Fuel Starvation Question

[GUMBALL]

Problem: Car stumbles (sometimes quits) on long freeway hills.

Ever since the initial fill up on my 42-gallon fuel cell, I have never added more than 27-gallons.

The car has no fuel level gauge. It has a fuel pressure gauge instead. I originally calculated 7.5 MPG for the car based on miles driven and fuel added to top off the tank.

I have noticed a few times now that after a long afternoon of driving, the car would start to stumble on long 2-3 mile inclined stretches of freeway. (like going over a summit) Now, once over the crest, the car drives fine. It always happened around 150 miles after filling up. I would proceed to the nearest gas station because I thought I was running out of gas. The problem is, it would only take around 22-27 gallons. Based on other's advice, I figured the problem was probably a misplaced pickup in the tank. That was until this weekend.

I had just filled the tank, put only 60-miles on it, and it stumbles real bad up a steep grade. I pulled off to the side a few times and it never quit, but came pretty close. Once again, after making it to the summit, I was able to drive another 30-miles home without any problems. Now, has the pickup in the tank moved again? ............. to a worse position? It also seems to happen more often on hot days. This could be coincidence. Could it be the float levels in the carb? Could it be poor tank ventilation? Vapor lock?

This last incident has me totally confused. Any ideas out there? How hard is it to check the level of the tank pickup?

Regards,

John

[Bob Putnam]

What is the fuel pressure gage reading when you're experiening the problem?

[GUMBALL]

Bob,

Thanks for the reply. I have noticed it drop to zero. However, this past weekend it was still reading 6 psi (normal) when it was faltering.

Any ideas?

John

[bran3b]

Do you have a mechanical pump or electric? I have an Edelbrock mechanical and was having similar problems. The symptoms were similar to vaporlocking. My final resolution was to install an electric "helper" pump. The electric pump doesn't need to be anything special, just a plain 7 psi. pump.

As for the reason why it seemed to be worse going up hill, I never could figure that out. But once the engine was shut down, it would not start again for an hour or so.

After adding the electric pump last week the car ran fine for a mountain drive on Sunday.

Good luck,
Bran

[GUMBALL]

Bran,

Thanks for the reply.

The engine has a mechanical pump. I have also tried turning on my "backup" electric pumps but they don't help. Also, when the car falters, I let off the gas a bit and try to keep it running. If it does quit, I can usually pop the clutch and get it going again before it comes to a complete stop. A few times it has completely died but I was able to get it started again immediately. BTW.... the fuel filter is clean.

Regards,

John

[cobrashoch]

Gumball - Sounds like a classic vapor lock problem to me to. Some ideas. Most times this can be helped if not cured by running larger fuel lines. You also need to check for crimps and reductions in the line to. You may get away easy if you find something there. I assume that you checked the fuel filter but did you check the little filter that goes to/inside the carb? A return line on a electric pump may whip the stall but you need the pressure gauge set to the carb after the regulator. Make sure you are using a full flow high performance fuel filter, not the stock production type. Lots of luck. P.S. - We don't have mountains here in INDY.
cobrashock

[SFfiredog]

Before you do any replacing of parts check the venting system on your fuel tank. An improperly sized or restricted (clogged) vent tube will cause the the problem you described. As the fuel is expelled from the tank the area must be replace with atmosphere. If the atmosphere inside your fuel tank overcomes the fuel pump's ability to pull fuel from the tank, the tank will actually suck the fuel back through the fuel line. This problem is more apparent with an engine mounted mechanical fuel pump because the fuel must travel the lenght of the fuel line before it is pressurized. Try a simple test. Drive your car with the fuel cap open. Be careful, of course. I had a drastic example of this condition happen when I was a Ford dealership mechanic. A Festiva came in the shop that wouldn't run. It sounded like it was out of fuel. The fuel gauge read full and fuel ran out the filler neck when we tried to put gas in it. I decided to look under the car and was shocked to find the fuel tank was crushed like an aluminum can. I thought is was road damage but during diagnosis we found that the evaporative control vent line had collapsed and the resulting vacuum had sucked the fuel tank closed like a straw in a plastic bag.
HTH,
Mike

[GUMBALL]

Ron and Mike,

Thanks for your replies. You have definately given me a few more things to consider. I plan to be underneath the car tomorrow night and hope to find the Gremlin(s). I'll let you know what we find.

Thanks again guys.

John

[Tony Ripepi]

Hello John,

Rick Currington and I saw the under side of your car when it was at Craigs place. The path your fuel line takes along the main rails seems very open to impact from road debris.

I would closely inspect the entire run of the fuel line for restrictions, additionally the line seems to be 3/8 " instead of 1/2" in diameter, I'm not sure but, with the amount of fuel your car would like to have to keep running the 1/2" line or larger would seem more appropriate. The line was installed with some subtle curves in it also, this seems like it would be an opportunity for vapor cavities on the run from the fuel cell to the pump. Fuel line should be straight to avoid the dreaded vapor lock.

Look at the gremlin chase as just part of the new car wringing out process........

Good Luck,

Tony R.

[GUMBALL]

Tony,

Thanks for the advice. As mentioned previously, we had worked like dogs to get it "on the road" initially. We decided not to touch it for a few months and just enjoy the ride. Well, now it's time to pay the piper. We'll take a closer look at the fuel lines. BTW...... what tools did you use to cut your turkey pan? I'm also new to this whole "fabrication" thing and believe me, I suck with tools. Remember my safety wire job???????

Good seeing you last weekend. Joanne had a great time.

John

[Tony Ripepi]

Hello John,

I used a nibbler attached to an electric drill, it lets you guide your cut on a line you draw with a sharpie marker.

Borrowed it from Rick C.

These cars are never truly done, you always end up revisiting thing after 1K, 5K, 10K etc....

Tony R.

[SCOBRAC]

Do you use a twist on fuel cap under your Le Mans style cap??? If you do take it off and see if the problem persists. I suspect much of what you are hearing referred to as "vapor lock" is really a situation in which the tank is not ventilated properly (this isn't vapor lock).

If the car runs fine without the cap you can do one of three things. leave it off.. Drill a 3/16 hole into the rivet holding the cap together or fabricate a tank vent.. 90% of the guys I know do not run a twist on cap..

5/16 or 3/8 fuel lines would not cause the symptoms you describe.. 289, 302 and even FE Mustangs ran 5/16 lines without a hitch.. Think of all that fuel being pushed through a .110" metering valve (typical Hollley valve or even two of those) But zero fuel pressure could cause the problem to occur if you sucked a line dry due to not having a vent. It would correct itself once the line refilled..

I do not suggest the following advice is safe or legal.. But it is effective.

Regards,

[Jim Maxwell]

I had the problem of my car running out of steam like this, and after much searching, found the fuel line had slipped into on the the clamps on it and was being pinched partially shut, so the suggestions to check for a dent or other restriction in your fuel line is a good one.

[GUMBALL]

Michael,

Thanks for the reply. I do not have a cap under the LeMans cap. I am running 3/8 lines and also believe they should be enough.

Jim,

Thanks also. I will check the lines for pinching too.

After much input and thought, I am lead back to the most basic denominator: HILLS!

Perhaps I should have simply stated the question this way:

"Has anyone ever had fuel starvation ONLY on long hill climbs?"

The rest of the time it is fine.

It must have something to do with gravity or car angle. With gravity I think of not enough fuel pressure. With angle, I think of fluid in a container. Perhaps there is always a problem that exists but doesn't rear it's ugly head until the problem is made worse by the hills.

Why only on HILLS?

Thanks again guys.

John

[bran3b]

How about floats? If they are far enough off, they will starve the carb on a hill or heavy acceleration.

Just brainstorming.

Bran

[GUMBALL]

Bran,

Floats? We are gonna check that tonight. It would be one of the simplest explainations as to gravity/angle. I hope you are right and the fix is that simple.

Regards,

John

[GUMBALL]

Oki-doki,

Hate to admit it but we had the lines crossed. We were running off the reserve the whole time and had the main capped. oops!

Anyway, we switched the lines and added a one-way valve to the "t" fitting off the mechanical pump for the reserve line. Have yet to run it up a hill but hope this will fix the problem. Fuel pressure looks real good.

I guess I get the idiot of the month award!

Regards,

John

[Tony Ripepi]

Hello John,

Welcome to the Club...any of us that has put their own hands on a Cobra and done anything has already had that moment. Something isn't working , you take it apart again and say to yourself.

"Damn that was stupid of me to do that!!!!!!"

Been there...Done that...Will probably do it again !!!!!!!

The good news you found it, nothing broke and the car is running great.

See you Soon,

Tony R.