Is this normal ?

[84E24]

I have a stock 73 3.0cs with triple DCOE 40 webers. I have been having issues with the electric fuel pump. The 1st pump I had was a Delco pulse type that had 4 psi at 30gph. I ran it for about 3 months and it failed on my way to the PVGP and had to be towed 100 miles back home. I replaced it with a Carter rotary type at 4 psi and 70 gph. This was recomended by Redline with no regulator.

Both pumps when steady read 4 psi on the fuel pressure gage. At idle both pumps will cause the gage to flutter between 0 and 8 psi. The Carter will stay between 3 and 8. When I hit the throttle the gage stays at 4 psi.

See this : http://picasaweb.google.com/steve.blingham/20100818RunningCarbS#5506922084233670546

Is this normal ?

What can I do to trust the car again?

What other electric fuel pumps are you triple guys using ?

Do you use a pre pump ?

Thanks, Steve

 

[jmackro]

I have a couple of Alfas with dual DCOE's. I use Facet cylindrical pumps like this one that Pegasus sells - see: http://www.pegasusautoracing.com/productdetails.asp?RecID=7371 No pre-pump. But, I do mount the pump as close to the tank as possible to minimize the length of fuel line under vacuum, which minimizes the liklihood of vapor lock.

It sounds as if you have two questions:

1) Why did your Delco fail after just 3 months

2) Why does the pressure fluctuate so much at idle, but hold steady at speed

My guesses would be:

1) How clean is your fuel tank? Might the first pump have become crudded up? Is the second pump more tolerant of contamination, or is it about to fail too? It might be worth installing a clear filter between the tank and pump and monitoring the sediment build-up. Or just removing and flushing the tank.

2) I wouldn't worry about the pressure pulses as long as the pressure is in the right range at mid-to-high engine speeds.

 

[61porsche]

Triples and Fuel Pumps

A prepump shouldn't be necessary.( XKE w/ much more hp)

Observations:

1) Guage flucuations at idle are normal. Caused by the float needles and the check valve in the pump.

2) Solenoid pumps fail usually because of the check valve. There's nothing to prime and hold the volume so the pump cavitates with no flow.

3) Triples use more gas- your rotary is better, more GPH. Watch for low high speed volume especially the outside carb if you use the lower GPH pump and cruise fast for very long.

Possible problems to look for:

1) Volume-Sender/ pickup. Besides crud in the tank... pull it. Look closely at the bottom of the tube and screen for two things...

a) There should be lugs- small 1/8" openings at the junction of the aluminum tube and the strainer. if not file them in. They're relief opening to allow fuel to bypass the strainer which is only for chunks of crud.

b) Location of sender to bottom of tank- usually sits directly over a rib in the tank. Tank deforms slightly ( top or bottom) and the sender is jammed on the bottom of the tank. Not ideal. If you have this condition, file off the bottom of the tube for a slight clearance so the sender sits correctly and the lock ring works easily than mashing down on the tank.

c) Fuel line/ hose size, I've seen two sizes. One is smaller,(2800?) which if you're running modified could be a problem for a thirsty 3.5 or triples.

Engineering-

1) Pump near the tank? ( Runs cooler from both temperature and fuel temperature)

2) CSIs/FI cars have what the British call a "swirl pot" which is the predecessor to in tank pumps. Since the pump can pull a suction much greater than a mechanical pump, it's ( Expansion tank) probably a good idea since a lot of engineers did it back then.

3) I've never yet had the opportunity to see the insides of a FI sender, but I suspect the pick up tube is larger within the sender. The CS one looks mighty small.

If all else fails- regulator and return fuel line like FI cars... but it would have to be an extreme engine.

Hope this helps....

PS- There's a UK Co- webcon with a good user board and info.( Similar to Redline)

 

[84E24]

Thanks for the input.

The tank was new when I bought the car. But, I took it out and stripped/cleaned/treated it. The Sender is new with new rubber lines. There is a new filter at the carbs.

This is where I mounted the pump and my gas tank.

I did notice that my a/f ratio has changed with the new pump. I plan on working that out this weekend.

Any more ideas let me know.

Thanks, Steve