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Old 07-01-2006, 03:58 PM
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fuel press problems

I was driving my car yesterday and it acted like it ran out of gas. The gauge showed half a tank. i got it hauled home and started investigating. as i cranked the motor over i never got any fuel press showing on the gauge. i finally poured gas in the float bowls and got it started but still now press and when the fuel ran out it died. i then removed the fuel line from the pump to the carb and stuck a squeeze bottle in it and fired the car. gauge showed i was squeezing 3 psi. so then i ordered a jegs 80 gph fuel pump for a BBC. it came today and i installed it. cranked the car up and all was good. had 5-6 psi and car was running good. i let it set in the garage and run for about fifteen minutes and i noticed the press was dropping off again. when it got to 0 it acted the same as with the old pump. so this time to eliminate the fuel line and the tank i took off the line coming from the tank and hooked up another line to the in side of the pump and stuck it in a bucket of gas. started car only had 2-3 psi and it started falling as the car run. i am at a loss. i was wondering if something in my carb is not holding pressure? i have a 68 camaro 454 with a 4150 750 vacuum secondary with 72 jets and a 3.5 power valve. any help would be nice

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Old 07-01-2006, 06:36 PM
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68ss
For starters I would replace your fuel line, it may be collapsing on the inside and causing you to loose all pressure, check each section at a time, with you using a squeeze bottle you may not be giving enough pressure to collapse the line. JMO

30dee
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Old 07-01-2006, 06:46 PM
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desoto is right. The problem is between the fuel pump and the carburetor.

You should have a steel line from the pump to the carb with only minimal rubber to get it connected. Actually you should be steel/brass fittings all the way.

Of course you are measuring the fuel pressure AT the carburetor.
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Old 07-02-2006, 11:51 AM
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frustraited

I replaced all of the fuel line today from the tank to the pump and to the carb. Started the car everything looked good. I had 5.5-6 psi on the gauge but as the car warmed up pressure started dropping I shut it off at 1 psi. next i am going to swap carbs to see if by some chance that is the problem.
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Old 07-02-2006, 12:02 PM
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Quote:
Originally Posted by 68ss
I replaced all of the fuel line today from the tank to the pump and to the carb. Started the car everything looked good. I had 5.5-6 psi on the gauge but as the car warmed up pressure started dropping I shut it off at 1 psi. next i am going to swap carbs to see if by some chance that is the problem.

Maybe the fuel strainer inside the fuel tank is sucking flat or plugging up. I remove them and install an inline filter before the pump.

There are also some rubber line connections at the top of the fuel tanks where the sender unit meets the fuel line. That rubber could be bad. It was on my 80 G body GM.

Another one I ran across about 6 years ago= on a G body GM the fuel line runs inside the frame rail over the rear axle. A pin-hole had worn through it and it was sucking air and caused a lot of wierd fuel delivery problems that seemed to go away temporarily when a new fuel pump was installed. I finally pressure tested the line and found the hole. Ran a new steel brake line as a fuel line and no more problem.
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Old 07-02-2006, 04:37 PM
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xntrik,
I thought about the fuel strainer but i haven't done anything about it. i have blown the line out with air and i can hear bubbles in the tank so maybe i will go ahead and remove it. i just ordered a -06 steel braid line kit for the car from the tank to the carb. i plan on swapping carbs out in the morning. a friend of mine let me borrow a edelbrock 600 just to see if it will hold press. thanks for your help.
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Old 07-02-2006, 04:43 PM
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xntrik is right on the fuel lines and the tank screen, if I remember correctly when I was a youngen there was a way to get back at some people and put a ping pong ball in their tank and the ball would soften up from the fuel and sink to the bottom when the car was started it would run fine for a few minutes and then the fuel pump would suck the ball up to the screen and fuel would eventually stop all together then when the engine shut down the ball would slowly come off the screen and when the car was started again a few minutes later it would start all over again. Understand I myself would never do this to cause a problem but I think I remember ummmmmmmm it happening to some people.

30dee
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Old 07-02-2006, 04:48 PM
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desoto,
The only reason i don't think there is something in my tank causing this is i have feed the motor from a bucket on the floor and it still lost pressure.
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Old 07-04-2006, 07:28 AM
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I have some more info and more questions. I have re-plumbed the car with new 3/8 rubber fuel line. I am waiting on my steel braid to get here. but even after i done this i cranked up the car and everything looked good 5.5-6 psi on the gauge. after about 15 min my fuel press dropped off slowly again. the next morning I cranked it up and the fuel press was back to 5.5-6 psi. are there something in the carb that could be causing this when it heats up?
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Old 07-04-2006, 08:31 AM
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just a guess

i had a problem where the flow was cut off and the pump could not make pressure. the tank vent lines were plugged and the gas cap was the non- vented type. thats kind of like having your finger on the tip of a straw when its dipped in a glass-o-liquid . you pull it out and the straw is stilll full.

hey, did you have a return line?
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Old 07-04-2006, 01:34 PM
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I guess you are running a mechanical pump dead heading into the carburetor with no regulator and no return line and have a gauge teed in at the carb.

Let's follow this.

It was OK
You had a pressure/delivery problem.
You installed a new pump
You replaced the line to the carburetor
You sucked fuel from a bucket and you still have the same problem.


There is only 4 things left.

1) wierd carburetor.......

2) new fuel pump bad......this is a mechanical engine driven pump I would say the odds of getting a bad pump is low, but possible....

3) If it were a fuel pump drive problem why would the pressure be OK for 15 minutes?

4) The guage fitting might have some problem there but you said that the squeeze bottle registered 3.

What else is left?

Try another carb?

Where's the Excedrin????????

Last edited by xntrik; 07-04-2006 at 01:59 PM.
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Old 07-05-2006, 11:24 AM
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thanks for all of the advice. I am going to drop the tank today and pull the sock off of the sender and get it ready to re plumb. i was thinking if i don't find anything in the tank it must be something with the carb? i eat Excedrin for breakfast right now!
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Old 07-05-2006, 03:37 PM
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Sounds to me like it may be vapor locking between the pump and carb.
you can try taking some of the rubber hose you have and slip it over the steel line from pump to carb. It should work like a coolcup for beverages
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Old 07-05-2006, 07:19 PM
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SS, you said in # 1 ====

If the car is running sucking fuel out of a bucket, how can the thing be vapor locking with the hood open and sucking from a bucket? How could it be showing 5+ psi and then start vapor locking.... illogical.

The problem is on the pressure side of the pump. It can't be back towards the tank.

You said you replaced the pump and the line to the carb. Check the gauge fitting or it has to be the carb itself,....... doesn't it?

Last edited by xntrik; 07-05-2006 at 07:26 PM.
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Old 07-05-2006, 07:47 PM
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Quote:
Originally Posted by 68ss
desoto,
The only reason i don't think there is something in my tank causing this is i have feed the motor from a bucket on the floor and it still lost pressure.
If the car is running sucking fuel out of a bucket, how can the thing be vapor locking with the hood open and sucking from a bucket? How could it be showing 5+ psi and then start vapor locking.... illogical.

xntrik: you may READ a little closer before bashing someone
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