Fuel system issues

shelby racer · #1 (**permalink**) 10-13-2007, 02:17 PM

Okay - just in case any one is wondering, I realize I am an idiot. With that out of the way, I can get to my dilema.

I tried to fire up my cobra for the first time to try and diagnose a clutch issue. The mechanical gauge was only reading ~ 1 psi at the end of the fuel log. I substituted the mechanical gauge on the end of a #4 braided line from one of my race cars. I was getting 1 psi on that gauge also. I measured it at the fuel filter and it was 1-1.5 psi. It the out flow from the two pumps in the trunk it is 7-7.5 psi. Is that enough pressure at the pumps? Oh yeah, and the fuel pumps don't always come on or stay on if they are moved up or down

. The wiring doesn't care and each pump seems to be running when they are running.

Now for the idiocy:
when I originally plumbed into the fuel lines that were on the car from SAI, I saw that there were 2 cloth covered lines. I assumed that they were both feed lines. Looking at the bottom of the fuel cell now, I see that they both come out of relatively the same place, but one goes up to the fuel pumps and the other one just heads towards the engine compartment as a .................. return line - doooh

.
-Is this the way the fuel cell is supposed to be plumbed?
-Do I need a return line for a 427 fe?
-Can I somehow some how run the both of the two -6 lines from the fuel cell to the pumps instead of using one as a return line since pumps push better than they suck?
-Any suggestion on plumbing the return line into the system if I do need it? (I am using a -8 aeroquip fuel log with the -4 fitting on the end to supply the remote fuel pressure transducer).
-Can I eliminate the fuel pressure regulator that I have plumbed before the fuel filter since I am only getting 7 psi at the pumps in the trunk?
-Is a single -6 line big enough to feed a 427 fe?
-Has anyone else has problems with their fuel pump and what did they replace them with?
I am tempted to plumb it like I did the race car I borrowed the fuel pressure gauge from -> -10 braided from the fuel cell to a holley fuel pump, - 8 braided to the fuel pressure regulator and filter, - 8 to the fuel log / carb.

Thoughts, help, insights all greatly appreciated. Thanks
John(;-)

Anthony · #2 (**permalink**) 10-13-2007, 06:41 PM

Well,

I think I have had problems with fuel starvation while drag racing, about 1/2 way down the track.

I'm using both 6 AN lines as supply lines, the bottom (reserve) fitting on the cell going to the trunk electric pumps, and the upper fuel fitting on the cell going to the engine compartment to feed a carter mechanical pump. No return line. Both lines then merge into a single 8 AN line. I'm getting ready to mount another electric pump down by the tank, as the "stock" electric pumps don;t seem to pump that well.

I would think if you are running a Hi-Flow electric pump with higher pressure, you'll need a regulator, but not with "stock" electric or "stock/street" mechanical pumps.

I would say remove the regualtor and then check the pressure.

kris-kincaid · #3 (**permalink**) 10-13-2007, 09:45 PM

You have your fuel system connected wrong. Lots of people do it, so no sweat. The electric pumps in the trunk are there for the reserve fuel system and are designed to only be used when you run out of gas. The other line is for the main fuel system. The main line goes to the input of the mechanical engine fuel pump. The reserve line goes to a "T" on the output of the mechanical pump. Typically all these fittings are -6. There is no return line.

I'm not sure what you have exactly. The standard Shelby fuel system works fine, and you shouldn't need all sorts of large fittings and complicated fuel lines. There are a lot of 500hp and 600hp Shelby cars running around with the standard setup.

Anthony · #4 (**permalink**) 10-14-2007, 06:59 AM

Quote:

Originally Posted by kris-kincaid

. The standard Shelby fuel system works fine, and you shouldn't need all sorts of large fittings and complicated fuel lines. There are a lot of 500hp and 600hp Shelby cars running around with the standard setup.

Kris, my car runs fine on the street, even OK runs on the chassis dyno. But, I can tell you with drag racing, the car starts to sputter and miss 1/2 way down the track, and on a speed way, on a back stretch, it seems to lose power, "hit a brick wall". Well, if I get this straightened out, I'll let you know, but I think there is a fuel supply issue with my car, as set-up, with the Carter super street mech pump and the stock electric pumps. What I need to do is to take it to the strip again. Not enough time this year.

GEORGE ANDERSON · #5 (**permalink**) 10-14-2007, 06:21 PM

This is an image of the standard CSX Shelby fuel fitting and an alternate upgrade AQP #8 fitting. For some applications the CSX lines are fine when running a Mechanical pump just like Kris suggested. On some like we do with Fuel Injections and some larger demand engines it may well be good to upgrade.
George

shelby racer · #6 (**permalink**) 10-14-2007, 07:25 PM

Quote:

Originally Posted by kris-kincaid

You have your fuel system connected wrong. Lots of people do it, so no sweat. The electric pumps in the trunk are there for the reserve fuel system and are designed to only be used when you run out of gas. The other line is for the main fuel system. The main line goes to the input of the mechanical engine fuel pump. The reserve line goes to a "T" on the output of the mechanical pump. Typically all these fittings are -6. There is no return line.

I'm not sure what you have exactly. The standard Shelby fuel system works fine, and you shouldn't need all sorts of large fittings and complicated fuel lines. There are a lot of 500hp and 600hp Shelby cars running around with the standard setup.

Thanks Kris,
I am not running a mechanical pump. I Have the two -6 lines running in to a fuel block and then running out to a fuel pressure regulator and then to a fuel filter and then over to the fuel log so the line that should have gone to the mechanical is acting like a return since there is less resistance than the other way. Hmmmm.... Now what?
John(;-)

kris-kincaid · #7 (**permalink**) 10-14-2007, 10:59 PM

Well, if I'm reading this right, you need to cap off the line that runs back to the tank; thats were all your pressure is going. Afterwards you should see about 7psi at the gauge. So, you'll have the line from the electric pumps in the trunk going to your carb(s) and the other line will be capped off and not used.

I would probably consider installing a mechanical pump just to make everything run as designed, but thats by no means necessary. If you don't have a fuel level gauge, then the reserve is a nice feature so you don't have to count the miles until empty.

Anthony · #8 (**permalink**) 10-24-2007, 08:47 PM

Quote:

Originally Posted by kris-kincaid

I would probably consider installing a mechanical pump just to make everything run as designed, but thats by no means necessary. If you don't have a fuel level gauge, then the reserve is a nice feature so you don't have to count the miles until empty.

Well. I just ran out of gas for the first time. Off of the mechanical pump, I saw the fuel pressure was dipping. So I turned on the electric pump and I got another 3 miles before it died, about 1/2 mile from a station.