e30 hesitation when acceleration . idle fine HELLP!

[tanner325ixx]

i have 1991 325ix and about 3 days ago my gas gauge started malfunctioning, going up and down and actuating erratically . then I felt a loss of power , and noticed my MPG gauge was really low . like in 4th gear at 2500rpms steady I was only getting 10-12 MPG I would usually get 20-25MPG . then today I was racing my buddy and when I punched it it started bogging , kind of sounded like a rev limiter , but more like a hesitsation .
i replaced the sending units and that fixed the wacky gas gauge . and i put in a used pump . no idea if it was good or not , but when i ran it it did the same thing . fine at idle , then when i got on it a little it hessitated for a couople secconds then accelerated , and it repeted that for the entirety of the drive
it was cold when i took it for the seccond drive . not sure if that would make a difference .
PLEASE HELP ME , Any imput is good

[beemerbird]

Hello, and welcome to the Zone. It may be a good idea to post your technical problems in the E30 Technical Help section

[Grrrmachine]

First off, did you replace the fuel filter under the car when you replaced the pump and sensors? It might be worth temporarily fitting an in-line fuel pressure guage so that you are sure your pump is delivering the required 3 Bar of fuel - silly things like split or kinked hoses can be the problem here.

[tanner325ixx]

First off, did you replace the fuel filter under the car when you replaced the pump and sensors? It might be worth temporarily fitting an in-line fuel pressure guage so that you are sure your pump is delivering the required 3 Bar of fuel - silly things like split or kinked hoses can be the problem here.

i replaced the filter a month ago
what hoses could be split or kinked ?
and how to do do a inline pressure check?

[Brianmoooore]

and how to do do a inline pressure check?

You buy a £10 fuel pressure gauge off of ebay and plum it in.