heres the skinny, when i got my zx there was alot of exhaust noise from under the intake. it turned out to be 2 holes in my exhaust manifold both about size of a dime. i replaced the manifold and gasket. before the engine would redline very easily now it tachs to about 4 grand then for some reason it looses steam and starts coughing. all of the vacuum hoses are connected properly. it has new ignition from coil to plugs, new injectors and new air filter. what could cause this, maybe cat convertor?????

 

Since you said you replaced the plugs, I would assume that would have included new plug wires, and that you installed quality spark plugs. The reason I ask is because the faster you drive, the more frequent the spark plugs fire, so if the plugs and/or wires are failing, it's most noticeable at high speeds, when they're at max. use. Also, I would replace the fuel filter if that hasn't already been done.

There's several other possiblities that could be causing your problem. The TPS could very well be the culprit. This sensor feeds data to the ECU which is then calculated to determine how much fuel the EFI should inject. Normally, this will cause stalling, but can also cause the problems you're currently experiencing.

BTW, how many miles are on the engine? I don't want to scare you, but when the rings and valves become worn, it will cause low compression under full throttle. Again, there's several possibilities here, so please don't get too worried about that just yet.

 

z babe i dont know what looks better, the pic by your name or the pic of your zx. may as well say the zx that way i dont offend any one! yes it has new dist cap, rotor, wires, and plugs. and i havent thought of fuel filter, but it is next. the tps it new (replaced stock throttle body with one off 240sx, much larger so bought new tps)so what do you think of the cat convertor could it cause these symptoms?

 

Awe, thanks! Well, sounds like you've already got a head-start on the problem. The answer to the cat would be a huge "yes". Absolutely.