Engine/Transmission (1998.5 - 2002) Taping the Pump Wire...

[Nate]

I was wondering if someone could explain what exactly does tapping the pump wire do to the pump? I know it signals for more fuel, but is that tap sending more voltage. . or??



Reason I asked is I installed the TST PowerMax I bought like 5 months ago today.



Also I had to tap another pump wire (black with brown chaser I believe) in the maine wiring harness that's on the pump. Anyone know what that wire does?





Also the setup uses scotchloks. I hate those things, so I cut the pump wire and used a butt connector. Well it proved to be a PITA to re-connect the other end of the pump wire cause there's not much room to work with, so I added another 3" or so of same gauge wire to make things easier to work with. I taped it all up and put wire loom on it. Not exactly my pride and joy, but I couldn't think of a better way of doing it after I had cut the wire. I'm sure someone is laughing at me right now



I was thinking... this wire doesn't need to be a special length or anything... right? (I hope). Truck seems to run fine and all.

 

[isb360]

I believe tapping the pump wire allows the box to increase the duty cycle of the pump. I think that info is available on the TST website, although I haven't looked at it in quite a while. Max duty cycle untapped is ~30% and with the tap, that bumps up to ~50%..... I am estimating the numbers.



Tim

 

[NoSeeUm]

I think...



After fuel leaves the HP section in the VP44 it can go basically two places. One place is the injector the second place is through a fuel solenoid valve that bypasses the injectior and eventually back to the fuel tank. When the fuel solenoid valve loses power it opens. This causes the fuel pressure to drop rapidly and go below the pop pressure of the injector. This power on / power off occurs for each cylinder for each injection event and is timed with the engine.



Holding power on the fuel solenoid longer periods of time will add more fuel. This is essentially what the TST does. The TST does it external to the ECM by piggy backing or fooling around with the signal from the ECM. The actual direct control and power application of the fuel solenoid valve occurs in the FCM which is located inside the VP44.



The wire that taps at the VP44 is the power lead, the other wire is the ground AFAIK. I believe, some people connect that other wire directly to the negative battery terminal.



I used the Posi-Tap type connectors with dielectric grease. I attached 2 of them jumpered together for the pump tap wire. There has been many documented failures of pump tap and grounding connections using Scotch-Loks.



Jim

 

[isb360]

Yeah Jim, that's what I was trying to say, just wasn't coming to me yesterday

 

[Nate]

Thanks for the info guys.



On the TST box, should the green light be flickering a bit when it's adding fuel? I didn't see anything in the TST directions that said it would do that.

 

[isb360]

The yellow light indicates the boost fooler is active (and it is always active even if the box is off), red light indicates the unit is turned on and green light varies from off to very bright depending on how much enhancement the box is adding to your fueling. Under light throttle conditions, the green light is likely to be very dim (little added fueling) or possibly flickering, but should become steady and get brighter the more you push on the "GO" pedal.



Hope that helps.

 

[NoSeeUm]

Keep in mind, depending on which TST remote you have the boost fooling feature does not work with the Smarty. The TST does wait on boost to fuel, but the Smarty SW has its own agenda concerning boost. I would guess that most times it cares very little about what the actual boost really is.



The reason I am bringing that up, because you if have the remote that defuels on high EGT it can also defuel beyond stock. With that remote this is another useful TST feature for trucks that are running bigger that stock injectors.



So for that case the TST boost fueling function has another role. It does it by fooling the ECM into thinking it has a high boost condition. Which in turn forces the ECM to defuel further based on its own parameters operating in the normal way that it would function under high boost. That feature of the TST is disabled when the Smarty SW is loaded into the ECM. That is because overboost function is removed by the Smarty SW.



Jim

 

[Nate]

I don't have a remote for the TST. Just the box.