90 laser wont go past 4 grand

[JBDdsmer610]

Alright well heres the deal, my buddies laser,which is stock except 2.5 exhaust, will go about to 4800 to 5000 rpms then it starts to vibrate and just stops accelerating pretty much. For example, on the highway in 5th gear ill get to around 105 at around 4500 then it would just vibrate but it would still accelerate but very slowly. The motor mounts are all in fair condition and I heard from some people it could possibly be the balance shafts and I also heard someone say it could be the ignition timing. Other than wut i said the car runs fine. So if you guys could help me out i'd appreciate it. Thanks

 

[nates6969]

Hey,

Mine has done the exact same thing. Is this under boost or low throttle? either way double check those plugs. Even if they haven't been replaced in even 6 months or so I'd replace them with some NGK BPR6ES (cheap and great plugs). Make sure you gap them to spec...anywhere from .028-.032 should do for a stock boost setup. Another thing you could check is the plug wires...sometimes if oil from the valve cover gets around the wire plugs, it can cause a short in the wire...this can be seen as a little burned hole in the wire plug (where they go into the the cylinder head)...next just make sure the wires are plugged firmly into the coils...lastly you could change the wires

 

[pedrick1]

CHECK YOUR TIMING BELT or REPLACE IT IF IT HASNT BEEN DONE SO IN THE LAST 45-60,000 miles. My 91 eclipse was doing the exact same thing and one day i noticed it more than other days so i revved it and when it got to about 5000rpm i heard a commotion from the engine then my engine died. Sure enough all of the teeth on my timing belt sheered off and my cylinder head was no more. Better to be safe than sorry with these cars

 

[nates6969]

Thats a good call, does it rev fine in neutral past 4? with no load on the motor, even bad plugs and wires should allow it to somewhat smoothly rev about 4. if it does the same thing as when accelerating, its probably something bigger then just plugs/wires...like pedrick said...maybe cam timing

 

[JBDdsmer610]

well i changed the plugs when I got it about a month ago. Even if its in nuetral it still wont rev past 4800-5000. The wires i put on it were used from my old talon which jumped timing. So im not sure, knock sensor possibly?

 

[95-talontsi]

I would check and make sure your wastegate isnt frozen shut.

 

[Karma]

Last summer my car would fall on its face and bog down at 5K. It was just wayyy too rich. I leaned it out on the dyno, fixed that problem.
Plugs or wires is usually the problem for these symtoms, becuase it takes much more energy to ignite the extra air and fuel put into the cylinder when under boost.

 

[nc90awd]

Have you done a boost leak test? You may have a big boost leak

 

[nates6969]

Really it won't rev past 5 in neutral huh? well that really rules of boost leak unless you have one HUGE boost leak, like an intake pipe blown right off. Try unplugging the MAF and reving it past 5 in neutral. it will throw the CEL however this would rule out a HUGE (which I doubt) boost leak as the computer is no longer relying on the MAF signal to determine airflow, it could also rule out a potential bad MAF. Just don't drive it like this. With no load on the motor, this won't hurt anything.

If you say it does it in neutral, it'll have nothing to do with the wastegate then. 95-talontsi where you thinking fuel cut?

If I were you pull the top timing belt cover and check the belt out. Better be safe then sorry and it only takes 5 mins. Then I'd go and test the coils, plug wires, and power transistor

 

[black91awdturbo]

I think you have a dead maf sensor, like the poster above said uplug it and rev the car and let us know what it does.