2nd gen lift pump and vp issues

[mikelutestanski]

Hello. Not sure where this belongs but my 2001 ram 3500 had (has?). Issues with flat pedal.
Changed 2. Tps ; vp44 ; added Fass system ; new battery cables ; changed battery cables (genos) ; new vacuum pump and pwr steering system; crank seal. (Last stuff was because of leaks on side of engine..
SO with all the main wiring harness exposed I cleaned the oil off and checked every connection. When i installed everything new (PS and Vac pmp) and started I found two connections had shorted where the fue tank pump was connected to the standard pump.. shorted out . bad connections .. the lift pump circuit would not pick up so I used the fuel heater line to power the fass pump... SO. The truck would not always start... sometimes it took three trys.. no code with the blue driver obd but the key trick gave me a 1693. But then it would start... On a hunch I checked the original ecm pump circuit feed line and it worked. SO I switched the fass pump back to the ecm lift pump feed line. THe 2 second start for the pump seemed to cure the problem. I wondered why the 2 second run was standard ? With the other line the pump built the pressure up to 18 by the time the lights cycled and I hit the key to start... SO far the truck is starting and I will now start dauly runs to build up my confidence on the truck..
I still wonder why the pump only runs for 2 sseconds betweeen key on and key start. I think the vp 44 does not like to much pressure before it starts. ??? Right or wrong ???? Dont know. Any vp guru have an answer?
This is my experience for what its worth,,,, Thanks for reading.

 

[KATOOM]

You have a lot going on in your post so...

The correct fuel pump procedure from the ECM is:
Turn key to ON = fuel pump 2 second prime cycle.
Turn key to ON and bump key to START position = fuel pump 25 second cycle.
Engine cranking = 12 volts to fuel pump alternates from 0 - 12 - 0 - 12 - 0 - 12 volts to reduce fuel pressure by half.
Engine running = fuel pump running 100% of time.

With the factory Carter lift pump the fuel pressure is regulated at 15 psi so cranking pressure is approx 7 psi at best. The problem is pumps like Airdog and FASS are more aggressive and pump more pressure/volume which will result in more cranking pressure even though the voltage is alternating. This can cause the fuel solenoid and timing ring in the VP to hydrolock until the pressure bleeds down which causes hard starts when the engine is hot.

You can eliminate this by installing a secondary delay relay which removes voltage to the fuel pump during engine cranking and works great...

In regards to "flat" pedal you mentioned. It sounds like dead pedal and is sometimes caused by an alternator generating excessive amounts of AC voltage. The ground system on these trucks/engines is horrible and because of that, any AC voltage is exacerbated causing problems with neighboring electronics like the ECM, PCM, PSG, APPS, etc...and resulting in phantom electronic anomalies. Check the alternator with a basic voltage tester that reads both AC and DC. Switch to AC and 200 and touch the red to the alternator hot post and black to the alternator body. With the engine idling it should be no more than .5

 

[mikelutestanski]

Hello. Thanks for the info. It clears up my thinking. Yesterday we did 60 miles ,8 stops ,, many starts. It was not until the last stop that the truck did not start first try. I did look at the fuel gage after the 2nd try it was at about 15. It finally started . I wonder if I can install a bleeder valve in the main fuel line to bleed the pressure off before I hit the start .
As far as the tps and ac voltage at the alternator; I installed a wire from the alternator to the passenger side battery positive. The main problem with ac is the bleedover to the negative cable from the positive running across the front of the engine. My solution takes the positive out of the wire way. How much ac is on the truck will be measured later and I will report it..no issues at the moment with tps... thanks for the reply. Mike