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ACCEL PUMP

Intake manifolds are going to get wet with fuel while running. This wetness changes with temperature, engine vacuum, and air flow speeds. This wetness also must be supplied in addition to the fuel that is intended to reach the cylinders. This wet film of fuel on the surface is much thicker at cold engine (fuel doesn’t evaporate well when cold), and also varies greatly with vacuum (bigger at high loads, smaller at low loads). The software has a strategy to supply that fuel and compensate for the changing size of the film. However, different manifolds have different characteristics, so some adjustments may be necessary to give the proper fuel during a “transient” event (transient is a term used to describe moving the throttle and changing the load). The fuel added during a transient has to be added in a special way to cause the wetness to build correctly over several injections. It starts out large, and decays to 0. The decay adjustments shape that curve. A larger decay value causes the accel “pump” amount to be ended sooner, and a smaller decay value allows the fuel to extend a little longer. It’s a fine art of calibration to get this perfect, requiring a super-fast reading of a lambda sensor. It’s recommended to only adjust these values when you notice it’s a problem. It also shouldn’t be adjusted much until the fuel learning has had plenty of time to adapt to the engine. The Accel fuel calculation uses 2 different signals that work mostly independently determine how much fuel to add/subtract. The MAP is directly used for “Accel Pump” fuel. The Alpha-N MAP is used for the “Fast Accel” fuel. Alpha-N uses the TPS and RPM to calculate a secondary “MAP” signal in case of the MAP fault. That value is also used to calculate the “Fast Accel” fuel, because it responds slightly faster than the real MAP signal.

Accel Pump 20F = Adjusts the fuel film compensation when very cold. 0 means it uses the default calibration directly.
Accel Pump 65F = Adjusts the fuel film compensation when cold. 0 means it uses the default calibration directly.
Accel Pump 170F = Adjusts the fuel film compensation when warm. 0 means it uses the default calibration directly. The default calibration already has a background table that is set up to work pretty good “out of the box” but it may be too lean or too rich during quick tip-ins for certain engines.
Accel Decay 20F = A larger decay will shorten the amount of time that the injectors are adding fuel during a transient. A smaller decay will extend the time. 0 will use the default values that are in the default calibration.
Accel Decay 65F = Same, but for 65F.
Accel Decay 170F = Same, but for warm engine.
Fast Accel 20F = Adjusts the fuel film compensation when very cold. 0 means it uses the default calibration directly.
Fast Accel 65F = Adjusts the fuel film compensation when cold. 0 means it uses the default calibration directly.
Fast Accel 170F = Adjusts the fuel film compensation when warm. 0 means it uses the default calibration directly.
Fast Decay 20F = A larger decay will shorten the amount of time that the injectors are adding fuel during a transient. A smaller decay will extend the time. 0 will use the default values that are in the default calibration.
Fast Decay 65F = Same, but for 65F.
Fast Decay 170F = Same, but for warm engine.
dTPS Acc Gain = In order to “help” the acceleration fuel be large enough to handle a sudden throttle snap open, the speed of throttle opening is used as a bit of a helper to make it bigger as the speed of the throttle is opened faster. A larger number here will make it more sensitive to throttle opening speed.
dTPS Acc Max = The dTPS fuel gain multiplier is limited to this amount. 100 means that no help is given by this function. 199 means that the Fast Accel fuel is nearly doubled if the throttle is moved quickly enough.
Tipout -20F = “Tipout” is the term used to describe when the throttle is closing. The MAP drops rapidly, which means vacuum increases rapidly, and the fuel suddenly vaporizes off of the wall, and the injected fuel quantity is less. The wall film of fuel will decrease greatly, and thus if the injection rate is kept the same, the engine will be very rich. The software compensates this using a default calibration for the wall film, but the adjustments provided here can allow more precise adjustment for the varying engine configurations.
Tipout 0F = Same.
Tipout 40F = Same.
Tipout 70F = Same.
Tipout 120F = Same.
Tipout 150F = Same.
Tipout 185F = Same.
Tipout 215F = Same.

10 comments on “ACCEL PUMP

  1. I have a boosted sbf and will be using the power adder 1200 with a aeromotive a1000 fuel pump. I know i have to have an external regulator before the tbi. But will i need to hook up a boost signal to the fitch regulator or to the aeromotive boost referenced regulator? Or will they both need boost signal

    1. If you are boosting the engine the fuel pressure regulator also needs to see the boost so it can increase fuel pressure. This line needs to be hooked up.

  2. I put a 400 hp system on my 69 camaro 350 with an edelbrock performance kit (heads, cam, intake). Everything worked great except I have stumble and flat spot issues right off idle. My question is at what setting on the accelerator pump setting is too much? I am now ant 75% and still have a tiny bit of stumble. Is that normal or is that high for a small block chevy with a fairly mild cam?

    1. That is very high with the accel pump settings which makes me think you may be loosing fuel pressure during accel.

  3. The flat spot is only when you barely touch the pedal. Other than that the acceleration is strong with no stumbles. I don’t have a pressure gauge on the line, is there a reading on the FItech for fuel pressure? I didn’t see one. If not a guess I have to add a gauge but it doesn’t sound right since there is no stumble what so ever except for when you barely touch the pedal off idle or in traffic when you get on the pedal again with that light touch. If you stomp it, it takes off just fine but the car lights the tire when you give it to much gas to get going. . it is also a brand new install with your inline pump kit, a new tank and pick up and no kinks anywhere.

    1. Your theory would be correct. You described the issue very well here. If you have a large cam in this motor maybe try leaning out the idle AFR target as the engine may load up slightly on take off. Also the accel pump setting is for load change and fast accel is for throttle change. You can play with the accel pump a little from the sounds of it as well.

  4. It doesnt have a large cam and the stumble was very bad at 0 accelerator pump. I kept raising all 6 until it is mostly gone at 70% but still there enough to make think it is going to die every time is lightly touch the throttle. I left in 3rd gear last night which keeps the revs up and it seemed much better as you get on and off the throttle but off idle still stumbles. what would be the afr target ranges it should operate within? If you guys would put out a list of setting and normal ranges it would sure help to know what’s not right.

    1. If you are on the top end of the accel pump adjustments you should check the fuel pressure while you are hitting the throttle.

      There are no NORMAL settings for system because every engine is different. What I can say is the base settings should be close for just about everyone.

  5. Another piece of info. I put a pressure gauge (b&m) on the fuel today. If it is to be believed it is running 40 p.s.i. and jumps up a hair with throttle.

    As I said, it is a brand new install with your inline pumps, filters and fuel line. There are no cinks and the pump is below the tank. It is returning ruel on the return which is why I suspect the regulator may be a problem. When I clamp down on the return line I easily make 60 p.s.i.

    Does that mean the EFI Carb is bad or can I just change the regulator?

    1. If anything it would be the regulator. If you have the Go Street EFI this system is designed and does run at 43 psi.