ignatz

Unlike '89gmcs15's experience with the Edlebrock 1792 "quietflow", I am very unhappy with it. I have it well positioned just under the fuel tank at the rear of the car. A 3/8" line runs to a Mallory fuel log which has a regulator set to about 6 psi. A 1/4" return line runs back to the tank. This is a 69 Corvette and these size lines were certainly able to handle the big block motors. The motor in there now is an LS3 crate with a Holley 750 Ultra.

What happens is this. I turn the car on and the pump starts out at about 6 as it is supposed to. As I cruise for a while it gets down to about 3 psi and if I get on it, it goes to zero with obvious fuel starvation. Logic tells me that this has to be the pump as the regulator in the fuel log should shut off completely. Also with a bigger line in than out the pump ought to be able to keep some pressure. So is the pump bad, or should I just keep increasing its pressure? Remember of course that as you increase the pressure at the pump, the flow in GPH is reduced. I've no experience with electric pumps and don't want to start throwing money at the problem. Is the pump bad? Is my setup bad? I don't know.

One more thing, I started out with the smaller 1791 (6AN) and it acted the same way. Thought the 1792 would fix this. So I am already into some serious $. WTF?

Also, it ain't that quiet!

wildcamaro

iTrader: (15)

What gauge wire are you running to the pump? Low voltage will def kill the pressure of the pump...I'm running 10 gauge to a Holley blue with a dead headed -6AN line and have no fuel issues what so ever...your return line and regulator should be helping that pump, it sounds to me like everything is set up good...I would test your positive wire back at the pump and confirm you have good voltage...also is your alternator charging at 14.5 or so?

ignatz

A good question 'wildguy'. I ran 12 GA back there. I'm out in the garage right now and measure a good 14 volts at the relay output to the pump. My wire gauge table shows two ohms per THOUSAND FEET for 12 GA. So divide that by 125 for an eight foot run and it shouldn't be that much different at the pump (I have the wiring nicely sealed up at the back and can't easily measure what's back there). The other voltage drop would be the ground, but I am tied into the frame with about a 6" run and copper washers and stuff. Should be good and I start out with good pressure.

I've cranked up the pump pressure and checked that the regulator regulates. I do note that the fuel log regulator can only do a couple of psi to reduce the flow. It seems to me it is in exactly the right place, after the feeds to the carb, and my pressure measurement is in exactly the right place, before the feed to the carb. I keep thinking I am doing everything right so this is mysterious still. Thanks for the input

wildcamaro

iTrader: (15)

I would still measure the voltage at your pump, I understand your theoretical resistance drop using the length and gauge, but if I were you I would replace that 12 gauge for 10 gauge just to be sure if its easy enough. I would also call the edelbrock tech line to see what the specific technical requirements are for that particular pump. Hope you figure it out...

89gmcs15

iTrader: (7)

i wonder if its not something other than the pump since it did it with the smaller pump and also with the larger pump...? have you made sure the regulator is closing fully or checked the pressure gauge for accuracy with another gauge? what amps is the pump pulling? i had some issues with the connection going into the pump but after opening it and finding nothing wrong its worked fine ever since... try a dead head regulator, easy to hook up and only $20 to find out if its the pump or the regulator... are you running a filter in the system?

wildcamaro

iTrader: (15)

I looked up the instruction sheet for that pump and saw that it had an adjustment screw for pressure so technically you shouldn't need the regulator at all other than for the return line...it's preset at 6.5 psi for reference

89gmcs15

iTrader: (7)

Yeah it's a relief spring that causes the pump to circulate the fuel instead of moving it. Simple but works I guess. I do t see how you could over heat it even runnin a dead head and bigger HP. I haven't had a issue yet.

ignatz

Appreciate both of your thoughts on this.

wild: My thinking about the voltage at the pump not being easily measurable is that it still must be OK since I can get it up to good pressure initially. The wire is not going to change while I'm running the car and if the voltmeter indicates charging hasn't dropped it should remain at the initial pressure. It is a big pain to change the wire. It runs along another wire bundle and under the rear deck carpet. There is a harness bar and seat belts that have to come out as well as the rear compartments. I will see if I can expose some wire and make a measurement at the pump.

89: I like what you said about both pumps behaving the same bad way and it points to possibly something else. The pumps are different designs. The 1791 is internally regulated and the 1792 must be externally regulated. Possible the fuel log is the culprit. If things aren't getting better I will take it apart and see how it works. I am starting to suspect it.

Given that the 1792 must be externally regulated I can't set the pressure so high (e.g. 12 psi max) that the return line can't bring it down to what the carb wants. Holley warns that it shouldn't see more than 7.5 psi. The return line being smaller can only reduce the pressure so much, a fact that I have observed by twiddling the fuel log regulator setting. I can only bring it down by about two psi.

Here is my primitive understanding of how this is supposed to work. Under load, the carb is using gas and that pulls the pressure down. If the fuel log regulator is a relief spring it should start to shut off return line flow to the tank as the carb demands enough gas. Until the return is completely shut off the pressure should be controlled by the fuel log regulator and be constant. Once the return line is completely shut off, the pressure should then be the pump output minus the carb draw. Have a very hard time believing that under light load the carb needs as much as the pressure drop I am seeing (about 3-4 psi).

I had checked once upon a time that the electronic gauge measures the same pressure as a mechanical gauge so I believe I am seeing an accurate pressure while driving.

My homework for tomorrow. I have bumped up the output pressure from the pump a bit more but it was too late to go for a drive. Also will see if I can measure the voltage across the pump. That is not easy. It is above my muffler and hard to get to. I don't think heat is a problem either when I come back from a drive the pump is still cool.

Also going to look through my photos for relevant pictures to post. Hopefully I am not hogging this thread too much. My problem has kind of gotten away from who is using what and whether they are happy with it. Maybe I should start a new one?

Bye and thanks again

niscur29

I'm running an denso supra efi in tank pump to a Mallory return regulator. 6an feed and return.

5.3dime

Mallory comp 140, 6an feed 8an return

ignatz

RE my 1792 post, wild and 89's thoughts. The voltage across power and ground AT THE PUMP was 14 with the motor running. So that wasn't it. I drove around until the pressure went south, (bumping down around zero), came home and pulled the supply line. Almost nothing ran out of the fuel log. Hooked up a hose and ran the pump for about 30 seconds into a gallon jug. Got maybe a quart. That equates to about 30 gallons per hour. When I was young I could almost pee that fast.

Hard for me to understand what could be going on inside the pump to make it unable to sustain flow. It's not running hot. I thought maybe the tank was pulling a vacuum after a while but that wasn't it either.

Guess I will see re-read this post to see what pumps other people like. I had an Aeromotive AEI-11203 sitting in my Summit Wishlist, not sure why.

Anyway thanks guys

Cliff (Ignatz)

wildcamaro

iTrader: (15)

How old is the pump? May get a warranty on it if you call edelbrock and complain a little...

likes cars

I use a single quiet little Walbro 255 and an FST filter to a Mallory bypass reg.
By quiet I mean I have to kneel down next to it to hear it.
It is fed 12v from a run of 10awg from a dedicated relay.
There is 8an fuel line from the tank sump to the filter (almost level), 6an fuel line filter to regulator on the firewall, 6an to the bowls, and 8an return. Reg set at 6.5. I'm not sure it is the best setup ever, but the very clean cool dry fuel gets where it belongs consistently and the pump is damn near silent.

I will never use a holley blue deadhead again.

Pop N Wood

iTrader: (1)

The size of the motor has nothing to do with the fuel lines. You need to size them based upon the flow rate of the pump. At 160 gph you have one big *** pump. That ¼” return line is not a good thing. Even the 3/8 feed line is marginal. Keep in mind the old big blocks had mechanical pumps. That means the flow rate varies with engine RPM. Your electric pump is trying to flow max volume all the time. What type of connectors are you using, hopefully low loss AN types? No banjo fittings, sharp turns or other restrictions in the lines?

I notice that pump has an internal regulator. My Mallory does to, but when used with a return style regulator the internal regulator can be bypassed to make the pump output full pressure. Maybe that will help your problem.

How do you have the suction side of the pump plumbed? Hopefully large diameter tubing with a low pressure drop prefilter? Also have you checked for air leaks in the intake side? Electric pumps do a poor job sucking fuel. Even a slight leak or loose fitting here will kill the flow through the pump. Have you cleaned the prefilter lately? Any debris in the tank that maybe got sucked up into the pump? Can you take the pump apart and check?

No pump that large is going to be. 160 gph will support a big block on nitrous, anything over probably 90 gph is just making more noise. The fact it is making noise could also mean your fuel system is too restrictive for the size of the pump. It is having to work too hard. Pay attention to the feed side of the pump. My car got massively quieter when I switched from a paper style prefilter to a low pressure drop screen one.

ignatz

Pop: Everything you said here makes sense and I can only agree. The plumbing I have to work with in the chassis is classic Corvette stuff. The lines that are there can't be changed without lifting the body off. Did my best to put the new stuff in the right place and make the plumbing flow with "sweeps" and AN fittings and the like.

What you say about the "big *** pump" sounds right and is most likely misapplication by me. Bigger is not always better. Spent some time talking to Edelbrock and Aeromotive. I think the Aeromotive guy pinned down what's going on. In a word "cavitation". The "big *** pump" is flailing and probably beating the fuel into a lather because it is not moving anywhere very fast if at all. Noise is probably indicative too because as you say the pump is working too hard and nothing much is happening. That all seems to fit with my experience.

There are two pumps in this family, the lower flow 1791 which according to the literature "doesn't need a regulator" and the 1792 which needs an external regulator. Both have adjustment screws. But I haven't found anything in any of the literature for these pumps which suggests either has an internal bypass. I haven't seen anything that explicitly says the 1791 has an internal regulator. Why the 1791 doesn't need an external regulator is a little mysterious to me. I would expect both would be susceptible to cavitation.

My choices seem to be to switch to the 1791, based on the statement "doesn't need a regulator" or find a pump that I know has an an internal bypass and use it with an external regulator. I find myself doubtful that the first choice works.

thanks for your input! I have some more understanding of the situation

89gmcs15

iTrader: (7)

I tore one of my 1792 apart and the regulator is basically a spring style pop valve that opens with too much pressure and routes the fuel back to the suction side of the pump housing. It's really simple and actually works well in my lower HP application, even with a deadhead regulator.

Pop N Wood

iTrader: (1)

Yep, cavitation is the fuel flashing to a vapor at the low pressure input part of the pump then collapsing back to liquid when it hits the high pressure outlet. Pretty much the same noise a tea kettle makes just before it hits full boil.

Like 89gmcs15 says the internal bypass valves are usually adjustable. This Mallory Instruction Sheet shows how to pull the spring and basically bypass the relief.

According to the picture below the 1792 does have an adjustable internal bypass. I didn't realize it has an internal prefilter too. That's a good feature. Should allow you to use some nice fat lines on the inlet side.

If I were you I would first clean the inlet filter then maybe crank down on that internal bypass a screw or two. If that doesn't fix it I would modify the inlet plumbing to be all 1/2 inch stuff. I had to do that to my tank with the 140 gph pump.

The other option would be to buy a smaller pump. Summit sells a 95 gph unit with 3/8 NPT inlets and outlets for just over $80. I ran one for a time when my big buck Mallory unit ate some debris and needed a $90 rebuild. If you were closer I would let you borrow it to see if it helps. It's always nice having a spare pump.

toxic99

Running the jegs knock off of the holley blue. Works fine, but its a loud *** pump. Just like the blue lol. Running a aeromotive dead style reg too, rock solid 6.5 psi so far.

ignatz

Pop: That picture is for the 1791. Sounds like the pump I should be using.

89gmcs15

iTrader: (7)

1791 and 1792 have the same cutaway. I think the main difference is the 1792 is 1/2 inlet and outlet and the 1791 is only 3/8