2000 Mustang GT Sct parameters

FP duty cycle is a number in reference in terms to 100%.

INJ pressure drop - not too sure on this one. But I think it's safe to say it has to do with some kind of fuel pressure drop at the rail or injectors.

LT fuel trims are the ECM's learning curves so to speak. It's the automatic fuel adjustment on top of the base tune. The ECM can +/- fuel depending on needs, up to +25%/-25%. Yours are perfectly fine. Meaning, with the current tune, the ECM is only adding 1% more fuel to reach the desired mixture.

The DTC for monitor testing is relatively normal. It will go away when you complete your drive cycles. You could get this after replacing the battery, disconnecting the battery, or possibly re-flashing the ECM.

P0308 you will want to check out. I had to replace a coil on mine not too long ago. Swap #7 & #8 coils and see the if the misfire changes to cylinder #7.

meangrnmachine said:

battery voltage- 14.00
coolant temp- 106.00
desired idle rpm- 880.00
fp duty cycle- .28
idle spd valve dc-.65
inj press drop- 40.00
intake air temp- 54.00
load-.30
lt fuel trim b1- 1.06
lt fuel trim b2- 1.12

There are many more but the top ones are the only ones i datalogged. Can anyone explain what the more obscure ones mean like fp duty cycle, inj press drop, and the lt fuel trims? Also, what are they supposed to be at?

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FP duty cycle:
The returnless fuel system varies fuel pressure by modulating the power sent to the fuel pump. It does this by varying the so-called "duty cycle" of the power signal with a rapid, pulsing voltage application called "PWM" or "pulse width modulation." Duty cycle is a measure of how long something is "on" compared to the total cycle time. So if the total cycle time is, say, 31.25mS (i.e. the pulse repetition rate is 32Hz), then a 25% duty cycle has power applied for 7.81mS and the remaining time, ~23.4mS, the power is not applied.

The closer this number is to '1', the harder the fuel pump is being driven to maintain the fuel pressure at the required fuel flow. Your reading indicates that at that time, a duty cycle of 28% is required.

If the PCM only wants to deliver 25% power to the pump, it will only apply voltage for 25% of the time. If more delivery is needed to maintain fuel pressure, the PCM will command more power by applying power 60, 70, 80 or more percent of the time.

28% at idle doesn't look abnormal. If you saw 60 or 70%, you might have to check the fuel filter, the pump output, the FPDM (the box that converts the logic-level signal from the PCM into a high-current output to drive the pump) etc.

idle spd valve dc:
The PCM controls fuel pump power by PWMing the voltage to it. The PCM also controls idle speed in a similar way. By applying a PWM signal to the idle air control (IAC) valve, the PCM can vary the size of the opening through which throttle bypass air is admitted to the engine. A large opening means a high amount of air and a high idle speed. A small opening allows little air in and the engine slows. The PCM controls the IAC with that PWM signal to achieve the desired idle speed.

Your reading indicates that to get that idle speed, a 65% duty cycle on the IAC is required. This may vary as engine conditions change: if you turn on the A/C and load the engine with the compressor...if you turn on the rear defogger, the blower motor or a cooling fan comes on the loading on the engine changes (alternator load) and the PCM compensates by adding or subtracting IAC duty cycle as needed.

inj press drop:
The fuel injectors are designed to operate with a known pressure drop. There is obviously fuel at some pressure on the "inlet" side of the injector and there is, for example, 18inHg of manifold vacuum present on the "output" side of the injector at idle. The whole fuel delivery system is designed around the idea of a contant pressure drop across the injectors. That way, the fuel calculations in the PCM become much more deterministic and frankly, easier. If you know every squirt of the injector will deliver a known amount of fuel regardless of throttle angle or engine condition, the process of calculating fuel injector pulse width becomes much simpler.

The Ford system wants to see 40-psi or so across the injector. As noted in the fuel pump section above, the PCM varies the fuel pressure as required to maintain a desired fuel pressure. It's doing this by reading the fuel pressure sensor on the fuel rail which is referenced on one side to the fuel rail (injector input) and to the intake manifold (injector output) on the other side. The sensor tells the PCM what the pressure differential is and the PCM tries to maintain it at 40-psi, give or take.

It's important because the absolute manifold pressure at idle is very low...say 6-psia but at WOT, it may climb to 14-psia or more. The PCM varies the absolute fuel pressure from, say, 46-psia at idle (46-6 = 40) to 54-psia (54-14 = 40) at WOT to keep the drop across the injectors at 40-psi.

lt fuel trim b1, b2:
Dragstr05 did a pretty good job with these. "LT" stands for "long term" and is one of several "learned" parameters the computer uses to trim fuel delivery. The "b1" and "b2" refer to the bank of the engine. Since it's a V-type and has two separate O2 sensors, in some ways the PCM actually treats fuel delivery as if it were feeding two 4-cylinder engines. It "learns" by using the feedback from the front O2 sensors to know how much fuel has to be added or subtracted from baseline calculations to get the mixture correct. As time goes by, trends develop and the PCM stores these as learned parameters.

These learned parameters, including things like IAC trims, explain why sometimes, after re-connecting the battery after a long-while of disconnection, the engine doesn't run quite right for a while. The battery disconnection erases the stored parameters and, with no learned values, the PCM spends some time doing a less than stellar job of trimming fuel and IAC PWM until it establishes some new learned values again.

Also, i got a DTC code that stated the OBD- II monitor testing not complete and a second one that said misfire detected cylinder #8.

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The PCM has algorithms to check each of the emissions subsystems. Certain criteria have to be met for certain tests to run. It may involve periods of idling, periods of extended sustained engine RPM over some value, temperatures, throttle inputs and so on. If these conditions aren't all met, not all of the tests may have run. This monitor testing code is really a means for emissions inspectors to check the system: If you come in with no MIL (malfunction light), it may simply mean you disconnected the battery a mile from the inspection office, erased the codes and drove the car in. If the station tech plugs a scanner into the car he'd see "yes, the car has no MIL but part of the reason why is because the monitor testing hasn't completed." Lack of a MIL means nothing if the PCM hasn't actually finished its testing.

The misfire is pretty self-explanatory. Cylinder #8 is the rear-most on the drivers-side. You might want to pull the COP and plug and have a look a the gap and condition of the plug. If it's older, consider replacing all the plugs.

meangrnmachine said:

Also, when i open the gas cap to put fuel it NEVER makes that sound that cars usually make when removing the gas cap.

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FWIIW, the 2000 Mustang will almost never have any pressure in the gas tank unless there is a problem. The charcoal canister is vented to the atomsphere. This tends to equalize the pressure inside the tank.

If the PCM were running an EVAP purge test, the gas tank could be under a vacuum. Hence the reason the gas cap still needs to have a good seal. Once the EVAP purge cycle is over or the EVAP leak test is over, the canister vent solenoid will open and the pressure inside the take will equalize to atomspheric.

FWIIW, a narrow band O2 sensor can NOT give a numeric AF ratio. It can only indicate if rich or lean. To get a numeric AF ratio requires a wide band O2 sensor.