loss of power at 5800 RPMs
 

Hi everyone, I am experiencing a loss of power at 5800 rpms. It happens under WOT and normal acceleration. Here's a list of
mods:
Vivid Racing ECU tune
75mm throttle body and plenum.
Full Cat delete with Circuit Werks V2 muffler
Short Shift kit
aFe Air filter
if anyone has experience with the Vivid Racing tune please let me know

What do you mean by loss of power? Torque is going to start dropping around 6k but there should still be plenty of oomph there. Are you noticing am inability to accelerate well or are you actually losing forward velocity past that point?

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It is a total loss of power almost as if I clutched in. rpms start dropping and I have no power until I lift fully off the throttle and give it some gas again.

Are any dash lights coming on? Could it be that your tune is causing knocking (running too lean because of new intake) and the knock sensors are killing fuel injection and retarding timing? Lights should come on if this is the case,

If thats not it then it sounds like a fueling issue. I would start with checking the fuel pump (theres a procedure to jump the relay and measure the amount that is pumped over the course of 30 or 60 seconds, I dont remember off the top of my head). If that's not it then go through the rest of the system and check components (btw when was the last time you changed the filter?)

No dash lights what so ever. I will definitely look at the fuel system. Not sure if or when the fuel filter was replaced, I have full records in New York however I'm currently in Florida.

Good luck, let us know what you find

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Depending on the diag equipment you have available, would not be a bad idea to get a 5v pressure transducer from Amazon. Attach it to your fuel rail and wire it in (simple 3 wire: 5v, sig return, and ground). Hooking that up to a graphing meter or scope would easily tell you what is happening in the fuel system pressure wise at wot. Is a/c still hooked up (not sure is this is a track car or not) but if so, see what effect it has by disconnecting it. Normally should cut out at WOT. Your tune may not account for that but I don’t believe that it would cause what you describe.

Did the car exhibit this condition before the mods ? Were the mods done all at once or in increments ? If in increments at what point did the condition show up ?

Assuming the car is mechanically sound I would suspect the tune . Was the car tuned on a chassis dyno ?

Lot's of fuel pumps failing these days.

Hey everyone quick update, got a Durametric now plugged it in for the first time today. Haven't done any physical work on the car yet but am getting my stock throttle body and plenum shipped down to me, gonna try that before replacing any parts I don't already own. The image below is the codes that came up from the Durametric.
http://986forum.com/forums/uploads02...1613093861.jpg
Here is a list of the codes as well.
P0830, Porsche Fault Code 446-Clutch Pedal Encoder (Think this is why my cruise control doesn't work)

p0638, Porsche Fault Code 402-DVE Fault Position Deviation (could this be the reason for my issues? Know BMW calls the ECU something similar to DVE. Would this narrow the issue down to throttle body or fuel pump? Can this be an issue with the tune?)

P0300, Porsche Fault Code 507- Misfire Detection (total)

P0306, Porsche Fault Code 509-Misfire Cylinder 6

P0304, Porsche Fault Code 511-Misfire Cylinder 4

P0305, Porsche Fault Code 513-Misfire Cylinder 5 (think these are all on the passenger side bank (Bank 2))

Also forgot to mention I have a vacuum leak on the drivers side of my plenum(74mm) currently being contained by Gorilla Tape. Car was misfiring like crazy and almost undriveable before the tape job now runs pretty smooth with out noticeable misfires.

Misfires in 4'5'6 are your vacuum leak. You're running lean on high vacuum pull. Ya gotta fix the leak right, no duct tape! Don't drive until this is fixed, as you can cause real bad stuff to happen (comic book version lol)

The clutch code is probably the clutch connector (red colored) - it senses clutch engangagement during running and is tied into cruise control.

The 0638 may just be that your e_gas needs to be calibrated. I think there's a procedure for it in the owners manual somewhere. If not, I found this one posted somewhere in the interwebs.

Let us know how things turn out! https://uploads.tapatalk-cdn.com/202...6b44a23b1b.jpghttps://uploads.tapatalk-cdn.com/202...a5fa7c333c.jpg

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Resolved
 

Hey everyone, I got it all fixed up now turns out the issue was the 74 mil throttle body. Put the stock throttle body back on and no more misfires and I can now rev all the way to redline with no issues. Thanks to everyone who helped me out and gave some input!

Did the vivid tune not take that into account? IIRC, 74mm TB is stock on early 996s. You could just dump the VR tune and go with a 996 tune instead.

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Could be that the 74mm throttle body had an air leak through the gasket and not the TB itself..?
.

I bolted on a 74mm TB from 1996 996 on my 2.5, stock tuning and no such power dip, it works great with quicker response and a but louder intake noise.

Hey I have my cats, upgraded muffler, afe air filter, and I still have the stock plenum and original TB. I did try to put on an IPD plenum but the bolt pattern didn’t align so I put it all back to normal minus the few beginning mods.

I am having the same issues as you mentioned. The car starts, I can rev for three seconds and have to let off the gas or the car dies just like you described. You said the problem went away when you put the original TB back on. What do I need to check now because I am at that same point but I am having issues. I don’t have a tune either. Any suggestions?

Are you having problems only at higher rpms? Does the engine run fine at idle?
Do you have any codes and what are your fuel trims?
Is your AFE filter the oiled or the dry one?
Have you disconnected your battery recently?

Edit: Seems like you have been searching for the part number for the 996 cable throttle body. The part number is 99611006553 in case you haven't found it yet.
I have it on my -99 boxster and have had no problems.

Hey guys old thread I know, I figure I'd throw in what led me to the throttle body. I hooked up the Durametric and had a friend watch all the numbers and info for anything strange/out of the ordinary and saw that the throttle body would just close at 5800rpms exactly. To this day I'm still not sure why it would shut but the stock throttle body fixed it. I still have the 74mm throttle body and might try to run it again someday if I find a good plenum.