Hi guys, i have a 91 Z28 305 TPIwith a 5 speed. The story is i was driving from phoenix to sacramento and i broke down in the desert, (fuel pump went out) i got that fixed at Pep Boys and continued my trip.
I got all the way to Fresno and i went in to a rest stop, when i took off it was hesitating and bucking in all gears and had a lack of power. When i got it all the way home i changed the wires and plugs and that didn't do anything. I changed the cap and rotor just for fun and it still did the same thing. I noticed that the engine will rev fine while sitting still but feels like it miss-fires and has no power like i had a wire crossed or something but i double and triple checked it, so i removed the cat converters from the exhaust and it did run better but didn't cure the bucking. The only thing i haven't checked is the timing and fuel injectors.
Is there something specific i should be looking at? Has anyone ever come accross this issue on thier car that can point me in the right direction?
Thanks in advance.

 

first off i would check the fuel filter, if your pump went bad and was replaced i would hope they replaced the filter, a clogged filter will give you enough at idle but not enough at higher rpms, next would be timing, since its so easy to check, if that doesnt fix it, i would have the injectors tested for pressure. also have it run for codes, they could reveal the problem very quickly

 

hell ya mine does the same thing!!!! almost the same car too!!!
i changed the motor mounts and it helped a LOT!!! if i could go back i would go for the solid mounts vs the rubbers that i put on.
what was happening to me was when i was going through a parking lot it would just "buck" (good word choice btw) until i put the clutch in or eased on the gas.
the problem is barely there anymore. i didnt really notice it at higher vehicle speeds until i was just coasting at idle and then got on the gas i would hear comething clatter together.
not anymore on that tho.
good luck with the prob

 

Yeah i told them to change the filter with the pump, but being a ghetto *** pep boys in Indio Cali, i would imagine they screwed something up.[:'(]
I just checked the fuel pressure and its at 42 psi which seems to be within specs.
The timing is next and my buddy is gonna let me borrow his timing light so i'll let you guys know how that goes.

 

Ok timing is at 2 degrees advanced, is that right? Shouldn't it be more like 6-8 advanced?

 

ya. did the filter help?

 

ya. did the filter help?

 

The filter was done with the pump when it broke down, after that it started bucking and jerking while accellerating, i checked the fuel pressure recently 42 psi, and the timing is at 2 degrees advanced.
All the plugs and wires were changed, coil, cap and rotor, i don't where to go from here?

 

Oh and there were no fault codes.......go figure. HELP!

 

If the bucking and jerking did not start untill after the fuel pump replacement, then the answer is really quite simple. I believe the wrong fuel pump was installed.
TBI fuel injection systems run from 25-40psi fuel pressure.
Port fuel injection systems require up to 75 psi. You would not get this type of pressure reading with the unit idling as fuel pressure regulator increases fuel psi under engine load, therefore you would not see the low fuel pressure problem unless you had a guage hooked to it during a test drive.
It will run with the wrong fuel pump in it, but will buck and kick when you put any load on the engine.
Just my thought. Hope this helps...........................