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NA FG XR6 loss of power after 4krpm and rough idle after revving


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Hi I've recently had a problem with my na fg xr6 zf6.

Since having this issue i've returned the car to stock tune and put new spark plugs in.

The issue started after running 3 passes down the quater mile. I suspect my spark limiter at 6k caused the issue when i was doing my burnout, however running the same limiter on other cars i've had never caused a problem.

When i'm driving on WOT, the car drives great until 4k rpm where it will start to loose power to the point where it almost feels like it is on limiter. If i hold my foot down the revs will start to drop and the car will shudder violently. If i shift while this is happening, the car will thud into the next gear.

When the car is in park it idles well. If i rev it to 3k and let go, it goes back to a good idle. If i try to rev it over 4k, it feels like there's a limiter and when i let go, the idle becomes so rough the car stalls if i dont keep revving to keep it on. Once it stalls it takes about 4-7 tries with pedal persuasion to get it started again. after around 30-40 seconds, the idle goes back to being good.

Anyone experienced this before or know what it could be?

I have a feeling it could be bad valve springs but i have no idea how to confirm this. I tried looking for a way to datalog oil pressure to see if something funny is happening on idle. My idea is this will show me if the lifters are getting clogged up when i see an increase in oil pressure and seeing the pressure drop once the car regains proper idle. I tried "engine oil pressure guage" but i dont think this was showing me oil pressure. 



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  • 4 weeks later...

So I’ve got an update, I still haven’t found the problem but here’s what I’ve done so far:

new spark plugs, new coils, new lifters, new vct solenoids, new throttle body, new fuel filter, new fuel pump, replaced injectors with known working ones, new cam angle sensor (exhaust side), new catalytic converter.

what else can I try replacing or data logging to help me find this issue?

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