Engine/Transmission (1998.5 - 2002) Bump Starter - Lift pump run sometimes?

[SLightfoot]

I noticed that normally on my truck when I "bump the starter, often the lift pump will run for 20 seconds or so.



But not always. Ususally just once, then after that, repeatedly bumping the starter only produces a run time for just a fraction of a second.



When I was bleeding the lines a couple of days ago after replacing the lift pump, the lift pump would run every time I bumped the starter as in those cases there was no backpressure.



(BTW, the new lift pump behaves exactly like the old one. )



So, is this normal? I'm guessing that in normal operation, the lift pump only runs to some preset pressure, then shuts down and subsequently bumping the starter (assuming the pressure is still there) will not yield a lift pump long-cycle run time?



Shawn

 

[JR2]

If you turn the key off and back on then bump the starter it will run again for the 20-25 sec.

 

[isb360]

True... if you shut key off and then cycle it back on to bump it a 2nd or 3rd time, etc, it will work fine. I purge remaining air from the system using this method after a fuel filter change.



Lately when I bump starter, or for that matter when I first start the truck, the FP comes up to 5-6psi for 4-5sec and slowly sweeps up to 15psi over a 2-3 second span. I am having difficulty determining if there is a fault in the pump itself, or a fault in the signal from ECM controlling what the pump does and when. Since the phenomenon has started happening, it happens every time on every start. I do have a "Campaign" lift pump to put in and need to get off my lazy ***** and install my pusher pump on the frame rail, but I am curious about the potential failure mode because all of my other previous LP failures did not fail in this manner.



Tim

 

[DVR]

i had a similar problem with my last lift pump. it would cycle most of the time but not all. it had been in place for 15k miles (it was a $180 one). i saw erratic fuel pressures on the gauge. i suspected problems with the gauge or LP connector.

mine would be putting out 12-14psi holding fine theen you would check it a minute later and the needle would be at about 3-4psi. strange thing was if you got into the trottle it would pop back up to 11-14psi and hold. i had never seen a pump throw a pressure spike at full trottle and no one i spoke to had either. everyone suspected the gauge.



i swapped in a campain lift pump ($65) and all is well. obviously there are some bad pumps out there that fail (very) early. sounds like we both lucked up and got one.



edit- i had the slow sweeping pressure build too.

 

[NoSeeUm]

True... if you shut key off and then cycle it back on to bump it a 2nd or 3rd time, etc, it will work fine. I purge remaining air from the system using this method after a fuel filter change.



Lately when I bump starter, or for that matter when I first start the truck, the FP comes up to 5-6psi for 4-5sec and slowly sweeps up to 15psi over a 2-3 second span. I am having difficulty determining if there is a fault in the pump itself, or a fault in the signal from ECM controlling what the pump does and when. Since the phenomenon has started happening, it happens every time on every start. I do have a "Campaign" lift pump to put in and need to get off my lazy ***** and install my pusher pump on the frame rail, but I am curious about the potential failure mode because all of my other previous LP failures did not fail in this manner.



Tim

I had heard (sometime in the past) that under some ECM programs this 5 psi for 5 seconds was intentional. The LP ran at 2 speeds. Slow speed initially for start-up then kicked to high speed for running. I had heard this from the diesel tech at the dealer who did my first warranty LP replacement. However, your mileage may vary.



From your discussion in another thread concerning the Smarty. AFAIK the Smarty loads (re-loads) only the very latest stock ECM SW that was available at the time you purchased it. DC might have changed the half speed start feature since the time you got the truck and the current Smarty version.



Jim

 

[isb360]

Good info Jim. I believe the partial pressure delivered by LP during starting cycle is accomplished by pulsing the 12v on/off in a certain duty cycle, but I am not sure.



Mine is a 1998. 5 and the last time I had a reflash (can't recall why) by the dealer was in 2001 or so... been quite a while. There could be an update since then that I don't know about.



Thanks

Tim