poor throtle responce

[TexasStyle280z]

im having issues with my throtle responce and low rpm's. in first gear, if i really get on the gas, the car just drives away and gradually gets up to speed. in 2nd, 3rd, and 4th everything seems fine. in 5th gear, once i get to cruising speed i can put the pedle to the floor and get very little if any responce.

but just this morning on my way home, i put the pedle to the floor and the car just took off, the way im guessing it should, and i havent been able to get it to do it since.

any ideas. im thinking its the throtle valve switch, but dont really know how to test it. any wires that could be lose that im not thinking about?

[ansell]

From my point of view i believe is the throtte body,

because my car used to do the same the only thing

i did to it,replace the throtte body and then adjust.

[TexasStyle280z]

ive been working on the problem im having and so far havent made any progess. so far i have..

replaced all sensors on thermo housing.

new plugs and wires.

new fluids and filters.

checked continuity of throttle valve switch.

cleaned throttle body.

checked throttle linkages.

checked all injectors(not replaced yet)

checked and adjusted AFM

checked exhaust for blockages

timing is dead on

the throttlr does open all the way when reved, as does the flap in the AFM. it cant be anything to major because the engine runs very good(smooth, sounds good, descent mpg)

im begining to lose my mind here. any ideas?

[Walter Moore]

I know fairly little about the fuel injected engines, but have you checked your fuel pressure? Could you have a weak pump?

Also, how did you "check" the injectors? Did you do just a resistance test, or actually cycle them somehow and confirm that they are opening?

(Be careful, it seems like a lot of fuel injectors operate at significantly less that 12V, but I don't know the particulars of the ones on the Z. I just remember that the Bosch J-Tronic system on my 74 Volvo had 3V injectors.)

I had a problem with the Volvo years ago that turned out to be two plugged injectors.

They tested fine with an ohm meter.

[sblake01]

Did you check the adjustment of the throttle valve switch? Continuity is great but it has to be at the right points. Idle contacts closed at idle, open in any other position, full throttle contacts closed at anything above 34 degrees of opening of the throttle valve.

[TexasStyle280z]

ive been working on my problem and have made some progress, but the problem still exists. along with the above mentoned fixes i have recently done the following...

new fuelpump

new tps

new (used but cleaned) injectors

new cap and rotor

new distributor

i have regained allot of the missing low end power. and the engine seems to be running smoother. there is a small kink in the fuel rail, but not very big. and my fuel pressuse is still low(around 28psi)

in 1st through 3rd i can get into the high rpms, in forth i seem to be leveling out around 4500. and in 5th i can bearly get past 2500..

any ideas

(warning...dumb question alert)

this is the first 5 speed ive owned so this is probably a stupid question. so forgive me. but.........

since 5th was basically added to improve fuel economy, am i not suposed to get to the higher rpms in 5th? is fith basically just a crusing gear and 4th is my high end gear?

you may now mock me.

[70 Cam Guy]

Don't the 280's have a fuel pressure regulator? If you have a new fuel pump and your fuel pressure is still low, that might be something to check