Help with z32 hesitation.

[MuseX13457]

Alright guys needing some help. My dad and I put a new vg30de in our 90 automatic. the engine ran fine but it had a slight hesitation between 1900-2400 rpms....when you stomped it it took off like a rocket and could do 60 smooth. sadly between 35-45mphs it had that constant, hesitation is the best way to describe it. We just swapped the old head onto the new engine hoping that might help...but if not dads getting really frustrated and talking about giving up on the Z. I really dont want that we have put alot of time effort and money into this thing and I just want it to run the way its suppose too. Does anyone have any Idea as to what may be causing this "hesitation"

~Mod list~
-stillen headers
-megan type 2 cat back exhaust
-one piece drive shaft


Could It be the cats? i just thought of that lol

[NolimitZ32]

What tests have you ran? Did you get the heads machined? are you re-using head bolts? You gotta get very specific with what you did, how you did it, and even the hardware you used because at this point it could be a hundred different things.

[MuseX13457]

Ok It was acting like that before I did the head swap, we are still in the process of swapping the head. We did not reuse the head bolts we did not get the head machined. For all I know it might work when we are done.

[NolimitZ32]

Are you sure that its the engine and not a trans problem, perhaps your valve-body needs a proper cleaning, is could be causing the trans to stick.

[MuseX13457]

It a Reman tran from greer nissan has less then 3000 miles on it, I dont think that would be the problem.

[NolimitZ32]

Hmmm. . . what else have you tested so far?

[DCaff300ZX]

Does it still have the stock air box, or have you put a cone filter on it?
The cone filters can cause the hesitation problem if you do...

[DCaff300ZX]

Another thought is your early style injectors in your '91, failing injectors can cause a similar situation to what you described where it takes off fine under hard acceleration but blubbers or misses or hesitates under light throttle and cruising conditions.
A vacuum leak could also cause similar problems, but usually with an idle problem as well.

[MuseX13457]

I do have a cone filter on it, thing is before we replaced the engine it ran fine. It has something to do with the new engine in the car. The new engine we put in has the fuel injectors off the old engine and they all worked fine. It should be on the ground tomorrow afternoon, hopefully itll be fine...

[RubyRed300ZX]

Check for proper voltage, at position, on the Throttle Position Sensor.

[MuseX13457]

well guys it was the 02 censor! running fine now

[DCaff300ZX]

Nice, one of the easier fixes...congrats!