Loosing Boost!?????

[91GSXbaby]

Hey everyone i am new to the site and new to the dsm world but no body has been able give me any answers about it... so i just got my 91 gsx about a month or so ago and was getting perfect boost until about a week ago when it would go up to 11 and then drop back down to 9 and stay at nine. I didnt think too much of it at the time until about a week ago when it started loosing even more. Now it is going up to 9 and dropping back down to 7. I dont know that much about turbos yet so any info at all would be GREAT before some mechanic tells me i need some new part! So any thing at will help , thankx!

 

[MrBoxx]

First thing to do (and I'll finally get to say it before oldman gets to you ) is to perform a boost leak test. That link will show you how to make your own boost leak test and perform it. Report back the results of that.

The second thing to do, and I only say this because steadily dropping boost like you're experiencing happened to me once, is to check the turbo for shaft play. Doing this takes five minutes and will alert you to any problems with your turbo's seals and bearings. Take off the intake pipe and stick your fingers into the compressor housing inlet. Grab the nut in the center of the compressor wheel. Try to wiggle the compressor wheel up and down, side to side, and in and out. A very small amount of side to side/top to bottom play is acceptable, since the bearings need a little room for oil pressure. However, in and out play is not acceptable. Any great amount of play in any direction, especially if the compressor blades are hitting the sides of the housing will mean that the turbo seals and bearings are failing, and the turbo will need to be rebuilt or replaced as soon as possible. After checking for shaft play, look inside the compressor inlet and see if the blades of the compressor wheel are all intact and not bent, which would indicate that they may be hitting the compressor housing or something may have gotten sucked through and damaged them.

Check your BCS and make sure that all the hoses are tightly on the nipples. The BCS is a small black box mounted to the car directly under the intake hose. There should be three vacuum hoses attached to it: one leads to the 14b's J-pipe nipple, one leads to the wastegate actuator, and one leads to the intake hose. Make sure all these are tightly connected to their respective locations and that none of the hoses are kinked or torn.

Can anyone else think of anything I might have missed?

 

[Gs Dewd]

First thing to do (and I'll finally get to say it before oldman gets to you ) is to perform a boost leak test. That link will show you how to make your own boost leak test and perform it. Report back the results of that.

The second thing to do, and I only say this because steadily dropping boost like you're experiencing happened to me once, is to check the turbo for shaft play. Doing this takes five minutes and will alert you to any problems with your turbo's seals and bearings. Take off the intake pipe and stick your fingers into the compressor housing inlet. Grab the nut in the center of the compressor wheel. Try to wiggle the compressor wheel up and down, side to side, and in and out. A very small amount of side to side/top to bottom play is acceptable, since the bearings need a little room for oil pressure. However, in and out play is not acceptable. Any great amount of play in any direction, especially if the compressor blades are hitting the sides of the housing will mean that the turbo seals and bearings are failing, and the turbo will need to be rebuilt or replaced as soon as possible. After checking for shaft play, look inside the compressor inlet and see if the blades of the compressor wheel are all intact and not bent, which would indicate that they may be hitting the compressor housing or something may have gotten sucked through and damaged them.

Check your BCS and make sure that all the hoses are tightly on the nipples. The BCS is a small black box mounted to the car directly under the intake hose. There should be three vacuum hoses attached to it: one leads to the 14b's J-pipe nipple, one leads to the wastegate actuator, and one leads to the intake hose. Make sure all these are tightly connected to their respective locations and that none of the hoses are kinked or torn.

Can anyone else think of anything I might have missed?

I too had the same problem about 2 wks ago. What I found in mine was the wastegate actulator was stuck partailly open and a hole on one of the vac. lines so check those also. As far as the bcs you have a 1g so it will be mounted on top is the air can with 2 hoses running to it. One going to the j-pipe and the other back to the aircan right next to the mas plug.

 

[MrBoxx]

Thanks for the correction about the 1g BCS. I forgot they were in a different location than the 2g's.