Poor acceleration on high RPMs
 

Hey guys I have a little problem. My car 1990 turbo 2 (all stock) has acceleration problems after like 5000 RPM. It does accelerate smoothly all the way through 7000 but after 5000 power starts to decrease and at 5500 rpm acceleration so week that it is better to switch to next gear so it would accelerate faster. Any ideas what would be casing this? My Idle is set correctly and timing for leading and trailing spark plugs is correct. Also my boost does not decrease so I know there is plenty of fuel/air mixture coming in. May be it is normal for stock S5?

does the boost increase? could be boost spiking to like 20 psi er sumthin (happend to me) an i had to switch at 6 grand. could also be major vacuum leak, or ur motor is jus weak. check compression.

Compression is fine and even if it would be compression wouldn’t I loose power on all rpms and have idle problems? And another reason I think there is nothing wrong with an engine itself is because the car will hit 140. And boost does not spike (at least I don't see it may because I have stock boost gage) it drops just a little bit, you can barely notice.

I personally actually leaning towards timing but I don't know at what timing should be at high RPMs? My idle speed timing is perfect.

my motor (88 tii) has 58-55-70 on rear rotor, 65-65-65 on front. has perfect idle. power is non existant at lower RPM, but at hi rpm (6k) is screams. boost spiking caused my motor to have such low compression. if i were you i'd check it. at least check for 3 strong WHOOSH, when u crank. also i went 155 on this motor. the stock boost gauge is shit, not reliable, since it is connected to the pressuer sensor. and the pressure sensor might be broke.

Do your basic tune up. New spark plugs, new wires, double check timing, change fuel filters blah blah. Im willing to bet its a spark problem.

My compression is 70-70-70 at 250 rpms at 4000 ft which is meets Mazda’s specs. Also I have reverse of your problem which actually proves my point if it was compression i wouldn’t loose much power at the high end but would loose in the low and I don’t.

your stock cats are probbaly cloged..

That should create a problem thru the entire power band though. And not stop at 7k...

hmm... maybe this is a little obvious, but I'll ask anyway.. (it took me a while to figure this out on my car...)

Is your clutch slipping?

reason I ask is 'cause at exactly those numbers my clutch starts to slip. :S

hmm... maybe this is a little obvious, but I'll ask anyway.. (it took me a while to figure this out on my car...)

Is your clutch slipping?

reason I ask is 'cause at exactly those numbers my clutch starts to slip. :S

No my clutch does not slip you actually can see that rpms are not increasing as fast after 5500. And I actually checked the clutch and it is in excelled condition..

Another thing I have magnicore 10mm wires with 0 ohm resistance and I heard that EMD from the 0 resistance wires can kill the signal which is coming to coils and make spark plugs not to fire maybe this is the problem but I have the same wires on my 87 and it does not have any problems.

I'm going to che fuel filter.

this happens in my car but the power decreases at like 7000rpm is that normal

What he said.

try switching back to stock spark wires too, just get some from a friend or junk car.

u have 70psi all the way around? isnt that the specs for a S4 tii. You have a S5 tii.

My tii (a s4) was doing 90psi in -20C weather with a small ass battery (like half the size of a normal one) that hadnt been charged in weeks (or even ran in a car, it was sitting on the ground for 3 or 4). So yeah, definately less than ideal conditions.

You can try gutting your cats, most people seem to think thats what it is. But IMHO you are getting ignition break up.

Hey Rotal,

This is Dave. It was nice to meet you and the other guys last night. I'm a bit clueless on your problem, maybe you could take me for a spin in the car some time, its easier to tell first hand.

Do you know if the converters in the car are the stock ones? Only reason I ask, is that in that 88 TII of mine, I had major issues when I got it, but the biggest one was severe bucking and hesitation at 5000+ RPM - Swapped out the exhaust and the problem went away.

But, could be a spark issue as well. Worth a look.