1988 Mustang GT Intake Swap

joel5.0 said:

Myth Case #4: Increasing FP will Raise HP Mythology Case #4:
Increasing fuel pressure will raise HP

Fact #4:
The amount of fuel added to the engine is calculated by the system based on engine conditions, and the feedback from the sensors in the system, including the O2's. A/F target is 14.64:1 and the ECM will make adjustments to the Injector Pulse Width (IPW) to reach the A/F stoichiometry goal.

EEC-IV tables are used for the calculations for IPW, including adaptive strategy learned for open loop and close loop operation, the only difference is, that once the system achieves close loop state, adaptive tables are updated....they are used under open loop, but not updated......like turning adaptive strategy off.

Fuel pressure setting does have an effect in the system since the amount of fuel will vary at the same IPW, the higher the pressure, more fuel is delivered at the same IPW setting....the system will get the feedback of this condition (O2 readings), and will trigger an IPW re-calc (shorten it) to reach A/F goal, thus cancelling the effect of a higher pressure setting at a point. However, fuel pressure setting IS important, since....

Quote:
The adaptive system has a range of roughly +/- 25%. If you had an adjustable fuel pressure regulator installed, and you needed more fuel, you could keep cranking it up until the EEC could no longer dial the fuel back out.


From: EEC-IV ADAPTIVE CONTROL - YOUR BEST FRIEND OR YOUR WORST NIGHTMARE! By: Mike Wesley
......and confirmed in EEC-IV setups with the datastream capabilities, watching "fuel trim" parameter while causing (or troubleshooting) extremely rich/lean conditions.

Fuel pressure setting has a "centering" effect of the ECM fuel trimming capabilites or limitations....EEC-IV has the capability of doing short and long term "fuel trims" within a 25% (+ or -) of its internal fuel tables. This means that it can either increase or decrease fuel trim given the real time conditions (short term) and the new center fuel trim (long term or adaptive learned).

Let's use an example.......if long term fuel trim is "learned" and set at +15% by the system, and you suddenly get a vacuum leak that requires a 13% fuel trim "addition", the system will be uncapable of compensating for it and lean codes will show up.....on the other hand,......... if you have the long term fuel trim at -5%, ......the system will compensate for the time the condition is present, w/out the lean codes showing up, since the correction trim required is within its pulse width compensation range limitation.

Keep in mind, that the system will continue to update long term trim, and raise its value (in close loop), ....if the vacuum leak is permanent, long term will reposition to +8% with time....leaving less "room" to add fuel when required due to..........other conditions.

How to ensure fuel pressure increase is in control for richer WOT runs?.....old EFI school trick for drag racing....increase fuel pressure, disconnect O2 sensors to force open loop and prevent adaptive strategy from updating tables, clear Keep Alive Memory (KAM) and adaptive strategy learned.....you're set until O2's are reconnected and O2 codes cleared.

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