2006_BLACK_GT

I am also not a mechanic and I am not trying to say you are not correct. I think it is physically possible. My thought is that when you let off the throttle, while in gear, the injectors revert back to the idle trim levels and do not cut out completely. But my only reasoning for this is that the added complexity for the system (assuming it is only few more lines of code for the PCM) does not outweigh the minor fuel savings that would occur. If you rev up to 5000 rpm on the highway and get off the throttle it takes maybe 5-10 seconds max depending on gear to get back to the 750 - 1000 idle rpm? The question would be is there another reason for the fuel cut off other than fuel savings?

_Slowbra_

the "dont blast me" wasnt to you specifically black gt, i understand we are just discussing (after all thats what forums are for). In fact i rather enjoy having a decent conversation on here, so dont take it personally, because it wasnt towards you; but with both know sometimes there are individuals on here that like nothing better than to blast guys who are just trying to discuss stuff. I just want to keep it civil for the both of us....

the only other reason i can think of for complete shut off is because during deceleration, the throttle is completely closed, so there wouldnt be any air...therefore no need for fuel right?

mustangman281

Like I said in the other thread, if you want proof ride in a car with a wideband o2 guage and watch it max out lean during decel.

2006_BLACK_GT

The wideband sensor is going to read max lean unless it is specifically designed to measure free air conditions. Otherwise any voltage beyond its operating limits will register max lean or max rich.

I looked at my copy of the Ford Technical Service DVD and found that the Throttle Position sensor considers idle and decelleration as "closed throttle". The voltage to the PCM is the same at idle or decel.

"Throttle Position Sensor
The throttle position (TP) sensor (Figure 44) is a rotary potentiometer sensor that provides a signal to the PCM that is linearly proportional to the throttle plate/shaft position. The sensor housing has a three-blade electrical connector that may be gold plated. The gold plating increases corrosion resistance on terminals and increases connector durability. The TP sensor is mounted on the throttle body. As the TP sensor is rotated by the throttle shaft, four operating conditions are determined by the PCM from the TP. Those conditions are closed throttle (includes idle or deceleration), part throttle (includes cruise or moderate acceleration), wide open throttle (includes maximum acceleration or de-choke on crank), and throttle angle rate."

mustangman281

The way your trying to explain it you think that during decel the computer adjust pulse width to idle. If this was true a wideband would read 14.7 and not maxed out.

Bottom line the injectors are cut during decel.

_Slowbra_

Right, the TPS will tell when the throttle is closed, so decel. and idle would show the same throttle position. But RPMs upon decel. are going to be higher than idle, which is why fuel cutoff only occurs while the car is in gear and revving above idle.

So wouldnt something in the computer recognize a difference between idle and decel. based on engine speed? so there would be a difference in how much fuel is injected in certain different closed throttle conditions?

It makes more sense that the injectors cut completely with high RPMs and a closed throttle

vanquish

Yeah what you said makes sense too. I just assumed that the injectors would go to idle levels like blackgt said.

whiterabit998

it has to be burning some fuel right? the iac lets air in when the throttle is closed.

and plus to get that wonder full sound out of the tailpipes it has to be burning fuel right?

2006_BLACK_GT

If the PCM sends a signal to the injectors to fire, and the TPS sends the signal to the PCM to tell it throttle position and relative opening, how does the PCM get input for a TPS position that does not exisit? If throttle closed signal = idle/decel, the TPS would have to be bypassed completely and you would not be able to accelerate until the TPS was back on. The rev limiter does cut fuel completely until your RPMs drop below redline, but that's a safety issue and you know when this happens.

As far as the wideband goes, what brand is it? What is the reading you are getting on decel? Do you hear any detonation during this or do you think the ignition is cut off completely too?

mustangman281

I use a autometer in car for daily use and an innovative motorsports LM-2 when tuning.