Fuel pressure fluxuation problems

RACER X #99 · #1 (**permalink**) 07-29-2007, 06:11 AM

You are spending too much money on guesswork remedies. Troubleshooting over the internet rarely works. Take your car to a race shop preferibly one with a chassis dyno. They will find and fix your problem and you can sell all those "extra " parts you have in your garage.

bermblaster41 · #2 (**permalink**) 07-29-2007, 09:19 AM

I am leaning towards a fuel supply problem to my pump. With the engine off it still cavitates and pressure low. {Only when hot} What type of fuel pickup Are you guys using. The one I replaced had a 1/2 plastic straw up to a hard 90 metal fitting{choked down to 3/8}. I replaced the pichup with 1/2 allum With a 90degree bend using tubing bender{No kinks in the line}. I had this problem before I replaced fuel pickup.. Dyno would be great but even more of a waste of time and money. I know this has to be something simple. I do plan on taking to a dyno but have to get the fuel supply problem fixed first. Thanks again Bermblaster

Dwight · #3 (**permalink**) 07-29-2007, 08:14 PM

Is the pick up in the bottom of the tank? Is the electric fuel pump to hot when it runs? I know they get warm when running but hot? Get a gas can attach a fuel line and see if it will pump 4 or 5 gal of gas. Get it off the carb or close, that way you will check the fuel line from the rear of the car. I wonder if it is the heat or the time that is the problem. Does the fuel pump get hot and fails or the fuel line/pick up in the tank stops up? Does the engine heat the carb till the fuel boils? Faulty regulator?

Hang in there with us, we will figure it out. Your correct, it's something simple.
We had a friend tell us that when he stomped it at 40 to 50 mph it would miss, spit and sputter. We check under the hood and found the air filter had two pounds of dirt in it.
Another friend had a miss at 2800 to 3800 rpm. We talked and looked swapped parts for 4 or 5 months. We were eat one Friday night and our Ford mechanic buddy was there. After we finish we all when outside and listen to the miss in the Cobra. Eddie said change the TPI and make sure you use heat sink grease. The grease was the problem. Lawrence had use dialectic grease before and it may have burned the TPI up. Changed the TPI and used the correct grease, problem solved.

Dwight

scootter · #4 (**permalink**) 07-29-2007, 09:05 PM

Bermblaster,
Have you checked to make sure the pressure guage is good. I was pulling my hair out with mine. Check this, change that, adjust the regulator everytime you look at it. It was the expensive f##cking liquid filled pressure gauge that was no good. It was brand new. Took it back and put a cheapo on, and it has been good since. If you have the Holley regulator with one in and two out, you should have both the outlets hooked to the carb like in my picture. I am also running the Holley black pump with the huge MrGasket filter you can also see in the picture.
Scott

bermblaster41 · #5 (**permalink**) 07-29-2007, 09:10 PM

Dwight.. That is a good IDEA. I am using the holley pressure regulater one side to carb and other side to pressure guage. Real easy to take cap off guage side and connect line to it and then to a gas can. I will check this in the morning. The thing is I had the same problem with the holley mechanical pump. Scott I know this is not an indication because of when the pressure drops the performance reflects it is starving for fuel. I even took the regulater out and had same problem. I will try and contact holley in the morning. Thanks for any help. Bermblaster

scootter · #6 (**permalink**) 07-30-2007, 12:44 PM

Bermblaster,
When it happens, did you try taking off the gas cap to see if there is any pressure or suction. I didn't read all the reply's, sorry if this is a repeat.
I feel your pain. My car would die after hard acceleration on the freeway. Come to find out, when my car gets bellow 1/2 tank of fuel, all the gas goes to the back of the tank and the pump sucks air.
Scott

bermblaster41 · #7 (**permalink**) 07-30-2007, 10:05 PM

Scott This is happening with a full tank... 1/2 tank ...low tank. Note: My fuel line pickup tube is in the back of the tank. I spoke with the manufacture of the fuel tank. They think my electric fuel pump is getting hot and vaporizing the fuel in the pump. I need to duplicate this and then wrap an ice pack around the pump to see if this is a fix. Thanks again for the help and any input from any one. Bermblaster