noble1978

Gents, i'm suffering with a problem details as best as can descrbe below:

I've recently had my car mapped (along with various other mods (997 TB and IPD Plenum, forge diverter valves, nine excellence 1 bar actuators and europipe 100 cell exhaust))

I originally had it mapped by revo but it was feeling rough at low revs and the boost wasn't getting to 1.2 bar. It would go to about 0.7, 0.8 on wot. Strange thing was if i took my foot OFF the throttle slightly then the car would boost more and accelerate!
The repo map was removed and the car checked for boost leaks. Found a couple leaks and the car was running well on standard map .8 or .9 boost.
Decided to get the car mapped again and am now using softronic as I got the durametric cable from them and they were responsive to all questions I had.

The car feels quicker, probably due to the timing but the boost issue is still there! If i go WOT in 3rd or 4th from 2k revs the boost never reaches 1.2. However if i go partial throttle or go WOT then back off slightly I can get max boost.

Now i've tried various experts in the field and i've changed the MAF and N75, adjusted the actuators and i'm still nowhere. No other ideas have been put forward. I fairness it's the weekend now and I only asked the questions yesterday but the issue has been going on for a couple of months now when you consider i've been through two remaps etc.

Please,please help!!! If you can!

powdrhound

I'd be interested in this as well if someone can offer some insight as I seem to have the same thing. I noticed on my car that when I have the throttle pedal depressed 3/4 of its travel, I get 1.3bar in 3rd and 4th. If I press the throttle pedal further then boost drops off to .9 or so and power noticeably drops off. Doesn't seem right to me....

993GT

Its not right at all.
I'll bet the wastegates are too slacked or the N75 is faulty...assuming no boost leaks or CEL's.

noble1978

i've no boost leaks. Changed the N75 and tried a new MAF. Actuators set up correctly and balanced. NO CEL, and no fault codes on the car.

993GT

try another N75... or...either the tune is bad and/or the W/G's aren't actually set right causing overboost protection...or set wrong and therefore low pressure...
Or you have a big boost leak somewhere you haven't checked....
if the system holds with NO leaks and the wastegates are set right, then the N75 is most likely faulty

Since you have a Durametric do a log....O2 voltage's, MAF reading, throttle value, actual throttle opening, engine load, ign. timing, rpm, boost pressure

noble1978

Powdrhound, have you tried anything to fix this issue?

What mao are you running with and what other mods do you have on your car? is it just something that has happened recently with you?

noble1978

I've no boost leaks, holding tight at 20 psi. The waste gates are set correctly and balanced. I replaced the N75 with absolutely no effect.

noble1978

I'll do a log tomorrow and post the results for you 993GT. Cheers.

993GT

can you explain where you did the air-leak checks...did you pressurize the intake manifold itself?
wastegates begin to open at what psi?

993GT

"02996ttx50

^ sounds like you're on the right track. in my limited experience assuming all else ( tune ) is ok and no obvious leaks?

it's always a combo of the check valves/n75 or waste gates being unequally adjusted. all that stuff has to be "just" right or boost issues are intermittent and frustrating as hell since the car runs otherwise fine.

once you do a pressure test i would replace ALL the check valves incl the n75. reset the actuators to suggested levels and hope for the best.

doing all that has cured ALL my boost issues and i struggled with them for a year plus. i'm now at 1.2 solid always when wot with spikes to 1.3. and throttle position or rpm doesn't matter when hammering down.

powdrhound

I just noticed it recently as I usually never pressed the throttle all the way to the floor, usually just enough to get full boost. I have Kevin's UMW K16/997GT2 Zero clearance turbos with his injectors and programming. The waste gates are adjusted by Kevin for his turbos. I installed everything at the beginning of this year including new plugs, new coils and a new MAF. A new N75 valve was installed 2 years ago preemptively. Car runs great otherwise. I spoke to Kevin about it a week ago and he went into a pretty technical explanation of engine load, rpm, etc., but it was mainly over my head. If I understood correctly, I think he was saying that was normal. It seems to me though, that if you are in 3rd or 4th gear and you fully depress the throttle, your boost should climb to it's maximum (in my case 1.3) as the rpms climb. If you you back off the throttle to say 75%, your boost and engine output should drop accordingly. I seem to have the reverse of that. The waste gates, ECU, and N75 valve should cap the boost relative to the amount of "throttle" your right foot is commanding, no? In my case for example, if I'm accelerating in 4th gear and I'm around 4000rpm with the throttle pedal pressed to about 75%, I am showing 1.3bar with the car smoothly pulling. If I now press the throttle further to 100%, boost immediately drops off to 0.9 or so as does acceleration. If I let up on the throttle a bit, boost jumps back to 1.3. I have a hard time believing that's right. Besides the above turbo package, my car has a larger RUF intake manifold and turbo intake hoses and RUF exhaust, and 997.2 ICs. Everything else is stock on the engine.

I will also check the throttle pedal/cable to make sure there is nothing binding that would be reducing power above a certain amount of throttle input. I highly doubt that however. I have to datalog it when I get a chance and have Kevin take look at the logs to see what is going on. If I recall when I did my original logs, my throttle body was fully open at max boost with less than 100% throttle pedal deflection. It seems to me that 50% throttle pedal deflection should equal 50% throttle body open, 70% should be 70%, and so on...

The only other problem I have is that when I'm in third gear in a highly loaded right turn at full boost, power starts to noticeably drop off at around 6500rpm as if the rev limiter was starting to kick in. In a straight line the car pulls strong and smooth all the way to 7200 however. It only does this once the car is about 10minutes into a track session when pulling high lateral Gs. It's strange.

993GT

Bolded a couple points to hit on:
-Car should not be losing boost at WOT, period. A tuned K24 car should be able to efficiently pull 1.1-1.2bar to redline at WOT through all gears, even on a hot day.
-Requested throttle opening vs actual is controlled by the ecu/tuner...mine is set to be 1:1 and hits the target viewing the logs.
-Almost sounds like the fuel pump is dropping off, fuel demand + heat.
If either of you guys wants to view one of my logs to compare, PM me.

993GT

+1..
I've had (and rebuilt and modded) many turbo cars, so I'll add, our cars aren't black magic, turbocharging is rather simple. need a:
-air-tight system
-a turbocharger(s) that match the engine size and needs(ie. can produce boost on a particular engine),
-boost is controlled by wastegate(s) that receive a feed signal (via MBC, EBC, or N75 in our case) to sort out the level of bypass/boost-held.
-Boost surge on over-run is bypasses through diverter-valves or blow-off valves for non-MAF cars.
-check valves are use for components requiring one-way air flow, ie brake booster vacuum
If one component isn't working right...

powdrhound

That is how I understand it also, both the wide open boost and the throttle opening. I thought maybe I have a fuel starvation issue in high G turns but it does it even at a fuel tank that is almost full. I'll have to do some logs to see what is going on.