Just came back from a long drive, SF to LA and back same day about 800 miles altogether...I was cruising at around 75-90 mph all the way and a few times floored it to oblivion and redlined (7k) the 5th gear. Probably going 140 (felt like it)...Anyway, after I slowed down and stayed under 4k rpm, the car started to jerk like fuel filter was clogged or something. But when i try to speed up again it was fine. It felt like the car didnt want to be driven slow...BTW, yesterday I replaced my ECU with a mugen chipped one that gives more fuel and raised rev limiter at 9500 rpm. i was thinking that the motor was getting too much fuel at lower speed and it was getting flooded...Any input?

 

It probably is because it was running on the rich side... I would buy some complete fuel system cleaner, and then maybe check those spark plugs to see if they've got any sort of buildup. The oxygen sensor might be coated in junk as well...

EDIT: Try cleaning out the entire intake manifold (especially inside the TB). It helps in hesitation.


[Modified by MrTodd, 7:22 PM 10/27/2002]

 

well it happens to my Z6... if i floor it a lot, and i wanna go rolling, it hesitates, pulls, struggles while just giving it a 10% ..... if i floor it or let go it goes away...
heres a few of my guesses..
i think that when we floor it, since the injectors get held open too long they tend to get a little hot and they keep getting open.... giving a not accurate fuel mixture... also i think that pressure gets build too much on the fuel system and runs rich as a consecuence.... wich means its going to hesitate until the pressure goes all the way back to normal... this will be kinda easy to find if the fuel press gauge was in the cockpit...this its a fuel problem if u ask me... not a spark or ignition issue... i have gave up on this,,, since i cant afford tunning at a shop... but i cant feel that if i drive it normal , let it sit until cold and drive normal ..see if it still there....
hope i helped and gave ideas

 

same problem in wife's miata. plugs and wires and fuel filter and it's gone

 

I will probably put the stock ECU in the meantime and go from there...I'll check the plugs too while I'm at it and check fuel filter...I know I havent replaced that in a bit.

 

well i can relate it to fuel since:
fuel filter, cap, rotor, plugs, cables, are all brand new.....
change ecu.. then go from there like u said.... its should be something stupid...