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Boost lost at high speeds. Help?

pizzi22

pizzi22

New member
Hey, im newer here, but i decided to take my GTP out for one last stroll before winter, and at about 80 or higher, The boost would be lost, to about half way, going up and down which in turn slowed accerleration down alot.:th_thumb-down: Wondering if this is a sign of knock retard, or what could cause this? New belt on the sc already.(3.4 pulley on car) Planning on new headers over the winter to reduce KR. Any suggestions on all this? Any help appreciated, Thanks>:th_king-normal:
 


wait a minute...did u put a 3.4 pulley on your car without tuning it? wow you r new....well u got three options....get a tuner, take the pulley off, or buy a replacemnt motor and hope you dont need to use it
 
i was thinking on putting a 3.5 onto it, maybe even 3.8, and see if there is a difference. Anywho, for tuning it. Any ideas on where to get one and how to tune it? Still new on engine modding here. Car still runs strong though.
 


yeah that's why i had the digital horsepower pcm, thought i could squeeze by with the 3.4 and supporting mods.(want headers tho) I will see if i can get a scanner and scan for KR. But otherwise, what do you guys suggest on fixing this? I'll check out Hp tuners
 
and yes...i believe your problem is knock but without a scan who knows....all i know is you need to read the "safely modding your car" section before you start throwing stuff at your car. thatll avoid you needing that new engine i spoke of earlier. my best peice of advise is read read read and when you get sick of reading read some more. read all the stickies here and in the hp tuners forum if u get a tuner.
 
first , if you r not already U MUST RUN 93 OCTANE FUEL!!!!!!!!!!!!!!!!!!!!!!!! NEVER RUN ANYTHING LOWER!!!!!!!!!1 THIS WILL HELP
 


yeah, i've done lots of reading, safely modding your 3800 sticky also. I know my exhaust isn't quite perfect for the supporting mods. But i never noticed this knock until very high speeds. As for Hp tuners, this is a program where i learn how to tune it myself, correct?
 
It's a pre programmed ECU (made by digital horsepower, some of the first to come out) to replace the stock one, i read they were very safe and reliable for these motors..
 
well u learn hp tuners form a lot of reading as well.....has your car just recently started this or has this happened ever since u modded it
 
i ask because knock will do this especially at high speeds and with the pedal to the floor for, but a bad plug, wire, or dis coil pack can do it too....does the car shake at all or stutter at high rpm or when u first get on it? also...have u had a variance learn done on the car since u added the new computer?
 
ive never noticed knock to pull boost, just timing for my car. but i have heard of torque abuse mods to pull boost.

hptuners is a custom tune that you make yourself. it can read/write/scan the computer.
 


Seems fine at first once you get on it, but at 80+ boost drops at high rpms, but just seems to lose power(gauge bouncing up and down) which makes sense for knocking, havent had 3.4 on there too long. Also just replaced plugs and wires. Problem is i bought this car with a diff pulley and already had the DHP pcm which was apparently tuned by some guy. But i put a 3.4 on here becuase i had no idea the size of the pulley on the car once i bought it. Also i heard you can tune the DHP's i just don't know how. And some mechanics around here i don't trust...
 
Note, i added the cai, 104's, wires, new mufflers, and replaced the MAF sensor since i've bought the car. I put a 3.4 mps on it so i'd know the size of pulley. All other work was done before i bought it (u bend removal, downpipe, tips, t stat, and that diff pulley..
 
you have to have a tuner to tune, like a hptuners or dhp powrtuner. yes that pcm is unlocked to tune. anyone that knows anything about tuning (make sure there car runs good tho, usally lsx guys) can tune your car with hptuner or powrtuner.
 
Btw, this is very much appreciated, Only problem is i'm broke haha! I ran codes and found out my maf sensor was shot. (even did tests) so i hadda get a new one for $180!! This turned my ses light off. and now has no idling problems. Yeah my boost gauge was fluctuating and u could feel it in the car. still accelerated to 115. I just am really concerned, don't want a blown motor!!
 
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