Boost Fluxuation (with no boost leak)!

[Maverick3169]

My car has been doing this for a while now, and I'm running out of idea's.

Also, I can't keep my boost steady for the life of me. I check for boost leaks, and nothing turns up... I tested up to 30psi.
Could this be symtoms of a bad GM MAF? I mean, I just don't know what it could be anymore. I've swaped MBC's, plugs, turbo's, everything that I could think of! I also get terrible boost spike, and the boost always drops off after 5000rpm in every gear. Its holding around 19psi or so after the initial spike(until 5K, then 17).

And just to explain the inconsistant boost levels a bit more, this is what happens:

1st- Spikes to 21-22psi, then down to 16psi, then right before its time to shift, 17psi.

2nd- Spikes to 21 psi, then down to 19psi, then at exactly 5000rpm it drops to 17psi.

3rd- Spikes to 20psi, then down to 19psi, then at exactly 5000rpm, its drops to 17-18psi.

4th(OD)- Spikes to 21, then down to 19.5 psi, until 5000rpm, then it drops to 18psi.

This is obviously an A/T car.

My mods are:
EvoIII 16G turbo(ported, 34mm Wastgate flapper), MHG, 3 inch tig welded turbo-back exhaust, 450cc injectors, Supra TT fuel pump, WAI, Man. boost controller, Evo 3 Exhaust manifold(ported 7cm), M/T ECU, Slow-Boy Racing tubular O2 housing, Fully gutted out, GM 3" MAF, MAFT, 3" Intake Pipe, Magnacore 8.5mm wires, 3rd Gen Revised Lifters, Dejontool Compressor Elbow,Extreme FMIC kit, IPT A/T "Boost Controller". IPT Custom High Stall TQ Converter, NGK plugs and more free mods.


Thanks ahead of time guys!

 

[dsmotorsports]

Well, if you think about it for a minute, what controlls boost? If you have a bad boost controller this spike problem will happen. Try taking your boost controller off and see what happens. If it is still spiking it would probably be a bad wastegate or a hole in your vacuum line to either your wastegate, or boost controller. Thanks and let me know if i helped you.

 

[Maverick3169]

I have tryed that. The turbo is brand new(less than 2000 miles on it now), and this was also happening on the old turbo.
I'm more concerned with the boost falling off after 5000 rpm in every gear. It's driving me nuts!

Thanks for the response though.
Maybe I need to shorten the MBC lines or something?

 

[Spyderman7]

I didn't see any mention of internal specs.You may want to perform a dry,then wet compression test to see if your rings or valve job are capable of holding 22psi.Maybe 17psi is all it will hold steady.It's a simple test and you'll know how tight your motor is.

 

[Maverick3169]

No, the higher boost you run, the higher it will hold after 5K. Like if I turn it up to 21psi, after 5K it drops to 19. It seems to lose around 2-3psi after 5K rpm no matter the setting.

 

[dsmotorsports]

Your car might be backing the timing off because you are trying to run too much boost. The average boost you can run on 93 pump gas is 16-17 psi and you might want to try hooking your factory boost controller back up and see what happens.

 

[92awddsm]

I would get a wideband or spend some time on the dyno tuning. A/F ratio over the rpm range has a lot to do with the spool characteristics of a turbo. Being overly lean or overly rich can both cause the problem you are seeing. Those 450cc injectors arent the greatest choice for your setup either.

 

[Maverick3169]

I would get a wideband or spend some time on the dyno tuning. A/F ratio over the rpm range has a lot to do with the spool characteristics of a turbo. Being overly lean or overly rich can both cause the problem you are seeing. Those 450cc injectors arent the greatest choice for your setup either.

I have a wideband now.
Check out my other thread, maybe you can make something out of this.
http://www.dsmtuners.com/forums/showthread.php?t=206712

I had 650cc injectors on order, but now I might just return them.