My 92 300zx TT has been chipped and is running 14psi, it performs fantastic in 1st, 2nd and 3rd gears.

 

However, in 4th on full throttle just as its coming up to full boost the car starts to hesitate "misfire", the boost stays constant so i know its not loosing pressure, the car starts to jerk and not accelerate as quickly.

 

I have tried to repeat the process in 5th gear but it seems to run ok...only 4th seems to have the problem.

 

I have also repeated the process running it on low boost but that does not clear the problem.

 

Any ideas anybody?

check plugs coils and associated wiring id put money on it been the plugs though also do a ecu engine diagnostics

changed the plugs this morning and it has made no difference at all, still hesitant in fourth with a misfire upon rapid acceleration in any gear...???...???...

changed the plugs this morning and it has made no difference at all, still hesitant in fourth with a misfire upon rapid acceleration in any gear...???...???...

check the plug thats on the maf, 2 zeds ago i had a problem like this and it turned out to be the faster i went the wind was pushing the plug back and caused it to unseat. made worse by the fact i had an apexi filter really low down and not behind the front bumper ;)

ok, where do i find this plug???

ok, where do i find this plug???

on your maf that comes from the filter under the front nose panel (2x10mm bolts) ;)

ok cool, just one plug is it? ile go check it now...

ok cool, just one plug is it? ile go check it now...

yea make sure its not missing the little wire clip and the contacts are clean

will do :-)

the pins are clean and the clip is present :-(

Make sure you are using the proper spark plugs (NGK platinums) and reduce the gap to 0.8 mm

when you accelerate hard does it hit a brick wall at about 3k rpm?

when you accelerate hard does it hit a brick wall at about 3k rpm?

 

mine ha started doing this of late. gets a real bad missfire with a noticeable drop in pull. Just yesterday put new plugs in, and have no idea what to try now

mine ha started doing this of late.

 

Classic dead MAF or connector symptom

Classic dead MAF or connector symptom

 

Would that not show on the ecu then ? i have done a check on my car, and get 55 all clear.

Would that not show on the ecu then ?

Yes it should. What gap have you got your plugs at ?

straight in, didnt check them if i'm honest.

 

But the hesitation/miss is not there at all times, its intermittent, at slightly different levels of rev range and not always missing as bad

Start by gapping the plugs at around 0.8 mm - it just rules one possibility out

yes i made sure also that mine were spaced at 0.8mm i think it might be everso slightly better (5000rpm in 4th gear as a pose to the entire rev range in 4th) but in no way fixed,

 

so when its plugged into a diagnostics will it show if theres a coil faulty or bad maf even though i have no "check engine" light on the dash...?

No, the ECU cannot check for a faulty coil but it sounds like you might be on the right track. Have you got a series 1 or 2 PTU?

not sure, my car is a 1992 J reg if thats any help...

check/clean the CAS connector

 

and if that doesn't help, try lowering the boost to see if the problem's still there.

if the problem is far less or gone, you may have a boost leak somewhere

Do a search on PTU's. The series 1 units give problems when warm.