProgrammer II is a good choice.
Trouble Codes The 92-93 LT1 F-Body and Corvettes had a really unique and time/money saving feature. You could use the ALDL and a paperclip to put the computer into Diagnostic Mode and actually tell you what DTC (Diagnostic Trouble Codes) were being thrown by the car. This would happen by the computer simply flashing the Service Engine Soon (SES) light. To accomplish this procedure:
Make sure the car is OFF. Looking straight at the ALDL cable, you will see the pinout. It's orientation is:
F-E-D-C-B-A G-H-J-K-L-M
Take your paper clip and straighten it out. Then Fold in half. Insert one end into pin "A" and one end into pin "B" (A is the ground, B is the diagnostic pin).
Turn the Key ON, Engine OFF. You should hear the fans start running at this point. Watch the SES light as it should start flashing in the following pattern:
Flast - Pause - Flash Flash - Long Pause, and repeat for a total of three times. This is DTC 12 showing that the computer is in diagnostic mode.
At this point, the computer will flash any stored DTC's in the same manner as above. A series of flashes for the first digit, pause, and a series of flashes for the second digit, long pause, and repeat for a total of 3 times.
Once all the codes have been flashed, the computer will return to flashing DTC 12 and continue until the car is shut off.
At this point, turn the Key OFF, and remove the paperclip from the ALDL.
Now that you have your DTC's, look HERE for the 93 Service Manual diagnostic trouble code charts.
Another option for extracting DTC's and engine information is the use of a datalogging program. Unfortunately, it seems that only one works on the 93's. TTS Datamaster
Fuel System Many differences in the 93 to 94+ fuel systems are noteworthy.
The 93's used 22 LB/HR fuel injectors while the 94+ cars used 24 LB/HR injectors.
The 93 Fuel Rails had the crossover located at the rear of the rails with an integral accumulator, and had no crossover up front. The 94+ fuel rails had the crossover at the front of the fuel rails which subsequently caused an intake manifold design change allowing a recess for the front located crossover, and the accumulator was deleted.
92-93 Fuel Rail Bolts are M8x1x35. 94+ are M6x1x35.
The 93 fuel pressure regulator was located on the bottom rear of the passenger side rail. For the 94+ cars this was moved to the rear of the driver side rail.
The schraeder valve on the 93 was located at the mid point of the driver side of the intake manifold. On the 1994+ cars, this was moved behind the manifold just inside of the FPR.
The fuel line connections on the 93 were located just forward of the Schraeder valve. On the 94+ cars, the connections were located adjacent to the rear of the driver side rail.
Driveline The 93 used the 4L60 transmission which was controlled by a TV cable attached to the throttle body. The 94+ cars used the 4L60E which was electronically controlled, and had no TV cable provision. Because of this, the 93 had a slightly different throttle body than the 94+ cars.
The 93 had two different manual transmissions available, both with different gearing than the 94+ cars. These were coded M28 and M29. The gear ratios were as follows:
GR - M28 -- M29 -- 94+ 1 -- 3.36 -- 2.97 -- 2.66 2 -- 2.07 -- 2.07 -- 1.78 3 -- 1.35 -- 1.43 -- 1.30 4 -- 1.00 -- 1.00 -- 1.00 5 -- 0.80 -- 0.80 -- 0.74 6 -- 0.62 -- 0.62 -- 0.50
Of note: The M29 is the more rare and desireable of the two, and is very similar to the gear ratios of the newer Corvette ZO6.
The 93's got two different rear end gear ratios: The M28 came with 2.73's, the M29 got 3.23's and the A4 was available with either.
The speedometer is unable to be recalibrated electronically for rear end gear/tire size changes in the 93's unlike the 94+ cars. The 93's have one a couple of options. If it's an A4 car, you could change the drive and driven gears in the transmission tailshaft to correct the speedo. Or, and this in your ONLY option with an M6 car, you could use a speedometer recalibration box like the SLP box or the Dakota Digital SGI-5. The SLP box is out of production, but eBay can be your friend
The 93's did not get blessed with CAGS.
Other 93 Differences Many small differences were noted between the 93 and 94+ F-Body years.
On the throttle body, the IAC on the 93's was a screw in unit which used a 4 wire square connector. The 94+ cars used a bolt in IAC with a flat 4 wire connector.
The 93's used a 1 wire non-heated oxygen sensor. The 94+ cars use a 4 wire heated oxygen sensor.
The 93 specification for an oil fill with filter change is 4.5 quarts. The 94+ specifies 5.0 quarts.
In the 93's the Firebird temperature gauge started at the 100* mark. In the 94+ cars, the gauge started at 160*.
The 93 Camaro Gauge face markings were yellow. The 94+ cars reverted to white.
