Compressor surge problem after MAFT install

90T04

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Mar 30, 2005
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I recently installed a MAFT and MAF in blow-through setup on my 1990. The turbo is a Garrett T04B on a manifold adapter. I have 2.5" custom hardpipes going to a spearco IC and a HKS SSQBOV.

The installation was straitforward, and the car started and ran fine after the initial adjustments were made on the MAFT, but I instantly noticed a completely different sound from my BOV. After talking to a more knowlegeable friend, he advised me that it sounded like compressor surge. Its a loud deep flutter sound that happens even with the slightest venting, not the signature SSQ whistle and whoosh.

I didnt make any other changes to the hardpipes except for putting in the MAF. I also am now running a 4 inch intake pipe to the turbo inlet and a universal filter due to the elimination of the AFM.

One other change I made is the idle air supply hose is now coming off the hardpipe right before the throttle body.

To give you an idea of how its laid out, the upper hardpipe comes out of the IC, goes up through the airbox hole and there the BOV sits. Then, about a foot later is where the MAF is located. After it comes out the MAF, it heads strait to the throttle body.

This is a stumper. Does the BOV have to be between the MAF and the Throttle? (that wouldnt cure the problem of stalling due to richness/unmetered air going out though, like the way it does how I have it setup) Does it have to do with where I have my idle air supply hose tapped into the pipe?

Im out of guesses, shed some light on this for me!

Ryan
 

90T04

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Mar 30, 2005
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Absolutely. Vacuum source has not changed(vacuum port near middle of injector rail) , its not cut or broken, and gets good vacuum at idle.

Thanks for the suggestion...
 

90T04

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Mar 30, 2005
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Thats good thinking, I just assumed that it sealed up after i stuck it back in there because I didnt hear any vacuum leaks. But you know what assuming does...

I'll check that and see if its the culprit.
 

90T04

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Mar 30, 2005
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That is exactly what I was thinking. Maybe its just the sound of the blow off valve, but from the other side of it, the inside of the pipes. I can still hear the BOV when I let off the gas, but its pretty hard to hear over the much louder "surge" sound.

Its just hard for me to go out and drive it like normal without knowing for sure.

Thanks for the ideas guys