olddodgetrucks

what should the gauge read before engine starts ,i have the f/p gauge on the filter housing

RVTraveling

Zero. On a stock setup the FP does not kick in until the starter hits.

Ken

olddodgetrucks

what is the reason it is wired that way,i would think fuel pressure when the key is turned to run would be better for the pump

Barney

There are two duty cycles for the stock lift pump. One is half-speed during cranking and the other is full speed during engine operation. You should see 4 to 7 psig during cranking and about 11-13 at idle. The engine usually starts quick enough that you have to be quick to notice the cranking pressure.

The VP-44 needs to be 'primed' to prevent damage during cranking. This is why they switched to the electric lift pump.


http://dodgeram.org/tech/dsl/mt_2_feb98/fuel_sys_2.htm
Controlled by the ECM, the transfer pump uses pulse width modulation to provide two duty cycles: full speed when the engine is running and half speed at crank to prevent overpressure that could keep the injection pump from operating.

johnh

the lp will run for 2 seconds after you turn the key on.....

VADSLRAM

As soon as I turn the key my LP cycles on. It did it with the stock pump and the FASS harness takes the relay power from the stock harness so it does it too.
I get about 14 psi on key. I usualy turn on the key, let the pump run a second then turn over the engine...don't know as how I need to but it's kind of a ritual now. Bat turbine to maximum and all.

RVTraveling

It may depend on how the truck is equiped. Mine is 24 valve, manual transmission, 2WD. When I change the fuel filter, I have to hit the starter, without starting the truck, to make the pump run and fill the filter.

YMMV

Ken

johnh

johnh;2298927]the lp will run for 2 seconds after you turn the key on.....[/QUOTE]

AggieJustin

Actually, it depends on the programming in the ECM. The later ECM updates shortened this cycle to less than a second when going key on. My '01 used to run for a second or two when the key was turned on. After getting an ECM reflash and now with the Smarty, it just hits long enough to see some movement on my gauge.

I believe they shortened the run time when trying to work out some hard start issues. Now if you actually bump the starter without starting, you get ~45 seconds of run time for priming.

olddodgetrucks

what would happen if fuel pump was wired to run when key is turned to run,would make bleeding filter much easyer

klx650a2

The safest way to refill/bleed the system is to bump the starter. You do not want the pump to run full blast while the engine is cranking. vp44's are expensive.