Author Topic: Fuel pressure issue  (Read 108 times)

Offline Too Fast

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Fuel pressure issue
« on: September 14, 2021, 02:23:54 PM »
 I installed a fuel pressure gauge to confirm my problem.  When it is hot out, over 75 degrees typically, my carburetor is not getting fuel.  I currently have a mechanical pump that normally is between 3-5 psi.  When I get on it, the pressure drops to 0 and I have no fuel until I let off the gas and then accelerate normally.  When the engine is not running hot, and it is a cool day, there is no issue with fuel pressure and I can floor it through 1st 2nd and 3rd up to 5500 RPM no problemo.  A new pump changed nothing.

Today I ordered a Holley Sniper in tank returnless electric pump regulated to 6 psi.  I know how to wire with relays so if the car loses oil pressure the pump will shut off.

My question is if I should eliminate the mechanical pump entirely or run the fuel through it.  I would gain about 2 HP if I lose the mechanical pump, but use about 1 HP running the electric pump (just guessing about the HP numbers, I am kidding anyway).

My car is a 68 LeMans droptop with a .030 over Pontiac 400, quadrajet, 2004R, 3.55 rear gears, 74cc Kauffman D-ports, 041 cam and 1.65 roller rockers, 4 tubes headers into Pypes 2.5" dual exhaust.  Random people compliment the way this car sounds, I love it also.

Car is currently running great except for this.  No stalling, idles well at 750 in drive when hot, no stumbles, only a minor hesitation when the secondaries open.  I also have 2 wide band O2 sensors to help me fine tune things.

I have ALWAYS had hot fueling issues with my Pontiacs for the last 30 years.  Hoping this will be a final fix.  In the middle of 2nd gear I lose fuel pressure (down to 0) on hot days, about a 50/50 chance.  Fuel lines have been checked and no kinks/dry rotting/issues I can locate.  Fuel filters changed, never helped anything.  In the past I have tried the old wooden clothes pin on the fuel line to help with vapor lock and that didn't do anything except make my fuel line look stupid.

Offline 77cruiser

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Re: Fuel pressure issue
« Reply #1 on: September 14, 2021, 03:57:50 PM »
I put an in tank pump & eliminated the mechanical. Been 3 years now. Sure nice to have it started immediately after sitting all winter.
Jim

Offline Cliff Ruggles

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Re: Fuel pressure issue
« Reply #2 on: September 15, 2021, 03:32:23 AM »
I've tried running dead-head with electric pumps over the years and not fond of that deal at all.

The manufacturer's of these pumps tell you they can be set-up that way but I've fond that they don't work well and give troubles in long term service.

Complete waste of time/funds to push thru a mechanical pump as the fuel flow starts and stops with each stroke of the pump so it's nothing but a stumbling block for a good free flowing electric pump.

The in tank pump is a great idea and it will certainly last longer than a frame mounted electric pump ran "dead head", but I would still use a return style regulator and send the fuel not used back to the tank for improved fuel cooling and to take some load off the pump........FWIW.....Cliff

Offline 73ss

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Re: Fuel pressure issue
« Reply #3 on: September 15, 2021, 05:49:31 PM »
I installed the same holley sniper unit in my car. It worked ok for about a week. It has a very poorly designed built in so called "regulator" that dumps the excess fuel right back into the tank. I would suggest going a different route or plan on getting an external regulator.

After dropping my tank no less than 4 times due to low/no fuel pressure, I plugged the internal regulator and plumbed an external edelbrock reg. It does work fine now. Holds 6 psi now and drops to 4~4 1/2 psi at wot. Car is still pulling and doesn't nose over. Works well in hot weather also.

Holley did try to help me out, sent a new pump & regulator in the mail but didn't help. The regulator is a simple spring loaded disk. The spring is weak and the design is very poor. It also sprays the return fuel on the underside of the gasket that seals the pump module to the tank, another very poor design. I was stuck with the holley unit at this point because I had cut the hole in the tank to mount it. >:( Currently, I have the reg plumbed with efi rated hose & clamps, Steel line to the front of the car. I just wanted to see if it would work without spending even more $ on AN lines, fittings, etc. Looks like it will so I'll come up with a better solution over the winter.

Offline Cliff Ruggles

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Re: Fuel pressure issue
« Reply #4 on: September 16, 2021, 03:38:00 AM »
I've had so many complaints about the Holley Sniper system I've lost count.

I typically don't go "public" with that sort of information because folks that are well vested in some parts and set-ups get their panties all wadded up when you bad mouth things they are using.

Since I haven't tried a Holley Sniper or any other electric TB carburetor I'll stop there.

As far as "dead head" set-ups as mentioned I've never had any luck with them in long term service.

A little over 20 years ago I sumped the tank on my Ventura and installed a Comp 140gph electric pump behind the tank.  I mounted a high flow spin on fuel filter assembly before the pump and their regulator right before the carb and 8AN lines/fittings everywhere.

It didn't work for chit from day one.  Initial starts ups were fine, and the engine ran fine, but after 10-15 minutes the pump started making noise and the fuel pressure was fluctuating all over the place and I was unable to adjust the regulator to smooth it out.

The pump failed (burned up the brushes) in about a month.

I switched to a Holley regulator and installed a return system, and bought another pump while Mallory was rebuilding that one under warranty.  That system has worked flawlessly up until about a year ago when the pump started making a little noise so I swapped back in the pump that was rebuilt by Mallory under warranty. 

I took the pump that I removed apart and the brushes were worn down to where they needed to be replaced.  For less than $10 I bought a brush kit, cleaned up the motor in the lathe and put that pump on the shelf.

So ran "dead-head" my pump lasted about a month.  The same part number pump ran 20 years with a return system and never once grumbled or required the regulator to be adjusted, etc.......Cliff

Offline Too Fast

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Re: Fuel pressure issue
« Reply #5 on: September 16, 2021, 08:37:09 AM »
Well crap.  I've already ordered, I may cancel.  I'm debating about going another way.  The more research about owner satisfaction with this pump, the more I wonder about it.  Not a good thing.  And I can't quickly find many reviews, another red flag.

Offline Cliff Ruggles

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Re: Fuel pressure issue
« Reply #6 on: Today at 04:35:45 AM »
I love everything about my sumped tank/electric pump behind the tank/8an line-fitting everyplace/return system set up except the look.  I tucked it up as high as possible but I still have a regulator and lines visible from behind the car and under the hood.

Having an external pump sure makes it easy to get to when there are issues, which happen about every 20 years since making it a return system set-up.

Since the pump is a gerotor style it is quiet and reliable.  Vane pumps are a lot more popular (less expensive), but they can be pretty noisy. 

There is some pretty "muddy water" when it comes to this topic.  I have NEVER had any success trying to have a fast street car with any type of mechanical pump sucking thru 14' or so of stock fuel lines.  Once I took steps to hook hard and run fast fuel delivery issues reared their ugly head.  With that said I've had folks come on and claim they have ran 10's with "stock" fuel pumps pulling thru stock 5/16" fuel lines, etc.

I often wondered if they meant 10's in the 1/8th mile or a 200 yard drag race on the street someplace, but for sure ALL the vehicles I've owned, built, set-up or helped folks with REQUIRED significant improvements in fuel delivery once we started making big power and running quick with them at the track.

I haven't looked into it lately but I've heard there are some really nice in tank systems and even baffled tanks available for some cars to use them.  That would be a nice clean look and for sure I'd go that direction with my car if doing all of this over again........Cliff

Offline 77cruiser

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Re: Fuel pressure issue
« Reply #7 on: Today at 10:52:48 AM »
I've been using this pump for about 3 yrs. with no problems. The install isn't quite as neat as I would've liked.

https://www.aemelectronics.com/products/fuel-delivery/high-flow-fuel-pumps/340lph-high-flow-in-tank-fuel-pump-offset-inlet
Jim

Offline old cars

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Re: Fuel pressure issue
« Reply #8 on: Today at 11:30:27 AM »
I've been using this pump for about 3 yrs. with no problems. The install isn't quite as neat as I would've liked.

https://www.aemelectronics.com/products/fuel-delivery/high-flow-fuel-pumps/340lph-high-flow-in-tank-fuel-pump-offset-inlet

So you run a 40psi pump for your carburetor?