Fuel System: Stranger then strange Fuel Problem

[beatnik64]

OK.. so i read every "Fuel System" thread in this forum and I didn't find anything that seemed to mirror my issue.

Here is the run down:
I have a 289 with and Elde 4bbl, mechanical fuel pump. tied into the fuel line is a see thru Mr. Gasket fuel filter and a Jegs brand fuel pressure gage.

When I first start up the car I get 4psi on the gage and gas can be seen running thru the filter, after about 15min and getting the car up to temp, the gage falls of to 0psi and slightly less fuel can be seen travling thru the filter.
This is where it gets strange:: The car still runs...HELL.. it runs fine... I drove the car in city traffic and highway the hour from my house to downtown Nashville TN. and it never gave me trouble.

I rev it up, drop it down, rev it up and keep it their (approx 2800 rpm) and the engine still sings along great..the whole time the fuel gage reads zero.. and it look like hardly any fuel is moving thru the filter

So whatcha think?

[mbstude]

If it runs, who cares?

[beatnik64]

If it runs, who cares?

HAHAHA... this is the most common thing said when I tell my friends... that and minor vapor lock... Oh some of them blame Burt Reynolds for some reason.

[mbstude]

Well, seriously.. Maybe the fuel is flowing past the gauge instead of into it? If that makes sense..

[41 Frank]

I have never had any experience with fuel pressure gauges since I've never used them. Could it be that the only time pressure will show is when the needle (float valve) is closed as when it opens there would be very little if any pressure as the line is open to the fuel bowl. So when the engine is running at higher rpm's the float valve is open most of the time so no pressure shows.

[PlainBrownR2]

If the pump is running, the fuel gauge should be reading all the time since there is pressure in the line. These things are pretty important since they are needed to set a fuel regulator, or tell you that the line is plugged. I would think that the gauge might be faulty, I've had one go bad on the Lark. It will still pump through the gauge without any trouble, just not read anything. Try swapping out for a new gauge and see what happens.

[dong]

I have the same problem. I left the car idling at a neighbors house and it just quit running and would not start, had spark but no gas. I towed it home and the next morning it started right up but showed no pressure when tested. So I replaced the fuel pump and thought problem solved. The next time I drove it, the same thing happened. Thinking that possibly the fuel gauge was bad I added some gas and it started right up. But when I got home it stalled again. Again after sitting it started. The fuel was just dribbling into the filter when it was running. I put on a test setup so I could monitor the pressure with the car running and it was less than 1 pound. I ran a gas line from the pump into a gas can and had over 4 pounds pressure. I then repeated that at the end of the gas line and still had good pressure, Did it again using the pickup tube/ sender unit. Again good pressure. So I took out the tank (I had it resealed a few years ago) and it was absolutely clean inside. I put it back together and at start up the pressure was good but started to go down after running awhile. The only thing I can think of is the gas cap is plugged and isn't venting thereby creating a vacuum in the tank. I just got a new cap yesterday and will try it out on the weekend. Hopefully this is the fix, because i am out of ideas. I also noticed that sometimes when I turned off the car there would be a gurgling sound that could be fuel being sucked back into the tank.

[alanahasan]

You may not be able to see fuel passing through your filter if there is no air to make bubbles. the gauge could be affected by the Brnoulli effect: liquids or air passing across an opening recuce the pressure in the opening [you can expoerience it in a strong wind by facing 90 degrees to the wind - it is hard then to breath; turn 90 degrees and you're okay. maybe so, maybe not.

[JohnM15]

Hard to imagine that there is such a high flow rate to create the Bernoulli effect. An engine will not run without fuel. So, there is some fuel flowing. I would put t "T" in the line going to the carb and run the hose to a bucket to create a larger flow and see what happens...

[JohnM15]

How about a vacuum gauge at the input to the fuel pump? Sounds like the line from the tank is getting plugged up partially and sometimes not...

[N8N]

or just take the gas cap off with the engine running and see what happens

nate

[PlainBrownR2]

That leads to another situation. If a vacuum is being created in the tank, is the vent line(if it has one if it's not a vented cap) near the gas fill plugged up? That line is needed to stop the gas tank from creating the vacuum, and if its plugged up, the tank might be collapsing a bit.

[E. Davis]

I have never had any experience with fuel pressure gauges since I've never used them. Could it be that the only time pressure will show is when the needle (float valve) is closed as when it opens there would be very little if any pressure as the line is open to the fuel bowl. So when the engine is running at higher rpm's the float valve is open most of the time so no pressure shows.

I have an Edelbrock 4 bbl on a 289 with a manual fuel pump and have never seen the need for a fuel pressure guage. If you are not running an elelctric pump I don't see the reason for it. Studebaker didn't provide them as factory equipment so why add it. I think part of our problems with these cars is adding accessories they don't need or weren't built for. Take it off and your problem is probably solved.

[Dan Timberlake]

I had a problem slightly similar, but with a factory installed electric oil pressure gauge. After running a while the oil pressure gage would read zero. YIKES. Actually the sender had the problem. I believe there was a diaphragm inside the sender, and a spring and a variable resistor in a cavity on the "dry" side. As the problem repeated after each cold start, I decided at the time the diaphragm developed a leak which eventually allowed the cavity on the "dry" side to fill with oil and eventually that oil would build up and reach the same pressure as on the engine side of the diaphragm. With equal pressure on both sides of the diaphragm it would return to the "zero" position, and that is what the gauge would read. Another symptom was a very slight oil leak out of the sender.

If the fuel gauge is the typical "buordon" tube type "http://www.efunda.com/designstandards/sensors/bourdon_tubes/images/Bourdon_tube_A.gif" then I'm not sure if having pressure on the outside would cause it to read zero or not
Is it a liquid filled gauge? Have you noticed a change in the air bubble size, or a change in the damping liquid color or clarity? It would seem a gauge like that might hide an internal fuel leak.

I think a (working) dash mounted fuel pressure gage sensing pressure right at the carb inlet would instantly answer a batch of important questions about fuel pump condition, fuel line and filter condition during a top speed run, or anytime the engine hiccupped or otherwise ran poorly.

[StudeRich]

I do not believe we have established what year or model beatnik's Car is. Only '62 to '66 Lark Types and possibly Avantis, have a Fuel Tank Vent and sealed cap, so all others have no vent pipe to clog, only the Cap which is very easy to remove to test.