cepowers18

I have a rebuilt 94 Mustang GT with H/C/I, engine bore, and full bolt-ons (no custom tune). Last time I had it at the performance shop, the guy told me that the computers in 94-95 5.0s pulls timing once it gets up to 4200 RPMs and causes it to fall flat on its face. Is there any truth to this? If so, what exactly does pulling timing mean? Pulling spark or fuel? Is tuning the car with a custom tune or chip a way around it? I've done some research online, but I haven't been able to find much...

Mike T

This is from Reinhold Racing's web page...1994-1995 computers: The TM40�s (94-95 GT computer) processor runs 3x the clock speed of the fox body processor and is based off of Volumetric Efficiency (VE) The TM40 also many more parameters to tune with but also has many built in timing retards that need to be addressed which is the main reason why 1994-1995 Mustangs are slower than a comparable fox body Mustang. In 1994 Ford did a major redesign of both the computer hardware and software which resulted in a smoother running and more emissions friendly car. These computers are more sensitive to modifications than the pre-1994 computers. Although the 1994-1995 Mustangs made the same horsepower on the dyno as fox body Mustangs but once you put the engine in the car things change. In the 1993 and older computers the spark advance at wide open throttle was based on engine RPM only. At wide open throttle the computer jumped to a separate spark function that Ford thought was the best spark curve. Everytime you go to wide open throttle in a 1993 or older car, you run pretty much the same spark curve run after run. In the 1994 - 1995 cars the wide open throttle spark function was deleted and computer uses the same spark tables for both part throttle and wide open throttle spark calculations. The spark table is based on RPM and engine load and the computer uses the mass airflow sensor to determine load. Any change in the calculated load will effect how much spark advance you get. Since the computer uses the mass airflow sensor to calculate load, changing the mass air flow sensor will change the load calculation. Changing the cam, heads, etc will also effect load. It is possible when upgrading the mass airflow sensor, heads, etc. the computer will remove timing resulting in an instant loss of horsepower. The loss in horsepower can be at any rpm or all rpm. In other words, anything that effects airflow into the engine will also have an effect on the spark advance and probably a negative effect. Another issue with the 1994-1995 T4M0 computers is spark retard during shifts. The automatic cars seem to pull more timing out than the manual transmission cars. This is due to the tip in retard in the T4M0 computer. When the throttle is moved from closed to an open throttle position (such as shifting a 5 speed car or passing on the highway) the computer will retard timing. The amount of spark retard varies but the computer can retard the timing as much as 15 degrees during shifts. This results in a loss of horsepower which is really why this feature is was programmed in the computer in the first place. Plain and simple doing this reduces power and is less damaging to drivetrain parts such as the transmission. Everyone knows how weak the factory transmissions were in Mustangs. Likewise with the automatic transmissions the computer retards the timing when it thinks its time to shift. The result is sloppy shifting and a slower car. A shift kit will make these transmissions shift firmer by manipulating fluid pressure in the transmission but the spark retard function in the computer will still be there. The solution for these issues is tuning. A device such as an SCT chip can remove all of these issues. The TM40 is a much better computer than the A9L, A9P and other fox body computers but it needs some tuning and tweaking to work optimally.

dawson1112

I would say that it is minimal at most. My 94 pulls hard all the way through 5,300. Now granted before the long tubes and explorer intake it did fall on its face way sooner but I believe it was an aspiration thing and not a timing thing. It just hit its limit of what it can intake as far as air. As soon as I did the intake swap and got the long tube headers on the engine was able to breath much much better

cepowers18

Thanks, Mike T and dawson. So it sounds like there is truth to it, but it doesn't pull timing at any specific range... it can be anywhere. Good news is that it sounds like it can be tuned out with a chip.

I think I have my answer, but any other info or experience with this is much appreciated.