I am thinking my hard starting might be related to a bad lift pump. Right now it sounds like a rabid chipmunk under my truck, turn the key on and it makes a rapid knocking sound. Brrrraappppppp. It is not always for the same length of time, sometimes not at all.

I am mainly familiar with the typical whine of a GM fuel pump but am wondering if these sound different. I would have expected a high pitched whine. It has no problem putting fuel to the filter to bleed the system. If I crack the bleeder on the fuel filter open with the key on before I start the truck it will pop right off, otherwise it cranks for 5-20 seconds before it starts when its cold. Once its warm, it still cranks for a while unless immediately restarted. Once started, it runs fine.

Mine clicks away no whine, I believe mine is OK. I think it's solenoid style pump as opposed to a rotating motor type.

Sound how much or how little isn't an indication of health only indication pump is getting power, only way to know is to install a gauge, and go for a drive, if pressure drops below 1.5 and stays there on WOT pump is on it's way out

The sound will change as pressure builds. In other words, the knocking is more of a sharp note and as it builds up resistance it will smooth out. If you want to maintain 1.5 psi as Turbine Doc notes, you'll need to do some serious plumbing. It is quite common (and acceptable) to see the psi drop to 0 as measured between the filter housing and the pump. This is OK as the IP has it's own transfer pump inside. If you were going for all out performance, then keeping a slight psi would be the goal.

In OBD-II as the pump builds pressure (possibly same in OBD-I) sound changes as pressure builds, in OBD-II once pressure builds fully the pump regulator can actually stop the lift pump, but a weak lift may run constant and takes longer to build to full pressure.

IIRC there is a requirement from Stanadyne that IP be supplied a minimum of 1 psi; dips below that at WOT are acceptable, sustained low pressure is not, IPs have internal transfer pumps and will pull their own fuel as John says but performance & IP longevity will suffer IMO; as IPs are also lubed by fuel, reducing lube flow in my minds eye can't be healthy over the long haul.

Maintaining lift pressure was evidently a priority as in OBD-II lift pumps have 2 power sources to the pump; PCM as primary backed up by OPS; now what I have not seen is documentation anywhere & I supect the effort was to insure IPs/PMDs have proper volume to keep the pump mounted driver cool.

One could extrapolate then if flow to IP is impacted enough that reduced volume causes cooling issues to a driver on pump, then also any reduction in volume would be bad for IP, yes an IP can live/deal with reduced fuel delivery of a weak lift pump but for how long.

"Feeding The Beast" mod I came up with using a GM 93 year higher volume pump, and then Walbro FRB-5, hasn't added any performance to make mention of possibly (I've never dynoed before/after the mod), but I never dip below 2 psi on WOT, and with that by seat of pant I feel like the truck maintains ability and slight advantage in acceleration time as compared to the stock pump/fuel line setup.

I've had pumps that purr like normal but fall off at WOT, they eventually recover, but recovery time has been up to about 30 sec to meet steady speed of the WOT request, and then only coming up to about 1.5 psi, that pump would be a good one, I just from my driving testing seem to get petter perfomance & better driveability when lift pressure is maintained above 2 psi.

In snot in my stocking post this summer where both the lift pump & transfer pump were not able to pull fuel thru a plugged in tank sock performance fell off to point only 35 mph was max speed attainable, worst case flow restriction in that, but shows flow restriction does pose a problem, so for me maintaining max flow to IP under all conditions is the objective.

Maybe too simplistic in my view but I think anything done to increase flow is a plus, for a stock truck maintaining stock delivery is fine and one can even live with a little loss, but once you start pushing performance envelope ie reflash etc. more is better to a point, IP will return any unused fuel to the tank, but you don't want to overwhelm the return circuit either with too big a pump.

I'm sure one of our more learned members can come up with the calculation for max pump sizing & plumbing reqs, I just did trial & error, in "FTB" I always wondered why it came from tank .280 ID then necked down to .187 ID out of fuel mgr and into IP, .280 all the way to IP inlet works better for my needs.

A 93 pump gives more than the later model pumps as it fed the mechanical IP, and is a direct replacement (Heath's H/O fuel pump is a derivative of that design) not requiring any additional work other than remove/replace the OEM pump; and the Walbro FRB-5 gives more than that but requires some plumbing modification, whatever pump one chooses to upgrade to it needs to be able when/if it fails it will flow thru on fail gear/vane pumps won't always do this.

Mine never made much noise but you could feel it when you turned the key on if you crawled unde rand put yoru hand on it

mine:

budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda...

:D

Weighing the issues, I've gone to a manual control. I'd discourage anyone from doing this but I've replaced all the related parts without success and I'm not about to re-wire the entire circuitry.

Anyway, if the truck has sat for an extended period, the lift pump will hammer away loudly and as pressure builds the intensity drops. Sometimes, if it's only been sitting for a brief period it is much quieter. Once pressure has built, I can turn the lift pump on and off and there's almost no sound.

I've wondered if the rate that the pressure on the line decreases between the lift pump and the IP while it's not running is a fair measure of the integrity of the line. I admit it - I still haven't fixed my fuel leak. I turn the lift pump on immediately before I turn the starter and turn it off about 1/4 mile from my house so residual pressure doesn't cause the truck to pee on the driveway.

where do you get the pressure gauge for the lift pump and where is the best , easiest place to put it.

Any 0-10 psi gauge would work, can be tapped into the horizontal port on the "T" valve near the oil filler. Secure the hose with clamps and run it to under your windshield wiper so you can watch it when you drive.

As an update I installed a new (to me) lift pump in my truck. I got it from a friend who parted one out, only had 1 month use on it, Carter brand. Much quieter, better starting. We shall see tomorrow when its 7 degrees.

mine:

budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda, budda...

:D


Mine is more of a....

Clack, clack, clack, clack, clack, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, thunk, *Silence*

:D