hi guys I'm new to the forum and new to building ford engine's well not really new to building ford engine's just haven't messed with fuel injected ford engine's beyond stock builds I'm a mechanic of over 25 years and have built numerous sbc race engine's and some caburated ford race engine's so that being said I want to do a few things to my 95 gt cam gt40 heads and intake and thats pretty much it because its my dd and i want it to have a good choppy idle and squeeze a little more hp out of it too on a budget I've been told by countless ford guys 94 and 95s computers wont handle a cam without a tune where as a 88 to 93 computer will and I'm just wondering if I can replace the computer and harness in my 95 with a 88 to 93 any help on this would be greatly appreciated thanks in advance
There is a great deal of difference between the pre 94 wiring and the 94 and later Mustang wiring harnesses. From a practical standpoint, this is not by any means a job to undertake. You'll spend less time money and aggravation using the 94-95 computer and getting a tune if it doesn't run well.
The 88-93 Mustangs had 2 different computer systems; the 87-88 were speed density while the 89 -93 were mass air systems.
Speed Density uses Manifold vacuum (MAP), Throttle position (TPS) and RPM, & Air Temperature (ACT) to guess how much air the engine is pulling in. Then it uses all of them plus the O2 and ECT sensors to calculate the air/fuel mixture. It is dependent on steady manifold vacuum and minimal changes in airflow from the stock engine configuration to maintain the proper air/fuel ratio. Change the airflow or vacuum too much and the computer can't compensate for the changes, and does not run well. Forget about putting a supercharger, turbocharger or monster stroker crank in a Speed Density engine, because the stock computer tune won’t handle it. Every time you seriously change the airflow through the engine, you need a new custom burned chip to make the engine run at peak performance.
Mass Air uses a Mass Air Flow meter (MAF) to actually measure how much air is being pulled into the engine. The computer uses this information and inputs from the O2, TPS, ACT, ECT, RPM and Barometric Pressure (Baro) sensors to calculate the proper air/fuel ratio. It is very tolerant of changes in airflow and vacuum and tolerates wild cams, high flowing heads, and changes in displacement with minimal difficulties. Just remember that large changes in airflow require more fuel than the stock fuel system can deliver. At that point, you will need larger injectors and a larger fuel pump to make the engine run like it is supposed to. Larger injectors can be used with either an aftermarket calibrated MAF or a custom dyno tune. This makes it possible to use the stock computer with engine displacements from 302-408 cu in, and make many modifications without a custom dyno tune chip. Put a new intake manifold on your 331 stroker and the computer figures out how much more fuel to deliver without having to have a new chip burned to accommodate the extra airflow.
The choppy idle may sound cool but it is a killer for a daily driver. Poor low RPM performance and a surging idle is hard to deal with in stop and go traffic or when idling through a cluttered parking lot.. How do I know this?
See the
Surging Idle Checklist. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.