Engine/Transmission (1998.5 - 2002) what exactly does 'tapping the pump wire' do?

[Pavemen]

Wondering what exactly tapping the VP44 wire does. Its not really adding timing, but duration, correct? If timing, how? Its a single wire in parallel, so it can not alter the physical electrical signal.

If its just duration, is there a percentage increase or a table/curve that someone can share?

I am wondering if the pump wire tap is what is effecting the overhead console MPG figures. Its likely calculated from the ECM data, but that is getting modified at the pump, so MPG figures are running high on the console because it does not know that we've messed with the pump 'timing'.

 

[Allnew2Me]

When I first installed my Comp I ran untapped. The timing and boost fooling are added through the CAN bus and even with just timing the truck is much more responsive. By tapping the pump wire you are now adding over stock levels of fuel by modifiying the fueling curve and fooling the ECM into seeing normal boost and fueling. I remember seeing the fueling curve and it is very much like the stock curve just higher, which is why the Edge Comp is so liked, very smooth increase in fuel without surges. Your overhead computer is off because the ECM still sees stock fueling and boost levels but in reality you are adding more fuel and generating more boost because of that. As far as I know the duration is not affected except for the added time to add the additional fuel. With larger injectors you can actually gain mileage because the added fuel is injected in a shorter amount of time increasing efficiency. I am guessing that the pump tap wire sends a signal to the VP44 that piggybacks the ECM signal and the VP sees a demand for more fuel. How the fueling is added I really don't know for sure. Perhaps the solenoid is opened wider, or as you said just held open longer. There has also been talk of the VP being capable of 2 injection events although I don't know if the Comp allows this, there seems to be some question regarding that aspect of it.

 

[BWagnaar]

I think my TST box does the 2nd injector event on the higher settings, i'm not 100% sure though. I've heard of the vp44 being capable of the 2nd shot, but i cant remember what box will do it... what i do know though, it makes the truck get up and go



Soon Dave you'll have to change your name to KnowItAll:-laf

 

[Pavemen]

i just have an ottomind that was on the truck when i bought it, so i was not sure exactly what it does timing-wise. i have read a bunch about the overhead being off (which mine is. shows 20. 5 when actual is 18. 5) and my pump is tapped. starting realizing that this could be the reason

 

[JR2]

I don't think anyone has a second injection event on a VP44 truck. The wire tap just keeps the solenoid open a bit longer to send more fuel into the engine.

 

[darkhorse]

What you are doing with the tap is holding the fuel bypass valve closed longer thus increasing the duration of the fueling event. When that valve opens the injection stops & the fuel remaining is diverted back to the tank.

 

[Allnew2Me]

Hey Ben, mostly I just guess with style, but it is all still new to me!

 

[BPINE]

Soon Dave you'll have to change your name to KnowItAll:-laf

Now that was a good one I wish I would have thought of that.



All kidding aside Dave is learning fast, I am going to start deverting calls to him real soon.



Blair