Fuel pressure fluxuation problems

[bermblaster41]

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

[Cobrabill]

Your fuel tank company sounds incompetent. Electric pumps are "pushers"NOT pullers.Vapor in a pump a couple of feet from the tank and away from the"real" heat?BULLCRAP!!!!
That pump would have to be hotter than a $2 pistol to effect fuel temps.

But in any event,a return line solves multiple issues.It re-circulates fuel(thus cooling it.The circulating fuel keeps the pump cool(er).And a return line keeps the pump from"dead-heading".(please no Jerry Garcia jokes)

And racer X-how about coming up with a solution other than "pay someone else to fix it"?

[bermblaster41]

Cobra Bill. Thanks for the input. I have a couple places that i can tap into the fuel line for the return. I can tap in on the fuel pressure guage side of the regulator or tap into the fuel line up next to the carb. Now my real ??? is do I dump the fuel back into the tank or do I tap into the inlet side of the pump??? Note: I drove the cobra home this morning about 65 degrees no fuel pressure fluctuations. Last night I drove to work about 100 degrees pressure dropped to .5 I am stumped. Any helpful input would be very much welcomed. Bermblaster

[Cobrabill]

Berm-i don't know if this will translate well to the wrtten word but here it goes:Using a "standard" Holley duel feed line,your fuel line comes up from the pump(rear of car)and hits the reg which is mounted on the carb hardline inlet.Then the return line takes of back to the tank.You can use 6AN or even 4AN for the return.

Option #2:Line comes up from the pump and hits a "T"."Down leg" feeds the rear bowl and the "thru leg" continues to the front bowl.Again,the down leg feeds the bowl with the reg being mounted on the "thru leg".Return line takes off from the reg,over to the frame rail and returns to the tank.Again,using the same size lines as above.THis set-up will not allow you to use the standard dual feed line as above.It will require you to build something along the lines of what appears in Scootters picture.

[bermblaster41]

Been out of town and haven't been able to try new fuel mods. To bring you guys up to speed. I installed a return line to my fuel tank right at the fuel manifold at carb with the exact same problem. I plumbed a steel braided line into the cockpit and installed a fuel pres. guage so I can watch the fuel pressure. I can watch the fuel pressure start to go down as I drive. When I start out it is at 6.5 psi. The pressure rolls back as things warm up. There are no spikes in pressure under different loads or rpm increases. I need to talk to the tank manufacture and see if there is a different design of pickup tube that may help this. I am at a total loss on ideas. Any other suggestions would be appreciated. Again this happens with a full tank half tank or close to empty. Thanks. Bermblaster

[392cobra]

Bermblaster,
I wish I had an answer to your pressure problem.

Just a word of warning : You could be playing with fire if you don't have a fuel pressure isolator in the engine compartment.

[bermblaster41]

Fred can you define fuel pressure isolator? I do have a fuel pressure regulator. Bermblaster

[xlr8or]

He is referring to a device that installs in the engine compartment and monitors the fuel pressure and uses an inert liquid on the other side to feed the gauge. This way you don't have a fuel line running into the passenger compartment. It's a bad idea, especially if the car catches fire while driving.

http://store.summitracing.com/partde...5&autoview=sku

[392cobra]

That's right.

Fuel goes to the isolator in the engine compartment.The liquid in the line from the isolator to the guage is a 50/50 mix of antifreeze.
If your line or a fitting failed,as it is now,you will have pressurized fuel spraying on you and over the passenger compartment.VERY DANGEROUS and I believe illegal.

[Tommy]

Bermblaster -
I tried to read this entire thread before posting, but I may have missed something. Here's my question. What specific fuel pressure regulator do you have and how do you know the outputs are run to the correct things? For example, one particular Holley regulator has two outputs, one for the carburetor and one for the return line. If the fuel pressure gauge were plumbed on the return line side it wouldn't show the pressure on the line going to the carburetor. Likewise, if the carburetor and return lines were reversed, the carburetor would get fuel intermittantly. Can you confirm the plumbing for the regulator is correct?

[bermblaster41]

I realize the danger of the fuel line. I am using aircraft steel braided line that is rated at 3000 psi. This is very temporary until I get this problem resolved. Bermblaster

[392cobra]

Just a thought,something I have run across a couple of times.

This is on the suction side of the pump....a line or fitting can be porous (sp?) enough to suck air in but not enough to leak.

[Tim Brewer]

I know this sounds weird, but as long as your car is running correctly, don't worry about it. My gauge (or pressure) fluctuates also, I've talked to many people that have the same problem that told me not to worry about it as well. My car has done this for years with no problems.

[Jerry Clayton]

You are ignoring the facts-----you are not getting the fuel out of the tank--that is why your fuel pump sounds like it does---arrange a temporary supply to the pump that is downhill--where the pump does not have to suck the fuel--and if your problem goes away you will have proven it is the tank to pump area of the system---

Jerry

[bermblaster41]

Tim if my car was running right I wouldn't be worried about it. My car is running lean when it warms up. My plugs reflect a lean condition. front plugs black and sooty and back plugs white{lean}. Jerry I do think the tank to pump is the problem. The thing is how do I correct the problem? I talked to the tank manf. they have no idea. At a loss. Bermblaster

[Jerry Clayton]

Talk to some other tank people-

A tank is a tank---but fuel pickup systems are a story/science all alone---can you take the rank out and install a fuel cell?

Jerry

[Jerry Clayton]

I believe that you have a new vehicle----many times I have seen crud from new tanks, lines, etc that will accumulate in an restriction( you said 1/2 necked down to 3/8) or turn. These accumulations will relax some when the system is deactivated and will gradually re accumulate after a few minutes on the next startup.--try blowing out the line from the pump toward the tank

Jerry

[cdnus]

sounds exactly like mine was behaving.
Fuel pressure dropping to "0" after warming up & driving for a while, engine idled like sh-t after warming up, front 4 plugs rich, rear 4 plugs lean.
After many hours changing out parts I now am 98% happy.
Solution was simple in the end.
Liquid filled guage was heat sinking & building internal pressure greater than pump pressure therfeore pressure reading would drop from 7lb. cold to 0lb. hot. Changed out to a non liquid guage. Problem solved.
As hood clearance issues prevent me from using a thick carb insulator I made up as large a heat diffuser plate as possible for the carb & found that by adjusting the throttle plate balance & idle air screws just right on my Pro-Systems carb I have fairly consistant plug colors front to rear.
To check if your problem is the guage try this, run the engine untill the pressure drops to 0 lbs. shut the engine off, apply a ice pack to the guage for a minute or so cooling the guage, if it climbs you have your answer.
I am amazed at the huge difference 1/8 turn on the idle air scews can make in my engine, not just at idle but low rpm driving.
I run a A/F meter so I can see the suttle changes.

Hope this is some help as I know the frustration you are feeling.

Craig

[Jerry Clayton]

Mostliquid filled guages have a vent hole that must be opened when installed so that the differential pressure thing doesn't become a factor---of course this also means that the angle that the guage can be mounted is restricted to somewhere with the vent up

On your cars that are running rich in the front cylinders----is your carb/manifold flat/level? If not----with a big cam, the wrong power valve, wrong float setting, the carb will run over into the manifold and will then run on the manifold floor into the front cylinders

Jerry

[bermblaster41]

Update: Made a 90* bend at pickup tube at bottom of tank pointing to the rear of tank. Changed out liquid filled gauge to normal guage. Back to ground zero. The performance is back and no more fuel starvation. Before when I had this problem it would die in hard corners . Now everything is running great. Plugs are a consitent color. The temps are in the 80s. For now every thing is great....I hope all is well come next summer when the temps are back in the 100s . With these cooler temps I can enjoy driving Better yet I can give some fun rides to a few female passengers... I imagine I will have to clean the passenger seat a few times... I want to thank everyone for their help and suggestions. Time to drive. Thanks again Bermblaster