Problem: Hard starting after injector size increased
After increasing the size of the injectors in a 94/95 Mustang the engine gets harder to start, especially hot. After it starts it may also be very rich and hunt at idle until it gets to Closed Loop (CL), This FAQ has applicability to other Strategy EEC's but is written specifically for the CBAZA with either W4H0, T4M0, or J4J1 calibrations.
Cause and related information:
There are two modes of EEC operation when starting the engine; cranking the engine on the starter and the period immediately after it starts. In the EEC these are the "crank" and "startup" modes. Startup lasts a variable amount of time depending on conditions but will typically be over in less than 2 minutes of operation after the engine fires and the key is released. After this startup phase the EEC will attempt to go into CL which is not going to be covered in this FAQ.
There are few inputs to the EEC during crank. The EEC has one objective, get the engine to fire. During this mode the EEC is commanding injector pulse widths (PW) based on both Engine Coolant (ECT) and Air Charge (ACT)temperatures being supplied to the EEC by their respective sensors. MAF plays no role in crank mode.
Because the EEC was programmed by Ford to expect 19# injectors (24# if J4J1) it is commanding a PW that is too long for the engine's fuel need if the injectors are larger than the original values. For example, if you have upgraded to 42# injectors during crank the EEC will be commanding a PW that is more than 2 times what is actually needed.
What to do:
In CBAZA there are 4 areas of tuning to consider: 1) the Cranking PW vs ECT function (PID: FN348A) and the Crank Pulsewidth table (PID: FN1350) need to be leaned (caution as too low a value will prevent a big injector from pulsing at all when the engine is hot); 2) the Injector Min Pulse Width scalar (PID: MINPW) needs to be reduced to almost 0;(again use care here as this value too low may cause bucking in closed loop cruising) 3) the fuel Open Loop Multiplier vs ACT (PID: FN300) can play a role if your ACT sensor reports a temperature in excess of 116 degrees F and 4) you may need to lean the Open Loop Startup Table (PID: FN1361). Theoretically this last item should not be needed if your MAF curve, injector slopes, injector offset vs battery voltage function and injector breakpoint are exactly where they should be. However, a lot of guys have reported the need to lean this table even when their tune appears to be very good during other modes of operation.
94 GT, CBAZA/J4J1, 347 (on a R302 block), F303 cam, Performer II Intake, 1.7 Crane RR's, 1 5/8 Shorties, 70MM BBK TB, C&L 85mm Tuner MAF, Pro-Charger D1SC, 60#'s, TKO 600. Runs 11:80's