Odd one

[wrenchhead944]

We have a 1972 911T 2.4 injected that is bucking under acceleration . It has a fresh tune up. cap, rotor, points, plugs , timing, valve adjust . Also has a new perma tune ignition module .The linkage length for the fuel dist. have been set . All the hoses for fuel distributor warm up are in place . Heated air intake is in place and working .The enrichment solenoid is good and appears to be working . Idle switch is good . I have even tried richening up the mixture . I does not seem to care if its hot or cold .

Any thoughts ?

Thanks

Brian

[docrodg]

Fuel pressure? Low pressure could be starving the system.

[wrenchhead944]

I can't find a spec on the delivery pump . Does anyone have the numbers ?

Brian

[wrenchhead944]

Fuel pressure is 11.5 lbs at idle and drops to 9.0 under throttle. Any thoughts ?

Thanks

Brian

[Flieger]

That sounds low. IIRC it is supposed to be 15 psi.

Have you confirmed that the in-tank fuel filter screen is not clogged with rust or other gunk?

[wrenchhead944]

Tank and its filter are spotless . Had the tank out . The fuel flow out of the line to the pump is great .

Brian

[Flieger]

Originally Posted by wrenchhead944

Fuel pressure is 11.5 lbs at idle and drops to 9.0 under throttle. Any thoughts ?

Thanks

Brian

Your fuel pressure is too low.

See here:
http://forums.pelicanparts.com/4507132-post23.html

[wrenchhead944]

Thank you for the info . That helps a lot

Brian

[wrenchhead944]

We got a rebuilt replacement pump from Emalig . No luck . The pressure is still low and now I am at a loss as how to proceed .
Any help would be great .

Thanks

Brian

[javadog]

If the new fuel pump doesn't meet specs, return it for one that does. If they can't supply one that works, buy one from Pelican (new Porsche-sourced pump), or get one of the aftermarket pumps made to fill this application.

JR

[tobluforu]

What changed, what I mean is if it ran fine then you replaced this and that and now it does not?

[silverc4s]

I would also suspect the Permatune & or the coil. Swap with known good units pretty easy to do..��

[wrenchhead944]

Ok Here is the story. We replaced the pump because of low pressure . The replacement brought the pressure up but not to spec .
I found the check valve in the return line was not keep the pressure up .
After trial and error I got the pressure up to 15lbs .
The bucking was gone but it still had a 4000 rpm miss.
The Permatune module was bad .
Put a different one one and it runs out good
. Some fine tuning and its up for sale .
Anyone want to buy a Porsche ?