Mike Roblin

So... I recently purchased an 03 996tt with just under 40k miles and what was advertised as a stock car but after doing some research regarding boost levels I think my car might have a tune of some sorts. I did have a PPI done before purchase but it did not indicate any modifications.

After doing a 4th gear pull in the car it built boost steadily and for a brief second hit 1.1 bar before leveling off at 1.0 (as indicated on the instrument cluster display). Checking it more often now and I am consistently getting 1.0 bar sustained at WOT and I understand from reading the threads here that stock should be 0.7 bar with an occasional spike to 0.8 bar before the wastegate opens fully.

For fuel I use either Shell or Chevron 93 octane fuel (with the state mandated 10% ethanol blend). Car does not have the X50 package and I live in Florida (sea level and regularly over 80 F ambient) so this should be stock K16's (how can I check this?)

Not necessarily disappointed to have more power, but I want to know if there are other things that I need to address to ensure reliability. I intend to track the car and I bought this to replace a 996 C4S just because I didn't want to deal with the unreliability concerns when tracking an M96 engine that wasn't designed to deal with high lateral G's.

After reading many of the posts here on the forum I know that at some point I'll need to replace the diverter valves even if the car was stock, but not sure if there is a more urgent need now that the car is making more boost. I also want to make sure the stock fuel injectors and fuel pump can handle this boost level or if an upgrade is necessary.

As always, any help is much appreciated!

Mike Roblin

I should also mention that the Check Engine Light came on about 500 miles after I bought the car but I have not yet researched what the code is. Could an engine tune throw a CEL?

I'll get the OBD II reader out this week and see what the code is and will post back once I find out.

"02996ttx50

a minor vac leak can affect boost numbers resulting in higher than *normal* numbers and if that's your problem it could also be the cause of the cel. if the car is not tuned it should certainly never see 1.1 with k16's and if you do have flashed k16 car, then most you'd see if all was buttoned up tight, was .9 with maybe spikes to 1.0.

i suspect you may have a minor leak. get codes read and/or a boost leak test is advisable.

T10Chris

I see 1.0-1.1 bar with K16, no boost leaks, usually 1.1 bar that tapers off to 1.0 at redline... Just depends on the tune and supporting mods.

Stock was 0.6-0.7 bar.

I'm guessing you have a tune, or something not allowing wastegates to open/n75 to control boost as it should.... Simplest answer, if car is running well, you have some sort of tune.

996tnz

Mike, you sound like you are pretty much across this already, and you are being sensible in checking that fueling and DVs match what looks to be your tune. Assuming she really has stock K16s, that's likely a Stage 1 tune if she looks stock visually - ie factory air filter, intake plenum, exhaust. And should be very safe if always filling with 93, even on track. When next you change your spark plugs go with one grade cooler than stock to match your tune.

The CEL could be almost anything so yes, read the code. Oxygen sensors in the cats/aftermarket (particularly oiled) air filter/bad MAF sensor/any air leak between MAF sensor and cylinders etc

For true peace of mind around your tune, log performance data during wide open throttle pulls (especially air/fuel ratio and injector duty cycle). If your OBDII reader can't log live data, consider getting a solution that can. I'm sure there are others out there too but I got mine with my tune from Kevin at UMW.

Enjoy your car Mike - these things are already fantastic out of the box, but they really do come alive with a mild tune.

32krazy!

more important than a tune is the fact that if you plan on tracking a turbo you need to research the coolant fittings and have them either pinned or welded. this is increasingly becoming a requirement for many tracks

Kevinmacd

Some Tunes do take the boost to 1.0.

fung0001

When next you change your spark plugs go with one grade cooler than stock to match your tune.

Great
May you pls explain what is meant by cooler plugs?
Currently i am using k22 grade for a stock untuned tt
Is it match? Thx

996tnz

Don't have the stock plug code to hand but my US93 Octane 1 BAR tuned 996T runs Bosch FR6LDC plugs now, which I was advised were one range cooler than stock.

Higher charge pressures in the cylinders already directly generate a little more heat just from the higher compression itself, never mind then burning that tuned extra fuel-air mix at each firing (hey the power has to come from somewhere). So the extra heat going into the plugs is offset by running cooler plugs to keep them in their happy place. Plus via some sacrificial fueling. Someone else can probably explain better of course.

Your friendly auto shop or Google should be able to tell whether those are a match or not.

Mike Roblin

Ok, so tonight I finally got the code reader out and built a boost leak checker tool from some jobsite PVC fittings... Bonus points to 02996ttx50 for pointing out a possible boost leak, as soon as I pressurized the intake boot I could hear a leak. Turns out there is good news and bad news; the leak was found on a vacuum hose attached to the rear diverter valve.

The good news was two fold; there were no other leaks that I could find and the diverter valves have been upgraded to the Bailey Motorsporst DV30 units.

The bad news is that the leak was due to the idiot who installed the Bailey valves using the straight vacuum fittings instead of the right angle fittings coming off the top of the valves. Due to this the jump start + connector bracket cut through the edge of the vacuum line and I think this is what threw my CEL. Anyone know where I can get the right angle fittings for the Bailey valves? I tried the local auto parts store and Home Depot with no luck. Any help would be greatly appreciated!

Speaking of that, the CEL code(s) were P0491 and P0492 which according to my checking the forums and the Google are the secondary air bank 1 and 2. Does this correspond to a vacuum leak at the diverter valve? Especially since they are connected to the F-pipe together?

Due to weather I will not be driving the car tomorrow, but I cleared the CEL with the reader tonight and will drive it Friday to see if I am still making 1.0 bar to confirm if the vacuum leak was causing the overboost or if it might be related to a tune. I'll report back when I have more intel

32krazy! - I have read about pinning/welding the coolant pipes and will be doing this before hitting the track. I will be doing the 6 I can reach with the engine in and the remaining 2 when I need to drop the motor next or if I can get to them by moving more out of the way with the engine in the car, I'll do them too. Planned on following the advice in the forum post found here:

https://rennlist.com/forums/997-gt2-...n-the-car.html

Thanks for all the input everyone!

Mike Roblin

996tnz - Yes, everything else appears to be stock, the airbox, plenum, exhaust, etc. The only aftermarket items I have found so far are the diverter valves. When I go test the car Friday or Saturday I plan to see if my OBD II reader can show me AFR and/or timing in real time to see how things are going. I'll report back when I have the info.

Thanks!

jeanmarcboilard

I think this is what you're looking for? These are the part numbers for the oem hoses for the diverter valves. Any Porsche dealer can get them.

"02996ttx50

thanks, I'm here all week. dont try the veal.

i think you're on the right track, and while those codes are exactly what you suggest P0491 Secondary Air Injection System, Bank 1
P0492 Secondary Air Injection System, Bank 2

SAI codes can be fairly generic and accompany a lot of vac leaks.

only thing i can add is that you might want to ( if you haven't already ) make certain that the #16 check valve at the plenum is not hairline cracked as it is made of plastic and a very common failure point ( for leaks ) if not tough to isolate! as a source of leaks at or near the plenum. here's a quick look at it if youre unfamiliar with it
not to further pile on but there is also a check valve for the sai pump. though i have never had to mess with it so i dont even know if its a potential cause of this issue as well. though if issues still point to the sai then any/all of the component parts is suspect obviously.

but back to this culprit, infamous #16 check valve noted above though *should* have revealed itself when you pressure tested? ( as in you'd usually hear air escaping ) but even if you did not, i'd make 100% sure it is in proper working order or even replace it since its a very cheap part. sounds like you've almost got it nailed down though, GL with fully sorting it out.

"02996ttx50

here's another set of clues from the esteemed jpflip wherever he is!

not to make you crazy, but these would be the next things i would look at. again, GL w it.

Mike Roblin

jeanmarcboilard - Those are the vacuum hoses and though mine are chafed, it is because my aftermarket diverter valves have the straight barbed vacuum line fittings instead of the angled ones like you see highlighted in the image below. Basically they stick straight up instead of laying flat across the top of the diverter valve and thus the rubber vacuum line chafes until it leaks.

These are the fittings that I need and maybe I'm wrong, but I dont think my Porsche dealer will be stocking these since they are aftermarket. Any ideas as to where to get the angled fittings anyone?