boost surge with TD04 upgrade - SaabCentral Forums
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NG900 & OG9-3 Performance, Mods & Tuning Covers Tuning & Performance modifications for the NG900 (1994 to 1998) & OG9-3 (1999-2002) & '03 Convertible

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  #1  
Old 14th April 2006
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Default boost surge with TD04 upgrade

replaced my t25 with a tdo4 15t after convincing myself i heard a whine from the t25 and it should be replaced so why not upgrade at the same time? now i am getting a surging type of boost , up to 20 psi back to 10 , up to 20-22 back to 10 before it finally settles at 16 psi or so. backing off the base boost from 7 psi to 5 solves the problem but then it seems kind of laggy. with the wastegate hose disconnected i get quick spool and high boost as expected .talked to nick at gs who thinks the ECU might not be adapting to the different flow characteristics of the tdo4 and he will talk to nordic about a reprogrammed ECU.

overall even at 16 psi there seems to be more pull than the t25 at 20 psi but i would like to see how good the tdo4 would be at a steady 20 psi!

has anyone else encountered this type of problem?
anyone else running a tdo4/t5 upgrade from a t25?did you see more lag as compared to the t25? what kind of max boost are you seeing?

thoughts? comments? thanks john
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  #2  
Old 14th April 2006
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Same boat as you nearly to a T. Excpet I have SQR Stage 4 software. My software was installed after the turbo was in too... I have been trying for 6 months to get this squared away with varying levels of success. I find that octane boost helps, so did adjusting the wastegate, but the computer always adapts back to where it would like to be. No consistency at all.

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Old 14th April 2006
nbndtrain nbndtrain is offline
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Sounds like the TB is opening and closing causing the surge.
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Old 17th April 2006
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hey blue did you get any input from SQR on the potential cause of this?
i am thinking what i am seeing is that the boost spike is related to the waste gate actuator not opening quick enough with the new turbo causing the spike and then the ECU cuts back on the boost with overcorrection, i might try a little experiment with an old bpc valve to look into it.
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Old 17th April 2006
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Sure this isn't another BPC issue?Using high octane gas?Proper base boost setting?
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  #6  
Old 17th April 2006
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have you replaced your wastegate spring? you should get a stiffer/stronger one if your pushing 20+ lbs
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Old 18th April 2006
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with the old t25 i had an stiffer spring in the actuator, with the tdo4 the stiffer spring is not needed per nick. with the wategate hose disconnected it will hold more than 20 lbs boost without problems. otherwise running 93 octane and base boost 5- 6 psi. the bpc seemed to work fine with the t25 , i have an old one around i might put in just to see.
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Old 19th April 2006
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Last night I did a little tuning up myself. I cleaned and re-oiled may K&N filter, cleaned my BPC with WD-40 and compressed air, changed out the spring in my BOV from the heavist spring that forge sells to their middle spring with a couple of shims and re-lubed the seals as well as regapped the plugs and did an exhaust back pressure test.

Results?

No more coughing burble after shifting from teh intake, more power than before and slightly better gas mileage. Still very little consistency though. At least theres more power. Tonight I am going to reset the ECU and take a couple of adaptation runs to see where I'm at.
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