So I've been chasing gremlins on my car for a year. The car just does not run well under casual driving condition(since all the mods). The one and only code I have ever got/get is a P1508...probably 4 or 5 times. It always happens under high load high torque roll ons.

P1508 is a bad DME code. I am starting to wonder if I indeed have a bad DME. Apparently it is very rare for a DME to go bad. My Tech also has a 996 TT so we put my DME and alarm module in his stock car and it seemed to run fine. His car is stock, mine has several mods.

My mods:
- COBB Mafless tune
- COBB 1000cc injectors
- 997 Throttle body
- IPD plenum
- Marksi large inlet piping
- AMS 1 bar wastegates
- Standard Issue DV's
- Billet K16(Sambot) turbos
- Wagner Intercoolers
- New Coils & plugs
- KLINE 3" X pipe exhaust
- Sachs 2.5 clutch
- No boost leaks

The issues are when not boosting or at partial boost and half throttle or less. Throttle tip ins and lift offs are very jerky. Small throttle inputs are herky jerky. There is a cut off / hesitation every time I lift off and re-apply throttle. Around town driving is down right annoying. WOT are OK most of the time. Some times they are not. When they are not, my AFR's are 10.7(rich) Every time there is a hiccup, my AFR spike rich. I don't know if the hesitation causes the the rich spike or does the hesitation cause the rich spike. Chicken or the egg?

I've been watching the ignition angles but I don't know what to look for. They seem to go from -9 to 35. The angle seems to change with throttle inputs and load. Again, I'm not sure what they should be doing or what I should be looking for.

I wish I had left the car the way it was before these mods. I had a simple stage 1 EPL tune and the car was great. I've had the car since it only had 5k miles on it. It now has 42k and I now truly hate this car.

Anybody out there have a DME go bad? What where your symptoms?

 

I had this code and i found my throttle body was dirty and oily. Go and take it off and clean it real good also get a new gasket. You might have a boost leak too.

 

i have seen at least 3 ipd plenums with leaks at the top of the plenum. its possible this is causing the hesitation but i have no idea why you get a bad dme code

 

Also you need to re adapt your throttle if you look up p1508.

Switch the igntion on but dont start it for 60seconds you will here the throttle adapting. Then turn it off for 10sec. Now restart it.

 

What happens if you put the MAF back in the system? Since this seems possibly throttle input related have you considered swapping back to the stock plenum and TB or could you just put the stock TB on the car to troubleshoot? I can't see the turbos or injectors causing this easily, I know we've discussed fuel pump too. COBB injectors don't use an adapter correct?

COBB can do datalogging, sounds like maybe that could be used to extensively log. MAF can cover many issues, a MAP sensed system needs to have the tune fairly accurate in my experience. Is this an off the shelf tune from COBB or has it been tweaked for your car?

I have no doubt once figured out you'll be really happy with it but I understand the frustration! Chasing weird gremlins is no fun

 

P1508 has nothing to do with maf or map. Its the throttle or a leak. For me it was throttle and i had to clean it and re adapt it.

These cars are so touchy lol with codes just popping up.

 

Yup, I'm ignoring the code since it's more sporadic than the issue and looking at the symptoms. MAP is a possibility, log the readings and see if they're clean or if they jump around. On my car Garth had to use a vacuum block to get clean readings at the sensors when I changed out plenum, TB, Y-pipe, and other things so even jumpy readings might not indicate a bad sensor.

 

Thanks...I've done that as well. Clean as a whistle and no boost leaks

 

Would a leak at the IPD show up when I do a boost leak test? I did a test at the Y pipe and was holding 25psi.

 

I've done the throttle reset many times as well...makes no difference

 

Good question...COBB gave me a Map for using a MAF...It ran significantly worse. I've sent them many logs. They have given me several maps to try to make it better with limited success. I tried two throttle bodies with no change. I have not tried the stock TB and or the stock plenum.

What I don't like is that COBB can't seem to tell me what they are seeing in the logs other than the car is constantly making correction for some reason but no direction on what to look at on the car. It would be nice if they could steer me in a particular direction.

 

Are there any COBB tuning shops near you? Garth can tune them in NJ but I don't know who else up there.

 

No where here in MA that I know of. I'm not familiar with Garth. Where in NJ is he? Maybe you can give me his info. At this point I'd be willing to drive down there to get this thing fixed.

 

I shot him a text and the link to this thread, Garth used to tune for Undercover and is now tuning on his own. My car is currently at AIM Performance in NJ being tweaked, home soon I hope! Between his tuning ability and the mechanical experience at AIM I suspect they could straighten you out and that you would be pretty happy with the result! On pump my car is in the mid 650whp range on hybrid K24. I know he's got experience with COBB as well as multiple other EFI systems.

 

Bren at Brentuning will be tuning my car with a cobb access port. He is located in Charlton MA