Ok so here is the deal...its an 87 244, Ive been having a problem with it stumbling when accelerating with anything less than 3/4 of a tank of gas, BOTH in-tank and HP pumps are working and a few months old (this issue was happening before replacement too) any thoughts?? Now here is another catch...So i was thinking that perhaps there is a hole in the in-tank pick up tube that starts pulling air when below 3/4 tank so i unplug both pumps (at the pumps themselves, NOT the fuse or relay) to let pressure out of the system to work on it and its still running!...and starts! and drives around like nothing is wrong!!?? Both pumps are offline with now fuses pulled AND relays! and still runs strong, so my real question is now...Could there be a suction type issue going on? where gravity is taking over or perhaps a siphon effect is happening!? any ideas??

 

Don't know how this could be unless it is running under residule pressure. Assuming that your car has the original LH 2.2 fuel injection system that came with it, it needs something like 45 psi pressure from the main pump in order for it to build pressure for the fuel injection.

 

to test the fuel delivery from the tank pump, you could put the car up on stands, and disconnect the fuel line that goes INTO the main pump, and stick it into a jug, then manually power the tank pump (jumper wires or whatever, just watch out for sparks around fuel!!) you should get a healthy steady stream of fuel with the tank pump running. don't let the power get to the main pump, as you don't want it pumping air.

and, yeah, the engine wouldn't run for more than 1 second on residual pressure, there's no pressure reservoir or anything. it WILL run, albeit somewhat poorly, with a good main pump and a bad tank pump, but it will be fuel-starved at high throttle/RPMs, and the lower the gas tank, the worse it will be.

 

Not sure how it happened but it was bad injectors pulling fuel from the tank! Very odd, I've owned 7 240s an not one has had this issue but its fixed an whadda know...it runs better! Haha thanks for the replies guys!