So I had this engine rebuilt maybe 30k ago and ever since then I have little low end torque and more recently a boost issue. Its a 93 TT automatic, here is a short list of the major things changed during the rebuild:
-Wiseco pistons
-Eagle rods
-Nismo 555cc injectors
-Stock turbo housing ported and T25 cartirdges installed
-JWT valve springs
-Stock cam gears welded
-Intake ported and polished
-Megan Racing Test/Down pipes
-Greddy Profec B II
-ECU tuned for new setupNow I have two problems. The first is that I have no low end torque, but the car is VERY strong from 3000 RPM's on. Very little boost is built at a stop and wont really increase till 3000+ RPM. Problem with this is I cant even squeal my tires from a dead stop or get a descent launch. Even standing on the brake and gas at a stop for 30 seconds I am lucky to hit 1-2 PSI before I drop the brake and launch and the car has almost no torque from a dead stop unless its boosting. I have had 2 NA's and both had noticeably better low end take off then my TT. The second problem is, I have inconsistant boost levels. I can make a pull, and hit a solid 18 lbs. Then without touching anything do another pull and only hit 11-12 lbs. I only recently noticed the problem because I upped the boost from a very mild 14 lbs to 18 lbs. It might have done it at the lower boost setting but since 14 is so close to 12 I wouldn't have noticed it. It is boosting very solid, smooth and holding the pressure when it gets there. No spiking, no drop off, very clean solid boost. Its almost like someone turned my boost controller off between runs. I cannot seem to replicate the exact conditions that cause the low boost. It just seems like it randomly doesnt want to boost over 12 lbs. What makes it even more interesting is during a 12 lb pull, I can let off the gas, jump on it again and it will usually jump up to the 18 lbs it should. Boost controller settings are as follows:
SET = 80%
GAIN = 18%
SET GAIN = 17.0 Now I have done the following to trouble shoot both of these problems. I have checked TPS, timing, boost leak test (up to 5 PSI), coil packs, spark plugs, new JWT pop charger 2 days ago, vaccuum lines, and fluid levels. I'm at a loss. Things I think could be effecting the low end are:
-ticking lifters (dont think this can cause performance issues, only excessive wear)
-stock cams
-welded cam gears (cant find any info on this but the mechanic that did it is VERY experienced with Z's)
-transmission issues (car had a level 10 billet torque converter [dont know enough about trannys to know what that means other then a higher stall speed] insalled before I bought it)
-ALC not functioning (Has an ALC installed on the tranny computer that used to flash my tranny light in the dash on startup but no longer does, I think the unit is dead. However, with this out of the loop and the stock computer doing all the work hesitation and boost issues are still present)
-Rebuild was not done properly Things I think might be effecting the boost issues:
-ticking lifters (dont think this can cause performance issues, only excessive wear)
-transmission issues (see above)
-exhaust leak (I can hear a sputtering on the drivers side near the exhaust manifold and turbo area but have been unable to pinpoint the leak. I installed the Megan pipes myself and I am 100% sure the leak is not from the downpipe back. The leak did not show up during the boost leak test so I am not sure if it would have any effect on the INCONSISTANTCY I am seeing. I am sure it is causing my turbo to work little harder but dont see that it would cause two dramaticly different boost levels at random)
-engine load (It seems that if I powerbrake the car and attempt to build boost that way I will hit the 12 PSI boost problem close to 50% of the time. If I just punch it and dont touch the gas till I launch it happens much less often)
-safety boost (I have a EBC on the car so it cannot control the wastegates, however I do believe it can still retard the timing on the car. I do not hear detonation but I am also not sure what it sounds like, I have been told I will just KNOW when it happens because its not a normal sound I am used to hearing.) Let me also say that I am suspicious of the transmission but it drives just fine. Shifts are solid but not rough, during the 18 psi pulls it doesnt slip and shifts smoothly to the next gear even under that kind of boost. I also have a tranny cooler installed so I dont think it is overheating. I just dont know much about auto Z's and the effect of changing things like torque converters. Lastly, I am a long way from where I was when I bought this car 8 years ago. I have learned so much from this site and the members here I feel confident doing things I didnt even understand before. It is still a learning process so dont flame me too much. I did searches and all kinds of research and testing on my own before I posted this so know I have done some leg work. I only drive my Z on the weekends and once a year for the drag races at Texas Motor Speedway as I now have a 350Z I drive daily. My tools are pretty standard for most DIYers so if any troubleshooting requires special tools let me know so I can source them. Thanks
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