Superduty

The ECM controls the lift pump on the 24V engines, right ?

Does it control the SPEED of the pump in any way ?

Or does it just turn a relay on and off ?

Bart Timothy

Power comes straight off the ECM. While the engine is cranking, the lift pump runs at a 25% duty cycle to keep fuel psi to 7 or so. I'm not sure how the ECM cuts back current to the pump for when the engine is cranking. I believe it does it by pulsing the current.

Superduty

Thank you.

lglamb

You might be able to check it with a non-digital voltage
meter. The needle would indicate a pulse width signal
by a reduced reading. Could be some new (expensive)
digital meters could show something, too.

piperca

Superduty, would this affect the performance of the Walbro you've been discussing?

BobQ

The ecm does pulse with modulation, very hard to check with a meter. I was on my fourth pump and did the Vulcan big line kit, that moves the pump to the rear near the tank. I actually put the pump right next to the tank, about 12 in from the fuel line connection. I would post a pic if needed, but don't know how. Any way, with the stock lift pump (100 GPH). The pressure is pinned at 15psi. If I floor it while climbing a hill with a trailer (I have a banks power pack) I can't get the pressure to go below 14psi! If I ever have to swap out the pump again, it is a 5min replacment.

I have no conection to Vulcan, just satisfied!

Bob

Superduty

"Superduty, would this affect the performance of the Walbro you've been discussing?"

It should be looked into, yes.

There is a guy over on dieselRam.com that has an ECM that is driving the fuel pump all the time. The ECM needs to throttle it back during startup ??? Someone said the VP44 is supposed to have an overflow valve. If it does, why the fuel pump need to be throttled ? I need to dig up a VP44 and have a look.

piperca

Yes, the pump does have an overflow valve, which is set at 14 psi, if I'm not mistaken. Would the regulator, set at 15 psi, being hooked up just before the VP not alleviate this?

Superduty

That is what I thought. But the guys on dieselram.com were waying the pump still has to be pulsed during startup.

Hearing that I suspect it is set up like the CP3 with a feed pump that limits flow. I've never paid attention to this part of the VP44.

Mike D

Why not just get a factory pigtail harness from Cummins, cut it in half and connect the Walbro pump up like the factory pump? Then it would receive the same pulse/start signal from the ECM....

043500QC

If the pump needs to be pulsed at startup, how are they(dealers) checking these pumps then ? It was my understanding that the test for a bad lift pump was to turn the key on, and if there was any less than 50 oz. of fuel pumped out, then the pump is bad or is dying ???

Superduty

"Why not just get a factory pigtail harness from Cummins, cut it in half and connect the Walbro pump up like the factory pump? Then it would receive the same pulse/start signal from the ECM...."

I have to admit that I don't know much about the 2nd gen fuel pumps or the VP44s exact needs.

I think the ECM limits the fuel pump current to 5A and that isn't enough to run a Walbro.

Smkndzl

the Cummins VP44 is PWM power to the lift pump, they have changed some of the lift pump output during starts to help hard starting issues, whenever you click the starter you will get a full output voltage for 25 seconds for testing the output of the lift pump. depending on the calibration age , if you just turn on the key you may not get any flow from the lift pump for more than 3 seconds if the ecm doesnt sense any RPM. so for testing you must click the starter and leave the key on for testing

the connector is a standard Duestch connector, 2 pin

Superduty

Other people are saying the lift pump gets PWM'd during start and fulls full output thereafter. They say the PWM's goal is 7 PSI during start up.

I don't know one way or another. I'm surprised that people don't know this given that they are putting aftermarket pumps on these trucks.

Geico266

The FASS comes with a 12 volt relay wiring harness. The relay is activated by the stock LP signal, but delivers a 12.5v supply to the pump direct from the battery. Maybe a relay setup would help the Walbro.

Also, some VP-44s are hard starting if the fuel pressure is high (10-15psi) at start up. This is why when you turn the key on (wait to start) the LP runs for 2-3 seconds and stops. You can aleviate this problem (if it's a problem) by adding an oil pressure switch to the ground side of the aftermarket LP. You should be able to add the switch to an existing port on the oil filter housing. Then the LP will only run when engine is running, the oil pressure is up past 3-4 PSI. Obviously, this is after you have purged the system of air and are in "normal" mode. The "bump the starter" method will no longer work until you bypass the oil pressure switch.