Ok here is the background. I have a 93 5spd. I recently installed a t70 turbocharger kit I pieced together. At the same time I upgraded my ecu to PFC with commander, installed 1600cc secondary injectors, FPR and braided fuel lines. I also removed everything from the UIM besides the air temp sensor. I also installed a wideband o2.
I put a map in the PFC I found for a t66 as a baseline to tune from.
I can drive the car easy to redline with no problems, I can even get partially on the throttle and boost 1bar to redline as long as I feather the throttle. The problem is when I floor it, Everything seems fine, huge power, quick spool, everything you want from an rx. Then at about 5k if boost is over 1.1bar, it feels like I get ignition cut. The car basically stutters really hard and then revs a little more (albeit roughly) and then stutters again, revs, stutters, does this all the way to redline.
One thing I noticed is that the wideband is reading an afr between 9:1 and 10:1 near the stutter. So I definitely know it is not any lack of fuel causing the problem. Could running rich be causing the stutter? Like maybe its so rich it is putting out the spark from my iridium plugs?? I know most people tune for 10.8-12:1 depending on boost level. And I am in the low 10s to mid 9s in boost.
During the stutter it almost sounds like a Pop, because it happens so fast. I am assuming from the excess fuel igniting in the hot manifold.
Oh, also during the "conversion" I relocated the battery behind the passengers seat. Could bad grounding to the battery be causing this??
I am posting this in the single turbo section and the PFC section since these problems could stem from either of these mods.

 

I'm still running stock twins but you might want to look into upgrading to a 3 bar map sensor and perhaps a HKS twinpower. Try a search on these, it might help you.


link to hks twinpower -
http://www.hksusa.com/categories/?id=1064

 

yea, I think if you go over the max stock MAP sensor can take, the PFC goes into 100% or almost 100% inj time.

 

The stock 2-bar sensor is only good for 16-17 psi, tops.

Also, you are insane to be boosting over 15 psi on an untuned map. Baby steps.....

 

Is that true?
I may be seeing this on mine. Time to install the 3 bar this weekend.

 

BTW, Do you have a large amount of gas/smoke out the back when this happens?

You just explained my problem to the T without a large cloud of rich exhaust.

 

I am in the process of tuning, thus I must push the car to see what I need to do in that area of the map.

I have the timing decent/conservative. No negative split, all that good stuff. And I am starting with a very rich fuel map. So I don't mind getting into the throttle to much right now. I don't do it often, just to get my baseline afr's to tune from. Then I tune some, do another pull, ect,ect

As a test, I adjusted the lag on the secondaries to -.06 to lean the top end out a little. It helped, I am seeing between 10.5 and 11:1 afrs now to 6k. It also cured the harsh stutter at 5k but there is still significant breakup over 6k, and the afr goes 9-10:1 over 6k still.

Also, my idle has been really bad lately when the car is warm. But I am associating that with the fact that my wastegate won't close all the way and is causing a huge exhaust leak before the turbo. I am going to take it out and dissassemble it and see what the deal is. Grind a little and see if I can fix it.

And to answer your question x605p747R1, yes there is a cloud of unburned gas emitted from my tailpipe during this time.

So anyway, here is what I am going to do next:
Change plugs to colder plugs
Correct inj lag
Ground Battery better
Tune fuel cells with new injector settings and unfouled plugs.

reza by 100% injector time, do you mean duty cycle? So far I haven't seen duty cycles over 75% Boosting 1.2 bar. But I haven't really pushed it to its 8k redline.
I have my base fuel pressure set at 43psi with 1:1 rising rate.

 

I don't see anything in your post about a 3-bar map sensor.....

 

I'm having the same stutter problem around 5K rpm. I'm waiting to get a 3bar map sensor and a wideband O2 before I do some tuning. I enriched my mapping to be on the safe side but it feels to me like I'm running out of fuel still. I don't see any smoke or anything out the back.

I'm running 1600cc for the secondaries and they are getting about 59% duty cycle under load. I'm only running 14LBS of boost. Let me know if you can figure that out.

Thanks

 

I'm having the same stutter problem around 5K rpm. I'm waiting to get a 3bar map sensor and a wideband O2 before I do some tuning. I enriched my mapping to be on the safe side but it feels to me like I'm running out of fuel still. I don't see any smoke or anything out the back.

I'm running 1600cc for the secondaries and they are getting about 59% duty cycle under load. I'm only running 14LBS of boost. Let me know if you can figure that out.

Thanks

 

Actually, the reason my car was studdering at 5k was because I was running too rich. The 1680's flow almost exactly double what your stock 850's would flow, so a 59% duty cycle at 14 psi around 5k, sounds kind of high to me depending on what turbo you are using, and what base fuel pressure. That would be like 120% on the 850's (if it were possible)
I was running 43psi bfp, 1:1 rising rate regulator. Max duty cycle I was seeing was around 50-55 and I was seeing afrs in the 9s on my wideband at 17psi boost pressure. So I took a bunch of fuel out and now I am seeing afr's in the low 11s and I don't get the 5k sutter anymore.
So It is very possible that you are running too rich. Without a wideband, I would be scared to take the fuel out and test though.