Fuel pressure fluxuation problems

bermblaster41 · #1 (**permalink**) 07-02-2007, 04:08 AM

Looking for some help from the experts. I have a 408 windsor with fuel pressure fluxuations. I have a holley mechanical fuel pump 130 gph feeding a quick fuel double pumper. Between fuel pump and carb I have a inline filter and holley pressure regulator. All lines are steel braided. Fuel line from tank runs along inside driverside frame to the pump. From pump back along frame up to firewall to firewall mounted pressure regulator then to carb. When the enginge is cold fuel pressure is at 6 psi. When the engine warms up pressure drops to approx 2psi, sometimes even lower. I have the holley press regulator with one inlet and 2 outlets. One outlet goes to the carb and other to pressure guage. I have change pres. regulator and guage with the same results. I suspect vapor lock. I have know idea how to fix this problem. I am using a victor jr intake without a spacer due to hood clearance. I also have wierd plug readings. The front plugs #1 #5 are black . #2 #6 are blackish brown. #3#7 are brown and #4#8 are gray. I am guessing another symtom of varpor lock/ fuel starvation. Any help would be greatly appreciated. Bermblaster

xlr8or · #2 (**permalink**) 07-02-2007, 08:02 AM

Is your fuel tank vented? Try running it for a while with the gas cap open.

Is this a new problem? Did it used to be fine? Check your fuel filters for crud and that they are flowing the correct direction.

bermblaster41 · #3 (**permalink**) 07-02-2007, 08:25 AM

Yes the tank is vented and I did check for negative pressure on the fuel tank. Check good I drove the cobra home this morning from work nice and cool outside and the fuel pressure stayed at 6 psi. I let it set outside for an hour and the pressure dropped to 3psi[hood closed] when I pulled it into the garage. I just finished the car. It was fast as hell when hood was off and before go cart. Performance dropped when car was assembled just started troubleshooting power loss and noticed fuel pressure low when car was warmed up. Note when driving car before outside temps was fair bit cooler. Thanks Bermblaster

J Persons · #4 (**permalink**) 07-04-2007, 09:58 AM

Your problem is probably the firewall mounted Holley regulator. Try moving it to a location in front of the engine where it won't see as much radiant heat. You could also install an electric pump near the tank to give the mechanical pump a little help.

Roscoe · #5 (**permalink**) 07-04-2007, 10:58 AM

My regulator is mounted on the top of the bell housing with a non-liquid gauge. Keep in mind that if you have a liquid filled gauge it will give you false readings when the liquid warms up.

Roscoe

bermblaster41 · #6 (**permalink**) 07-08-2007, 10:13 AM

To give an update I have replaced the fuel regulater. No help. Took the regulator out and ran fuel line from pump to front of engine to carb... No help. Replace fuel pump. No help. I don't believe this is an indication problem because when it warms up I can feel the loss of performance and tell the car is running out of fuel. The temp in Idaho has been in the 100's so it has been hard to test in cooler temps. I am running out of ideas???????? Any help would be great and thanks for the replies. Bermblaster

Roscoe · #7 (**permalink**) 07-08-2007, 12:01 PM

Is the fuel tank vented? You may try running with the gas cap cracked a bit.

Roscoe

bermblaster41 · #8 (**permalink**) 07-08-2007, 05:47 PM

yes the fuel tank is vented. any help wou be a great help Bermblaster

wtm442 · #9 (**permalink**) 07-08-2007, 05:49 PM

Is the fuel boiling inside the carb bowl? Add an isolator between carb and intake manifold.

http://www.jegs.com/webapp/wcs/store...43789_-1_11747

bermblaster41 · #10 (**permalink**) 07-28-2007, 03:48 PM

To bring everyone up to speed. This is driving me crazy. VAPOR LOCK. After 2 mechanical fuel pumps I decided to try an electric holley pump. The pump is mounted just fwd of the fuel tank.. I replaced the 3/8 pickup tube to1/2. Fuel line up the inside of frame rail up firewall to regulater to the back of the carb. The problem is still there. I know the pump is cavitating because I can here the change in sound of the pump when it produces 6 psi and 0 to 1 psi. I am at a loss. Note I have moved the gauge to several locations with the same indication. Thanks Bermblaster... Any help wold be great.

Cobrabill · #11 (**permalink**) 07-28-2007, 05:22 PM

Return line

Dwight · #12 (**permalink**) 07-28-2007, 05:39 PM

Do you have a 3/8" steel fuel line from the tank to the regulater? Is your fuel line close to the headers? Is the electric fuel pump mounted as low as the bottom of your fuel tank? Do you have a phenolic spacer under the carb? We have bought "new" but bad regulaters.
Dwight

bermblaster41 · #13 (**permalink**) 07-28-2007, 06:47 PM

thanks for the replies. I am using 1/2 allum tubing from tank to pump. The pump is mounted low. inlet below bottom of fuel tank. Cobra Bill not sure how to do the fuel return??? The pump has 1 inlet and 1 outlet. I have tried a new regulater and taking it completely out. When the fuel pressure is low the pump sounds like it has gravel in it...When the pressure is 6.5 it sounds normal. I don't have a spacer do to hood clearance...There is no evidence of the fuel boiling in the carb. My carb has the fuel level sight gage. The fuel line is not close to the exhaust. I just drove it with fuel cap of with no help. I have verified my tank vent is clear.

Thanks for any help. Bermblaster

MadDog · #14 (**permalink**) 07-28-2007, 11:13 PM

What kind of filter are you running in the fuel line? Some filters are specifi to fuel injection systems with high gpm pumps. I diiscovered this when we put my car on the dyno. One of the sensors is tapped into the fuel line and showed a pressure loss after 3000 rpms. I was having a problem with fuel starvation on a long hard run through the gears.
I also had a problem with the carb getting too hot when sitting after a long run. The carb would soak up the heat from the engine and intake. I fixed that with a isolator kit from Jegs. I also have hood clearance issuse so it took a little head scratching but I made it work.

RACER X #99 · #15 (**permalink**) 07-29-2007, 05:11 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 · #16 (**permalink**) 07-29-2007, 08:19 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 · #17 (**permalink**) 07-29-2007, 07:14 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 · #18 (**permalink**) 07-29-2007, 08:05 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 · #19 (**permalink**) 07-29-2007, 08:10 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 · #20 (**permalink**) 07-30-2007, 11:44 AM

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