Fuel pressure

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Malibu ss 64
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Joined: Wed May 27, 2009 2:28 pm

Fuel pressure

#1 Post by Malibu ss 64 » Wed May 26, 2010 3:36 am

Ok here we go again had same issue last summer removed the fuel filter between the pump and carb+changed the rote of the line slightly.

Before

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After

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It seems to work better now with the rerote and removement of the filter but when I´m cruising at carshows and similar and the elctric fans goes on the pressure drops after a while, not as fast or as much as before and recovers faster just needs little more speed then idle for a while and pressure is right back.

Can I isolate the line to keep it cooler since heat seems to be the enemy? if with what? or is my pump to much? I have a carter 172 gph mech pump shall i try a 110 gph pump I has laying around and see if it works better? Or shall i use some kind of return line? like gm did on some vehicles? a small line from the pump?


It takes some time in my eyes to get the pressure drop but if possible I want to get rid of it. The car and weather needs to be really warm. The times it has happen is after trips that has been 50-60 miles and after that cruising at idle speed for 15-30 min with fans on. It gets pretty hot under the hood
Before i removed the filter and reroted the line as far from heatsourches as possible the problem was much worse. So pretty sure heat is the problem.

What can i isolate the line with? The car has dual 11'' spals, msd box stereo with amplifier except what it left factory with. 140 amp powermaster alternator and a mech Carter 172 gph pump.
Upgraded all wiring when I changed to electric fans, bigger alternator and this engine, so pretty sure theres nothing wrong with the wiring. No AC.

If I just start it in the garage and get it warm so it can idle it holds pressure all day with fans on in the garage.

Before I removed the filter and rerouted the line the problem was much worse pressure droped to 2-3 psi at idle and took long time to recover, now after it drops to 4-5 psi and only needs a little bit of open road to recover.

Think underhood heat and the hot air the fans put on the line is the issue, if I shut it off it looks like the bowls are empty after a while. Takes some time before it starts and the pressure is back, only place that seems to has fuel is the accpump. Whats best? shall I try an isolate plate between carb and intake+isolate the line with something? if with what?

I only think it´s an issue cruising now and not like before every time the car and weather was hot so maybe it´really not a problem since the pressure is right back a 6-7 psi if I only let it cools 10-20 min and the conditions a track and a cruising is´nt comparable at the track I do not have to stand at idle speed for hours.

Has a electric autometer fuel pressure gauge.

Your inputs please is there a way to solve this problem completely?
Except electric pump with return style regulator has everything including a new tank and a sump for a swap but not sure if a electric pump will be reliable? Also my combo is´nt that extreme so theres need for a electric pump in my opinion.

Will shield like this cure some of the problem or at least not make the problem worse?

http://www.summitracing.com/parts/HLY-108-70/

Marcus

HPDRIFTER
Posts: 157
Joined: Thu Aug 17, 2006 11:47 am
Location: High Plains

Re: Fuel pressure

#2 Post by HPDRIFTER » Wed May 26, 2010 7:15 am

Just a thought: With an electric fuel pressure gage, are you sure the pressure drops or could it be the gage giving a false reading when the electric fan kicks on? I don't see how an increase in electrical load could effect your oil pressure.
I think that I would try a mechanical fuel pressure gage and see what happens. Good luck.

Malibu ss 64
Posts: 16
Joined: Wed May 27, 2009 2:28 pm

Re: Fuel pressure

#3 Post by Malibu ss 64 » Wed May 26, 2010 10:01 am

HPDRIFTER wrote:Just a thought: With an electric fuel pressure gage, are you sure the pressure drops or could it be the gage giving a false reading when the electric fan kicks on? I don't see how an increase in electrical load could effect your oil pressure.
I think that I would try a mechanical fuel pressure gage and see what happens. Good luck.
Thanks! Never mentiod my oil pressure. Pretty sure its not electric. The fuelpressure doesnt drop when the fans goes on or rises when they go off. Like I said it takes quite a while.
Marcus

505r10
Posts: 34
Joined: Sun Apr 11, 2010 6:17 pm

Re: Fuel pressure

#4 Post by 505r10 » Wed May 26, 2010 11:41 am

Sounds like you're on the verge of vapor lock. I work on a lot of street bound hot rods and fuel percolation is a constant problem for a lot of people. The easy fix is to eliminate the mechanical pump and put an electric pump in the rear of the car. That pressurizes the whole fuel line to the front and will eliminate the negative pressure in the line before the pump. The combination of negative pressure and high temperatures is the perfect condition for vapor locking and vapor related fuel problems. If you want a fairly quiet pump use the Holley HP gerotor type they are fairly quiet when running. A return style system will work also. Hope this helps.


Roger
soon to be 582r10

Malibu ss 64
Posts: 16
Joined: Wed May 27, 2009 2:28 pm

Re: Fuel pressure

#5 Post by Malibu ss 64 » Wed May 26, 2010 5:11 pm

505r10 wrote:Sounds like you're on the verge of vapor lock. I work on a lot of street bound hot rods and fuel percolation is a constant problem for a lot of people. The easy fix is to eliminate the mechanical pump and put an electric pump in the rear of the car. That pressurizes the whole fuel line to the front and will eliminate the negative pressure in the line before the pump. The combination of negative pressure and high temperatures is the perfect condition for vapor locking and vapor related fuel problems. If you want a fairly quiet pump use the Holley HP gerotor type they are fairly quiet when running. A return style system will work also. Hope this helps.


Roger
soon to be 582r10
If possible I would like to stay away from electric fuelpump, has a Mallory 140 gph with return style regulator, a sump,a new tank and all the lines and hoses thats needed laying in the garage. Could it be possible tor un a small vapor return 1/4" or so like gm did on some vehicles? If should i try to mount the small return on the pumps output or fuelline on carb?

Marcus

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BracketNova
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Re: Fuel pressure

#6 Post by BracketNova » Fri May 28, 2010 9:33 pm

505r10 wrote:Sounds like you're on the verge of vapor lock.
I would have to agree here. When I had a mech pump and didn't have electric fans if I hot lapped it it would vapor lock. DEI makes a sleeve you could put your fuel line in. Not sure if it would help for sure...
http://www.summitracing.com/parts/DEI-010418/

Greg
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Malibu ss 64
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Joined: Wed May 27, 2009 2:28 pm

Re: Fuel pressure

#7 Post by Malibu ss 64 » Sat May 29, 2010 2:29 am

spaz109 wrote:
505r10 wrote:Sounds like you're on the verge of vapor lock.
I would have to agree here. When I had a mech pump and didn't have electric fans if I hot lapped it it would vapor lock. DEI makes a sleeve you could put your fuel line in. Not sure if it would help for sure...
http://www.summitracing.com/parts/DEI-010418/

Greg
I have put some insulate on the fuel line to try but afraid it wont work, I belive it´s the oil that heat up the pump and the fuel, guess the fuel almost stand still at idle. If the insulate doesn´t work I may try a small an3-an4 return line from the pumps output.

Marcus

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