VP44 amp draw

[Linux]

Has anyone ever measured the amp draw of a VP44? I have been having some weird issues with one I just bought, so I did some logging and what I'm seeing is that it pulls about .2amps when it is idling smooth, then it jumps up to between 12 and 18 amps and the engine starts to run rougher, then it drops back to .2 and smooths out again. I'm curious if that is normal or the sign of a bad pump. Luckily I have a Blue Chip VP44 that works great, and I'm building a brand new ultimate bullet proof engine, so if this one is bad its not the end of the world...

[Great work!]

To get an good measurement you need a current sense resistor in line with the power, about 0.05 ohms. Connect an oscilloscope across it. A battery operated or isolated power scope is best.

 

The logic part draws maybe 150 - 200 ma.

The timing solenoid has a 10 ohm coil and operates at 50 or 60 Hz at about 20 to 75% duty cycle so that's about 1.4 amps when switched on.

 

The injection solenoid is done in 3 stages.

It is about 0.2 ohms and 250 micro Henry's and changes to about 320 uH when the plunger is seated.

 

Step 1 an electronic switch completes the solenoids path to ground the current ramps up according to the inductance formula V=L di/dt. So rearranging we have dt=di/(battery V/ L). The solenoid is saturated at about 18 amps. Using 300 uH for L.  Gives us 385.7 micro seconds for the current to ramp to 18 amps with a 14 volt battery.

 

Step 2 the current is reduced to about half that for another 150 to 300 uS so the plunger doesn't slam it's seat so hard to reduce bouncing. Like hitting an anvil with a hammer. 

 

Step 3 for the rest of the injection duration a 2 ohm high wattage resistor is switched in series with the solenoid that gives about 7 amps at 14 volts. The resistor and switch transistors are cooled by fuel flowing under the psig controller. 

 

The two solenoids also cause voltage spikes when switched off. The timing solenoid can reach 100 v spikes. All the rapid current surges and voltage spikes can cause all kinds of electrical noise. That's why proper grounding and wiring layout is so important. 

 

If the current in the solenoid is too high for too long the solenoid will cook within seconds. That pump definitely has a problem.

[Linux]

I'm powering it with a Hardwire PDM, so I can monitor the amp draw in real time and log it. It's pretty sweet. I guess I'll have to install my known good blue chip pump and see what it does. My truck is smoking like a damn campfire gone wrong and won't build more than 23psi of boost so something is certainly not right. Could be a bad injector too, I'm using ones that came with an engine I bought that I never got to hear run. Man I'm looking forward to getting my new engine assembled and installed... It will have brand new 7x009 injectors from PDD and fire ring etc 

[Great work!]

Definitely check the solenoid wiring on the back of the pump. The insulation gets old and crumbles away which can cause momentary shorts. Usually the timing solenoid wires go first which throws the timing to extreme advance or retard.