pulling the same at different boost levels?

[Novablue454]

A few days ago I installed a MBC on my 90 Talon, and upped the boost to 15psi. It pulled strong for a few days, but recently it seems to have lost power. Last night I pulled the MBC off and returned everything i could back to stock, and now its at between 9-10psi. it feels the same as it did at 15psi. What could be causing this? Im going to perform the boost leak test tonight or tomorrow, but in the meantime are there any other suggestions?

 

[diablos991]

It sounds like you are on the right track to diagnosing your problem.

The most probable cause is a boost leak. That would easily cause 15 psi to feel like 10 psi.

Let us know how your boost leak test turns out and we can go from there.

 

[Dsmx17]

A few days ago I installed a MBC on my 90 Talon, and upped the boost to 15psi. It pulled strong for a few days, but recently it seems to have lost power. Last night I pulled the MBC off and returned everything i could back to stock, and now its at between 9-10psi. it feels the same as it did at 15psi. What could be causing this? Im going to perform the boost leak test tonight or tomorrow, but in the meantime are there any other suggestions?

Ok, first the boost leak test is a good starting point, but let me ask a few questions to maybe save you some time.

you are using a aftermarket boost gauge to moniter you boost? if you are, did it still read 15psi when it "felt" slower? if so is you boost gauge tapped in the manifold vac. sources? if it is then a boost leak is probably not your problem, also, a 5psi leak would make the car run very very rough at full throttle.

assuming you leak test and all is good, what was the outside temp when your car was at 15psi feeling "fast"? and now taht it feels like 9-10, whats the ambient temp? two reasons I ask, 1) a few degrees differece can make a big power difference on stockish cars (stock i/c fuel control etc etc..) 2) assuming it may have gotten hotter, (as it has here in the last few days) Knock at 15psi could be pulling timing, thus power. have you logged any passes? is it knocking? hope this helps a little.

 

[Novablue454]

yes i am running an aftermarket autometer boost guage. it was reading 15psi, well it would go to 16, then hold at 15 from about 3000 to 5300 rpm, then fall of to 13-14. the tempature has been around the same, im guessing around 50-60 degrees. There havent been any major weather changes. it always sounds like its knocking slightly, but i think its either the lifters or a really loud injector tick.

 

[nightspeed87]

make sure your fuel flow is adequate because some knock will pull back timing and make you feel slower also.

 

[Goodguy162000]

Agreed, I was looking over your vehicle profile and well... there is no vehicle profile. If you don't have the fuel to support that much boost, or a clogged fuel filter, you're basically turning up your boost AND your knock and slowing your timing. Nothing good is going to come of that.