Fuel Pressure problem on LA 360

Posted By: 53fopar

Fuel Pressure problem on LA 360 - 02/26/14 12:55 AM

I've been fighting a fuel issue for about 8 months on my 360. It's a LA 360 with al high riser intake, Edelbrock 600 carb, one inch plastic spacer between carb and intake. Electric fuel pump is Holley 12-125 with 100 micron Holley filter between tank and pump and 40 micron filter between pump and carb. All fuel line is new 3/8 hose. Tank was pulled last year and cleaned and sealed. Fuel pump is mounted on the frame next to the fuel tank.

Last summer I thought I was having vapor lock issues and put on the spacer, replaced fuel pump and line and cleaned the tank. Still had issues with loss of fuel pressure. Last fall, I installed a relay in the fuel pump wiring with 12G wire running direct from the battery to the relay which is located next to the fuel pump. Ran two 12G wires, power and ground direct to battery. About that time the weather got cool. Everything ran great all winter. No fuel pressure issues, no stalls. Today it got into the mid 70's here and took the truck out. Started running rough, wouldn't idle right and then just died. Same as last summer. Waited about 20 minutes and it re-started and ran till I got home. Let it idle in the driveway and it died again. Engine temp's are fine (180-190*), no signs of overheating. Before it died the fuel pressure started jumping all over from 2 to 8 psi. Then went to zero.

It appears the fuel pump is getting hot and cutting off the fuel flow. When it failed in the driveway I got some temps off the pump:

Pump base (hottest area) 112
Inlet filter 103
Outlet filter 110
Fuel pressure at engine 0

Put an ice bag on the pump for about 10 minutes and cooled it down to 97. That gave me the bouncing fuel pressure (3-7) but no start.

Pulled the fuel line from the tank to the pump and no fuel. Gave a blow on it to get the fuel flowing and re-attached it to the pump. Pumped the carb and engine re-started with 7 psi fuel pressure.

Is there anything I can do to keep the fuel pump cool or prevent it from getting hot? It only seems to be a problem in warm weather, it ran fine all winter.

Sorry for the long post, this is driving me nuts.

Posted By: Challenger 1

Re: Fuel Pressure problem on LA 360 - 02/26/14 01:13 AM

IMO, it's several things, the pump is mounted too high. Gas must free flow to the pump on a hi performance pump like yours. Sometimes tough to do, I know.

Then a return line is important to help keep the gas cool with hi performance pump on the street.

Then a voltage controller may be necessary with a hi performance pump like that on the street?

Then the inlet strainer even though it's rated at 100 microns looks awfully small to me.

Does a 360 need that kind of fuel system? How many RPMs are you turning and for how long?

It's not recommended to screw the filters directly into the fuel pump, because vibration from the pump or from the solid mounting can cause the spring loaded filter element inside the housing to lift off/bounce off there seats inside under severe vibration which occurs with hi horse power cars.(Tire shake)

Plus the heat spreads to the filters from the fuel pump as you found out.

Lastly the filters can break off easier mounted that way in a accident and then.

Posted By: stumpy

Re: Fuel Pressure problem on LA 360 - 02/26/14 01:18 AM

No reason a stock pump and lines couldn't work just fine. You are going over kill with the system you are running.

Posted By: RapidRobert

Re: Fuel Pressure problem on LA 360 - 02/26/14 01:19 AM

Quote:

It appears the fuel pump is getting hot and cutting off the fuel flow. Sorry for the long post, this is driving me nuts.

My first thought was that the sock is partly plugged & cavitating the pump but then I read further & with it only happenening in the summer I'm thinking replace that pump! That was not a long post (I enjoyed it) & we sure dont need more crazy individuals than we already have

Posted By: Supercuda

Re: Fuel Pressure problem on LA 360 - 02/26/14 01:20 AM

Quote:

IMO, it's several things, the pump is mounted too high. Gas must free flow to the pump on a hi performance pump like yours. Sometimes tough to do, I know.

Then a return line is important to help keep the gas cool with hi performance pump on the street.

Then a voltage controller be be necessary with a hi performance pump like that on the street?

Then the inlet strainer even though it's rated at 100 microns looks awfully small to me.

Does a 360 need that kind of fuel system? How many RPMs are you turning and for how long?

Sounds like the pump is deadheading and overheating. As mentioned, run a bypass regulator and return line. BTW, running all hose is usually not a good idea. It restricts flow and contributes to the deadheading issue.

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 02:46 AM

Quote:

IMO, it's several things, the pump is mounted too high. Gas must free flow to the pump on a hi performance pump like yours. Sometimes tough to do, I know.

Then a return line is important to help keep the gas cool with hi performance pump on the street.

Then a voltage controller may be necessary with a hi performance pump like that on the street?

Then the inlet strainer even though it's rated at 100 microns looks awfully small to me.

Does a 360 need that kind of fuel system? How many RPMs are you turning and for how long?

I'll take a look at lowering the pump. I might be able to fab a bracket to get it lower.

The fuel filters, inlet and outlet are what Holley recommended for a carb'd motor.

Guess I'll buy a return regulator. I've got a regulator out in the shop somewhere, but I don't think it's a return style.

Yeah, this is over kill for the way I use the truck.. just a street driver, rare to be over 4000 rpms. I ended up here trying to solve this problem last summer. At first I thought it was vapor lock, so I got rid of the manual pump. Just kept working my way back to the tank trying to solve it.

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 02:50 AM

"No reason a stock pump and lines couldn't work just fine. You are going over kill with the system you are running. "

That's where I was last summer when this all started (stock manual pump & fuel lines). Maybe I just moved the problem to a new area....

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 02:55 AM

Quote:

Quote:

It appears the fuel pump is getting hot and cutting off the fuel flow. Sorry for the long post, this is driving me nuts.

My first thought was that the sock is partly plugged & cavitating the pump but then I read further & with it only happenening in the summer I'm thinking replace that pump! That was not a long post (I enjoyed it) & we sure dont need more crazy individuals than we already have

I don't think it's the pump. Worked like a champ all winter. Seems to be temp related. Anything under 75-80 is OK. But hotter than 75-80 and it cr@ps out. No sock in the tank. Replaced the original pickup with a new 3/8 inch SS pickup when I cleaned the tank.

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 03:00 AM

Quote:

Sounds like the pump is deadheading and overheating. As mentioned, run a bypass regulator and return line. BTW, running all hose is usually not a good idea. It restricts flow and contributes to the deadheading issue.

Thanks. Guess I'll order the regulator. The all hose is a temporary thing. I did it to eliminate plugged fuel line as an issue last summer. Planned on making some new fuel lines, some day....

Posted By: Challenger 1

Re: Fuel Pressure problem on LA 360 - 02/26/14 03:00 AM

Quote:

Quote:

Quote:

It appears the fuel pump is getting hot and cutting off the fuel flow. Sorry for the long post, this is driving me nuts.

My first thought was that the sock is partly plugged & cavitating the pump but then I read further & with it only happenening in the summer I'm thinking replace that pump! That was not a long post (I enjoyed it) & we sure dont need more crazy individuals than we already have

I don't think it's the pump. Worked like a champ all winter. Seems to be temp related. Anything under 75-80 is OK. But hotter than 75-80 and it [Email]cr@ps[/Email] out. No sock in the tank. Replaced the original pickup with a new 3/8 inch SS pickup when I cleaned the tank.

That pump can not suck through a 3/8 pickup during warmer weather.
I though you said there was 1/2" line through out?
That hi po pump needs a min #10 line and #12 would be best on the inlet side. The outlet size don't matter and 5/16 would work for the line going forward.

Mounting so the fuel is gravity feed is still important, but so is the inlet sizing which needs to be bigger than the outlet side on just about any pump.

Gasoline is very hard to suck, it vaporizes very easy at the inlet of your fuel pump when it's under vacuum. The hotter it get's the harder it is to suck. Fuel pumps can't suck gas with vapor bubbles in it, they lose there prime so to speak.
Vapor lock occurs, at the inlet of the fuel pump. Got to battle it with all my suggestions. Not up by the carburetor .

Vapor locking also causes the pump to overheat because there is no liquid gas inside to cool it.

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 03:11 AM

Quote:

[
That pump can not suck through a 3/8 pickup.
I though you said there was 1/2" line through out?
That hi po pump needs a min #10 line and #12 would be best in the inlet side. The outlet size don't matter and 5/16 would work for the line going forward.

Mounting so the fuel is gravity feed is still important, but so is the inlet sizing which needs to be bigger than the outlet side on just about any pump.

I thought it was 1/2" when I first posted, but I checked and it's 3/8" so I edited the post. The Holley pump came with 3/8" hose barbs for both ends so that's what I went with. The inlet hose is short, about 18" or less. Would the temp make that much difference on the ability of the pump to suck from the tank?

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 03:14 AM

OK, so the return regulator should be mounted up front, maybe on the firewall? Should the return go to the tank or to a T fitted before the fuel pump inlet?

Posted By: Challenger 1

Re: Fuel Pressure problem on LA 360 - 02/26/14 03:21 AM

No do not return to the fuel pump inlet side, you will introduce vapor into the fuel pump. It needs to be returned to the fuel tank.

Posted By: YO7_A66

Re: Fuel Pressure problem on LA 360 - 02/26/14 03:38 AM

That pump is rated for 7psi and you are running an Edy which should be kept down around 5psi.
I too agree with lowering the pump and adding the return. Once you make those changes, it should run cooler.

Note: I added an electric pump last year and I was told by many to keep the pump inlet lower than the bottom of the gas tank.

Posted By: RapidRobert

Re: Fuel Pressure problem on LA 360 - 02/26/14 03:48 AM

Lots of good high level tech has been posted

. You wouldn't be running E10 gasahol (ethanol) would you

& if so that's the problem. You have no sock on the pickup it is just laying horizontle close to or on the bottom of the tank? When it was vapor locking with the mech pump you had the elec one in tandem operational at the same time & the problem was the same as now? You're fuel delivery requirement ain't that high (stock 360/4500 rpm/street) & 3/8 line is more than plenty. Did you say the elec pump has been replaced? gotta be either E10 or the line setup is cavitating it on the inlet side(restricted filter/lower the pump "as said"/or deadheading it (my last choice) on the downstream end. If you add a reg up front I'd T at the carb inlet then run a short line from the T to a nearby reg so the 3 port holley reg is in series in the return line only in other words the Line from the T goes to the "in" port then the "out port goes to the tank & the other "out" port is capped off & you regulate the amount of return flow (& that's if deadheading is the issue)

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 03:54 AM

OK, thanks everybody. I am going to order the return regulator and see if I can get the pump lower. I am not sure I can get the pump lower than the tank, but I'll drop it down some. Regulator on the firewall with 3/8 return line to the tank (or 5/16th?). I'll pull the filters to make sure they are clean and then get them off the fuel pump.

I report back on my results.

Posted By: RapidRobert

Re: Fuel Pressure problem on LA 360 - 02/26/14 04:03 AM

Actually 1/4 is plenty for a return. You could make a temporary bracket (tailpipe hanger strap with the holes would work great) to lower the pump for a quick test when it gets hot and T at the carb inlet & run it back to the tank with a long hose(restrict it) being safe of course & 1 test/mod at a time. That'd tell you (& us) ASAP if it's cavitation (pump too high) or deadheading (needed the return) then you can permanantly mount/fab the solution or the problem might be elsewhere. Holler with any news

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 04:10 AM

Quote:

Lots of good high level tech has been posted . You wouldn't be running E10 gasahol (ethanol) would you & if so that's the problem. You have no sock on the pickup it is just laying horizontle close to or on the bottom of the tank? When it was vapor locking with the mech pump you had the elec one in tandem operational at the same time & the problem was the same as now? You're fuel delivery requirement ain't that high (stock 360/4500 rpm/street) & 3/8 line is more than plenty. Did you say the elec pump has been replaced? gotta be either E10 or the line setup is cavitating it on the inlet side(restricted filter/lower the pump "as said"/or deadheading it (my last choice) on the downstream end. If you add a reg up front I'd T at the carb inlet then run a short line from the T to a nearby reg so the 3 port holley reg is in series in the return line only in other words the Line from the T goes to the "in" port then the "out port goes to the tank & the other "out" port is capped off & you regulate the amount of return flow (& that's if deadheading is the issue)

No E10. Use only mid-grade ethanol free. The new pick-up was a SS 3/8 tube that I ran down to about 1/4 above bottom of tank to reduce junk pick-up. The electric pump replaced the mech pump, never ran both.

Maybe I should just try lowering the pump first and see if that solves it?

Not sure I get your plumbing for the regulator. I thought the IN line on the reg was from the fuel pump. One OUT goes to the carb and RETURN goes back to the tank. Are you saying to use a regulator with one in and two outs like for dual carb setup? I have one of those in the shop.

Posted By: RapidRobert

Re: Fuel Pressure problem on LA 360 - 02/26/14 04:20 AM

Yes, T at the carb inlet & run the line from the T to the reg "in" then run either reg "out" port to the tank & cap the other "out" port so you are in series regulating the return line only. You want to keep the psi not over 5.5 psi right at the carb with a known good gauge (they are notoriously inaccurate) & not less than several psi at WOT & the side bennie is the problem at hand & the contant return flow keeps the pump happy even if deadheading ain't the issue the constant flow will prolong its life. EDIT It acted badly with the mech and the elec seperately, & that is puzzling as I feel I am missing something especially since your fuel delivery requirements ain't that high & it was acting up with just the mechanical pump

which takes the (elec pump) cavitation/deadhead/pump height out of the picture which would lead me to believe that the issue might not be in the front/rear delievery path. Just had an idea, is the crossover functioning & the intake getting real hot & there's NO pinholes in the front to rear lines?

Posted By: GO_Fish

Re: Fuel Pressure problem on LA 360 - 02/26/14 04:27 AM

try loosening the gas cap, just to be sure an incorrect cap, or tank venting issue is not causing a vacuum on the tank that stops fuel from flowing. This creates a lean condition that makes underhood temps rocket before the engine finally quits from no fuel. Quick easy test. This problem would show up in hot or cold weather, but would be worse with extra heat added.

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 06:21 AM

Quote:

Yes, T at the carb inlet & run the line from the T to the reg "in" then run either reg "out" port to the tank & cap the other "out" port so you are in series regulating the return line only. You want to keep the psi not over 5.5 psi right at the carb with a known good gauge (they are notoriously inaccurate) & not less than several psi at WOT & the side bennie is the problem at hand & the contant return flow keeps the pump happy even if deadheading ain't the issue the constant flow will prolong its life. EDIT It acted badly with the mech and the elec seperately, & that is puzzling as I feel I am missing something especially since your fuel delivery requirements ain't that high & it was acting up with just the mechanical pump which takes the (elec pump) cavitation/deadhead/pump height out of the picture which would lead me to believe that the issue might not be in the front/rear delievery path. Just had an idea, is the crossover functioning & the intake getting real hot & there's NO pinholes in the front to rear lines?

OK, I got it. Just using the regulator for the return, no regulation on the line coming from the fuel pump. When the pump is working correctly, it puts out about 5psi which should be about right for the Edelbrock.

I replaced the mech pump before I cleaned the tank and there was some cr@p in the tank. Maybe it wasn't vapor lock at all but just the fuel pickup getting blocked. Now I created new problems with the elect fuel pump.

The crossovers on the intake are blocked. All the fuel line in the truck in new 3/8" hose.

I was thinking about it, and recall that the tank is just below 1/4 full which would put the fuel level in the tank below the fuel pump rotor. Maybe the pump can't suck the fuel up through the pickup to the top of the tank. I am going to lower the pump and see what happens. Of course, the weather is going to get cooler this week so I am sure everything will work fine again.

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360 - 02/26/14 06:24 AM

Quote:

try loosening the gas cap, just to be sure an incorrect cap, or tank venting issue is not causing a vacuum on the tank that stops fuel from flowing. This creates a lean condition that makes underhood temps rocket before the engine finally quits from no fuel. Quick easy test. This problem would show up in hot or cold weather, but would be worse with extra heat added.

Thanks Scott. I went through the gas cap dance last summer when this first started. Tank has good venting and I never got any pressure sounds from the cap. Good thought though.

Posted By: 53fopar

Re: Fuel Pressure problem on LA 360-UPDATE - 03/03/14 03:22 AM

Thought I'd update this post in case someone does a search later. I lowered the fuel pump about 4-5 inches. Got the bottom of the pump, where the rotor is, even with the bottom of the tank. Took the truck out Friday, temp's in mid 60's. No luck. Pump still got hot and lost fuel pressure.

Yesterday I did the fuel return line as suggested by Rapid Robert. Used a Quick Fuel regulator I had in the shop from a old project. Installed a brass T just before the fuel pressure guage at the carb with one leg going to the carb and the other to the IN side of the regulator. One of the OUT ports on the regulator goes back to the tank via 5/16's hose. Other OUT port is blocked. Adjusted regulator till I had steady 5 psi at the carb. Took the truck out today, temp's in mid to upper 70's. Drove it for over 2 hours with no issues. Temp's on the pump and fittings around 85*. Problem solved.

Thanks to everyone for the input, esp. Rapid Robert. You guys are the best. I always bring my questions/problems to MOPARTS because I know I'll get a straight answer with out the BS. Thanks again.