fuel system

Have question; altered bbc 1471 hi helix hat and port injection, at about 2 tenths into the run, 21 lbs boast, leaving from idle 1600rpm powerglide trans 164 first gear 5200 ptc converter 429 rear gear 34.5x17x16 hossiers air pressure anywhere from 6 to 7 lbs, the fuel system has been flowed taken back off rechecked nothing wrong with the fuel pump (990) the problem we are having is with the pump on the engine, fuel pressure start up then at about 2 tenths take a nose dive starts back up take another dive looks like sharks teeth on the data logger(rpm pro blower unit) at about this time we go into a bad tire shake to the point of damaging the chassis. on the flow bench the fuel curve is nice and smooth at around 5500 rpm reading about 74lbs of pressure but on the car the sharks teeth then around 5500 the pressure smooths somewhat out to only about 53 lbs of pressure. we are running donavon gear drive front mag drive(pioneer), then the pump off the mag drive.we are thinking the motor is not making enough power to get upon the tires, we thought we were having a fuel cell disign problem took and put the car on jack stands trans braked it same results as going down track. anyone had this problem! hope i worded this where it is understandable.

 

We had the same thing happen a few years ago with our roots funny car, and it ended up being the fuel shutoff closing on its own. Wrapped a piece of tape around it and the problems went away.

That said, also make sure you have sufficient fuel pressure at stage so that if it does drop a bit at the launch, you don't bang the blower. Make sure your pump is big enough, and your nozzles are trimmed back on size enough, to keep your fuel pressure above 130 psi, they seem to run better that way. Of course, check that there are no vacuum leaks in any of your intake hoses as well.

 

You might want to check your fuel line to the pump could be you have a tear inside and its acting like a flap and shuting of the flow. I have seen this happen. also your vent hole ,is it big enough?

 

If you are running metal fuel line between the tank and the pump with rubber hose connections on both ends, make sure the pump suction isn’t collapsing the 90* rubber elbow between the metal fuel line to the bottom of the pump. Have seen this happen more than once. The wrong size vent in the tank could also cause the hose to collapse. Let us know what you find.

 

we had a similar problem a few years back. our car would run good for 40-50 feet, fall on it's face, and take off again. if you run a solid aluminum line to tank, with the rubber hose connections on both ends i would recomend on the 90 degree side under the pump that you use a hose with a spring in it. i think it is actually a heater hose. we run a 3/4" vent in the tank also. we also ran into a problem with fuel filters one time on an injected motor. we had it lying on its side next to the frame rail. we used a #12 line out of the tank to the filter, and out of filter to pump. the problem was that the filter was larger than the line, and it pulled air. took off the filter, problem solved. also, like Ken said.....use a strip of duct tape on the shutoff. if you get it figured out, please post.
Darren Russell

 

Until you said that it did the same thing on the jack stands, the first thing that came to my mind was possibly fuel cell baffles. Obviously if you are on stands your fuel isn't sloshing around.
Eli may be right, if you have rubber lined fuel lines, the internal lining may be broken or torn loose and moving into the flow path, causing irregular fuel flow. Hmmmmmmm

 

Duct Tape

It sounds like Ken Sitko is just trying to get the duct tape thread started again!

 

Just to eliminate the vent issue....our New Nitro Madness AA/FA driver Sean Belt suggested that we use the "Hillbilly glug test"....pull the fuel hose off before the pump and let the entire contents of the fuel tank drain into a big bucket (with the cap on the fuel tank).....if it "glugs" once, then the vent is too small....pretty simple way to check the vent volume....

 

Any chance you have the fuel filter cartlidge up side down? Don't ask

Do you have an on-board primer? When we were injected we had a line tee'd in between fuel pump and hat with a one way check valve that we could prime with an electric pump. Seems valve was bi as it went both ways. When pump pressure came up it forced valve to open and routed the fuel headed to the barrel valve back to the tank through the electric pump.

 

I have same thought about fuel filter in upside down. Been there done that. Luckily it was on the flow bench at the time and not the motor.

 

Fuel filter

The one time I saw a filter cartridge upside down in a System One fuel filter there was not enough fuel flow for the engine to run once the bottle was taken away. Dont know about other filter brands.
Jim