The Stovebolt Site Forums The Shop Area Engine Shop Fuel system wont keep steady pressure

this has been a thorn in my side for a while now, ive been racking my brain and combing the internet as well as holley's tech line; but to no avail. Its a 66 c-30 with the original style tank behind the seat. All components have 150 miles or less on them. From tank to carb- 3/8 line all the way, a corse bag screen in the tank, a clear screen filter just outside the tank, holley blue electric fuel pump mounted on the frame; it only has about 20 min run time on it (had the problem, replaced the pump, still had the problem), then a fine filter, simmilar to an oil filter- its a permacool fuel/water sepperator filters to 2 microns, thento a holley fuel pressure regulator, deadhead style (#12-803) brand new as of today, with a guage on the inlet side as well as on the outlet side, then into a holley 600cfm 4160, non adj floats, vac sec's. The problem is that something is causing a pulsing effect. I checked the voltage and its getting a steady relayed feed, the clear filter in the cab is wooshing. . . ? Fuel shoots through then stops, thenshoots through etc. at the regulator guages show that the incoming pressure slowly drops down to 6psi then goes up to 12-14 pretty randomly, which affects the outlet side accrdingly and it has something like a shudder that can flick the inlet psi up over the 15psi mark, which the holley tech guy told me the pump cant go that high unless there is a voltage spike, but ive tested the leadsand they are fine. Any help or suggestions?

I'd say ya got way too many filters on it, bypass them for starters, particularly the one before the pump, but that fine filter as well .... maybe the tank sock alone is too much restriction for the volume the pump moves and is collapsing, then opening again when the suction falls

Bill

Its not really a sock, its a stainless steel mesh that I hand sewed with stainless string, very proud of that little hidden gem, its very rigid and I had the stock 1/4 line in there (minus the sock) when this problem started. I just replaced that part after this problem started. And the 2 filters that are outside the tank are what holley recomends; a corse one before the pump, and a fine one between it and the carb. So if im understanding you, your saying to run no filters?

What's wrong with the way the Chevy engineers designed it? Untold MILLIONS of small block Chevy engines have run hundreds of millions of miles on a plain old mechanical pump. Is there something wrong with doing it the way it's supposed to be done?
Jerry

are you afraid of someone dumping some sand in your new tank? get a locking cap! I'd say eliminating all the obstructions is the best place to start, the restriction of the filters before the pump are different than the water filter after, who knows how that'll affect an electric pump, they blow better than they suck

I know some folks here prefer to run filters both sides of the pump, but I never run more than an inline can right in front of the carb [with an old original tank], the fuel pump can pass pretty large bits without problems, and the carb inlet screen will prevent any crud getting in there - start simple and if adding another component after it's working is a problem you'll see it immediately

Bill

Ok, ill try it without filters. Red you got a point- inlet screen and all. And Lincoln there is nothing wrong with the way its supposed to be, but if everyone had that point of view what would happen to speedshops. Could it still be called hot rodding if its always stock, the same as every other of that vehicle? Arnt our vehicles extensions of ourselfs? if everything was all the same I think it would make for some very dull motoring.

I've run 600+ HP round track engines at 7,000 RPM or more on a stock-appearing Carter mechanical fuel pump. I was just wondering why you'd need all that Rube Goldberg plumbing (that's obviously not working) to provide fuel to a street-type Holley 4BBL. The 2-micron filter might be necessary on a Peterbilt to protect the internal workings of a Cummins PT-series injection pump, but there's noting in that Holley that requires fuel that clean. Maybe it's all just for the bragging factor- - - -"Look at what I've got!"
Jerry

yeah, actually I was thinking that filter with the water separator was more appropriate for a diesel
as for the SS screen, depends how fine a mesh it is, I use 36 mesh SS for coarse screening in my juice plant, the original plastic socks in the gas tank are much finer than that and don't cause problems even if there's quite a bit of corrosion junk in the tank

Bill

Unhook the carb inlet and route a line back to the tank. Let the pump run for a while measuring voltage and pressure at the regulator. You should have steady regulated pressure, if not work backwards till you find the problem. What pressure are you trying to run at? I would start at 4 psi and see if it steadies out, 4 will be plenty of pressure and the standard Holley regulator should be quite happy there. The Blue pump should also be happy at 4 psi.

Any restriction before the pump will cause a low pressure, not a high spike. I suspect the regulator in the pump might be sticking or the regulator #12-803 is acting up. What spring is installed in it? The repair kits include a heavy and light spring, don't remember what pressure range they are for, but install the lightest one if available. Is the tank vented? Try running with the fill cap loose.

To eliminate any voltage problems, add a 40/50 amp Bosch relay pulling power right off the battery terminals. Run a power and ground and use the existing wires to trigger the relay. Use heavy 12 gauge wires, it will increase the life of the pump motor and reduce any weak circuits.

If all else fails, you can add a return line off the regulator. Plumb the carb to the pump side and add the return line to the regulated side. The carb will only see the regulated pressure and the tank will get the unused fuel. This is a way to keep the pump cooler and insure full flow to the carb. A lot of alcohol burning race engines use this to method.

Joe

Because im a newb to this. This is the first pre-smog that ive pulled from a field and im learning as I go; im more acustomed to cars that have I-4s and you have to have a special sticker just to swap the aircleaner. Basicaly im flying half blind. I dont have a lot of money so when I bought a new carb after saving up for it for a few months I wanted to protect it-thus the filters.

Brian - complexity doesn't = safety, the carb should have a simple, very fine, filter on the inlet .... and I'd think the electric pump, filters and pressure regulator cost a lot more than the common original mechanical pump and a $5 inline filter .... and now Joe suggests you spend more to insure the electric pump is dependable

Bill

Ditto on that advice! As long as the carb gets fuel that doesn't have huge chunks of trash in it big enough to block the needle valve open and flood the float bowl, it's a pretty forgiving system. I've raced Holleys since the early 1960's, and while they don't get any points for originality or out-of-the-box correct calibration, they're very tunable.

I believe once you radically simplify the fuel supply side of things, you can move on to getting the correct mixture for good all-around performance. Yes, you'll probably be doing some jet swapping, and possibly changing the accelerator pump cam to avoid having some flat spots and/or problems with an over-rich mixture. Holley likes to jet 'em rich from the factory to avoid the possibility of inexperienced engine builders burning pistons and valves. Almost every Holley I've ever run on the dyno needed leaning out, sometimes a bunch!
Jerry

a 2 micron filter?

Ok so I removed all my filters except for the metal sock in the tank just to keep the big chunks out of the line. So all I got now is the pump and regulator. I flushed all the lines and purged them. With the line disconected at the carb it flows evenly with incomming psi @ 3lbs and regulated side @ 0, but a nice healthy flow. But when I conect it to the carb it starts freeking out again; and ths is with the truck not running. And with the truck running it still does it. At one time with the truck not running and the lines all connected it did steady out, but when I let go of the switch and let it sit for a minute then hit it again it was back to being all jittery. So I disconnected the line at the carb again and just plugged it, same thing. I tried with and without the gascap and it made no diffrence. im lost. This setup worked great for 6 months or so. Ive replaced the pump and regulator and removed the filters; and its still doing it. What could I be missing?

why a regulator if the pump is only delivering 3psi?? .... sounds like a flow rate problem someplace .... something improperly sized [why oversize the fuel lines, then throttle with a regulator?] .... or sucking air someplace .... try bypassing the regulator, eventually you'll be back to a mechanical pump and a good running truck

Bill

Joe- I measured voltage for both control side and switch side, its reasonably steady (the battery starts to run down a little) with the truck off, and with it running its fine. I have been running the pressure at 7lbs. Is 4 really what it should be at? Im not sure where I got 7 from, but it was runningfine with it, ill try 4. As for what spring is in the regulator I dont know. Are they collored like the vac secondary spring kit? Ill have to get one of the rebuild kits to figure it out if they arnt colored, ive never opened one up.
Red- got the pump because the mech. One was shot, and I wanted a good pump to go with the carb. The water sepperator I had from an older project that I never got around to installing, and the clear glass filter I got because I can see when its dirty and replace the elemen before it was a problem; there is 46 yrs worth of crud in the bottom of the tank and without that filter it would have gone straight to the pump. And when I got the carb and the pump both said to have a corse filter before the pump, and a fine one after.

Brian, 4 will be plenty of pressure for your truck. The regulator springs are colored, but I couldn't tell you what it is, you can tell with both side by side, the higher pressure has bigger wire.

The pump has a by-pass valve in it to keep from burning out the motor when the flow stops, it might be sticking letting the pressure rise and fall. Pull the screw cap off the lower side of the pump (about dime sized) and see if the valve moves easily. Thats about the only thing that will cause it to rise, but the regulator should control it. Try plumbing a gauge right to the pump, it should hold steady when plugged once the relief valve opens.
Next install the regulator and recheck pressure on the outlet side. Going one step at a time is the only way you are going to solve it.

Joe